A system for displaying surfaces of volumetric data determines surface cubes by a simple method without interpolation. A central voxel is selected. The central voxel is tested against a threshold. If it is below the threshold, a different voxel is chosen as a central voxel. When one is found which is above the threshold, diagonal cubes, those at each of the corners of the central voxel, are tested against the threshold. When one is encountered with at least one voxel below the threshold, it is categorized as a surface voxel. The values of the adjacent voxels are then used to determine a vector normal to the surface at the central voxel. This is repeated for a number of central voxels to determine a surface. The surface then may be displayed. If anisotropic voxels are used, the elevation angle is converted to an effective elevation angle. The normal vectors to the surface are also adjusted to compensate for the anisotropic nature of the data. The voxels are then assumed to be isotropic being displayed with the effective elevation angle and using the adjusted surface normals.