The gps_vertical command

gps_vertical location

Defines how covariances are transformed from topocentric components to geocentric components and vice versa for GPS baselines and point position observations. There are two options:

• a separate rotation rotation matrix can be calculated for each point or baseline (based on the midpoint of the baseline)
• a single rotation matrix can be used for all observations based on a central point of the network. The reference point in the network can be specified with the topocentre command. This provides some computational efficiency, but is less rigorous.

By default SNAP will calculate a separate matrix for each observation or baseline.

location

can either be "individual" to compute individually, or "topocentre" to use a single point for all transformations.

For example:

gps_vertical topocentre