Can you also tell me why is a posteriori uncertainty zero value for directions?
I am not sure which value you mean, because no residuals can be estimated in the simulation. Therefore, no a-posteriori values can be calculated.
If you have least square root concepts that you implemented in software, please give me link.
The stochastic model of the terrestrial observation can be found in the Wiki (German only).
applied-geodesy.org - OpenSource Least-Squares Adjustment Software for Geodetic Sciences