Alti diff slope norm and angular diff

[adebardo]

Context

The goal of this ticket is to implement the equivalent of dem_processing from demcompare. These are altitude difference visualizations.
Thus, the following need to be implemented:

• AltiDiffSlopeNorm
• AngularDiff

Code

We propose implementing these two processes directly in the DEM class, with the creation of two methods:

def alti_diff_slope_norm() and def angular_diff().

Example Usage:

dem1 = xdem.DEM("path1")
dem2 = xdem.DEM("path2")

diff = dem1 - dem2
slope_norm = diff.alti_diff_slope_norm()

The idea is to take inspiration from what is done for terrain attributes.

For alti_diff_slope_norm:

• Adapt this class and its [code](https://github.com/CNES/demcompare/blob/master/demcompare/dem_processing/dem_processing_methods.py#L146).

For angular_diff:

• Adapt this class and its [code](https://github.com/CNES/demcompare/blob/master/demcompare/dem_processing/dem_processing_methods.py#L324).

Additionally:

• Add logging to make it clear to the user that this function only makes sense if the DEM is an altitude difference.

For Tests

Take inspiration from what was done in demcompare.

Documentation

Update the documentation.

[rhugonnet]

Sounds good to have those as class methods of the Raster objects, as for terrain attributes! 🙂

We have a Raster-type class for altitude differences, dDEM, that we use for elevation differences instead of DEM to avoid the confusion. It would be perfect for this. We don't have that much in there right now, but there are many class methods specific to elevation differences (volume change, uncertainty analysis) that would be more relevant here than for the DEM class.

A note though: The dDEM class is old and some aspects of it might have to be slightly adjusted, but that should not be much work. The class has not been documented much, so it can easily be reworked and re-framed, including renaming (for instance with DH that is fairly commonly used for "difference in height").