[Geotiff] ModelPixelScaleTag

[Grissom, Ed]

There are three ways to specify the raster-to-model relationship

1) point and scale    (no rotation, raster is orthogonal in coordinate
system)
2) list of tie points (at least three points for affine relationship,
unlimited for "mesh")
3) transform matrix. 

I would venture to say that specifying _only_ the tie points REQUIRES 3 or
more points.  I would not consider a file georefernced with less than that
(absent other info). 

-- 
ed grissom
ed.grissom at intergraph.com



> -----Original Message-----
> From: geotiff-bounces at remotesensing.org 
> [mailto:geotiff-bounces at remotesensing.org] On Behalf Of Gillian Walter
> Sent: Thursday, August 26, 2004 9:24 AM
> To: geotiff at remotesensing.org
> Subject: [Geotiff] ModelPixelScaleTag
> 
> 
> Hi,
> 
> I have a question about the Geotiff ModelPixelScaleTag.  On 
> page 25 of 
> the Geotiff specification, there is a diagram indicating that either 
> ModelPixelScaleTag and ModelTiepointTag, or 
> ModelTransformationTag alone 
> will be used to geocode an image.  However, the next page 
> indicates that 
> ModelPixelScaleTag and ModelTransformationTag are optional.  
> Is it valid 
> to specify only the ModelTiepointTag and not 
> ModelPixelScaleTag?  I was 
> under the impression that it was, since the ModelPixelScaleTag and 
> ModelTransformationTag parameters can't always accurately represent a 
> dataset's geocoding (eg. slant range SAR imagery), but one of our 
> customers disagrees, and I can see how the spec could be interpreted 
> either way.
> 
> Gillian
> 
> _______________________________________________
> Geotiff mailing list
> Geotiff at remotesensing.org
> http://xserve.flids.com/mailman/listinfo/geotiff
>