[Gdal-dev] saving GeoTiff

Frank Warmerdam warmerdam at pobox.com
Sat Mar 15 10:15:09 EST 2003

Ayman Kamal wrote:
> 1.
> You mentioned that
> adfGeoTransform[0] =   /* top left x */
> adfGeoTransform[3] =   /* top left y */
> -Does top left x mean the value of longitude for top
> left corner?
> -Does top left y mean the value of lattitude for top
> left corner?


Yes, if the coordinate system of the image is lat/long.

> 2.
> What does horizental, vertical pixel size mean?

The width of a pixel is the coordinate system being used.

> 3.
> Are adfGeoTransform[2],adfGeoTransform[4] always 0?

No. If the image is not "north up", that is the image is
rotated or sheared from the normal map orientation these will
be non-zero and then the interpretation of the pixel size is
more complicated.

In common use these values will be zero.

> 4.
> If the user doesn't give me any of these data, and
> still wants me to generate a GeoTiff file out of his
> faces' images for example, 
> are there default values that I can supply to generate
> a valid GeoTiff file?

It is pointless to create a "Geo" TIFF file without knowing anything
about a meaningful coordinate system.  If you feel the need to do so pick
any random values you feel like.

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