KartoMNT is a free software of height model digitalization.
This software allows you to create your own Digital Height Models (DHM) with a simple map. Then you'll be able to visualize DHMs with the KartoMNT 3D viewer.
A Map Server, Viewer & Editor partially implementing the W3 standards for GML & SVG with some extensions to aid in designing and maintaining the PSTN cable networks (and other networks) in city scale.