3D height visualization

Visualize 3D volume behind the current plane. The algorithm uses a fast distance transform and gradient trick to give the impression of 3D iso-surface visualization. These work is inspired by those of Luc Vincent (see below), adapted to the visualization of a 3D volume. Take the opportunity to take a look at the other works of the one behind Google Street View.

Update 20220429 : added option to save only height map without post processing.