1. A method of determining neighboring voxels that contribute to a surface of an object, comprising: evaluating a primary voxel corresponding to a side of a reference voxel, the side of the reference voxel being adjacent to an outside voxel, the outside voxel being outside the object, the primary voxel being adjacent to the outside voxel and adjacent to a corresponding secondary voxel, the secondary voxel being adjacent to a corresponding tertiary voxel; and determining whether the primary voxel, the secondary voxel or the tertiary voxel is on a same surface as the reference voxel.