[fthriezw] connected 3D barcode

encode data into a 3D object with a 3D printer.  read the data with a CAT scan.

set voxels ("1" bits) must be connected the entire structure, not free floating.  if the material is flexible, set voxels must not be too far from connection, or else sag or vibration.

previously on cubes connected through edges and vertices.

previously, assuming one could print at two different densities.  given the complexities above, two densities seems better: set voxels completely filled with material, unset voxels filled with porous support.