[Geotiff] GeoTIFF spec - ModelTransformTag is not invertible

Grissom, Ed ed.grissom at intergraph.com
Mon Feb 5 06:56:12 PST 2007

Frank - 

I am not sure that anything needs to be changed.   

After Niles pointed out that the K value is the pixel value and not
another coordinate, it is clear that the matrix does not have the same
definition as our internal 4x4 transform matrix and we should always be
modifying this matrix before using it. 

If anything, the "Summary" quoted below might be appropriate somewhere.
I looked at the FAQ, and it appears to be more high-level than this
issue, so I am not sure where would be the right place for it.   Perhaps
an editorial repository ? 

ed grissom
ed.grissom at intergraph.com

-----Original Message-----
From: Frank Warmerdam [mailto:warmerdam at pobox.com] 
Sent: Sunday, February 04, 2007 7:50 PM
To: Niles Ritter
Cc: Grissom, Ed; GeoTIFF Mailing List
Subject: Re: [Geotiff] GeoTIFF spec - ModelTransformTag is not

Niles Ritter wrote:
> Summary:
> ----------
> GeoTIFF files which have a zero on the (3,3) coordinate in
> the ModelTransformTag is perfectly valid GeoTIFF, even
> though the matrix is not invertible. GeoTIFF readers 
> should not crash on encountering this situation.

Niles / Ed,

I am open to specific suggested changes to clarify this in the document,
or perhaps also in the FAQ.

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    | President OSGeo,

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