Hei,
Looking at the Tie-Point Grids created when opening a Sentinel-1 image (GRD, EW) and comparing them with values for corresponding points given in the geolocationGrid from the annotation metadata, I noticed a slight difference between them.
As far as I understood the Tie-Point Grids are (bi-)linearly interpolated from the geolocationGrid metadata and hence I would expect the values to coincide at the tie points .
To understand this deviation, it would be very helpful to know, how the Tie-Point Grids are actually calculated/created.
Thanks for your help,
Wiebke