# A posteriori reference variance

Hallo,

I have been studying JAG3D through my concrete project of a geodetic network adjustment and deformation analysis. Furthermore, I have read almost all the topics in this forum and the user manual guidelines, and have some questions and uncertainties I hope you will answer me.

Firstly, in the initial adjustment steps, JAG3D calculates the weight matrix P of all observations. Weights of all observations are calculated based on the given a-priori uncertainty (e.g. a-priori uncertainty of horizontal distance) and a-priori reference variance σ. The default value of the a-priori reference variance σ is 1, and can't be changed in JAG3D. Are the stated facts correct?

Furthermore, during the adjustment procedure JAG3D calculates te a-posteriori reference variance factor and uses it to calculate all confidence measures defined by the adjustment model. Where does JAG3D directly shows the calculated a-posteriori reference variance factor?

Next, after the adjustment of two consecutive epochs, during the deformation analysis, does JAG3D calculates and shows the displacement vector between the points of the two measured epochs?

And finally, let's say I have a 2D geodetic network measured in two consecutive epochs. The network is adjusted as a free network (the minimum trace datum is defined). My goal is to determine if unstable points exist in the network (between epochs) and to calculate the deformation vector of the unstable points. What would be the general workflow (main steps) in JAG3D to accomplish the above stated goal?

I would very much appreciate if you took the time to read and answer my questions.

Thank you,
Antonio