The gelocation transformer does not work properly with modis swath

[winkey]

The geolocation transformer takes an average of the latitude of two rows.

padfY[i] =   padfGLY[0] 
           + (dfGeoLocPixel-iX) * (padfGLY[1] - padfGLY[0])
           + (dfGeoLocLine -iY) * (padfGLY[nXSize] - padfGLY[0]);

Each modis strip (10 geolocation rows) overlaps the previous strip. so when averaging the latitude of the 10th and 11th geolocation rows large errors are introduced.

[winkey]

The only idea I have for a fix of this is to add a new metadata item "GEOLOCSTRIP_HIEGHT" to the geolocation metadata. Then check if the if current row is a increment of the geolocation strip height, if unset it would not change the current behavior.

<VRTDataset rasterXSize="5416" rasterYSize="8120">
  <Metadata domain="GEOLOCATION">
    <MDI key="X_DATASET">x.tif</MDI>
    <MDI key="X_BAND">1</MDI>
    <MDI key="Y_DATASET">y.tif</MDI>
    <MDI key="Y_BAND">1</MDI>
    <MDI key="PIXEL_OFFSET">1.5</MDI>
    <MDI key="LINE_OFFSET">0</MDI>
    <MDI key="PIXEL_STEP">4</MDI>
    <MDI key="LINE_STEP">4</MDI>
    <MDI key="GEOLOCSTRIP_HIEGHT">10</MDI>
  </Metadata>
  <SRS>GEOGCS[&quot;WGS 84&quot;,DATUM[&quot;WGS_1984&quot;,SPHEROID[&quot;WGS 84&quot;,6378137,298.257223563,AUTHORITY[&quot;EPSG&quot;,&quot;7030&quot;]],TOWGS84[0,0,0,0,0,0,0],AUTHORITY[&quot;EPSG&quot;,&quot;6326&quot;]],PRIMEM[&quot;Greenwich&quot;,0,AUTHORITY[&quot;EPSG&quot;,&quot;8901&quot;]],UNIT[&quot;degree&quot;,0.0174532925199433,AUTHORITY[&quot;EPSG&quot;,&quot;9108&quot;]],AXIS[&quot;Lat&quot;,NORTH],AXIS[&quot;Long&quot;,EAST],AUTHORITY[&quot;EPSG&quot;,&quot;4326&quot;]]</SRS> 
  <VRTRasterBand dataType="Int16" band="1">
    <SimpleSource>
      <SourceFilename relativetoVRT="1">b1.tif</SourceFilename>
      <SourceBand>1</SourceBand>
      <SrcRect xOff="0" yOff="0" xSize="5416" ySize="8120" />
      <DstRect xOff="0" yOff="0" xSize="5416" ySize="8120" />
    </SimpleSource>
  </VRTRasterBand>
</VRTDataset>

[winkey]

fixed spelling of GEOLOCSTRIP_HEIGHT and removed a misplaced * in the patch

[Even Rouault]

This ticket has been automatically closed because Trac is no longer used for GDAL bug tracking, since the project has migrated to GitHub. If you believe this ticket is still valid, you may file it to ​https://github.com/OSGeo/gdal/issues if it is not already reported there.