TerrainTile - All OPENSCAD

/*
TerrainTile.scad
Public Domain Code
Based on Metaballs By: William A Adams 4 June 2011

This code is a simplified implementation of "Marching Cubes" over Noise + a Z gradient. A isosurface which is the interaction of the Noise field in tree octaves: half, one and four. All Cubes are tested and a joint hull is generated of each corner that lies inside the threshold of the metaball

*/