I have 2000 PNGs, each at 2000x2000 pixel resolution. Combined, they produce an 8 billion voxel data set. I understand that Shapeways supports the following formats: .stl, .dae, .x3d, .x3db, wrl, and x3dv. Is there any way to easily convert aforementioned PNGs to one of the above formats to allow 3D prints? If there's a more 'standard' voxel format, then I would be prepared to write my own software to convert the PNGs to that format as a part of a 2-step conversion process. But obviously I would prefer the voxel format specification to be pretty simple to make this easier. Any ideas?