I’ve just carried out a topo survey using 2 x RS2’s with the base pinned to exact coordinates. As a check for my orthometric heights I carried out a levelling exercise from a BM to certain key points. I have checked these levelling results.
Whilst my horizontal positions are accurate my GNSS derived heights after transformation are 3.349m LOWER than those from the levelling exercise. This is a constant offset across all points. It does not equal either antenna height (entered into Reachview) or any obvious interaction of them. My transform is WGS84 to UK OSGB using OSTN15/OSGM15.
Is there anything obvious that I might have missed that would cause this?