Description of the desired feature

Our gravity processing will need the Bouguer correction. The correction aims to remove the effect of masses above the reference ellipsoid (topography) or the mass difference below the ellipsoid (oceans). The function should take two densities, one to apply to the masses at height > 0 (above) and another for masses at height < 0 (below). No contrasts should be calculate (i.e., to remove the effect of the oceans the user should give density_below=1040 - 2670). It's OK to provide defaults for above and below densities.

This should be a straight forward function:

def bouguer_plate(height, density_above=2670, density_below=-1630):
    ...
    return results

Notice that this function doesn't perform the correction itself, it calculates the effect of the Bouguer plates that has to be subtracted from the data. This makes it more inline with calculating a topographic effect using prisms or tesseroids.