Post processing in RTKLib with base at different heights

Hi All,

We had collected beach topography data using REACH M (rover) and REACH RS (base). Base station was kept at two different places for two dates (lets suppose). One very near to the beach of interest and one on an elevated region (in our University) which is 10 km far. The reason behind setting up base station in our University is that we can securely keep it for longer time and conduct survey. While processing the rovers data (collected at two different times, with bases at two locations), we have found variation in the height of beach levels by more than 30 m. Actually, the beach levels must vary around 3-5 m above MSL. When we process the rover data with the base station located at nearest location in the beach side (on a road), the elevations are coming fine. But, I could not understand when we process the same beach (of course for different date), with base on an elevated region, the beach elevation is no where in the range. Base station coordinates were obtained from CSRS PPP service.

My questions are

  1. Does the Base station height influence the rover height.? Then how can we get absolute position and height.?
  2. Does RTKLib Kinematic solution absolute or relative to the base?
  3. How to adjust the output of the rover ( as we need to process some files, which were taken when base was setup at beach and some were from University).

I’m totally confused with so many things. Help required.

For absolute positioning yes, for relative no.

Always relative to the base

How do you input the base positions?
Are you sure you supplied the height in ellipsoid?

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Were the 2 bases observed relative to each other? Not via CSRS signals?
If not then I would connect the 2 base via static observation of at least 2 hours or more at 1 sec intervals. If you have a certified benchmark preferably in MSL values then I would also connect this to either base via static. You can then transfer the MSL value to the bases via post processing. Once you have positions of the 2 bases in MSL datum then use these values in your RTK survey. No need to connect to CSRS signals every time you use the base.

Thank you @wizprod. We found there is an error in the RTKLib POST configuration settings. We have noticed that the solution is significantly varying with the tropospheric model. Also, the heights are changing of the order of 1m when we consider different constellations (with only GPS and with GPS+GLONASS_GALILEO). We are inputting the base coordinates and height in reference ellipsoid only (the one which we got from NRCAN PPP service). However, the standard deviation is ~2m. What to do in this case?

To avoid this confusion, is there any standard settings for PPK in RTKLib to get a good solution.

Can you upload the rawfiles and base position?

raw_201810240918 (1).zip (9.3 MB)

Raw data of base station is attached. The base position is 17 46 48.40686 N, 83 23 9.90933 E and -65.741 m (obtained from NRCAN PPP service)

Please provide the rover as well.

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