This scene has been lying around for years.
It began as an attempt to create a model of a 'juggernaut' (the infamous "thing what kicks") from Marathon. Of this, nothing remains except the rear section of the vehicle, which was made in Ray Dream's Free Form modeller.
The rest is pure Bryce, mostly primitives glued together or Booleaned in various fashions. The tank tracks are symmetric lattices, based on a greyscale map painted in Photoshop. A few custom textures and a circular spotlight finished it off.
25 Dec 1999