Hello,
I have been working in the last few days with a Trimble R8 receiver in RTK mode. This GNSS technology is very amazing. The term "antenna dump" will have to be revised from my GPS jargon. You really have to hide the antenna for it too loose its lock.
One quick question: On the new Access controllers, are the displayed specifications of precision (HD and VD) are at 68% confidence or 95% confidence? The RMS is expressed in mm's or wavelength cycles?
On a side note, I did some testing yesterday with RTK and PPK simultaneously. PPK provided better results. Sections of jobs where vertical peaked to +/- 30mm compared to +/- 20mm with the PPK method.
Great technology.
Georges
OK, but RTK to what? To one base station? How far away?
Stephen
1 GNSS RTK base station
baselines < 2000m
Glad you found it... GPS/GNSS has been around since the 90s
Just like the other Trimble units the HD and VD display is somewhat meaningless because it depends on the integer fix, which may be good, or it may be bad. Looking at the display and watching how the unit is behaving will give you a better idea if you have a good fix or not. Over time you should get a feel for when it’s not good but I still find bad fixes that I didn’t expect. They have become rare, but they still show up now and then. Instead of seeing one at least once or twice a day like in the old days (back in the 90’s) I probably see one a few times a year.
You need to develop error trapping of your own and never trust the unit without some checks.
Also, I don’t work with GLONASS unless I think it will help. The accuracy seems to become somewhat degraded when it is introduced. Not a big thing anymore, unlike in the early days (when the R8 first came out), but still things just seem to work better when I stay on just the US satellites. Out here on the plains in open country I will often be turning off a satellite to make it work better so GLONASS is just unnecessary. But GLONASS has its uses.
As far as the confidence level goes I guess my "confidence" level is low but not as low as it was and getting better.
The difference between RTK and PPK is interesting. Were you letting it set the same amount of time for each solution and collecting the same data? Say a 2 minute control point?
As for the RMS: if I remember this right I think it is always expressed in meters even if your job is set up in feet.
> One quick question: On the new Access controllers, are the displayed specifications of precision (HD and VD) are at 68% confidence or 95% confidence? The RMS is expressed in mm's or wavelength cycles?
RMS represents the standard deviation (68% confidence) of a measurement set. The difference between RMS and standard error is that the mean of the measurement set may be biased with respect to the true value, i.e. the mean may not accurately represent the true value.
If your controller denominates positional confidence in terms of RMS (common with GPS equipment), it's using 68% as the limits. It's also saying that the 68% confidence is with respect to the mean of its position estimates, not with respect to the true position.
Thanks guys for this information.
The PPK data was recorded at 1 second interval. RTK & Logging survey style. Truck survey.
I sat for 10 minutes near the base to initialize the PPK, went for a cruise recording RTK & Logging (less than 2000m from base), drove back near the base, sat for another 10 minutes to pick-up another initialization (as back up) and ended the recording sessions. Many shots show stats with vertical precision of ~50mm in RTK. The maximum vertical precision of the post-processed data in PPK is ~20mm (at 95% level).
