Problem with coordinate implementation

[marina-ricci]

We recently merged a PR to specify the coordinate system for the shear, but it lacks some functionalities. First, it should be explained in details in a notebook, so that this bug would have been found. E.g : showing a profile taken with an incorrect coordinate system and showing all intermediate steps.

At the moment, the keyword is missing from compute_tangential_and_cross_components. You can pass it to the Galaxy Cluster object, but it does not imply that it will be used (this should be avoided).

Also, we might consider adding a simple way to convert between the two coordinate, once compute_tangential_and_cross_components is run (not having to rerun all steps).

(Note : I discovered this while trying to implement in TXPipe and seeing no changes).