[Geotiff] algorithms for interpreting between tiepoints

[Frank Warmerdam]

On 1/4/06, Butler, Jason <Jason.Butler at dsto.defence.gov.au> wrote:
>
>
> Hello everyone,
>
> I am implementing a geotiff reader for a client, and need some assitance
> with implementing the case where a geotiff is georeferenced using 3 or more
> tie-points.
>
> Could anyone tell me what the standard method is for generating the set of
> lat/long coordinates from the raster space of the geotiff when only
> tiepoints is specified?

Jason,

I would say that the most common approach is to develop
best fit polynomials in X and Y.  The order can be determined
based on the number of tiepoints available.  Some code
implementing this (but not tied into libgeotiff) can be found at:

  http://www.gdal.org/srctree/alg/gdal_crs.c

Of course, lots of other mechanisms are also possible.   A
tesselation based breakdown of the surface based on the
tiepoints may give better results in some circumstances.  Thin
Plate Splines are another approach.

Best regards,
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