G2139, RGF93: ground truth is not valid without PROJ on both sides

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Валерий Заподовников

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Sep 30, 2022, 3:18:31 PM9/30/22
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Okay, so this is like color managment of images, you have WGS 86 version used in GPS antennas and that is often corrected, last one to G2139 (2139 is GPS week), which was a big change. On the other hand the Google Maps and OpenStreetMap are not really using WGS 84, not even close, not even G2139. They use whatever the map service provider uses. [1] Thankfully you do not need to go anywhere: look up some key survey marker up in Space Force's base station database in G2139 and ITRF2020 or ITF2014 (with base stations one calculats all the stuff about rotation of Earth and thus leap seconds and about earthquakes that corrupt GPS stuff). 20 years of calculations are what ITRF2020 was all about, released in April this year.

Next problem is that WGS 84's G2139 is dynamic. And so is ITRF2014, ITRF2020. Thankfully ITRF creators publish all info, [2] [3] tectonics for [3] are there https://www.unavco.org/software/geodetic-utilities/plate-motion-calculator/plate-motion-calculator.html 

Last: near seas and rivers you need to fix reflections in data. This is done with https://github.com/kristinemlarson/gnssrefl (access will end on 1 October).

Google maps may have different problems. Some people asked what GXXX is used by Google maps, no answer.

Finally, if you think this is not important. No. Glonass e.g. still uses ITRF2008, but it is not ITRF2008, there is a Helmert transform. With final migration to G2139 the error is now decimetres, it is big! This was done almost after the moment G2139 was activated, the person was shoked how innacurate PPP is now, see comments section, some clever people fixed his strange results. IGS08, nice. https://rtklibexplorer.wordpress.com/2021/01/08/exploring-kinematic-single-receiver-solutions-with-rtklib-and-the-u-blox-f9p/ 


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