[Freegis-list] Polynomial approximation of control points

[Frank Warmerdam]

Ronan wrote:
> I’m looking for a C/C++ source code for a polynomial approximation of 
> control points.
> 
>  
> 
> Input : X Y LAT LON of control points.
> 
> Output : polynomial coefficients, any degree of polynomial (1, 2, 3…)
> 
> Can be used from projected coordinates (XY) to LAT / LON and back.
> 
>  
> 
> The purpuse is to georeference raster charts from a paper source.


Ronan,

I know that GRASS and GDAL have some level of support for polynomial based
warping of images.   The code in GDAL can be found in gdal/alg/gdal_crs.c.
I have had some robustness problems with it at 3rd order and I don't think
it does any higher orders.   The code can be used with the gdalwarp and
gdalwarptest utilities, but it isn't that easy to specify the control points
if they are not already contained and supported by the format driver.

I am interested in hearing if you find a better resources.

Best regards,
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