Better default for depth in equivalent sources about harmonica HOT 4 OPEN

@santisoler would you like me to first make a PR with a warning that the default will change that can go into v0.7 and then we make the change for v0.8?

from harmonica.

Just to clarify, the depth should be set to 4.5 times the median distance between first neighbor sources, right?

If that's true, then we can use:

depth = np.median(verde.median_distance(coordinates, k_nearest=1))

Is this the idea?

from harmonica.

Should we take the mean of the median distances?
depth = np.mean(verde.median_distance(coordinates, k_nearest=1)) * 4.5

from harmonica.

I guess the mean would be better? Then it wouldn't favor close points. Perhaps it would be good to have a verde.mean_distance function as well.

from harmonica.