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

A:
This occurs normally for Eagle or Hawk data that are too large for the HDF 4 file format. This format is normal for ARSF delivered Eagle and Hawk data.

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

For user created level-2 BIL files the options -Bi, -Bs or -Be have to be used. -Bi and -Bs require a -B parameter command to provide the image file details. -Be expects an ENVI/BIL/BSQ pair of files with at least the items on the header file: samples, lines, bands, "header offset" ( to skip header info/data etc at the start of the binary file), "data type" ( = 4 or 12 only ie f32 or u16 ), interleave ( = bil or bsq ), "sensor type" ( = atm, casi, az16 or ccd ), "default bands" = ( r g b band numbers )

See the -help command for more details.

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