RTK and Stop and go are all 23cm off

So I’m doing a bathymetry scan on Friday at a mine and ask the surveyor to mark a pin location for my base. He gives me an orthometric height, not ellipsoid. Won’t be able to contact him until Tuesday and the project needs to be done Monday lol. So he’s working in WGS 84 UTM and HT2-2002_v70 (hybrid geoid), just happens to be Canada. I presume the vert datum would have to be CGVD28. I converted a height above ellipsoid for the base, but I think my reference frame was NAD83(CSRS). I’m thinking the reference frame should be a ITRF, but which one? The only reference frames available for NRCan’s GPS-H tool are NAD83 or the Various ITRF. To make things more confusing for myself, my options for a project in View 3 is WGS 84 UTM CGVD28. Doesn’t say what geoid or reference frame I’m using. I know, a boring topic but I could use some help lol. Wouldn’t even known there was a problem, but I had a current water level for that day. Why can’t we all just use CGVD2013 and NAD83, life would be so much simpler.

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Geodesy is never boring :laughing:

The fact that the surveyor uses WGS84 baffles me. When going into centimeter accuracy job, this is the best you can do to have errors on your survey.

I would say the less risky here would be to use his/her coordinates as-is in the base, and select a coordinate system in the rover that will not apply any transformation, neither on the projection, neither on the height. You may apply transformation afterwards on the CSV export based on the what the surveyor replied.

So you can convert the UTM coordinates into latitude and longitude first, input them manually in the base page, and input the orthometric height as the ellipsoid height, which is false, but can be done anyway.

On the rover, select the UTM projection as coordinates system, and let ellipsoidal height as the vertical datum. This is not perfectly rigorous but will work.

The problem I can’t measure by doing that is the correction brought by the geoid grid is not applied. So if the survey is very wide, you will neglect geoid undulation variations, which can be several centimeters on a few kilometers - I’m speaking of what I know best which is the French geoid.

This is maybe not that clear of a message. Feel free to ask.


I’ll give that a try. Nice thing about View 3 is I can create new projects and import the collected points. His WGS 84 is projected UTM and the vertical uses the older CGVD28 and the hybrid geoid model HT2v70. It’s still supported and used by a lot of mines for some weird reason. Maybe I’ll try entering the ellipsoid height as orthometric as you suggest. I can apply geoid height differences in excel afterwards. Thanks for the suggestion.

Hi Shaun,

I’d suggest you another option that is available in ReachView 3 since 7.3 version. If the surveyor gives you local base coordinates in WGS84 UTM and CGVD28, you can input them in base mode without any manual conversion.

You need to create a project with an appropriate coordinate system, and input or import a given point’s coordinates. ReachView 3 will convert the local coordinates into the geographical ones, and you’ll be able to pick up this point in the base mode.

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