Coordinate conversion from ellipsoid to geoid

[saskiag]

Hi,

I imported the image coordinates in WGS84 (EPSG::4326) and converted them in CH1903/LV03 (EPSG::21781).
Can you please tell me what kind of transformation you (Agisoft) used to convert them from the ellipsoid to the geoid? (WGS 1984 Geoid? or  EGM96 Geoid ?)

Cheers,
saskiag

[Majaa]

Maybe its Helmert transformation. I think It is the best transformation in geodesy. isnt it?

[Sascha]

Helmert tranformation is the easiest way for 7-parameter transformation.
So i assume its helmert.

EGM 96 is part of the WGS84 definition, so the geoid model u use when selecting WGS must be EGM96.

That was my contribution to the solution .

Now my question (i am quite new to agisoft):

How did u convert the project into another coordinate system?EDIT:  FOUND IT

[MPB]

If I understand the question: Converting ellipsoid to geoid isn't really a full transformation - it's just a matter of the geoid height being subtracted from the ellipsoid height for each node/xy position, to produce 'orthometric heights.' Each ellipsoid has an associated geoid. EGM08 is the current best for IGS08 (i.e., WGS84) ellipsoid/reference frame as I recall, and GEOID 12B for NAD83. Geoids come in various resolutions, for example EGM08 on a 2.5' and an 1' (~ 1 GB file) are common. Hope this helps.

[saskiag]

Thank for your inputs and maybe I should have added that the Swiss Coordinates CH1903/LV03 (EPSG::21781) are a projected coordinate system (and WGS84 a geographic coordinate system). Therefore one need to re-project the coordinates  and therefore choose an ellipsoïd for the vertical correction.

In this case, I dunno if Agisoft chose the WGS 1984 Geoïd, the current Swiss Geoïd CHGeo2004, or a European one?
I'd like to know which one and what are the resulting elevation (Orthometric height, Ellipsoïd, Geoïd?)

Any thoughts?