# Variance-covariance matrix for a network adjustment

Hallo Micha,

I would like to do a local tie analysis including calculations of vectors between invariant points of a VLBI antenna, a SLR telescope and several GNSS pillars.
My problem arises using JAG3D when I want to include the centers of the VLBI and SLR instruments in the variance-covariance matrix estimation.

My data include:

1) 236 level measurements between 16 altimetric marks (and some auxiliar points) in different instruments or concrete platforms in our Observatory. We placed the instrument in 13 diferent positions so I treated every position as independent sets.
Based on the used instrument (Leica LS15), I defined an uncertainty of 0.1 mm for each measurement in the properties tab.

2) Measurements of an horizontal network (directions and horizontal distancies) composed of 10 sites that have forced centering bases. 6 of these points materialize the main axis of GNSS instruments, while the others are located on the concrete platforms of the VLBI and the SLR instrument. Like height measurements, each position of the total station was taken independently.

3) Measurements of marks sticked to the VLBI and SLR instruments. In each concrete platform, we placed a total station (Leica TS60) and a theodolite in front of each other and from both intrument we take measurements to at least two fix marks located on platforms and several measurements of a rotating mark linked to the intrument of interest. Last measurements describe two circles and the centers of those circles define the main and secondary instrument axes.

4) GNSS continuous measurement in 6 pillars for the campaign days. One of this pillar represents the main GNSS station of the observatory and is a IGS station. The other pillars conform the GNSS control network. The observatory occupies an area of ​​around 40x40m.

So, my question is, knowing the precision of each measurements of points that make up the circles around the axes, is it possible to do a network adjustment and determine a variance-covariance matrix that includes the invariant points of VLBI and SLR?