The sea level on heightmaps we’re currently handling. If characters are to be able to swin in the sea, we must model the sea bottom, so we need heightmaps which cover at least the continental shelf. However, the sea bottom is not walkable territory and can be culled from walkmaps.

Note must be a floating point number. (= 0 0.0) returns false!

Ye cannae walk on water. Remove all facets from this stl structure which are at sea level.

Of a facet, is the altitude of every vertice equal to *sea-level*?