# 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