Ellipsoidal DEM?

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Ellipsoidal DEM?

Andyjo

I’ve been digging through the ossim site, and a bit of code, and haven’t been able to figure out if you can use a DEM that is relative to an ellipsoidal model, or if they always have to be relative to the geoid.

If the DEMs have to be relative to the geoid, is there an easy way to ‘subtract’ DEM values between two files?

IE: <GeoidalDem>.tif  = <EllipsoidalDem>.tif - <EGM2008>.tif

 

Thanks!

 

Andrew Johnson


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Re: Ellipsoidal DEM?

David Burken
Use "identity" for "geoid.type"

// elevation_manager.elevation_source1.geoid.type: geoid1996
elevation_manager.elevation_source1.geoid.type: identity

Snip from:
http://trac.osgeo.org/ossim/browser/trunk/ossim/etc/templates/ossim_preferences_template

// Identity geoid is 0 everywhere, so MSL = Ellipsoid. Useful when DEM provides posts
// relative to ellipsoid instead of customary MSL. This is specific to each elev database:
//elevation_manager.elevation_source3.geoid.type: identity

// With geoid (see Height above ellipsoid):
$ ossim-info --height 27.9 -81.0
Opened cell:            /data1/elevation/srtm/1arc/N27W081.hgt
MSL to ellipsoid delta: -29.3161998748779
Height above MSL:       25
Height above ellipsoid: -4.31619987487793
Geoid value:            -29.3161998748779

// Identity:
$ ossim-info --height 27.9 -81.0
Opened cell:            /data1/elevation/srtm/1arc/N27W081.hgt
MSL to ellipsoid delta: 0
Height above MSL:       25
Height above ellipsoid: 25
Geoid value:            -29.3161998748779

Take care,
Dave


On 08/21/2014 02:38 PM, Andrew D. Johnson wrote:

I’ve been digging through the ossim site, and a bit of code, and haven’t been able to figure out if you can use a DEM that is relative to an ellipsoidal model, or if they always have to be relative to the geoid.

If the DEMs have to be relative to the geoid, is there an easy way to ‘subtract’ DEM values between two files?

IE: <GeoidalDem>.tif  = <EllipsoidalDem>.tif - <EGM2008>.tif

 

Thanks!

 

Andrew Johnson



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