[Gdal-dev] Assigning correct projection info to GEotiff extracted from MODIS 08 atmospheric HDF

William Hudspeth wbhk at unm.edu
Fri Aug 13 12:31:44 EDT 2004


To begin with, I am trying to import MODIS08 atmospheric data files in 
HDF-EOS format with GDAL_TRANSLATE. According to the documentation and 
metadata associated with MODIS08 files, they are distributed as a 
1-degree resolution grid (hence 360 by 180 pixels in dimension) in 
Lambert Azuthimal Equal Area projection (measured in degrees). Again, 
according to the metadata in the file (using gdalinfo), latitude values 
range from -90 to 90 degrees, and longitude values range from -180 to 
180 degrees. No information is provided for dataum or ellipsoid.

I have used GDAL_TRANSLATE to successfully extract a single band (1) 
from one of the subdatasets (472) in the HDF file using the following 

gdal_translate -of GTiff -b 1 -a_srs "+proj=laea +x_0=-180 +y_0=-90" 
HDF4_SDS:UNKNOWN:"MOD08_D3.A2002174.004.2003228005230.hdf":472 mod08test.tif

The output I get is as follows:

Input file size is 360, 180
0.Warning 1: Lost metadata writing to GeoTIFF ... too large to fit in tag.
...10...20...30...40...50...60...70...80...90...100 - done

However, the problems are:

1. Using GDALINFO on the output file, no coordinate system is reported:

Driver: GTiff/GeoTIFF
Size is 360, 180
Coordinate System is ''
Corner coordinates:
Upper Left ( 0.0,  0.0)
Lower Left ( 0.0,  180.0)
Upper Right ( 360.0,  0.0)
Lower Right ( 360.0,  180.0)
Center ( 180.0, 90.0)
Band 1 Block=360X11 Type=Int16, ColorInterp=Gray

2. Looking at the file in something like ArcMap, the image looks right, 
but as seen in the output above, the lower left corner is 0,0, while it 
should be something like -180, -90.

3.  I have experimented with using different values for x_0, y_0, long_0 
and lat_0 that I use in the -a_srs argument to the gdal_translate 
call.The results summarized above are identical regardless of the values 
I use.

I would appreciate any ideas on how I can assign the correct projection 
to my output data file. I ultimately want to convert its coordinates 
back to standard geographic lat-long.

 Many thanks for considering my question. Bill

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