<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:arial, helvetica, sans-serif;font-size:10pt"><DIV>Hi all, </DIV>
<DIV>I'm quite new to gdal and GIS in general and I need some help here.</DIV>
<DIV> </DIV>
<DIV>I'm trying to figure out how to make the PixelToCoord and CoordToPixel transformations</DIV>
<DIV>for an open source project (amerigo) where I would like to use the gdal library in order to read NOAA/BSB files.</DIV>
<DIV> </DIV>
<DIV>If I generate the world file for a BSB file with gdalwarp, the generated values for the affine transformation parameters </DIV>
<DIV>do not produce a good result. If I use the affine trasformation to (basically the transformation is not very precise).</DIV>
<DIV> </DIV>
<DIV>I believe the parameters for a more precise transformation are already in the BSB header in the WBX,WPY and PWX, PWY fields,</DIV>
<DIV>but I'm not sure what are the correct data to use.</DIV>
<DIV>For example if we consider the chart file 11013_1.KAP (STRAITS OF FLORIDA AND APPROACHES)</DIV>
<DIV>the following values are in the header.</DIV>
<DIV> </DIV>
<DIV>WPX/3,74057.63283,914.1573321,-4.457688988e-006,0.9314526304,4.199727384e-007<BR> 8.909433511e-007,0.003888412047,4.049230257e-009,4.656999088e-009<BR> -7.344637416e-009<BR>WPY/3,24849.77398,-0.0001719938458,-841.3888082,-2.236403169e-006<BR> -4.23802978e-007,0.5645817982,-9.615822208e-009,-2.118680351e-009<BR> 1.85245272e-009,-0.05788953807<BR>PWX/3,-85.82846924,0.001190193579,1.242062009e-015,1.177436646e-010<BR> 4.828087799e-020,-4.158931771e-019,-7.813843316e-015,-1.938704561e-024<BR> -3.205324874e-024,3.339741723e-023<BR>PWY/3,28.48799091,4.631711681e-016,-0.001052175742,-7.983285528e-020<BR> -7.030373462e-020,-5.245662991e-009,4.239300639e-024,1.848231681e-024</DIV>
<DIV> </DIV>
<DIV>What are the parameters between them to take into account?</DIV>
<DIV>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?</DIV>
<DIV>This is an example of a REF point and ERR associated from the same BSB file.</DIV>
<DIV> </DIV>
<DIV>REF/1,422,8543,19.1436611111,-85.3263888889</DIV>
<DIV> </DIV>
<DIV>ERR/1,0.1694080000,0.2849210000,0.0002953620,0.0002017170</DIV>
<DIV> </DIV>
<DIV>Does anybody understand how I could use these values to have a precise result?</DIV>
<DIV> </DIV>
<DIV>Best regards,</DIV>
<DIV>Marcello Ferrero</DIV>
<DIV></DIV></div><br>
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