[gdal-dev] Lat/Lon projection from satellite swath

[Andrew Brooks]

On Tue, 17 Nov 2009 07:07:59 -0000, Raspaud Martin <martin.raspaud at smhi.se> wrote:
>
> Now I would like to project satellite data for which I have the 2d lat
> and lon grids onto, say, a polar stereographic projection for example.

GDAL can do this using VRT files.

First create a VRT file to represent your raw data set, eg.
<VRTDataset rasterXSize="2048" rasterYSize="100">
  <VRTRasterBand dataType="UInt16" band="1" subClass="VRTRawRasterBand">
    <SourceFilename relativetoVRT="1">input.dat</SourceFilename>
    <ByteOrder>LSB</ByteOrder>
    <other stuff like ImageOffset, PixelOffset, LineOffset, ...>
  </VRTRasterBand>
  <other bands...>
</VRTDataset>

Then do similar for each of your latitude and longitude files, eg.
<VRTDataset rasterXSize="2048" rasterYSize="100">
  <VRTRasterBand dataType="Float32" band="1" subClass="VRTRawRasterBand">
    <SourceFilename relativetoVRT="1">latitude.dat</SourceFilename>
    <ByteOrder>LSB</ByteOrder>
    <other stuff like ImageOffset, PixelOffset, LineOffset, ...>
  </VRTRasterBand>
  <other bands...>
</VRTDataset>
and similarly for longitude.dat

Finally add pointers to the lat/lon VRT files into your data VRT
  <Metadata domain="GEOLOCATION">
    <MDI key="X_DATASET">longitude.vrt</MDI>
    <MDI key="X_BAND">1</MDI>
    <MDI key="Y_DATASET">latitude.vrt</MDI>
    <MDI key="Y_BAND">1</MDI>
    <MDI key="PIXEL_OFFSET">0</MDI>
    <MDI key="LINE_OFFSET">0</MDI>
    <MDI key="PIXEL_STEP">1</MDI>
    <MDI key="LINE_STEP">1</MDI>
  </Metadata>

Then use the data VRT as input to the gdalwarp program.  You may need to
use the -tps option, see the manual page.

That's the general idea; let us know if you have any success or problems.

Andrew