[gdal-dev] gdal_translate -a_srs

[Frank Warmerdam]

Greg Coats wrote:
> Following Frank's suggestion, and in accordance with the web page GDAL 
> Utilities http://www.gdal.org/gdal_utilities.html Creating New Files
> I issued these GDAL commands
> 
> $ gdal_translate --version
> GDAL 1.7.2, released 2010/04/23
> $ gdal_translate -of GTiff -ot Uint16 -a_srs NAD83_UTM18N.wkt in.tif out.tif
> $ gdal_translate -of GTiff -ot Uint16 -a_srs EPSG:26918       in.tif out.tif
> The two out.tif files created are identical.
> 
> gdalinfo shows that out.tif has the expected values for PROJCS through 
> AUTHORITY, including
> UNIT["metre",1,
> but gdalinfo shows out.tif still has latitude longitude values for 
> Origin and Pixel Size  
> Origin = (-78.000555555559998,40.000555555555515)
> Pixel Size = (0.000092592592593,-0.000092592592593)
> rather than the expected Origin and Pixel Size values for NAD 1983, UTM 
> Zone 18N of about
> Origin = (271500.000000000000000,4335000.000000000000000)
> Pixel Size = (38.385826771653548,-38.385826771653548)
> 
> This Origin and Pixel Size difference prevents out.tif from being 
> displayed by Qgis along with the original NAD 1983 UTM Zone 18N .tif. It 
> is though the gdal_translate -a_srs process is only partially complete? 
> What additional step is necessary so that out.tif has Origin and Pixel 
> Size values in UTM, rather than lat/long?

Greg.

The -a_srs switch assigns a new coordinate system.  It does not reproject
the image.  I think you want to use gdalwarp like:

   gdalwarp -t_srs EPSG:26918 in.tif out.tif

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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