Converting dem and geotiff to collada model with texture?

I have a digital elevation model (dem) file with corresponding orthophoto in geotiff format.

What I need to do is to create a 3D model of the terrain with textures (preferably in collada file)?

I would like an opensource or freeware solution, but I will consider commercial software if need be.

Answer

Here is 3D plugin for Qgis: http://qgis2threejs.readthedocs.org/en/docs-release/index.html

Hope it helps.