GNSS Solutions verses Topcon Tools

Are you figuring grid/ground in this right?
N

Nate,

The distances involved are small enough that the grid to ground should not be that much of a difference.

I am stumped.

Thanks,
Jimmy

How do the coordinates of the points compare?

If they are similar then the processing is probably fine and you are dealing with different ways part of the software reports "distances". The coordinates are the primary result of most processing software, whether geodetic or some defined grid like SPC values.

Without checking I couldn't say, but I would not be surprised if some software doesn't report distance as the point to point vector distance (essentially slope distance) and not a ground relatable distance. Obviously software varies, but perhaps one is reporting grid distance, the other point to point, still another poaaibility would be ellipsoid distance.

So again, how do the coordinates compare?

PS "Grid to Ground" can still be significant depending on where you are in the grid. Grid scale factor varies with location, not even mentioning the elevation scale factor. Still I suspect some software is reporting vector point to point distance and not grid or ground.

- jlw

Jerry,

I basically export the coordinates, and do the comparisons in Carlson. I create a separate drawing for each set of points from each software, and then compare by xrefing one drawing into the other.

I am still trying to wrap my head around the post processing stuff. I don't do enough of it yet to be totally fluent with the software.

Thanks,
Jimmy

First You Have To Compare Apples with Apples

Topcon Tools and GNSS Solutions give many options in how to establish your Spatial Reference System. Do not expect the program defaults to be equal.

Once that is done you might expect results to be equal, but that is not the case. In order to get comparable solutions, both programs must also have the same orbit data available and they must know where that data is.

Once that is done results can still vary because each program may hold a different point fixed as it's default. Get that comparable and recompare the results.

Since you are taking data both ways (Topcon to Ashtech and vise versa) be careful that each program is finding and using the correct antenna model and antenna height.

I regulary use GPS tied into traverse points 100-200' apart and I notice grid to ground differences even without large elevations. Depending on where you are in an SPC the scale factor can easily exceed your elevation factor.

Now to your traverse comparison. If you do not carry elevations in your traverse you are wasting a rather significant data check. One of the first checks I did in the past (before putting total trust in my GPS) was the vector check. The GPS vector is 3D and on the same surface that my traverse was on. My first check was to compare my GPS vector to my traverse slope distance with no need for concern of scale factors. If you are comparing traverse horizontal distances you can use pythogarean theorem with the differences in ellipsoid or geoid height (because we are talking differences either works) and reducing the 3D vector to a 2D distance.

Now to answer your question, yes there is a video training available for download.

You have the option of submitting your Topcon files for OPUS-S or OPUS-RS solutions. Request OPUS extended data so that you also get SPC in feet. That is a very powerful third party check on your software setups. I put my OPUS results in as control points in geodetic coordinates with ellipsoid heights. I then switch my software settings to SPC and ellipsoid height in meters and compare my results with OPUS and then I switch to SPC in US Survey feet and ortho height for my last check. If my results are only differences in the third decimal place I know life is good. BTW, only hold 1 control point at a time as fixed or you can warp your solution.

Paul in PA

First You Have To Compare Apples with Apples

Paul,

Thank you for your reply.

I will hopefully have some time to do some comparisons in the next few days.

I really need to get this down better.

I may be posting more questions as I do more comparisons and checking.

Do you have the url for the ashtech ftp site? I assume that is where the videos are located at.

Thanks,
Jimmy

These Are BIg Files

"GNSS Studio" is what "GNSS Solutions" was first called, so that is what you want. Most upgrade changes since then are in smaller pdfs.

ftp://ftp.promagellangps.com/Land%20Survey/GNSS%20Solutions/Application%20Notes/Video/

I fully expected more questions.

Paul in PA