Hello
I have some basics in surveying but I am looking for some advices on some discrepancies I came across while trying to georeference a station we set in the field. I am processing the result with RTKlib 2.4.2 in static mode to use a nearby base station and trying to acheive the best available accuracy (which would be centimetric I believe considering our configuration).
As I am not experienced with RTKlib, here is my configuration to rule out any beginner mistake (ambiguity resolution is continuous and I am not sure about the calibration files for antennae):
back to my problem, the results are quite different depending on wether I am using the forward/backward/combined mode. I found this article quite helpful PPK vs RTK: A look at RTKLIB for post-processing solutions – rtklibexplorer
Similarly, I thought “combined” would give the best result in most cases, but it turns out not as can be seen here. The position saved if I put the output in “single” is one of the points on the down left side, while the rest of fixed solutions seem more appropriate (and because I checked with another data source for the same obs)
Here are the plots of each coordinate :
So I have quite a lot of question :
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Why is combined not performing well compared to backward and forward methods here ?
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seeing the plots, I feel that there is quite a lot of incertitude/moving going on on the coordinates for an immobile station on the field, is that normal ?
Regarding acquisition,
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using a known base station from an official station network (SGIL from RGP in my example), should i use the coordinates filled in the rinex header of the base station ? or overwrite them with exact coordinates from the official website for this station ?
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There were some high trees nearby (like 50m high, 25m away from the gps station). While I know clear areas are better to survey in, is there a general advice on the distance one should keep with high trees ? 10,50, 100m ?
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How much time is necessary to acheive a centimetric accuracy, in some cases, the base station was set up for an hour and a half, and I am concerned it could not be enough. I was thinking 3h would be a minimum, 5h good
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The height of the gnss was not measured on the field, although the antenna height is filled (1m or 1m80 depending on acquisitions) in the RINEX header file. Is the only concern the height accuracy or can it negatively influence the convergence of computations too ?
And more regarding RTKlib / coordinates reference frames
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The output coords are in WGS84, to which ITRF does it correspond ? From what I understand, the current WGS84 reference frame is the G2296 from the WGS84 G series, which is aligned to the ITRF2020. However, I can’t find the epoch at which it is aligned.
So I suppose the resulting coordinates (as well as most hardware/softwares working with WGS84) are aligned with ITRF2020 and not ITRF00 (current epoch). Am I right ? -
Edit: How to correctly estimate the accuracy of the result ? It seems RTKlib gives the last fixed position as result if you ask for “single” output. Shouldn’t it be maybe a weighed mean or median of all the fix solutions found ? I though the standard deviation elements (which were around 1cm) would indicate the true position is clearly within this interval but it seems not
Thanks for your help