RTKLIB datums for REACH

Quick question here, for my mapping work, I have included the local Geoid in REACH’s RTKLIB. For context, my location is Singapore and we use SGeoid09 and gives more locally relevant elevation. My workflow is RTK using single base station from an IGS service near me, my baseline is about 15km. Pardon me if it sounds silly but anyone knows if using different datums from my base station will affect the horizontal geopositioning accuracy of the positions i collect?

Some recommend using ellipsoidal datums because the base station may be using ellipsoidal datum as well but I’m not sure how much that will affect the corrections that RTKLIB calculates.

I believe that you still can use the WGS84 coordinates if your base supports them, but then project them on the local ellipsoid. Hope that someone with more surveying experience can shine some light on this.

When you say “if using different datums from my base station” do you mean using geiod datum one time then ellipsodial datum another time?

Your IGS station may publish coordinates for ellipsodial and orthometric. The difference between these two elevations is the Geiod height and can be used to check elevations, same difference applied every time.

Elevations generally are not considered in corrections and should not have any affect on position.

Thanks for the explanation. Yes I mean if there are differential corrections from IGS, I suppose they use ellipsoidal, but my REACH geoid is the local one I am using, I was wondering if that would affect my positional results.

I remember reading that vertical positional accuracy is a great contributor to horizontal position accuracy, so I thought perhaps that would affect corrections. Don’t quote me though, that was what I remember reading from Trimble’s brochures for their “floodlight technology” which is essentially GLONASS plus an inbuilt pressure barometer to correct erroneous altitude readings.

Using a geoid model will have no effect on your horizontal positioning. Think of a geoid model as just a transformation from “gps” derived hieghts to fit a local hieght datum.

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