calculate metrics for an inserted point

[evetion]

For purposes of tin decimation or incrementally building up a terrain, it would be useful to retrieve a metric along the id of the inserted point.

For example, the change in volume of the TIN due to the insertion, or the length of the longest edge created, among others. The user can then decide to remove the inserted point if the metric exceeds a certain threshold.

I'm not sure about the API, in Julia one would do, dispatching on Volume.

insert_one_pt(22.2, 33.3, 4.4, get_metric=Volume())

Otherwise we keep it simple and do

insert_one_pt_get_delta_volume(x, y, z)