That did the trick.  Thanks!

Greg


On Jan 9, 2009, at 12:21 PM, Frank Warmerdam wrote:

Greg Ederer wrote:
...
Note that the pixel/line coordinates in the above are from (0.0,0.0) at the top left corner of the top left pixel to (width_in_pixels,height_in_pixels) at the bottom right corner of the bottom right pixel. The pixel/line location of the center of the top left pixel would therefore be (0.5,0.5).
</end docs>
But, I'm still unsure how to compute the required values. The docs don't give units for GT(1) and GT(5), and for GT(0) and GT(3). My data have a resolution of 0.1 deg lat X 0.1 deg lon, and the upper left lat/lon is 40N,20W. Could you give me some pointers on how to compute the transform values?

Greg,

The geotransform coordinate system is whatever is defined by the <SRS>
tag.  So in your case I believe long/lat WGS84.

I imagine your GeoTransform would be:

 -20.05, 0.1, 0.0, 40.05, 0, 0.1

This is assuming that the upper left corner really reflects the center
of the top left pixel in which case a half pixel offset is needed. I'm
also assuming north up image orientation.

Best regards,
--
--------------------------------------- +--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmer...@pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush | Geospatial Programmer for Rent


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