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.