I noticed some worrying discrepancies between VRS and PPK results on a test point this week.
The location is in a (fairly shallow) valley. In short, my concern is that the VRS solution was c.130mm out in z compared to PPK.
Some more details:
VRS - 2-minute average with constant fix
PPK - average single 1-hour. Corrected using same RINEX data as source for VRS. In Emlid Studio, no fix when using default 15 deg elevation mask. Fix solution only when using 45 deg elevation mask. (I can share the skyplot if needed)
My question really is, is the Emlid giving a ‘false fix’ in this scenario when working from the VRS? If we assume that the VRS solution is less accurate (is it?), is there some way to identify that conditions are sub-optimal and that the result is likely to be far less accurate than the displayed H and V deviation at the time of capture?
Hi @survey2, is the shift only on the vertical? If so, could you please check the antenna height in Emlid Flow and Emlid Studio? 130mm sounds like the antenna phase offset.
That’s a point. Can’t see how that would happen though, as the antenna position is always added to the measured height by the software surely? But I will check on this also. If we had inadvertently included it in the measured height then this discrepancy would occur, but we haven’t.
Could you please check the height in the RINEX header and compare it against the height in Flow? When logging, you have to manually specify the measured height in Flow. Otherwise, you need to change it in Emlid Studio.
Hi - definitely 1.8m in header and in Flow (and that is definitely the pole height)
I just did another test in the same location and this time I have PPK reading almost 20cm lower than the VRS observation. I needed to set a 45 degree elevation mask and combined filter to get a fix in PPK.
It still concerns me that the VRS fix may be the wrong one, and I would never have known. But how do I work out which is more accurate?
Yes, please. Which NTRIP service are you subscribed to, and which CORS base were the RINEX logs from?
Please email the raw data logs (RINEX) and CSV to support@emlid.com. I’d like to investigate further. Also, did you happen to record the RTCM3 logs? Could you please share them with me as well?
