[Gdal-dev] Affine Transformation and Calibration Equation for Maptech/BSB format

[marcello ferrero]

Hi all, 
I'm quite new to gdal and GIS in general and I need some help here.

I'm trying to figure out how to make the PixelToCoord and CoordToPixel transformations
for an open source project (amerigo) where I would like to use the gdal library in order to read NOAA/BSB files.

If I generate the world file for a BSB file with gdalwarp, the generated values for the affine transformation parameters 
do not produce a good result. If I use the affine trasformation to  (basically the transformation is not very precise).
 
I believe the parameters for a more precise transformation are already in the BSB header in the WBX,WPY and PWX, PWY fields,
but I'm not sure what are the correct data to use.
For example if we consider the chart file 11013_1.KAP     (STRAITS OF FLORIDA AND APPROACHES)
the following values are in the header.
 
WPX/3,74057.63283,914.1573321,-4.457688988e-006,0.9314526304,4.199727384e-007
    8.909433511e-007,0.003888412047,4.049230257e-009,4.656999088e-009
    -7.344637416e-009
WPY/3,24849.77398,-0.0001719938458,-841.3888082,-2.236403169e-006
    -4.23802978e-007,0.5645817982,-9.615822208e-009,-2.118680351e-009
    1.85245272e-009,-0.05788953807
PWX/3,-85.82846924,0.001190193579,1.242062009e-015,1.177436646e-010
    4.828087799e-020,-4.158931771e-019,-7.813843316e-015,-1.938704561e-024
    -3.205324874e-024,3.339741723e-023
PWY/3,28.48799091,4.631711681e-016,-0.001052175742,-7.983285528e-020
    -7.030373462e-020,-5.245662991e-009,4.239300639e-024,1.848231681e-024
 
What are the parameters between them to take into account?
Also, what kind of trasformation is this one? Is it a sort of calibration equations that uses also the ref points and errors contained in the same BSB file?
This is an example of a REF point and ERR associated from the same BSB file.

REF/1,422,8543,19.1436611111,-85.3263888889

ERR/1,0.1694080000,0.2849210000,0.0002953620,0.0002017170

Does anybody understand how I could use these values to have a precise result?

Best regards,
Marcello Ferrero


       
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