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Cedar Rapids, Iowa | The receiver would have been generating GGA position messages, which the Insight would have been using. In the GGA message structure is a number that represents the quality of the position data. The commonly used numbers are:
2 = DGPS
4 = RTK
OmniStar isn't really DGPS, and it isn't really RTK, so various receiver manufacturers will assign it different numbers. Trimble seems to report OmniStar positions as a quality of 4 (RTK), which lets you tell it apart from when you're on a lower quality signal like WAAS or VBS.
To add to the confusion, the Insight has a bug where it incorrectly reports the position quality. RTK (4) data shows up as DGPS and DGPS (2) data shows up as dGPS. The difference of that one character is hard to see on the screen.
Some receivers allow you to map certain signal types to a quality number other than the factory default. The following link shows how to do it on a NovAtel receiver, which is irrelevant to you, but it shows where the number is within the GGA message.
http://lefebure.com/articles/novatel-gga-quality/
You could check the GGA messages coming out of your receiver to see what number it shows. I suspect it is a 2 if your screen is showing "dGPS". The next thing to do would be to go in to the configuration software for the receiver and see what signal it thinks it is running on. If it is really running on OmniStar HP, you shouldn't see 5 feet of position drift.
-Lance | |
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Need help with Insight with Topcon receiver
