Question about Regional POD with Sparse Network

[sunyu0703]

Hello GROOPS developers,

I would like to ask if GROOPS can perform regional orbit determination under challenging conditions (approx. 20 stations unevenly distributed in China, with only GPS L1/L2 and BDS B1C/B2a signals). I have encountered several problems:

I initially received the error not enough estimable epochs (119). I had to change parametrizations->transmitterDynamicOrbit->minEstimableEpochsRatio from 0.75 to 0.25 to get past this.

After fixing the first issue, I then encountered the following errors:

3002.G11:ambiguity2of2(L1L2)::... has zero diagonal element
15792 parameters have zero diagonal elements -> set to one
in /data/sy/groops/source/parallel/matrixDistributed.cpp:540 (cholesky): ...
Diagonal block (292, 292) is not set. continue...
To solve the singularity issue, I tried turning off many parametrizations (e.g., transmitter bias, ambiguities). Now, the process fails in iteration 2 with nan values:

sigma = nan
Cannot compute sigma = sqrt(nan/113389)
...
C1CG**: sigma0 = nan, redundancy = nan, count = 39559, outliers = 4037 (10.21 %)
...
Could you provide any guidance on this? Thanks.

Thank you very much for your time and consideration.

Best regards,

[zhedumi]

Hello,

Could you provide me with the logfile? So I can check the number of parameters etc. Also do you intent to compute orbit + station position or only orbit determination? So basically only the orbit of the satellites?

Best regards,
Patrick

[sunyu0703]

Hi Patrick,

Thanks for your reply.

Unfortunately, the previous logfile was lost.

Regarding the computation, you are correct. I am currently performing only orbit determination, without estimating station coordinates.

Therefore, I would like to ask for your advice: for an orbit-only solution, do you have any suggestions on how to disable or fix the estimation of other parameters (e.g., station coordinates, Earth rotation parameters, etc.)? I want to ensure my setup is focused solely on the orbits themselves.

Thanks in advance for your guidance.

Best regards

[sunyu0703]

It is also worth noting an issue I sometimes encounter. The processing appears to be normal before ambiguity resolution, but after resolving ambiguities, a rank-deficiency occurs with the error: W'W=A cannot compute decomposition, error=24.