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NTRIP Horizontal Datum
346 3 9-26 09:53
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cstokes
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Hello,

Recently started using a P4RTK in the U.S. We have really good real time network coverage, so we purchased without the DJI base, and are planning on flying with NTRIP corrections. All of our local networks are tied to the NAD83 datum. The controller and drone don't have a way to define the datum. Does anybody know how it's resolving these differences, or if it is at all? The output in the exif data appears to be WGS84, but it seems to me the system is assuming the NTRIP base location is also WGS84? I'm getting decent results in my positioning, but I wonder if some of the small inaccuracies are caused by this.

Thanks
9-26 09:53
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UAS
lvl.2

United States
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How has Vert been?
11-14 07:42
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Skyveyor112
lvl.3
United States
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Does it matter?  My understanding is the RCTM message largely corrects for atmospheric conditions. I read the Phantom RTK uses RCTM_3 MSM5 format. According to SNIP this message contains the following

RTK uses, Pseudorange, PhaseRange, Doppler, CNR.

These corrections are applied real-time in the GNSS receiver resulting in WGS 84 lat, long and ellipsoidal heights accurate to a few cm.

What small inaccuracies are you seeing?  They could be related to GEOID corrections or the focal length not being calibrated for the height of the drone. Great discussion here about the focal length.

Dave
11-15 17:47
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cstokes
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So it turns out the issue was the post processing software we were using was assuming the data was in WGS84, even though the CRS was being set to NAD83. There was simply no way to define the coordinate system of the exif input. While using the local base stations, our lat/lon values were stored as NAD83. This caused a datum shift of around 2-3 feet. Once I switched to a post processing platform that supported alternate input datums, our RMS went to around 3cm horizontal and 5cm vertical.
11-27 08:16
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