[Therion] Point Depth

[Bruce]

It seems there are many interpretations of what a point depth might be in
the context of the whole cave (as compared to just a feature such as a pit).
I think Torsten is thinking of an interpretation that I did not think of
until his last post.

Depth = elevation up or down relative to one of the entrances
Depth = elevation down relative to the highest survey station
Depth = elevation below (or above if negative) the free water surface
Depth = distance below the ground surface directly above the point
Depth = others?

The first two can be imitated with point altitude as Stacho says, if you
don't mind using an arbitrary z origin for your map coordinates.

If you adopt the third meaning then the value of a new depth entity could
usually be calculated by therion (once modified to include this feature).

If you adopt the fourth meaning, then it's value must always be manually
entered by the user, as the ground is generally undulating.  Mind you, I
imagine that therion could perhaps be modified to calculate the depth below
ground if a surface grid entity has been entered.

Bruce