Normalise calculated area to patch angle (steepness)

[murraycutforth]

I touched on this on my other post, how about using the 30m resolution elevation model from the elevation package (https://pypi.org/project/elevation/) to get the surface gradient?

[SimonFisher92]

@murraycutforth has generated a solution for elevation with @SimonFisher92 adding functionality for slope direction