My local CORS station (blwy) data sheet shows positions for the ARP (antenna reference point) and the L1 Phase Center. Which one of these should I use (to augment my Locus data)? ARP seems to be the one recommended, but with our L1 Locus units, should we use the L1 Phase Center position?

And why do I get an "antenna height error" message when I import the CORS observation data into Project Manager?

Skylar, I just went through some of this with Bill Martin the other day. It seems that the folks at NGS don't have the ability or equipment setup to model the L1 phase center on their own to get a precise distance from the ARP up to the L1 phase center, so no external data is available. Therefore, you should use the distance printed on the bottom of the Locus receiver as the offset from ARP up to mechanical antenna element center.(The same place that the antenna ring screws on).

As to the antenna height error, in the settings/miscellaneous tab, you probably have the defaults set to 1 meter/3 meter or something like that for antenna bust checking...The antenna height of the cors is 0, thus the error message appears.....bob

Bob,

Thanks for your response, though I'm not sure I understood the first part of your message. In talking to a local Trimble rep, I am given to understand that the ARP is the location where the antenna attaches, and that the L1 Phase Center position is for the current antenna. The CORS data sheet gives positions (lat/long/ellip) for both points. It would seem to me that if the ARP position is used, one would need to use a vertical antenna offset reflecting the difference between the two (0.361' in my case). And that if the L1 Phase Center position is used, then a vertical antenna offset of 0.0 should be employed.

The CORS observation data must be referenced to one of the two points. It would seem to me that it would be the L1 Phase Center, but I have nothing to base this on.

You were right about the cause of my antenna height error message.

Finally, all vectors from the CORS station fail after processing (F5), but pass after adjusting (F7). Could this be a function of the settings in Project/Settings/Miscellaneous/Desired Project Accuracy?

Use the L1 phase center for the CORS data. For your units, measure the height to the mark on the receiver.

Skylar, sorry I confused you with my post. In rereading my words, yes, you use the L1 phase center data for use with the cors data and the locus data. The antenna reference point is the physical mounting point at the base of an antenna, ie the 5/8x11 thread as it meets the base of the plastic on your locus. You would then need to add the offset of the battery case, etc. to get up to the phase center.

Cors stations have the ARP listed for many reasons, one of which is that a different antenna could be screwed on to a mount without resurveying in the entire cors site, just by changing antennas and then providing a new offset from the ARP up to the phase centers. sorry for the poor wording...bob