Ugrid3d: collection of remarks

[Huite]

I'm taking a cursory glance at what's required for fully unstructured 3D support according to UGRID conventions.

Z-coordinate

I'm making a distinction between lat-lon and x-y (is_projected / is_geographic). It looks like another distinction is required for the direction of the z axis positive_up.

    "node_z": {
        PROJECTED: {
            "standard_name": "projection_z_coordinate",
        },
        LATLON: {
              UP: {"standard_name": "height"},
              DOWN: {"standard_name": "depth"},
        },

There's a whole slew of names to consider:

Z_STANDARD_NAMES = (
    "projection_z_coordinate",  # Simple Cartesian
    "height",                  # Height above surface
    "depth",                   # Depth below surface
    "height_above_reference_ellipsoid",
    "height_above_mean_sea_level",
    "depth_below_mean_sea_level",
    "ocean_sigma_coordinate",  # Terrain-following
    "ocean_s_coordinate",      # S-coordinates
    "atmosphere_hybrid_sigma_pressure_coordinate"  # Atmospheric hybrid coordinates
)

I think projection_z_coordinate, depth and height are reasonable (terse) defaults; they're easily modified anyway.