[gdal-dev] gdalwarp : how many gcp's for -order n?

[Frank Warmerdam]

WolfgangZ wrote:
> Hi,
> 
> I know that I've seen it somewhere but I cannot find it any more, can 
> anyone tell me how many gcp's are needed for transform of order n? How 
> does -tps work, any literature reference about that option?

Wolfgang,

  * Note that 2nd order requires at least 6 GCPs, and 3rd order requires at
  * least 10 gcps.  If nReqOrder is 0 the highest order possible with the
  * provided gcp count will be used.

  * The GDAL Thin Plate Spline transformer is based on code provided by
  * Gilad Ronnen on behalf of VIZRT Inc (http://www.visrt.com).  Incorporation
  * of the algorithm into GDAL was supported by the Centro di Ecologia Alpina
  * (http://www.cealp.it).

I don't have any other info on the TPS algorithm.

Best regards,
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