Q: What is the azgcorr ASCII DEM format?
A:
The ASCII DEM format used by azgcorr is a flat ASCII file with regularly-spaced height values, with a header line included at the top. The header data items are:
North->South Xsize YSize Xmin Ymin Xmax Ymax grid size
So eg.
1 2000 2000 400000 850000 410000 860000 5
..means a DEM that starts in the north-west corner, is 2000x2000 cells, has X values from positions 400000-410000, Y values from positions 850000-860000 and a resolution of 5. This particular example is from a British National Grid projection DEM, as would normally be used for flights in the UK, so the positions are in metres and are related to that projection.
Note that if your DEM runs from south to north rather than north to south as above, you should use a 0 as the first number (rather than 1).
As well as the original and extended ascii headed files the -eh option will accept a file with a standard ARC ASCII grid header. This has pairs of identifiers and values on single lines:
ncols, nrows,[xllcorner, yllcorner OR xllcentre, yllcentre], cellsize and optionally nodata_value