Ko'proq

NAD83 (NSRS 2007) ma'lumotlarini NAD83 (CORS 96) ga qanday o'zgartirish mumkin?

NAD83 (NSRS 2007) ma'lumotlarini NAD83 (CORS 96) ga qanday o'zgartirish mumkin?


Men bu borada o'z imkoniyatlarimdan tashqarida emasman, lekin men bu masala bo'yicha har qanday nuqtai nazarni juda qadrlayman. Menda NAD83 (NSRS 2007) da joylashgan NGS -dan ba'zi nazorat punktlari bor, men ularni nazorat nuqtasi ma'lumotlar bazasining qolgan qismi bilan birlashtirmoqchiman, lekin bizda mavjud ma'lumotlar NAD83 -da (CORS 96) ... Menimcha ... yoki bu NAD83 bo'lishi mumkin (2001). Ehtimol, men so'rashim kerak:

Qaysi NAD83 ESRI ning NAD_1983_StatePlane_Georgia_West_FIPS_1002_Feet koordinatali tizimiga xos (Geografik: GCS_North_American_1983 ma'lumotlar: D_North_American_1983)?

Qanday bo'lmasin, kimdir NAD83 (NSRS 2007) ni "oddiy" NAD83 ma'lumotlaridan biriga aylantirish uchun har qanday o'zgarishlarni biladimi? NGS hech qanday nashr chiqarmaydi va ESRIda uni o'zgartirish filtri yo'q. Har qanday yordam minnatdor bo'ladi. BTW, men o'tgan yilgi NAD83 <--> HARN konvertatsiyalari haqidagi GIS-SE xabarlarini o'qidim, lekin o'shandan beri kimdir bu masala bilan muvaffaqiyatli shug'ullanganmi deb o'ylayman.


Esri ArcGIS 10.0 ga HARN/NSRS2007, NSRS2007/WGS84 va CORS96/NSRS2007 konvertatsiyasini qo'shdi, lekin ularning barchasi "buxgalteriya hisobi"-parametrlari nol. O'ylaymanki, har ikkala tizimda ham nazorat nuqtalari yordamida mos keladigan eng kichik kvadratlarni ishlatib, transformatsiyani hisoblash uchun sizga geodeziya o'lchagichi kerak bo'ladi. Men g'arbiy sohilda shunday qilgan ikkita shaharni bilaman.


NSRS 2007 va CORS 96 funktsional jihatdan ekvivalentdir. NAD (CORS96) ni amalga oshirish faqat CORS stantsiyalarini o'z ichiga oladi. Keyinchalik passiv belgilar CORS96 pozitsiyalaridan foydalangan holda CORSning GPS kuzatuvlari asosida qayta sozlandi. Passiv belgilarni qayta sozlash NSRS2007 deb nomlanadi.

Hozirgi amalga oshirish - NAD (2011). Ko'p joylarda NSRS2007 va NAD (2011) o'rtasidagi farq 0,025 m dan kam. Agar nazorat nuqtalarida 0,025 m dan kam tarmoq aniqligi xatosi bo'lsa, ma'lumotlaringizni NAD (2011) ga moslashtirishga urinib ko'rishingiz mumkin. Ammo agar sizning nazorat nuqtangizdagi xato 2007-2011 yillardagi o'zgarishlardan kattaroq bo'lsa, ma'lumotlarni to'g'rilashga urinishning ma'nosi yo'q.


Birinchi savolga kelsak.
Vertikal ma'lumotlar esri gorizontalidan alohida boshqariladi.
Yangi xususiyatlar sinfini sozlashda "Z qiymatlarini o'z ichiga oladi" ni tekshiring, so'ngra "z koordinatalar tizimi" koordinata tizimining yonida boshqa yorliq mavjud.

Va z funktsiyasi mavjud xususiyatlar sinflarida.
Dialog shunga o'xshash ko'rinadi.

Ikkinchi savol…
Men buni amalga oshirish yo'lini o'ylay olaman. Aniqlik haqida gapirolmayman.
1. Shaxsiy yoki fayl geodatabazasini yarating,
2. Xususiyat ma'lumotlar to'plamini yarating va
3. maqsadli crs va vertikal tizimni aniqlash,
4. bo'sh funktsiyalar sinfini yaratish
5. maqsadli funktsiyalar sinfining sxemasini aniqlash uchun dastlabki ma'lumotlardan foydalanish.
6. Dastlabki ma'lumotlarni maqsadli funktsiyalar sinfiga yuklash uchun yuklash kamerasidan foydalaning.


NAD83 ma'lumotlari va vaqtga bog'liq transformatsiya parametrlari bilan qanday ishlash kerak

Qo'shma Shtatlardagi GNSS foydalanuvchilari tomonidan tez -tez so'raladigan savol: NAD83 va ITRFyy tomonidan belgilangan kadrlar orasidagi koordinatalarni qanday o'zgartirish mumkin?
Evropadagi foydalanuvchilar uchun savol tug'iladi: men qanday qilib o'zgaraman? ETRS89 va ITRFyy?

Darhaqiqat, plastinka tektonikasi va boshqa geofizik hodisalar kabi vaqtga bog'liq jarayonlarni yaxshiroq moslashtirish uchun zamonaviy tayanch ramkalarni o'zgartirish tobora murakkablashib bormoqda.
Darhaqiqat, ko'plab zamonaviy ramka transformatsiyalari Helmertning 7 parametrli klassik konvertatsiyasini 14 parametrli murakkab formulalarga kengaytiradi, bu esa dastlabki 7 parametrni o'z vaqt hosilalari bilan oshiradi.

Ushbu hujjat quyidagilarni o'z ichiga oladi:

Ma'lumot: O'zgartirish parametrlari qiymatlari

Odatda transformatsiya parametrlarining qiymatlari e'lon qilinadi.

Ko'pchilikni QPS ma'lumot bazasida topishingiz mumkin: ITRF Transformation Parameters.xlsx.


ITRF2014, WGS84 va NAD83

1983 yildagi Shimoliy Amerika ma'lumotlari (NAD83) Meksikadan tashqari Shimoliy Amerikaning hamma joylarida ishlatiladi. Ma'lumotni ushbu yozuv bo'yicha oxirgi amalga oshirish NAD83 (2011) 2010.0.0 davri. Qo'shma Shtatlar va Alyaskada buni amalga oshirish Milliy orqali amalga oshiriladi CORS (uzluksiz ishlaydigan ma'lumot stantsiyalari). Milliy CORS va Kooperativ CORS saytlari soni har oy bir nechta yangi stantsiyalar qo'shilishi bilan doimiy ravishda o'sib bormoqda.

ITRF, WGS84 va NAD83 ni taqqoslash (Manba: GPS uchun yer tadqiqotchilari)
Yil Amalga oshirish (davr) Barcha amaliy maqsadlar uchun:
1987 WGS 1984 (ORIG) NAD83 (1986)
1994 WGS84 (G730) ITRF91/92
1997 WGS84 (G873) ITRF94/96
2002 WGS84 (G1150) ITRF00
2012 WGS (G1674) ITRF08
2013 WGS (G1762) Agar davrlar bir xil bo'lsa, ITRF08 va ITRF2014 bilan taqqoslaganda 1 sm o'rtacha o'rtacha kvadrat (RMS) ichida.

Yuqorida aytib o'tganimizdek, o'tmishda biz 1987 yilda joriy qilingan NAD83 (1986) va WGS84 o'rtasidagi o'zgarish haqida qayg'urmasligimiz kerak edi, chunki bu kelishmovchilik bizning umumiy xato byudjetimizga to'g'ri keldi. NAD83 va WGS84 dastlab bir -ikki santimetrga farq qilgan. Bu endi to'g'ri emas. Yangi ta'riflarida - NAD83 (2011) va WGS84 (G1762) - Amerika Qo'shma Shtatlari kontinenti ichida bir yoki ikki metrgacha farq qiladi. Boshqa tomondan, ITRF08, ITRF2014 va WGS84 (G1762) deyarli bir xil, agar ularning davrlari (vaqt lahzasi) bir xil bo'lsa. Ikkalasi uchun odatiy standart davr - WGS84 (G1762) va ITRF08 - 2005.0. ITRF2014 uchun odatiy standart davr - 2010.0 NGS pozitsiyalarni bir davrdan ikkinchisiga o'zgartirish uchun vaqtni gorizontal joylashtirish (HTDP) deb nomlangan dasturni ishlab chiqdi. Boshqacha qilib aytganda, ushbu dastur pozitsiyalarning bir sanadan ikkinchisiga o'tishiga, bir ma'lumotnomadan ikkinchisiga o'tishga imkon beradi va NAD 83, ITRF va WGS84 -ning so'nggi amalga oshirilishini qo'llab -quvvatlaydi. Bu shuni ko'rsatadiki, ITRF va WGS84 tizimlari globaldir va ularni amalga oshirish butun dunyo bo'ylab tektonik plitalarning siljishi tufayli doimiy harakatda ekanligini hisobga oladi. Biroq, NAD83 bitta plastinkaga - Shimoliy Amerika plastinkasiga o'rnatiladi va u bilan harakatlanadi. Shunday qilib, Amerika Qo'shma Shtatlaridagi NAD83 ITRF va WGS84 mos yozuvlar tizimlarini amalga oshirish bilan bog'liq ravishda yiliga taxminan 10 dan 20 millimetrgacha harakat qiladi.

NAD83 boshqaruvi

GPS bilan geodezik aniqlik nisbiy joylashuvga bog'liq bo'lgani uchun, tadqiqotchilar o'z ishlarini avlodlar kabi boshqarishda NGS stantsiyalariga tayanishda davom etadilar. Bugungi kunda tadqiqotchilar NGS -ning ba'zi stantsiyalari NAD83 -da koordinatalarini e'lon qilishganini va boshqalari, ehtimol, xuddi shu loyihani nazorat qilish uchun kerak bo'lsa, faqat NAD27 -dagi pozitsiyalarga ega ekanligini aniqlashlari odatiy hol emas. Bunday vaziyatda ko'pincha NAD27 pozitsiyalarini yangi ma'lumotlar koordinatalariga aylantirish maqsadga muvofiqdir. Ammo, afsuski, buni aniq bajaradigan bir bosqichli matematik yondashuv yo'q. Asl NAD27 pozitsiyalari orasidagi buzilishlar qiyinchilikning bir qismidir. Qadimgi koordinatalar ba'zida 15000dan 1 qismgacha xato qilgan. Vertikalning burilishidan, geoidal dalgalanmalarning tuzatilmasligidan, sifatsiz o'lchovlardan va boshqa manbalardan kelib chiqadigan muammolar, ba'zi NAD27 koordinatalarida noaniqliklarni keltirib chiqardi, ularni tuzatish mumkin emas, faqat ularni boshqa nuqtaga aylantirish.

NAD27 dan NAD83 ga o'tish

Shunga qaramay, NAD27 koordinatalarini NAD83 qiymatlariga aylantirish uchun har xil taxminiy usullar qo'llaniladi. Masalan, doimiy mahalliy tarjimani hisoblash uchun har ikkala tizimda koordinatali stansiyalardan ko'rsatma sifatida foydalanishga harakat qilinadi. Boshqa usul - bu uch yoki undan ortiq umumiy stantsiyalarning kenglik va uzunliklariga asoslangan alohida joylar uchun ikkita tarjima, bitta aylanish va bir o'lchovli parametrni hisoblash. Balki, eng yaxshi natijalar 3 o'lchamli Helmert transformatsiyasi yordamida kartezian yoki ellipsoidal koordinatalarda ifodalangan koordinatalar farqlari uchun ishlab chiqilgan polinomli ifodalardan kelib chiqadi. Biroq, ettita parametrni talab qilishdan tashqari (uchta siljish, bitta shkala va uchta aylanish komponenti), bu yondashuv barcha nuqtalar uchun ellipsoid balandligi mavjud bo'lganda eng yaxshisidir. Agar etarli ma'lumot mavjud bo'lsa, NGS dasturi NADCON kabi dasturiy paketlar koordinatalarni taqdim etishi mumkin.

Hatto mahalliy transformatsiya ushbu texnikalar yordamida modellashtirilgan bo'lsa ham, natijada NAD27 pozitsiyalari nisbatan past aniqlikda bo'lishi mumkin. NAD83 milliy tarmog'ini sozlash NAD27 tizimini qo'llab -quvvatlagan kuzatuvlar sonining qariyb 10 barobariga asoslangan. Ma'lumotlarning katta miqdori, NAD83 asosidagi o'lchovlarning umuman yuqori sifati bilan birgalikda, kutilmagan natijalarga olib kelishi mumkin. Masalan, NAD27 koordinatalari yangi tizimga aylantirilganda, alohida stansiyalarning siljishi mintaqaviy tendentsiya ko'rsatganidan ancha farq qilishi mumkin. Muxtasar qilib aytganda, bitta loyihada NAD83 va NAD27 nazoratini bir vaqtning o'zida ishlatganda, tadqiqotchilar qiyinchilikni kutishdi.

Aslida, transformatsiyaning yagona ishonchli usuli - bu koordinatalarga umuman tayanish emas, balki asl kuzatuvlarga qaytishdir. Shuni esda tutish kerakki, geodezik kenglik va uzunlik, boshqa koordinatalar singari, ma'lum bir ma'lumotga (mos yozuvlar ramkasiga) havola qilinadi va ular qandaydir mutlaq ramkadan kelib chiqmaydi. Ammo to'g'ri o'lchangan kvadratchalar moslamasiga kiritilgan asl o'lchovlar eng qoniqarli natijalarni berishi mumkin.

NAD83 ni zichlashtirish va takomillashtirish

Ba'zi hududlarda NAD27 va hatto NAD83 pozitsiyalarining nomuvofiqligi munosabatlar tubdan o'zgarganini kuchaytirmoqda. Ilgari, geodeziya ishlarida nisbatan kam muhandis va geodezatorlar ishlagan. Balki, turli geodezik tadqiqotlar ma'lumotlarining eng muhim ahamiyati shundaki, ular aniqlik nuqtalarini taqdim etishgan, shundan so'ng past aniqlikdagi ko'plab tadqiqotlarni bog'lash mumkin edi. Milliy boshqaruv tarmog'ini geodezik qobiliyatsiz geodeziklar uchun ochiq qilish uchun ishlab chiqilgan davlat samolyot koordinatalari tizimi dizayni bu tartibni aniq ko'rsatib berdi. Biroq, vaziyat o'zgardi. Mahalliy tadqiqotlar aniqligi va milliy geodeziya ishlari o'rtasidagi tafovut deyarli GPS yordamida yopiladi, bu esa xususiy amaliyotda mahalliy tadqiqotchilar va geodezistlar o'rtasidagi munosabatni o'zgartirib yubordi. Masalan, ikki guruh orasidagi ko'prik sifatida davlat tekisligi koordinatalarining ahamiyati keskin kamaygan. Hozirgi geodezer GPS orqali geodezik koordinata tizimlariga nisbatan nisbatan oson va to'g'ridan -to'g'ri kirishga ega. Darhaqiqat, GPS-dan olingan nisbiy pozitsiyalar tarmog'idagi 1-2-ppm mumkin bo'lgan xato, ularni boshqarish uchun mo'ljallangan NAD83 pozitsiyalarining aniqligidan tez-tez oshib ketadi.

Yuqori aniqlikdagi ma'lumotnoma tarmoqlari

Bu yo'nalishdagi boshqa muhim ishlar shtatlararo super tarmoq dasturlarida amalga oshirildi. Ning yaratilishi Yuqori aniqlikdagi ma'lumotnoma tarmoqlari (HARN) ular NGS va shtatlar o'rtasida kooperativ korxonalar bo'lgan va ko'pincha boshqa tashkilotlarni ham o'z ichiga oladi. Kampaniya dastlab sifatida tanilgan Yuqori aniqlikdagi geodezik tarmoqlar (HPGN). Taxminan 62 milya va kamida 16 millik stantsiyalar oralig'i shtat miqyosidagi tarmoqlarning maqsadi edi. Aniqlik millionga 1 qism yoki stantsiyalar o'rtasida yaxshiroq bo'lishi kerak edi. Boshqacha qilib aytganda, GPS kuzatuvlariga katta tayanib, bu tarmoqlar yuqori aniqlikdagi, transport vositalariga kirish mumkin bo'lgan, muntazam ravishda bir-biridan ajratilgan boshqaruv punktlari yodgorliklarini ta'minlash uchun mo'ljallangan edi. Bu stansiyalar o'zlariga bog'langan kundalik GPS kuzatuvlaridan olingan vektorlardan yuqori boshqaruvni ta'minlash uchun mo'ljallangan edi. Shunday qilib, HARN punktlari foydalanuvchini past boshqaruvga mos keladigan vektorlarni burish zaruriyatidan qochish vositasi bilan ta'minlaydi. Bu GPS -ning birinchi kunlarida sodir bo'lgan. HARNda bunday izchillikni ta'minlash uchun, GPS o'lchovlari tugagach, ular NGSga davlat tomonidan mavjud NGRSni shtat miqyosida qayta tuzishga kiritish uchun topshirildi. NAD83 qiymatidan 0,3 dan 1,0 m gacha bo'lgan koordinatali siljishlar 1998 yilda tuzilgan bu o'zgartirishlarga xos bo'lgan. HARN pozitsiyalarining eng muhim jihati ularning oxirgi pozitsiyalarining aniqligi edi.

Asl NAD83 sozlamasi 1986 yil qavs ichida, ya'ni NAD83 (1986) qo'shimchasi bilan ko'rsatilgan. Biroq, yangi tushuncha mavjud bo'lganda, qavs ichidagi yil tuzatish yili bo'ladi. Eng so'nggi amalga oshirish - NAD83 (2011).


Sharh

Milliy fazoviy ma'lumotnoma tizimi 2007) NSRS2007) bir necha yillardan beri mavjud bo'lsa -da, yangi tizim tomonidan belgilangan o'zgarish, avvalgi tizimga (NAD83/96, aka HARN, HPGN, NAD83/91) nisbatan, biz ushbu RFCda HARNdan foydalanamiz. Hujjat) belgilangan o'zgarish ta'rifiga loyiq emas, deb juda kichik hisoblangan. Ya'ni, siljishlar bir necha santimetrga to'g'ri keldi va o'sha paytda bu xato darajasidek kichik deb hisoblanardi. 2013 yilga mo'ljallangan yog'lar va NSRS2007 uchun aniq va aniq geodezik siljish modellari ishlab chiqilgan. Bu AQSh Milliy Geodeziya Tadqiqoti 2011 yildagi Milliy fazoviy ma'lumotnoma tizimini aniqlagan paytda amalga oshirilgan. Shunday qilib, hozirgi vaqtda geodezik koordinatalarni HARNdan NSRS2007 ga va keyinchalik NSRS 2011 ga ko'chirish uchun aniq modellar va algoritmlar mavjud.


OPUS aniqligi

Oddiy sharoitlarda ko'p pozitsiyalarni bir necha santimetr ichida hisoblash mumkin. Biroq, ma'lum bir echimning aniqligini baholash qiyin, chunki rasmiy xatolarning tarqalishi GPS -ni kamaytirish uchun optimistikdir. Foydalanuvchi xatolar (masalan, antennaning noto'g'ri aniqlanishi yoki ARP balandligi) aniqlanmaydi. Mahalliy ko'p yo'lli yoki salbiy atmosfera sharoitlari ham sizning qaroringizga salbiy ta'sir ko'rsatishi mumkin.

  • Statik: Har bir koordinata uchun (X, Y, Z, & Phi, & lambda, h va H), statik ishlov berish uchta alohida baza chizig'ini beradi. tepadan tepaga xatolar. Eng yuqori darajadagi xatolarning afzalliklaridan biri shundaki, ular CORS (tayanch stantsiya) koordinatalaridagi har qanday xatoni o'z ichiga oladi.
  • Tez-statik: Koordinata xatolarining eng yaxshi baholari - bu bitta boshlang'ich tahlil tomonidan berilgan standart og'ishlar. Bizning tajribalarimiz shuni ko'rsatadiki, haqiqiy xato 95 foizdan ko'proq aniqlikdan kamroq. O'z hududingizdagi aniqlikni baholash uchun OPUS-RS xaritasiga qarang.

Koordinatalarni konvertatsiya qilishning bosqichma-bosqich tartibi-To'g'ridan-to'g'ri rejim

Aytaylik, biz SiteA nomli saytning koordinatalarini o'zgartirmoqchimiz. Ushbu saytning koordinatalari 2005 yil 1-iyunda ITRF2008 ma'lumotlarida ko'rsatilgan ma'lumot bazasi yordamida GPS yordamida olingan. Biz bu koordinatalarni NAD83-NSRS ga aylantirmoqchimiz. Bu konvertatsiya qilish uchun zarur bo'lgan asosiy qadamlar:

1. Datum ochiladigan maydonidagi kirish koordinatalari ma'lumotlarini tanlang:

Hech kimdan foydalanmang: Agar koordinatalarni vaqtincha o'zgartirish kerak bo'lmasa yoki sayt harakati to'g'risida ma'lumot yo'qligi yoki kirish va chiqish davrlari bir xil bo'lsa, bu variantni tanlang. E'tibor bering, agar bu variant tanlansa, chiqish davri avtomatik ravishda kirishlar bilan bir xil bo'ladi va uni tahrir qilib bo'lmaydi. Shuningdek, kirish va chiqish tezligi qutilari o'chirilgan.

Kirishdan foydalanish: Agar sizda sayt tezligi haqidagi ma'lumotlar kirish nuqtasi uchun bo'lsa, ushbu variantni tanlang. Bu misolda, agar ITRF2008 da sayt tezligi haqida ma'lumot mavjud bo'lsa, biz bu variantni tanlashimiz mumkin. Keyin tezlikni kiritish qutilari yoqiladi va ularni kartezian (xyz) formatida yoki mahalliy geografik (shimoli-sharqdan yuqoriga) formatda to'ldirish mumkin. Tezlik, shuningdek, interpolatsiya orqali avtomatik ravishda baholanishi mumkin (Qarang: Koordinata konverteri - stansiya tezligidan foydalanish).

Chiqishdan foydalaning: Agar sizda sayt tezligi haqidagi ma'lumotlar chiqish nuqtasi uchun bo'lsa, ushbu variantni tanlang. Ushbu misolda, agar ITRF2008 uchun tezlik haqida ma'lumot bo'lmasa, lekin sizda NAD83 uchun bo'lsa, siz ushbu variantni tanlashingiz va chiqish tezligi qutilarini to'ldirishingiz mumkin.

U koordinatali konvertorni ko'rsatadi.

Keyingi qadam, ma'lumotlar konvertatsiyasini amalga oshirishdir:

E'tibor bering, chiqish koordinatalari davri kirish koordinatalari davri bilan bir xil.

Faraz qilaylik, koordinatalar GPS yordamida markerda olingan, ular uchun rasmiy koordinatalar mavjud, lekin NAD83 ma'lumotlar bazasida, 2002 yil. Biz ikkala koordinatani ham to'g'ridan -to'g'ri taqqoslay olmaymiz, chunki ular turli davrlarga ega va sayt bu ikki davr o'rtasida ko'chgan bo'lishi mumkin. . Biz bu erda Yerning barcha nuqtalariga ta'sir qiladigan turli xil tektonik va geologik jarayonlar tufayli harakatni nazarda tutyapmiz. Bu harakatni aniqlash uchun "sayt tezligi" tushunchasi ishlatiladi. Bu tezlik 3D vektor bo'lib, uning komponentlari odatda yiliga millimetrda (mm/y) beriladi. Agar biz koordinatalarni bir davrdan boshqasiga o'zgartirishni xohlasak, sayt tezligi haqida ma'lumot kerak. Etti parametrli konvertatsiya etarli emas.

Agar tezlik vektori ( ) to'g'ridan -to'g'ri taqdim etilgan yoki interpolatsiya orqali baholangan bo'lsa, biz vaqtincha ikki davr orasidagi koordinatani tarjima qila olamiz. Bizning misolimiz uchun bizda:

Shuni yodda tutingki, bu usul ba'zi cheklovlarga ega. Birinchidan, tezlik har doim ham doimiy emas, lekin yildan -yilga o'zgarishi mumkin. Ikkinchidan, agar interpolatsiya usuli qo'llanilsa, bu usul har doim ham tektonik plitalarning, ayniqsa, yoriqlar yaqinidagi murakkab harakatlarini aniq modellashtira olmaydi. Koordinatali konvertorda ishlatiladigan interpolatsiya usullari haqida ko'proq ma'lumot olish uchun, iltimos, "Koordinatali konvertor - Stantsiya tezligidan foydalanish" maqolasiga qarang.

Effigis ostida Windows asosiy menyusida OnPOZ asboblarini ishga tushiring. Keyin koordinatali konvertorni tanlang.

2. Koordinatalar davrini tanlang. Bu erda biz uchta format variantini olamiz:

a. Yil Oy kuni (yyyy mm dd) formati: 2005 yil 06 01

b. Yil + Yil kuni (yyyy doy) formati: 2005 152

v. O'ninchi yil: 2005.41370

E'tibor bering, biz ma'lum bir formatga ega bo'lgan davrni kiritganimizda, format yana o'zgartirilganda, davr avtomatik ravishda o'zgartiriladi.

E'tibor bering, kirish koordinatalari maydonlarida faqat raqamli qiymatlar, minus belgisi va kasrli nuqta qabul qilinadi.

4. Koordinatalarni vaqtincha sozlash uchun sayt tezligi ma'lumotlarini qo'llashni xohlaysizmi, tanlang.


Florida G'arbiy shtati samolyot koordinatalari bilan ishlash

ExpertGPS -da Florida West FIPS 0902 shtat tekisligi koordinatalari bilan ishlashda yoki konvertatsiya qilishda birinchi qadam - loyihangiz uchun tegishli koordinata formatini va ma'lumotlarini kiritish. ExpertGPS -da Tahrir menyusida bosing Tanlovlar. Ni bosing Mening koordinata formatlarim yorlig'ini bosing va ni bosing Format qo'shish tugma.

Ichida Koordinatali format qo'shish dialogi, dialogning chap tomonidagi Manzilni o'zgartiring Dunyo/Shimoliy Amerika/AQSh/Florida. Floridada ishlatiladigan barcha koordinatali formatlarning ro'yxati yuqori o'ngdagi Format panelida paydo bo'ladi. Florida G'arbiy FIPS 0902, Metrni tanlang (yoki oyoq, agar siz AQSh tadqiqot oyoqlarini tayanch birlik sifatida ishlatmoqchi bo'lsangiz). Endi o'ng pastki panelda Datum deb belgilangan NAD83 yoki NAD27 ni tanlang. (Eslatma: WGS84 Florida shtatidagi NAD83 bilan bir xil, shuning uchun agar siz WGS84 shtati tekislik koordinatasidan konvertatsiya qilmoqchi bo'lsangiz, NAD 83 ma'lumotlarini tanlang.)

FL West -ni UTM -ga o'zgartirish

Siz ExpertGPS Pro -dan UTM konvertoriga Florida shtati samolyoti sifatida foydalanishingiz mumkin. Florida G'arbiy koordinatalarini UTMga qanday o'zgartirish mumkin:
Birinchidan, yuqorida aytib o'tilganidek, FL West SPCS -ni qo'shing.
Florida West -ga ma'lumotlarni kiriting, Excel -dan joylashtiring yoki "Fayl" menyusidagi Import -ni bosish orqali shaklli fayl yoki SAPR rasmini import qiling. ExpertGPS Pro sizning samolyot koordinatalarini o'zgartiradi va ularni Florida xaritasida yoki havodagi fotosuratda ko'rsatadi.
Endi koordinata formatini qo'shish muloqot oynasiga qaytib, siz tanlagan UTM koordinata formatini va ma'lumotlarini qo'shing. Mening koordinatali formatlarim ro'yxatida UTM -ni tanlaganingizda, sizning barcha ma'lumotlaringiz bir zumda Florida shtati samolyotidan UTMga qaytariladi.
Siz endi qayta ko'rib chiqilgan UTM ma'lumotlarini Fayl menyusidagi Eksport tugmasini bosish orqali eksport qilishingiz yoki elektron jadvalga nusxalash va joylashtirishingiz mumkin.

Florida shtati samolyot koordinatalarini qanday qilib Lat / Long ga o'zgartirish mumkin

Yuqoridagi ko'rsatmalarga amal qiling, lekin chiqish formati sifatida UTMni tanlash o'rniga, ExpertGPS Pro kenglik va uzunlik formatlaridan birini tanlang. ExpertGPS Florida G'arbiy koordinatalarini o'nli daraja, daraja va daqiqada (min.min) yoki daraja, daqiqa va soniyada (DMS) lat-longa o'zgartirishi mumkin.

Florida G'arbiy koordinatalarini Garmin yoki Magellan GPS -ga yuborish

Sizning GPS qabul qilgichingiz AQSh shtati samolyot koordinatalari tizimi yordamida sizning joylashuvingizni ko'rsatolmaydi, lekin siz ExpertGPS Pro yordamida GIS yoki SAPR dasturidan X, Y nuqtalari yoki polylinli ma'lumotlarni GPS qabul qiluvchiga yuborish uchun foydalanishingiz mumkin. Ma'lumotlaringizni yuqorida ko'rsatilgan tarzda import qiling yoki kiriting. ExpertGPS sizning GPS -da ko'rsatiladigan qiymatlarni ko'rsatishini xohlamasangiz, UTM yoki lat/long kabi chiqish formatini tanlashning hojati yo'q. Shunchaki bosing GPS -ga yuborish GPS menyusida. ExpertGPS sizning Florida -G'arbiy koordinatalaringizdagi Sharq va Shimoliyni GPS qabul qilgichingiz ishlatadigan formatga o'zgartiradi va ularni to'g'ridan -to'g'ri GPS -ga yuklaydi. Endi siz GIS yoki SAPR haqidagi barcha ma'lumotlarni Garmin, Magellan, Lowrance yoki Eagle GPS -da ko'rishingiz mumkin!

Florida shtatining G'arbiy shtati samolyotining GIS ma'lumotlarini Google Earthda ko'rish

FL West SPCS -ga GIS yoki SAPR ma'lumotlarini ExpertGPS -ga import qilganingizdan so'ng, uni boshqa variant - uni KML -ga aylantirish yoki to'g'ridan -to'g'ri Google Earth -da ko'rish. Shtat tekisligini KML -ga aylantirish uchun Fayl menyusidagi Eksport -ni bosing va Google Earth KML fayl turini tanlang. Agar siz FL West SPCS ma'lumotlarini Google Earthda ko'rishni xohlasangiz, shunchaki bosing F7, Google Earthda ko'rish buyrug'i ExpertGPS -da.

ExpertGPS -ni Florida West Converter -ga UTM sifatida ishlatish

ExpertGPS -ga UTM koordinata formatini qo'shing, so'ngra UTM ma'lumotlarini import qiling yoki kiriting. UTMni shtat tekisligiga aylantirish uchun, yuqorida aytib o'tilganidek, Florida SPCS -ni qo'shing va tanlang, shunda UTM Northings va Eastings shtat tekislik koordinatalariga aylanadi.

Lat/lon yoki GPS ma'lumotlarini Florida G'arbiga o'zgartirish

Kenglik va uzunlik ma'lumotlarini Florida shimoli va sharqiga aylantirish uchun yuqoridagi texnikadan foydalaning. Garmin, Magellan yoki Lowrance GPS yo'nalish nuqtalarini yoki yo'llarini Florida -G'arbiy shtat samolyotiga aylantirish osonroq - bosish kifoya. GPS -dan qabul qilish. ExpertGPS Pro GPS ma'lumotlarini avtomatik ravishda siz tanlagan koordinata formatiga qaytaradi: Florida shtati tekisligi, UTM yoki lat/long. Keyin siz qayta ko'rib chiqilgan ma'lumotlarni ShAP formatidagi GISga eksport qilishingiz, SAPR dasturiy ta'minotingiz uchun DXF eksport qilishingiz yoki Excel yoki CSV fayliga nusxalashingiz va joylashtirishingiz mumkin.

G'arbiy Florida koordinatalarini GPS -da qanday ko'rsatish mumkin

Ko'pgina GPS -qabul qiluvchilar Florida shtati samolyotining koordinatalarini mahalliy ravishda ko'rsatolmaydi. Agar sizda eski Garmin yoki Magellan GPS qabul qiluvchisi bo'lsa, u sizga a Foydalanuvchi panjarasi (GPS qo'llanmasining mosligini tekshiring), siz quyida keltirilgan Florida G'arbiy Transvers Mercator proektsiyasi sozlamalarini ishlatib, GPS -ni aldab, Florida koordinatalarini metrlarda ko'rsatishingiz mumkin. Magellan GPS qabul qilgichlarida SETUP ekraniga o'ting va keyin COORD SYSTEM, PRIMARY, USER GRID -ni bosing. Agar siz Metr o'rniga US Survey Feet -dan foydalanmoqchi bo'lsangiz, UNITS TO METERS CONV tugmasini bosing va 0.30480061 kiriting.


Savollar: Carter koordinata tizimi nima?

Carter koordinatali tizimi - bu kenglik va uzunlikka asoslangan, Kentukki shtatidagi neft va gaz quduqlari ma'lumotlarini aniqlash uchun ishlatiladigan quruqlik tarmog'i. Tizim Carter Oil Company tomonidan ishlab chiqilgan bo'lib, u so'rov o'tkazilmagan hududlarda shaharcha va joylashuv tizimini taqlid qilish uchun ishlab chiqilgan. Shtat odatiy tarmoqqa bo'linadi, uning har bir katakchasi (yoki "to'rtburchaklar") besh daqiqalik kenglik va besh daqiqalik uzunlikdan iborat. Bu kvadratlar janubda "A" dan boshlanib, "Z" va "AA" orqali shimolda "GG" ga ko'payadigan harflar (shaharchaga teng) tayinlangan. Quadlar g'arbda nol (0) bilan boshlanadigan va sharqda 92 ga ko'tariladigan raqamlar (diapazonga teng) bilan belgilanadi. Har besh daqiqadan besh daqiqagacha to'rtlik bir daqiqali 25 daqiqaga bo'linadi. Bir daqiqali bo'limda, joylashuv aniqlanadi, bu qo'shni bir daqiqalik kesim chegaralaridan quduqgacha bo'lgan masofani aniqlash orqali aniqlanadi. Karter koordinatasi har bir qism uchun bir daqiqali chegaralar va mos yozuvlar chegarasi (shimoliy, janubiy, sharqiy yoki g'arbiy), bir daqiqali bo'lim raqami, besh daqiqali to'rt harfli va besh daqiqali to'rtinchi raqam. Kentukki shtatining Carter koordinatali va topografik indeks xaritasi so'rov bo'yicha mavjud, Jamoatchilik axborot markaziga murojaat qiling (Nashrlarni sotish).

Karterning koordinatali joylashuvi faqat 1927 yildagi Shimoliy Amerika ma'lumotlari uchun aniqlangan (NAD27). Agar siz NAD83 manzilini Karter koordinatasiga aylantirish uchun KGS koordinatali konvertatsiya qilish vositasidan foydalansangiz, chiqish faqat NAD27 bo'ladi.

Menda Carter koordinatasi bor va uni kenglik va uzunlikka aylantirmoqchiman.


NAD83 (NSRS 2007) ma'lumotlarini NAD83 (CORS 96) ga qanday o'zgartirish mumkin? - Geografik axborot tizimlari

Qassim A. Abdulloh, fan doktori, PLS, CP
Savollaringizga Javob
Texnik nazariyaga oddiy va rsquos nuqtai nazari
va xaritalash va GISning amaliy qo'llanmalari

Iltimos, savolingizni [email protected] elektron manziliga yuboring va sizning ismingizni nashr etishni blokirovka qilishni xohlaysizmi, ko'rsating.
PE va ampRSda chop etilmagan barcha savollarga javoblarni www.asprs.org/mapping_matters saytida topish mumkin.

Doktor Abdulla EarthData International, MChJning bosh ilmiy xodimi, Frederik, MD.

Bu ustunning mazmuni bu erda keltirilgan ma'lumotlarning faktlari va to'g'riligi uchun javobgar bo'lgan muallifning fikrlarini aks ettiradi. Tarkibi Amerika Fotogrammetriya va masofadan zondlash jamiyati va/yoki EarthData International, LLC rasmiy qarashlari yoki siyosatini aks ettirmaydi.

Savol: ASPRS va NSSDA standartlari bo'yicha vertikal aniqlik gorizontal aniqlikka qaraganda qattiqroq ekanligini payqadim. Misol uchun, agar men 15 sm (6 dyuym) raqamli tasvirdan ortofoto mahsulotlarini ishlab chiqaradigan bo'lsam, ASPRS standarti yordamida ko'rsatilgan gorizontal aniqlik 30 sm (1 fut), kutilayotgan vertikal aniqlik esa 20 sm (0,67 fut). Biz har doim har qanday xaritalash mahsulotining vertikal aniqligi gorizontal aniqlikka qaraganda kamroq qattiqroq ekanligiga ishonganmiz. Nima sababdan? Evgeniya Brodyagina, Frederik, Merilend - AQSh

Bu javob grafikalar va jadvallarni o'z ichiga oladi. PDF -ni ko'ring

Savol: ASPRS va NSSDA standartlariga ko'ra, vertikal aniqlik gorizontal aniqlikka qaraganda qattiqroq ekanligini payqadim. Misol uchun, agar men 15 sm (6 dyuym) raqamli tasvirdan ortofoto mahsulotlarini ishlab chiqaradigan bo'lsam, gorizontal aniqlik uchun belgilangan ASPRS standarti 30 sm (1 fut), kutilayotgan vertikal aniqlik esa 20 sm (0,67 fut). Biz har doim har qanday xaritalash mahsulotining vertikal aniqligi gorizontal aniqlikka qaraganda kamroq qattiqroq ekanligiga ishonganmiz. Nima sababdan?

Doktor Abdulloh: II QISM: Javobimning birinchi qismida (PE & ampRS, 2010 yil avgust), men savollarga javob beradigan aniqlik ko'rsatkichlari ziddiyatli bo'lgan muammolarni hal qildim. Men tushuntirdimki, bugungi kunda, xususan, AQShda qo'llaniladigan xarita aniqligi standartlarining ko'pchiligi kino sensorlar va qog'oz xaritalaridan olingan. Birinchi qism oxirida men AQShning barcha manfaatdor agentliklari va tashkilotlarini zamonaviy geografik ma'lumotlar mahsulotlariga qo'llaniladigan yangi milliy standartni ishlab chiqishga chaqirdim. Ikkinchi bo'limda men qanday qilib bunday standartni yaratish bo'yicha munozaralar olib borish uchun yuqori darajadagi fikrlar va g'oyalar bilan tanishtirmoqchiman va umid qilamanki, bu g'oyalar bunday standartni ishlab chiqishda ham foydali bo'lishi mumkin.

1. Yangi standart milliy darajada foydali bo'lishi kerak:
Standart AQShda ASPRS, FGDC, USACE, FEMA va boshqalar kabi xarita standartlarini tarixan nashr etadigan va saqlaydigan barcha agentlik va tashkilotlar tomonidan qabul qilinishi va tasdiqlanishi kerak. Bundan tashqari, yangi standart shaffofligi va foydalanish qulayligi orqali xaritalash va GIS hamjamiyatining turli sohalaridagi foydalanuvchilarga yoqishi kerak. Geofazoviy mahsulotlar haqida gap ketganda, bitta standartdan foydalanish mumkin, agar u ehtiyotkorlik bilan va foydalanuvchilarning turli talablariga javob beradigan tarzda tuzilgan bo'lsa. Turli agentliklar yoki foydalanuvchilar bir xil standartga har xil aniqlik ko'rsatkichlarini qo'llashlari va o'z mahsulotlarining o'ziga xos to'plamiga xos bo'lgan natijalarga erishishlari kerak. Bunga mahsulotning aniqligi yoki xaritalar sinfiga asoslangan aniqlik bilan solishtirish orqali erishish mumkin. Men ushbu maqolaning oxirida ushbu kontseptsiya haqida batafsil ma'lumot beraman. Hozirgi vaqtda turli idoralar o'z shaxsiy standartlarini o'rnatgan yoki tuzish jarayonida. Masalan, FEMA, ASPRS va USGS kabi agentliklar lidar ma'lumotlarining aniqligi bo'yicha o'z standartlari yoki ko'rsatmalarini e'lon qilishdi. Lidar tizimlari bir xil asosiy lazer texnologiyasiga asoslanganligi sababli, turli xil lidar tizimlarining xom ashyolari bir xil sifat va aniqlikka ega. Sifat va aniqlik asosan ma'lumotlarni qayta ishlash va qayta ishlash usullari bilan belgilanadi, shuning uchun foydalanuvchilar qo'llaniladigan usullarga xos bo'lgan aniqliklarni hisoblash uchun foydalanadigan yagona standartga ega bo'lishlari kerak.

2. Yangi standart modulli bo'lishi kerak:
Eski "bitta sensor, bir nechta mahsulot" tushunchasi hozirgi zamonaviy xaritalarni tuzish amaliyotiga amal qilmaydi. Hozirgi vaqtda xaritalarni yaratishda qo'llaniladigan turli xil texnologiyalar assortimenti lidar (topografik lidar va batimetrik lidar), interferometrik sintetik diafragma radarlari (IFSAR va InSAR), raqamli kameralar kabi yangi sensorli texnologiyalarga qo'llaniladigan yangi standartlarga bo'lgan ehtiyojni taqozo qilmoqda. sonar va boshqalar tomonidan suv osti tadqiqotlari. Shuning uchun standart modulli bo'lishi kerak, bu ma'noda u har xil texnologiyalarga individual qo'llanilishi mumkin bo'lgan pastki standartlar to'plamini o'z ichiga olishi kerak. Masalan, tasvir sensorlaridan olingan mahsulotlarning aniqligi va spetsifikatsiyasini aniqlash uchun bitta pastki standartdan foydalanish mumkin. Natijada, bu mahsulotlar guruhi (masalan, ortofoto, tuzilgan xarita va balandlik ma'lumotlari) bir xil vertikal va gorizontal aniqlik talablariga ega bo'ladi.

Boshqa sub-standart lidar va IFSAR ma'lumotlarining aniqligi va to'g'riligiga javob berishi mumkin va balandlik ma'lumotlari va orto-shunga o'xshash intensivlik tasvirlari kabi mahsulotlarni aniqlab berishi mumkin va dengiz, daryo xaritasi uchun sonar texnologiyalaridan foydalangan holda akustik tadqiqotlar uchun qo'shimcha standartlar aniqlanishi mumkin. va ko'l pollari.

Sensorning har bir turiga sodda va o'ziga xos tarzda javob beradigan yagona standartni ishlab chiqish orqali, bu modulli yondashuv bir nechta aloqador bo'lmagan agentliklarning bir nechta bog'liq bo'lmagan standartlarini talqin qilishda chalkashliklarni yo'q qiladi. Modullik vaqt o'tishi bilan o'zgarishi va kengayishiga ham yordam beradi. Vaqt o'tishi bilan eskirgan va qo'llanilmay qolishning o'rniga, bu modulli standart o'zgaradi va moslashadi, chunki yangi geografik xaritalash hamjamiyati tomonidan yangi sensorli texnologiyalar va mahsulotlar qo'shiladi.

3. Yangi standart yakuniy mahsulotlarning aniqligini tasniflash uchun quyidagi ikkita chora -tadbirlardan birini qo'llashi kerak:

a) yakuniy etkazib berilgan mahsulotlarning aniqligi
Masalan, 15 sm GSD bilan ishlab chiqarilgan ortofoto, ishlatilgan sensordan yoki uchish balandligidan qat'i nazar, RMSEX = RMSEY = 1.25*GSD (oxirgi etkazib beriladigan mahsulotning) gorizontal aniqligiga yoki 18.75 sm ga ega bo'lishi kerak. The proposed accuracy figure is a little aggressive when compared with the current practice of assigning an ASPRS Class 1 accuracy of RMSEX = RMSEY = 30 cm for such a product. Vertical accuracy can be derived using a similar measure of RMSEV = 1.25*GSD (of the final delivered product) or 18.75 cm, versus the current practice of labeling such products with an ASPRS Class 1 accuracy of RMSEv = 20 cm for 2 ft contour intervals.

The standard should not allow for the production of orthophotos with a GSD that is smaller than the raw imagery GSD (the GSD during acquisition). However, the standard should allow for re-sampling of the raw imagery for the production of coarser orthophoto GSDs, as long as the final accuracy figures are derived from the re-sampled GSD and not the native raw imagery GSD. Using the resolution or GSD of the imagery in referencing the final product accuracy introduces a more scientific and acceptable approach since a product’s accuracy is no longer based on the paper scale of a map.

One may argue that some users (e.g., a soldier on a battlefield) may need hard copy maps for field investigations. This is a valid concern. The new standard should allow users the option to produce paper maps using any scale they choose, as long as the map accuracy is stated on the paper map and the scale is represented by a scale bar that automatically adjusts to the map scale.

b) Accuracy according to national map classes In this case, the standard can specify multiple map categories for all users, and the standard will provide specifications and accuracy figures to support each of these classes. The following proposed categories represent reasonable classes that should fit the needs of most, if not all users:

1. Engineering class-I grade maps that require a horizontal accuracy of RMSEX = RMSEY = 10 cm or better and vertical accuracy of RMSEv = 10 cm
2. Engineering class-II grade maps that require a horizontal accuracy of RMSEX = RMSEY = 20 cm or better and vertical accuracy of RMSEv = 20 cm
3. Planning class-I grade maps that require a horizontal accuracy of RMSEX = RMSEY = 30 cm or better and vertical accuracy of RMSEv = 30 cm
4. Planning class-II grade maps that require a horizontal accuracy of RMSEX = RMSEY = 50 cm or better and vertical accuracy of RMSEv = 50 cm
5. General purpose grade maps that require a horizontal accuracy of RMSEX = RMSEY = 75 cm or better and vertical accuracy of RMSEv = 75 cm
6. User defined grade maps that do not fit into any of the previous five categories.

This concept provides more flexibility for data providers in designing and executing the project. However, it may be problematic for users who are not well educated in relating map classes to product spatial resolution (GSD). Keep in mind that due to the fact that digital sensors are manufactured with different lenses and CCD array sizes, different scenarios for image resolution and post spacing may result in the same final product accuracies and therefore, it is important that users clearly define their required GSD or work with the vendor to determine the optimal GSD for their needs.

4. The new standard should address aerial triangulation, sensor position, and orientation accuracies:
Currently, there is no national standard that addresses the accuracy of sensor position and orientation. As a result, the subject has been left open to interpretation by users and data providers. The accuracy of direct or indirect sensor positioning and orientation (whether derived from aerial triangulation, IMU, or even lidar bore-sighting parameters) is a good measure to consider in determining the final accuracy of the derived products. Furthermore, issues can be detected and mitigated prior to product delivery if the standard defines and helps govern sensor performance. In the past, we adopted the rule that says aerial triangulation accuracy must be equal to RMSE = 1/10,000 of the flying altitude for Easting and Northing and 1/9,000 of the flying altitude for height. Obviously, the preceding criteria were based on the then-popular large format film cameras that were equipped with 150 mm focal length lenses. Today’s digital sensors come with different lenses and are flown from different altitudes to achieve the same ground sampling distance (GSD), so relying only on the flying altitude to determine accuracy is no longer scientific or practical and new criteria needs to be developed.

When examining the 1/9,000 and 1/10,000 criteria, the following accuracy figures apply for 1:7,200 scale imagery that is flown using a large format film metric camera. such as Leica RC-30 or Zeiss RMK, to produce a 1:1,200 scale map:

RMSEX = RMSEY = 1/10,000*H = 1/10,000*1,100 = 0.11 m
RMSEZ = 1/9,000*H = 1/9,000*1,100 = 0.12 m

When using the current ASPRS class 1 standard, the following accuracy figures would be expected for a map derived from the same imagery:

RMSEX = RMSEY = 0.30 m
RMSEZ = 0.20 m (assuming 0.60 m [2 ft] contours were generated from the imagery)

The previous accuracy figures call for aerial triangulation results that are 270% more accurate than the final map accuracy. Old photogrammetric processes and technologies required stringent accuracy requirements for aerial triangulation in order to guarantee the final map accuracy, and past map production methods have transitioned through many different manual operations that ultimately resulted in the loss of accuracy.

Today’s map-making techniques have been replaced with all-digital processes that minimize the loss of accuracy throughout the entire map production cycle. In my opinion, the new standard should support accuracy measurements for aerial triangulation based on the resulting GSD. Considering all of the advances we are witnessing in today’s map making processes, aerial triangulation horizontal and vertical accuracy of 200% of the final map accuracy should be sufficient to meet the proposed map accuracy. Accordingly, the aerial triangulation accuracy required to produce a map product with a final GSD of 0.15 m, regardless of the flying height, is shown below:

RMSEX = RMSEY = RMSEZ = 0.625*GSD = 0.625*0.15 = 0.09 m
(if the final map accuracy is based on RMSEX = RMSEY = RMSEZ = 1.25*GSD = 0.1875 m)

Similar calculations can determine the required accuracy for direct orientation (no aerial triangulation required) using systems such as IMUs. To derive the required accuracy for raw, pitch, heading, and position, the previous aerial triangulation error budget of 0.09 m can be used to mathematically derive the acceptable errors in the IMUderived sensor position and orientation.

Lastly, I feel that a new approach should be developed to calculate lidar orientation and bore sighting accuracies. Since the sensor’s geopositioning and not the laser ranging is the main contributor to the geometrical accuracy of lidar data, this calculation should link lidar final accuracy to sensor orientation and positioning accuracies. In the forthcoming issue of PE&RS, I will introduce the final part (Part III) of my answer which focuses on the importance for the new standard to deal with data derived from non-conventional modern mapping sensors such as lidar, IFSAR, and under water topographic survey using acoustic devices such as active SONAR (SOund Navigation And Ranging). In addition, Part III will provide recommendations on the statistical methodology and confidence level to be used in the standard.

Question: I noticed that according to both ASPRS and NSSDA standards, the vertical accuracy is more stringent than the horizontal accuracy. For example, if I produce orthophoto products from 15 cm (6 in.) digital imagery, the stated ASPRS standard for horizontal accuracy is 30 cm (1 ft), while the expected vertical accuracy is 20 cm (0.67 ft). We always believed that the vertical accuracy of any mapping product is less stringent than the horizontal accuracy. Nima sababdan?

Dr. Abdullah: I am glad you brought up this important issue concerning existing mapping standards and how they apply differently to imagery acquired by the new digital sensors. I would like to correct your understanding of the ASPRS and National Standard for Spatial Data Accuracy (NSSDA) standards as they relate to the example you’ve provided. The horizontal and vertical accuracies figures in the example are contradictory not because the ASPRS standard is stated incorrectly but because of the way we associate the image resolution or the Ground Sampling Distance (GSD) with the standard’s defined map scale or contour intervals.

When softcopy photogrammetry was introduced in the early 1990s, it was standard practice to scan the film or the dispositive with 21 micron resolution or 1200 dpi (dots per inch). Therefore, for a negative film scale of 1:7,200 (1”=600’), which is designed to support a map scale of 1:1,200 (1”=100’) according to 6x enlargement ratio, the resulting Ground Sampling Distance (GSD) after scanning is 15 cm (6 in.). When we transitioned to digital aerial sensors, which essentially replaced film cameras, we maintained the same standards and conventions that we used for film products. As a result, digital imagery flown with 15 cm GSD are routinely used for the production of 1:1,200 (1”=100’) scale maps or orthophotos and 2 ft contours. So the confusion actually originated when we adopted the old conventions for the new mapping products from digital cameras.

The ASPRS standard did not specify a certain GSD for a certain map scale, but it did state that for class 1 mapping products, a 1=1,200 scale map should meet a Root Mean Squares Error (RMSE) of 30 cm horizontally. Also, the standard did not specify that imagery with 15 cm GSD had to be used for the production of 2 ft contours. The ASPRS standard states that the class 1 vertical accuracy for elevation data with 2 ft contour intervals must meet an RMSE of 20 cm however, when we extract accuracy figures for 15 cm imagery, we use the above mentioned association of map scale and GSD to apply the ASPRS accuracy standard for evaluating the new digital sensor data products.

This is clearly a confusing situation that we created ourselves due to the lack of concise mapping standards for the highly accurate products produced from modern digital sensors. Immediate needs forced the mapping community to adapt conventions and measures that were originally designed for film cameras and paper-based products. The well known “enlargement ratio”, which had been used in the past to determine how much film or dispositive could be enlarged to produce a final map with minimum or no degradation in quality, is no longer applicable in today’s digital world of geospatial data production. An enlargement ratio of 6 was widely accepted and used in the mapping industry when dealing with film-based mapping products however, some of the modern digital sensors are built with diiferent CCD size (i.e. 6 microns versus the 14 or 21 microns of scanned films) and a variety of lenses, and therefore, the enlargement ratio becomes irrelevant when compared to film scanned at 21 microns. In fact, the application of scale to digital imagery is not valid and only adds to the confusion, particularly since the concepts of paper scale and enlargement ratio are based on film or paper-based maps. Again, the contradicting accuracies represented in our original example are not derived from the ASPRS standard, but result from our misconception that digital imagery with a GSD of 15 cm is only suitable to produce a 1=1,200 (1”=100’) scale map with 2 ft. contours.

The ASPRS mapping standard, however, is problematic when applied to data from digital sensors. The ASPRS standard materialized in the 1980s and was approved in the 1990s, before digital sensors were used (or even existed) for mapping purposes. When we consider our level of achievement using today’s mapping processes, the ASPRS standard is outdated and no longer suitable for further advancement of digital passive and active sensors and to support technologies such as GPS and IMU, especially when the standard is based on mapping scale. Modern standards that are more suitable for digital maps and current and future technologies, such as digital cameras, lidar and IFSAR are needed to replace both the National Map Accuracy Standard (NMAS) and the ASPRS standard. A new set of standards should be developed based on the GSD of the digital data and the resolving power of the imaging sensor, and not on scale since digital scale can vary from one user to another based on the zoom ratio used to evaluate the data. These same arguments are valid for the more modern standard published by the Federal Geographic Data Committee, which is called the National Standard for Spatial Data Accuracy (NSSDA). The phrase “Accuracy Standard” in the NSSDA title is misleading and should be called “Testing Guidelines”. The term “standard test method” is defined by Wikipedia as follows: “to describe a definitive procedure which produces a test result. It may involve making a careful personal observation or conducting a highly technical measurement”. This definition does not apply to NSSDA since it does not quantify the testing threshold. To determine the final accuracies, the NSSDA provided a statistical acceptance formula based on 95% confidence level without addressing the threshold (in this case the “RMSE”). Users typically derive an RMSE value in order to use the NSSDA. When users address the NSSDA, we find they are often confused by these guidelines and misrepresent the standard in some way, such as mislabeling requirements (i.e., 2 ft RMSE at 95%). This example statistically makes no sense, since the term RMSE always refers to test results with a confidence level around 68% and not 95%. In my opinion, the industry desperately needs to reform and consolidate all three standards - NMAS, and ASPRS, and NSSDA - into one single unambiguous national standard that clearly defines procedures and acceptance or rejection thresholds for the different mapping products. This effort requires constructive and focused cooperation between the ASPRS and the FGDC (which represents almost all federal agencies) to draft a standard that’s based on today’s knowledge, practices, and vision for the future. This effort should focus on developing sets of standards that will remain applicable over time and will not quickly become obsolete as today’s innovations and technologies rapidly progress. In the next issue of this column, I will further discuss my ideas and thoughts on developing this standard, as well as the different conditions and parameters on which it should be based.

Question: What is a “bias” in mapping processing? Where does it come from? How is it calculated? How would one deal with it at different stages of the process?

This answer contains graphics and tables. Please see the PDF

Question: Due to plate tectonics, the Earth’s crust is moving at a rate of 5cm per year. What impact does this have on our GPS solutions and the accuracy of jobs that requires very high coordinate measurements?

This answer contains tables. Please see the PDF

Question: My questions are about accuracy degradation of horizontal and vertical data during the photogrammetric process for airplane based platforms. I know that there are many variables involved but is there a relative constant multiplier that determines the loss of accuracy between ground survey and AT results, as well as between AT results and final vector data and contours? Also, can I assume digital and film cameras will result in different multipliers? Finally, should the flying height be the sole determinant of the data accuracy?

This answer contains tables. Please see the PDF

Question: Data re-projection is done all the time by both GIS neophytes and advanced users, but a slightly wrong parameter can wreak havoc with respect to a project’s destiny if undetected. Many update projects were originally performed in NAD27 and the client now wants the data moved to a more up-to-date datum. What happens behind the scenes when data gets re-projected? Other than embarking on an expensive ground survey effort, what assurances exist to give the user confidence that what has been done is correct? What special considerations should be taken into account when data is re-projected and what are the potential pitfalls? Is every dataset a candidate to be re-projected, if not, why not?

Complicating the re-projection piece, older projects may have been done in NGVD29 and need to be moved to NAVD88. Similar to what is above, what happens behind the scenes, and how do we know the result is correct? What are some of the commonly performed vertical shifts done in the industry? Is there a standardized practice to perform this task? What impact, if any, does this vertical shift play on contours. Why do some firms/clients/consultants feel it necessary to recollect spot elevations and regenerate the contours in the new vertical datum, rather than just shifting the contours generated from the older vertical datum? Under what circumstances would a vertical shift be ill-advised?

Dr. Abdullah: I personally consider this question among the most important issues I face as a mapping scientist. Despite full awareness of the importance of coordinate and datum conversions and the role they play on the accuracy of the final delivered mapping products, most users and providers have a very limited understanding and knowledge of the topic. The question accurately describes the common mistakes, misunderstandings, concerns and anxiety that many concerned users experience when accepting or rejecting a mapping product. I will try to address all aspects of the question as much as I can for its importance. I will start by describing “what is happening behind the scenes”.

Datums and Ellipsoids: Defined by origin and orientation, a datum is a reference coordinate system that is physically tied to the surface of the Earth with control stations and has an associated reference ellipsoid (an ellipse of revolution) that closely approximates the shape of the Earth’s geoid. The ellipsoid provides a reference surface for defining three dimensional geodetic or curvilinear coordinates and provides a foundation for map projection. Here in the United States, the old horizontal North American Datum of 1927 (NAD27) was replaced with a more accurate datum called the North American Datum of 1983 or NAD83. NAD83, which is a geocentric system with its center positioned close to the center of the Earth, utilizes the GRS80 ellipsoid that was recommended by the International Association of Geodesy (IAG). The NAD27, on the other hand, is a non-geocentric datum, utilizes an old reference ellipsoid or oblate spheroid (an ellipsoid of revolution obtained by rotating an ellipse about its shorter axis) called the Clark1866 spheroid.

Conversion Types: There are two types of conversions that can occur during any re-projection: datum transformation and projection system transformation. Datum transformation is needed when a point on the Earth used to reference a map’s coordinate system is redefined. As an example of datum transformation is upgrading older maps from the old American datum of NAD27 to the newer NAD83 datum. The coordinate system (not the coordinate values) such as the State Plane may be kept the same during the transformation but the reference datum is replaced. Projection system transformation is needed when a map’s projected coordinates are moved from one projection system to another, such as when a map is converted from a State Plane coordinate system to Universal Transverse Mercator (UTM). Here, the horizontal datum (i.e. NAD83) of the original and the transformed map may remain the same.

Datum Transformations: In the process of updating older maps produced in reference to NAD27, a datum transformation is required to move the reference point for the map from NAD27 to NAD83. Several different methods for transforming coordinate data are widely accepted in the geodetic and surveying communities. In North America, the most widely used approach is an intuitive method called NADCON (an acronym standing for North American Datum conversion) to translate coordinates in NAD27 to NAD83. NADCON uses a method in which are first and second order geodetic data in National Geodetic Services of NOAA (NGS) data base is modeled using a minimum curvature algorithm to produce a grid of values. Simple interpolation techniques are then used to estimate coordinate datum shift between NAD 83 and NAD27 at non-nodal points.. Those who utilize NADCON rarely obtain bad conversion results. Most of the common blunders and mistakes made by users while using different conversion tools result from not fully understanding the basics of geodetic geometry. As such, the process of conversion should be handled by individuals who have some understanding and experience in dealing with datum and coordinates conversion.

Once the Global Positioning System (GPS) came along, the discrepancies inherent in the original NAD83, which was first adjusted in 1986 and referred to as NAD83/86 to differentiate it from newer adjustments of NAD83, became apparent. New adjustments of NAD83 (HARN adjustment, designated NAD83 199X, where 199X is the year each state was re-adjusted) resulted in more accurate horizontal datums for North America. The multi-year HARN adjustments added more confusion to the already complicated issue of the North American Datum, especially when the user had to convert back–and-forth to the World Geodetic System of 1984 (WGS84)-based GPS coordinate determination. An ellipsoid similar to the GRS80 ellipsoid is used in the development of the World Geodetic System of 1984 (WGS84) coordinates system, which was developed by the Department of Defense (DoD) to support global activities involving mapping, charting, positioning, and navigation. Moreover, the DoD introduced WGS84 to express satellite positions as a function of time (orbits). The WGS84 and NAD83 were intended to be the same, but because of the different methods of realization, the datum differed slightly (less than 1 meter). Access to NAD83 was readily available through 250,000 or more of non-GPS surveyed published stations which were physically marked with a monument. WGS84 stations, on the other hand, were accessible only to DoD personnel. Many military facilities have WGS84 monuments that typically were positioned by point positioning methods and processed by the U.S. military agencies using precise ephemeris.

In 1994, the DOD decided to update the realization of WGS84 to account for plate tectonics since the original realization, as well as the availability of more accurate equipment and methods on the ground. In that decision, the new WGS84 was made coincident with the International Terrestrial Reference Frame (ITRF) realization known as ITRF92 and was designated WGS84(G730), where G730 represents the GPS week number when it was implemented. In the late 1980s, the International Earth Rotation Service (IERS) introduced the International Reference System (ITRS) to support those civilian scientific activities that require highly accurate positional coordinates. Furthermore, the ITRS is considered to be the first major international reference system to directly address plate tectonics and other forms of crustal motion by publishing velocities and positions for its world wide network of several hundreds stations. The IERS, with the help of several international institutions, derived these positions and velocities using highly precise geodetic techniques such as GPS, Very Long Base Line Interferometery (VLBI), Satellite Laser Ranging (SLR), Lunar Laser Ranging (LLR), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS). Every year or so since introducing ITRF88, the IERS developed a new ITRS realization such as ITRF89, ITRF90,…, ITRF97, ITRF00, etc Since the tectonic plates continue to move, subsequent realization of WGS84 were published such as WGS84(G873) and WGS84(G1150). One of the newest realization is equal to ITRF 2000 2001.0 (i.e., ITRF 2000 at 1/1/2001).

As time goes on, the NAD83 datum drifts further away from ITRF realization unless a new adjustment is conducted. The later HARN adjustments, for example, are closer in values to the NGS coordinated network of Continuously Operating Reference Stations (CORS) system than the earlier ones. CORS provides GPS carrier-phase and code-range measurements in support of three-dimensional positioning activities throughout the United States and its territories. Surveyors can apply CORS data to the data from their own receivers to position points. The CORS coordinates in the U.S. are computed using ITRF coordinates and then transformed to NAD83. The problem with using ITRF for this purpose lies in the fact that the coordinates are constantly changing with the recorded movement of the North American tectonic plate. In the latest national adjustment of NAD83, conducted in 2007, only the CORS positions were held fixed while adjusting all other positions. This resulted in ITRF coordinates for all NGS positions used in the adjustment as opposed to only CORS published ITRF positions.

Projection System Transformation: Projected coordinates conversion, such as converting geographic coordinates (latitude and longitude) of a point to the Universal Transverse Mercator (UTM) or a State Plane Coordinates System, represents another confusing matter among novice users. State plane coordinate systems, for example, may include multiple zones (e.g., south, north, central, etc.) for the same state, and unless the task is clear, the user may assign a certain coordinates set to the wrong zone during conversion. The vertical datum conversion poses a similar risk as here in the U.S., maps were originally compiled in reference to the old North-America Geodetic Vertical Datum of 1929 (NGVD29) and conversion is necessary to relate data back and forth between the NGVD29 and the new more accurate vertical datum of 1988 (NAVD88). Similar problems arose since most surveying practices are conducted using GPS observations. Satellite observations are all referenced to the ellipsoid of WGS84 and the user has to convert the resulting elevation to geoid-based orthometric heights using a published geoid model.

As for NAD83 updates, the geoid model also went through many re-adjustments and different geoid models were published over the years such as geoid93, geoid99, geoid03, and the most recent geoid06, which only covers Alaska so far. Without having details about the data at hand, a user may easily assign the wrong geoid model during conversion, resulting in sizable bias in elevation for a small project. When a new geoid model is published, a new grid of geoid heights (the separation between ellipsoid and geoid) is provided and most conversion packages utilize these tabulated values to interpolate the elevation for non-nodal positions. As for the vertical datum conversion between NGVD29 and NAVD88, a program similar to NADCON called VERTCON is used throughout the industry to convert data from the old to the new vertical datum.

Judgment Calls: As for the question of whether “every dataset is a candidate to be re-projected”, the answer is simply NO. To transform positional coordinates between ITRF96 and NAD83(CORS96), U.S. and Canadian officials jointly adopted a Helmert transformation for this purpose. Helmert Transformation, which is also called the “Seven Parameter Transformation”, is a mathematical transformation method within a three dimensional space used to define the spatial relationship between two different geodetic datums. The IERS also utilized a Helmert transformation to convert ITRF96 and other ITRS realization. The NGS has included all of these transformations in a software package called Horizontal Time- Dependent Positioning (HDTP), which a user can down load from the NGS site http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.html.

While the Helmert transformations are appropriate for transforming positions between any two ITRS realization or between any ITRS realization and NAD83(CORS96), more complicated transformations are required for conversions involving NAD27, NAD83/86, and NAD83(HARN) as the inherited regional distortion can not reliably be modeled by simple Helmert transformation. Even with the best Helmert transformation employed in converting positions from NAD27 to NAD83(CORS96), the converted positions may still be in error by as much as 10 meters. In a similar manner, NAD83(86) will contain distortion in the 1 meter level while NAD83(HARN) will contain a distortion in the 0.10 meter level.

In summary on the conversion possibilities and tools, HTDP may be used for converting between members of set I of reference frames [NAD83(CORS96), ITRF88, ITRF89. and ITRF97] while NADCON can be used for conversion between members of set II of reference frames [NAD27, NAD83(86), and NAD83(HARN)]. No reliable transformation tool is available to convert between members of set I and set II of reference frames, in addition no conversion is available for transforming positions in NAD83(CORS93) and/or NAD83(CORS94) to any other reference frames. As for WGS84 conversions, it is generally assumed that WGS84(original) is identical to NAD83(86), WGS84(G730) is identical to ITRF92, and that WGS84(G873) is identical to ITRF96. Other transformations between different realizations of WGS84 and ITRF are also possible.

Based on the above discussions, data conversion between certain NAD83 and WGS84 is not always possible or reliable. As I mentioned earlier, existing data in NAD83 may not be accurately converted to certain WGS84 realizations as NGS did not publish all reference points in WGS84 and most WGS84 reference points are limited to military personnel. Unless a new survey is conducted in WGS84, it is always problematic to convert older versions of NAD83-based data from and to the newer WGS84 realizations. Conversion packages that make such tasks possible assume the term “WGS84” to be equal to the first realization of WGS84, which was intended to be equal to NAD83/86.

Free Conversion Tools:
GEOTRANS: The US Army Corps of Engineers provides a coordinate transformation package called “GEOTRANS” free to any US citizen. In a single step, user can utilize GEOTRANS to convert between any of the following coordinate systems, and between any of over 100 datums: Geodetic (Latitude, Longitude), Geocentric 3D Cartesian, Mercator Projection, Transverse Mercator Projection, Polar Stereographic Projection, Lambert Conformal Conic Projection, UTM, UPS, MGRS. The “GEOTRANS” is also distributed with user manual and Dynamic Link Library (DLL) which users can use it in their software

CorpsCon: Another good free package called CorpsCon is distributed by US Army Topographic Engineering Center (TEC) and solely for coordinates conversion for territory located within the United States of America.

Effect of Datum Conversion on Contours: When existing sets of contours are converted from one vertical datum to another, the resulting contours do not comply with the rules set governing contour modeling. Contours are usually collected or modeled with exact multiples of the contour interval (e.g., for 5-ft contours, it is 300, 305, 310, etc.). Applying a datum shift to these contours could result in the addition or subtraction of sub-foot values depending on the datum difference therefore the contours will no longer represent exact multiples of the contour interval (for the previous 5-ft contour example, the new contours may carry the following values 300.35, 305.35, 310.35, etc., assuming that the vertical datum shift is about 0.35 ft). Consequently, after conversion, a new surface should be modeled and a new set of contours that are an exact multiple of the contour interval should be generated.

Similar measures should be taken for the spot elevations, as they represent a highest or lowest elevation or a region between two contours without exceeding the contour interval. When the new contours are generated, the new contours are no longer in the same locations as the previous set of contours. The existing spot elevations may no longer satisfy the condition for spot elevations, and new spot elevations may need to be compiled. Vertical shift based on one shift value is not recommended for large projects as the geoid height may change from one end of the project to another. The published gridded geoid heights data should be consulted when converting the vertical datum for large projects that span a county or a state. Small projects may have one offset value and therefore applying one shift value that is derived from the suitable geoid model tables for the project area may be permissible.

Conversion Errors and Accuracy Requirements: As a final note, the previous discussions on the effect of conversion accuracy on the final mapping product may not pose a problem if the accuracy requirement is lenient and the discrepancy between the correct and assumed coordinates values fall within the accuracy budget. To clarify this point, the difference between NAD83(86) and NAD83(HARN) in parts of Indiana, is about 0.23 meter. Therefore, if you provide mapping products such as an ortho photo with 0.60 meter resolution or GSD (scale of 1:4800) and whose accuracy is specified according to the ASPRS accuracy standard to be an RMSE of 1.2 meter, the 0.23 meter errors inherited in the produced ortho photo due to the wrong coordinates conversion may go by undetected, as opposed to providing ortho photos with 0.15 meter resolution (scale of 1:1,200) with an accuracy requirement of 0.30 meter where the error in the data consumes most of the accuracy budget for the product. However, errors should be detected and removed from the product no matter how large or small they are.

Best Practice: In conclusion, I would like to provide the following advice when it comes to datum and coordinate conversion:

1. When it comes to coordinate conversion, DO NOT assign the task to unqualified individuals. The term “unqualified” is subjective and it varies from one organization to another. Large organizations that employ staff surveyors and highly educated individuals in the field may not trust the conversions made by staff from smaller organizations that can not afford to hire specialists. No matter what the size of your organization, practice caution when it comes to assigning coordinate and datum conversion tasks. Play it safe.

2. Seek reliable and professional services when it comes to surveying the ground control points for the project. Reliable surveying work should be performed or supervised and signed on by a professional license surveyor. Peer reviews within the surveying company of the accomplished work represents professional and healthy practices that may save time and money down the road.

3. GIS data users need to remember that verifying the product accuracy throughout the entire project area is a daunting task if it is all possible. Therefore, it is necessary to perform field verification for the smallest statistically valid sample of the data and rely on the quality of the provided services and the integrity of the firm or individuals provided such services for all areas fall outside the verified sample. That is why selecting professional and reputable services are crucial to the success of your project.

4. When contracting surveyors to survey ground control points for the project, ask them to provide all surveyed coordinates in all possible datums and projections that you may use for the data in the future. Surveyors are the most qualified by training to understand and manipulate datums and projections and it does not cost them much to do the conversion for you. It is recommended that in your request for proposal you ask the surveying agency to provide the data in the following systems:

Horizontal Datum: NAD27 (if necessary), WGS84, NAD83/86 (if necessary), NAD83/latest HARN, NAD83/CORS, NAD83/2007.

Coordinates System (projected): Geographic (latitude, longitude), UTM (correct zone), Sate Plane Coordinate System

Vertical Datum: WGS84 ellipsoidal heights NGVD29 (if necessary), NAVD88 (latest geoid model).

5. When you are asked to provide data for a client, always make sure that you have the right information concerning the datum and projection. It is common to find that people ask for NAD83 without reference to the version of NAD83. If this is the case, ask them specify whether it is NAD83/86, NAD83/HARN (certain year), NAD83/CORS, or NAD83/2007.

6. If you are handed control data from a client or historical data to support their project, verify the exact datum and projection for that data.

7. If a military client asks you to deliver the data in WGS84, verify whether they mean the first WGS84 where the NAD83 was nominally set equal to WGS84 in the mid 80s. Most of their maps are labeled WGS84, referring to the original WGS84. Otherwise, provide them with NAD83/CORS or ITRF at a certain epoch suitable for the realization they requested, unless they give you access to the WGS84 monument located in or near their facility. The most accurate approach for obtaining WGS84 coordinates is to acquire satellite tracking data at the site of interest. However, it is unrealistic to presume that non-military users have access to this technique.

8. Pay attention to details. People are frequently confused about the vertical datum of the data. Arm yourself with simple, yet valuable, knowledge about vertical datums. If the project is located along the U.S. coastal areas, the ellipsoidal height should always be negative as the orthometric height (i.e., NAVD88) is close to mean sea level or zero value and the geoid height is negative. Therefore, if you are handed data with an incorrectly-labeled vertical datum, look at the sign of the elevations given for the project. A negative sign for elevation data on U.S. coastal projects is an indication that the data is in ellipsoidal heights and not orthometric heights (such as NAVD88).

9. Equip your organization with the best coordinate conversion tools available on the market. Look for a package that contains details of datum and projection in its library. Here apply the concept of the more the better.

10. Cross check conversion from at least two different sources. It is a good practice to make available at least two credited conversion packages to compare and verify conversion results.

11. If you are not sure about your conversion, or the origin of the data that you were handed, always look for supplementary historical or existing ground control data to verify your position. Take advantage of resources available on the Internet, especially the NGS site. Many local and state governments also publish GIS data for public use on their web sites. Even “Google Earth” may come in handy for an occasional sanity check.

Question: What is the correlation between pixel size of the current mapping cameras in use and the mapping accuracy achievable for a given pixel size? masalan. for data collected at a 30 cm GSD what would be the best mapping horizontal accuracy achievable?

Dr. Abdullah: Unlike f lm-based imagery, digital imagery produced by the new aerial sensors is not referred to by its scale as the scale of digital imagery is diff cult to characterize and is not standardized. Digital sensors with different lenses and sizes of the Charge Coupled Device (CCD) can produce imagery from different altitudes with different image scales, but with the same ground pixel resolution. In addition, the small size of the CCD array of the digital sensors results in very small scale as compared to the f lm of the f lm-based cameras. This latter fact has made it diff cult to relate the image scale to map scale through a reasonable enlargement ratio as is the case with flm-based photography. As an example, the physical dimension of the individual CCD on the ADS40 push broom sensor is 6.5 um therefore for imagery collected with a Ground Sampling Distance (GSD) of 0.30 m, the image scale is equal to (6.5/0.30x1000000) or 1:46,154. Such small scale can not be compared to the scale of the equivalent f lm imagery or 1:14,400 which is suitable to produce maps with a scale of 1:2,400 or 1&rdquo=200&rsquo. Here, the conventional wisdom in relating the negative scale to map scale, which has been practiced for the last few decades is lost, perhaps forever. Traditionally in aerial mapping, the f lm is enlarged 6 times to produce the suitable map or ortho photo products. This enlargement ratio is too small to be used with the imagery of the new digital sensors if we equate the CCD array to the f lm of the f lm-based aerial camera. Imagery from the ADS40 sensor as it is used today has an enlargement ratio of 19! Traditionally, aerial f lm is scanned at 21 um resolution and Table 1 lists the different f lm scales, the resulting GSD, and the supported map scale based on an enlargement ratio of 6.


Kalit so'zlar

Theme Keywords

Thesaurus Kalit so'z
GCMD Instruments/Sensors Keywords GPS : Global Positioning System
GCMD Platform Keywords GPS > Global Positioning System Satellites
GCMD Platform Keywords GROUND STATIONS
GCMD Platform Keywords GROUND-BASED OBSERVATIONS
GCMD Platform Keywords NAVSTAR > NAVSTAR Global Positioning System
ISO 19115 mavzular toifasi geoscientificInformation
ISO 19115 mavzular toifasi Manzil
NGDA Portfolio Themes Geodetic Control Theme
NGDA Portfolio Themes National Geospatial Data Asset
NGDA Portfolio Themes NGDA
NOS Data Explorer Topic Category Geodetic/Global Positioning

Videoni tomosha qiling: CORS - Cross Origin Resource Sharing, Совместное использование ресурсов между разными источниками