SurvCE RTK Base Elevation Error

Please let us know...

I may be way off base here and possibly too simplistic, but the distance from the base of the antenna to the base mount on the GR-5 is 0.78'. When we reboot our dc there's an offset setting in there somewhere (sorry I can't remember where without it front of me) that has to be reset, or all the elevations are 0.78' too low.

Yes, there is a setting that you can toggle from slant to ARP. all of our settings appear to be correct. In fact we get incorrect elevations whether it is measured either to the slant mark or vertically to the ARP.

One of the problems that I ran into when trying to ascertain the problem was that Carlson does not record the actual measured HI value of the base antenna in the raw data (amazing flaw, imho). They also do not record whether it was measured to the slant mark or vertical to the ARP (compounding flaw). It appears that when it comes to the base HI, they only record calculated values in the raw data. I spent many hours trying to figure out where the problem was. It seems to be how Carlson handles the offset in the RTCM 3.0 protocol.

The bottom line is that you may have some incorrect elevations of base points that were recorded in this manner.

Scary, huh?

Ed

Edward

Have you tried reverting to RTCA to see if the error persists? As I understand we now have to use RTCMv3 to handle the Glonass message format in SurvCE.

I'm going to try a test set up today to check this. The raw file records the vertical height from station mark to antenna phase centre as 'Base rod hgt:' - is that where you identified the error?

Yes, I've noticed it. Using SurvCE 2.6 with Altus APS3. The raw data stored for the base is a reduced ARP and seems to be right. The height stored to the receiver I've seen in the RINEX files is wrong. The height used to reduce the coordinate elevation is right. I can set up with the total station on a base point (observed with a slant height) and tie to a rover point (observed with an ARP height) and the vertical hits right on.

So, when I upload to OPUS, I use the height stored in the RW5 file, convert to meters and I'm good to go. I have to ignore what's stored in the RINEX file, because it's bogus. I agree that the RW5 should reflect what is actually measured in the field (you know, because it's a raw data file).

Artie,

No I haven't tried RTCA but I have tried CMR+ and the software calculated a correct elevation using that.

As I understand it; CMR+ does not broadcast the antenna offset as part of the message correction, but RTCM 3.0 does.

I believe that the error is caused by the software applying the offset correction to the already corrected RTCM 3.0 message. But that is just a guess.

I have performed enough tests to be convinced that there is a problem with the software.

Hopefully someone from Carlson will see this thread and chime in.

Ed

Interesting Shawn. Are you using RTCM or CMR+? We have done a test where we changed from one to the other and it calculates a different elevation for the same point.

The fact that they don't store the raw measurements in the raw data made this very hard to track down. I have requested that they include both the raw, measured HI; and the measurement point in the raw data.

> Hopefully someone from Carlson will see this thread and chime in.
>
> Ed

I dispatched a message into the Carlson Technical Support staff regarding this issue yesterday and was informed (as stated above) that switching to the CMR+ protocol should address the problem as a temporary solution.

The development team has been made aware of the problem and will be taking corrective actions but I can't say when a permanent solution will be made available.

Thanks Ladd.
I had already reported it to them.
Having your software reporting incorrect elevations seems like it should be pretty high on the "To Fix List".