I was reading through some of the information on the OPUS site today and read that if you submit a file with a antenna height of 0 the results will give the position at the antenna reference point (ARP). So just for the fun of it I submitted a file twice one with antenna height at 0 and one at 1.8m (our measurement to ARP.) The results I got back on the ortho height came back within .005m of each other. So now I am confused, I would think that the ortho heights would differ by 1.8m! Sent an e-mail to NGS, but haven't had a reply, what are your thoughts?
Cy
Can you post the OPUS returns? This is a little unsettling. Suppose I could try it myself.
I can in the morning when i get back into the office.
OPUS may have remembered your antenna height from the previous submissiom and just used the "None" antenna.
Paul in PA
If you have a profile setup I believe it will use the HI in the profile, which is contrary to what I think it should do.
I think the profile is fine to have, but should ALWAYS be overridden by what is entered with the occupation.
Even better would be an option for OPUS to read the information in the header of the RINEX file (or in the proprietary format such as trimble .dat). My files always have the correct antenna type and HI, why not be able to use that?
> If you have a profile setup I believe it will use the HI in the profile, which is contrary to what I think it should do.
>
That might be it John. If that's the case then it's fine, we use a fixed height tripod so our ARP is the same everytime.
Cy
Ditto John on the profile. I deleted mine a long time ago. It bit me on a few occasions although it was clear in the report what was used. Dangerous if you don't have one type of equipment and fixed height rods for everything.
That is very dangerous.
I thought OPUS was intended as a check rather than a final, one-shot solution.
It is in most cases, but in areas of the country where there is nothing else to use and the consequences and need for accuracy are very low it is a good resource. I use it routinely as a basis for elevations for projects where I just as easily could have used an assumed elevation. Of course when I do that I supply all necessary the documentation and caveats.
Most often when checked the OPUS elevations I get are within a couple of tenths of the verified elevations. One would expect some level of consistency IMHO.
Ha Ha Ha! Sorry, but I have to laugh at this comment, Cliff. Most of the folks I deal with think an OPUS solution is absolutely correct 100% of the time. I have spoken with several people who didn't every know how to read the report and were unaware of the disclaimer printed on every one. One national firm was adjusting their data to match the OPUS position even though they suspected it was incorrect (which it was.) Very few of the young guys distrust (or know how to check) any number produced by a computer or a handheld box. Both cost money so they must provide the correct answers, right?!
The 1.8 meter discrepancy discussed above is a perfect example...
Isn't that nice?!
It beats the typical 60 second jump out of the truck with the network rover shot.
All measurements, particularly GPS measurements, should be treated with a healthy dose of skepticism.
I use OPUS to position my Surveys, usually a single OPUS solution held fixed with OPUS checks on other points in the network. Obviously the report should be examined for peak to peak errors and the percentage of observations used and the ambiguity number. Sometimes on a remote project with marginal sky view we have to accept a marginal OPUS solution which is OK as long as you know what you have and it serves the needs of the project.
I've gotten OPUS observations on boundary monuments in the Forest where I cut down small trees to improve the sky view. The main task was to recover the boundary and the OPUS was just a "nice to have" thing.
