Trimble "Nominal" Phase Center
Can anyone tell me what the Trimble definition of "Nominal" Phase Center is?
I have assumed in the past that the nominal phase center per Trimble was the same as the NGS L1 relative phase center. That being about 20mm above the IGS absolute phase center for L1.
Recently I have found Trimble nominal phase center heights that are 20mm above IGS L1 height, I have found one that is within 1mm of the IGS L1 height, and several that are about 20mm below the IGS L1 height. Those being about 40mm below the old NGS L1 relative height.
The only thing I think I could be missing is Trimble's definition of "nominal" phase center, how do they calculate it?