There is sometimes a need to present geometry in a specific axonometric projection view. Here's a grasshopper definition for the "military projection" (xy plane rotated by 45deg, not skewed).

The principle is that the model itself is deformed (sheared) so that it's  image in the top viewport looks like an axonometric projection:

Method source:
http://www.arch.virginia.edu/computing/training/online/pdf/Creating...