Is the antennae height input wanting slant or real height!
I measure up using slant to a topcon pg-a1 antennae!
Do I need to convert myself?
The antenna height is the vertical height to the antenna reference point (ARP). The ARP is usually where the antenna screws into the tripod. With a fixed height tripod it is the height of the tripod. If you measured a slant height you have to convert it to the vertical height to the ARP.
Peter Lazio
Vertical ARP height.
You can use a fixed height tripod or I simply measure the the ARP (usually the bottom of the antenna mount on the bottom) height directly when I have the receiver on a tripod. If you measure the slant height then you have to calculate the ARP height. The receiver manual should have a diagram to show you how to get the ARP from the slant height. But like I say I don't bother with that, I just measure the ARP height. OK it's a little slanted but for OPUS purposes I think a millimeter or two won't make any difference.
The other replies are correct. I recently was retracing some control work from 2008 that others had used Topcon antennas on, they had based their OPUS on measurement to the noted antenna measuring point on the antenna, it amounted to around 0.2' of difference in the vertical. So yes, vertical to the ARP, everyone should study the NGS antenna diagrams carefully for any antenna you are using and make the appropriate corrections (both slant and offset) PRIOR to submitting the data to OPUS.
This is one of those errors that will bite you if you always use the same antennas and always make the error in the HI, it will look good, i.e.: agree with itself, BUT it is wrong.
SHG
