# Forum

### Author Topic: Coordinate conversion from ellipsoid to geoid  (Read 7408 times)

• Newbie
• Posts: 3
##### Coordinate conversion from ellipsoid to geoid
« on: June 01, 2015, 02:04:43 PM »
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,

#### Majaa

• Newbie
• Posts: 10
##### Re: Coordinate conversion from ellipsoid to geoid
« Reply #1 on: June 01, 2015, 03:10:48 PM »
Maybe its Helmert transformation. I think It is the best transformation in geodesy. isnt it?

#### Sascha

• Newbie
• Posts: 11
##### Re: Coordinate conversion from ellipsoid to geoid
« Reply #2 on: June 02, 2015, 03:23:13 PM »
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
« Last Edit: June 02, 2015, 03:29:32 PM by Sascha »

#### MPB

• Newbie
• Posts: 1
##### Re: Coordinate conversion from ellipsoid to geoid
« Reply #3 on: June 04, 2015, 01:58:39 AM »
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.