Hi, I have a question that i hope you can help me.
I want to use some aster Dem, but in specifications I read that aster Dem is using EGM96
geoid . Do I have to do something special to use those DEM’s?
The zone that I work is WGS84 147N.
Thanks in advance for the answer.
Hi Javier,
EGM96 (I guess somethin’ like ‘Earth Geodetic Model’) refers to the
vertical datum. If you only need relative height information (e.g. for
watershed analysis), you do not need information retrieved from the
vertical datum. However, if you need absolute heights (e.g. height
above sea level), you should recalculate the height values (substract
EGM96 offset from Aster DEM heights) according to the region of your
DEM.
Hope that helps
Stefan
Quoting “Javier García [via OSGeo.org]”
<[hidden email]>:
Hi, I have a question that i hope you can help me.
I want to use some aster Dem, but in specifications I read that
aster Dem is using EGM96
geoid . Do I have to do something special to use those DEM’s?The zone that I work is WGS84 147N.
Thanks in advance for the answer.
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Hi Javier,
EGM96 (I guess somethin’ like ‘Earth Geodetic Model’) refers to the
vertical datum. If
you only need relative height information (e.g. for watershed
analysis), you do not need
information retrieved from the vertical datum. However, if you need
absolute heights
(e.g. height above sea level), you should recalculate the height
values (substract EGM96
offset from Aster DEM heights) according to the region of your DEM.
Hope that helps
Stefan
Quoting “Javier García [via OSGeo.org]”
<[hidden email]>:
Hi, I have a question that i hope you can help me.
I want to use some aster Dem, but in specifications I read that
aster Dem is using EGM96
geoid . Do I have to do something special to use those DEM’s?The zone that I work is WGS84 147N.
Thanks in advance for the answer.
grass-user mailing list
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The zone that I work is WGS84 147N.
Normally the Aster DEM comes with a WGS84 lat-long grid, so your
settings seem to be ok, except that you have a zone; there are no
zones for WGS84. Maybe your location is UTM zone 147N? Then the import
of the Aster DEM will not work. You have to set up a WGS84 location.
Or just do the following in your current loacation:
r.in.gdal in=aster.tif out=aster.dem location=aster
With that, r.in.gdal will create a new location corresponding to the
projection information of the Aster DEM.
Stefan
Quoting “Javier García [via OSGeo.org]”
<[hidden email]>:
Hi, I have a question that i hope you can help me.
I want to use some aster Dem, but in specifications I read that
aster Dem is using EGM96
geoid . Do I have to do something special to use those DEM’s?The zone that I work is WGS84 147N.
Thanks in advance for the answer.
grass-user mailing list
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On Sat, Mar 24, 2012 at 5:18 AM, Stefan Sylla <stefansylla@gmx.de> wrote:
EGM96 (I guess somethin' like 'Earth Geodetic Model') refers to the
vertical datum.
FWIW, you can find a gridded version of the EGM2008 here
http://grass.osgeo.org/wiki/Global_datasets#EGM2008_Geoid_Data_.28Earth_Gravitational_Model.29
Markus
Don’t forget that afterwards you’ll have to reproject the raster using r.proj into the old location.
Daniel
–
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Geschäftsführung für Forschung und Entwicklung
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On Mar 24, 2012 5:29 AM, “Stefan Sylla” <stefansylla@gmx.de> wrote:
The zone that I work is WGS84 147N.
Normally the Aster DEM comes with a WGS84 lat-long grid, so your
settings seem to be ok, except that you have a zone; there are no
zones for WGS84. Maybe your location is UTM zone 147N? Then the import
of the Aster DEM will not work. You have to set up a WGS84 location.
Or just do the following in your current loacation:r.in.gdal in=aster.tif out=aster.dem location=aster
With that, r.in.gdal will create a new location corresponding to the
projection information of the Aster DEM.Stefan
Quoting “Javier García [via OSGeo.org]”
<[hidden email]>:Hi, I have a question that i hope you can help me.
I want to use some aster Dem, but in specifications I read that
aster Dem is using EGM96
geoid . Do I have to do something special to use those DEM’s?The zone that I work is WGS84 147N.
Thanks in advance for the answer.
grass-user mailing list
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Am 25. März 2012 20:33 schrieb javier Garcia Prieto <fjgarciaprieto@hotmail.com>:
Oh yes, of course, I’m going to reproject to an UTM Location so I can use other maps that I already have. Just a aquestion, with the Aster DEM, it comes togeher a NUM file. ¿Do you know what is for?
Having rarely worked with ASTER, I can’t say - my suggestion would be to look in the metadata, in whatever form the publish it in. Otherwise I’d instinctively say it sounds like a kind of metadata raster (I’ve seen this with other datasets) where the value of the pixels is some kind of unit for quality in the actualy elevation data.
Oh yes, of course, I’m going to reproject to an UTM Location so I can use other maps that I already have. Just a aquestion, with the Aster DEM, it comes togeher a NUM file. ¿Do you know what is for?
I understand that this is an indication of the quality of the DEM data. The ASTER elevations are a merge of several satellite images from different times, and the NUM value in each cell shows how many images were averaged to get the value at that cell location. If it’s low, the elevation might not be reliable, and if NUM is high, it’s probably OK.
--
Micha Silver
GIS Consultant, Arava Development Co.
[http://www.surfaces.co.il](http://www.surfaces.co.il)