Can we eliminate the need for positive_down kwarg in setup_bathymetry method?

[navidcy]

regional-mom6/regional_mom6/regional_mom6.py

Line 905 in 52c3d5d

positive_down=False,

A discussion begun in #147; see, e.g., #147 (comment) and below.

[ashjbarnes]

To automatically read in bathymetry, we need to know which bits are land and which are ocean. The mask table is built from the bathymetry. If "positive down=False" (which is the case for gebco as it goes from -X ... 0 ... + X, with positive values representing land, then we interpret negative values as the ocean cells we want. The package then masks out the land accordingly

However, if you give it the topo file from an existing ocean model, chances are it's already positive down. We'd need an automatic way of identifying these two scenarios to do away with this kwarg.