Sometimes, you just get really lucky in how well the benches you tie to fit together.
Today, I set a base unit up for a static observation of 2 hours.
Using a 2 minute RTK shot, I tied into a temporary benchmark that I had set on a nearby site earlier this year, which had static ties to two published benchmarks.
I then tied into two additional benchmarks on the opposite side of the current job site. On both, I did a 2 minute RTK shot and on one I did a 10 minute static.
I submitted the base observation to OPUS.
I translated all points observed today so that the RTK shot on the bench that had the 10 minute static observation matched the published elevation.
The temporary bench on the earlier site was off by 0.018' (RTK).
The second bench that was observed today just by RTK was off by 0.004'
The elevation at the base unit was off of the OPUS solution by 0.014'
Reducing the base station static observation by holding the rover static observation on the published bench as fixed matched the RTK shot within 0.012'
That accomplished about 2 miles of leveling all around a town environment in about 30 minutes.
All of this in order to report elevations to the tenth of a foot.
I had a check with older work, checks between RTK and static observations, a check between two additional benches, and a check with OPUS.
I remember the days when it used to be basically an all day affair with two to three guys to run levels from various sides of a project.
RTK is funny like that...sometimes off by 0.1' vertically, sometimes right on.
I thought you had to observe 15 for minutes (static) for OPUS RS though?
I think this GPS stuff is here to stay!:-P
I love it when a plan comes together...
RTK height transfer can achieve low-order leveling accuracies when:
1. The geoid is well-modeled throughout the area of concern. This can be determined through sufficient experience.
2. The ionosphere and troposphere are well-modeled. This is much harder to control.
3. The distances between observed stations are modest. This can be controlled by the user by choosing appropriate locations.
4. The GNSS constellation is cooperative. This can be controlled by the user by choosing appropriate times of observation.
It sounds like all the variables came together well in your project.
> I thought you had to observe 15 for minutes (static) for OPUS RS though?
The 10 minutes was with the rover on an offsite bench. I then processed between the bench and the on site base station to get the elevation of my onsite point.
I left the base unit cooking for 2 hours while I was doing additional total station work. This was the session sent in to OPUS. That just gave me an additional check on the reported numbers from the paragraph above - and all I had to do was leave it running while I worked on another portion of the project.
1, 3, 4 = check check check.
Your post did bring to mind an interesting experiment I should conduct. I should go out and measure all those point again using RTK with NO GEOID selected in the collector. It would be interesting to note how much difference that would make.
As the distances involved were not particularly far, I wonder how much of a difference using the geoid file actually did make.
You do not need to re-observe to find your ellipsoid heights. Just compute the geoid separation at each of your points and subtract from your computed elevations and you will obtain your ellipsoid heights which is all your receiver was observing anyway.
Good point.
If I had been using my brain for more than keeping my skull from collapsing, I would have realized that.
Quickly looking at the datasheets for the benchmarks, it looks like there could have been about a tenth of a foot difference from the eastern to the western limit of the marks tied if I had not been applying the geoid separation by uploading a geoid file into the collector.
