Q: My image data is in a .bil file not an HDF, how do I geocorrect it with azgcorr?

A:
For ATM and CASI, the image data is held in the HDF file along with the image metadata. You get only a single HDF data file per flightline that contains all of the relevant data and azgcorr operates on this. Unfortunately, the HDF 4 file format used has a limit of about 2GB on how big the file can be, and data files from Eagle and Hawk frequently exceed this limitation.

To get around this problem, for Eagle and Hawk only the image metadata is held in the HDF file. The image data itself is held in a BIL (Band Interleaved by Line) file that has the same base name - this can be directly viewed using many GIS packages such as ENVI or ERDAS Imagine. For more information about this file format see the description at ​http://www.vterrain.org/Imagery/formats.html. Further information describing this file is held in an associated ASCII .hdr file that you can view in any text editor. So for each flightline, you should have three data files:

• flight_data.hdf - HDF file holding flight metadata such as project code and navigation data.
• flight_data.bil - BIL file holding the image data collected by the sensor but no descriptive metadata.
• flight_data.hdr - ASCII header file holding metadata such as the image dimensions.

Despite this, however, as long as all three files are in the same place you only need to pass the HDF file name to azgcorr to geocorrect the flightline. Azgcorr will transparently detect the other two files and extract the data from them as needed. So your azgcorr command might be something like:

azgcorr -mUK99 osgb02.cgrf -p 1 1 -bl 30 15 7 -1 -eh my_dem.dem -1 flight_data_l1.hdf -3 flight_data_l3.hdf

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