A method for generating a bitstream representing a 3D model, comprising: determining a surface smoothness measure for each one of a plurality of sub-cells of a cell in an octree, the octree being representative of the 3D model, characterized in that: wherein the determining the surface smoothness measure comprises, for a particular sub-cell of the cell: determining a plurality of cells as neighboring cells for the cell; forming a plurality of triangles in response to the particular sub-cell and the neighboring cells of the cell, wherein each one of the triangles is defined by a point representative of the particular sub-cell and two points representative of two cells of the neighboring cells, determining an area for the each one of the triangles, determining a sum of the areas of the plurality of triangles for the particular sub-cell; forming a plurality of angles in response to the particular sub-cell and the neighboring cells of the cell, wherein each one of the angles is defined by the point representative of the particular sub-cell and the two points representative of two cells of the neighboring cells, the point representative of the particular sub-cell corresponding to a vertex of the each one of the angles, determining an angular measure for the each one of the angle, determining a sum of the angular measures of the plurality of angles for the particular sub-cell, determining a difference between 2π and the sum of the angular measures, wherein the surface smoothness measure is determined based on the sum of the angular measures if a scaled difference between 2π and the sum of the angular measures is greater than the sum of the areas, and wherein the surface smoothness measure is determined based on the sum of areas if the scaled difference is not greater than the sum of the areas; and determining a traversal order of the sub-cells of the cell in response to the surface smoothness measures of the sub-cells, determining a bit for the each one of the sub-cells, wherein the bit indicates whether a corresponding sub-cell is empty, forming a bit string using the determined bits for the sub-cells in response to the traversal order, and entropy coding the bit string into the bistream. wherein the determining the surface smoothness measure comprises, for a particular sub-cell of the cell: determining a plurality of cells as neighboring cells for the cell; forming a plurality of triangles in response to the particular sub-cell and the neighboring cells of the cell, wherein each one of the triangles is defined by a point representative of the particular sub-cell and two points representative of two cells of the neighboring cells, determining an area for the each one of the triangles, determining a sum of the areas of the plurality of triangles for the particular sub-cell; forming a plurality of angles in response to the particular sub-cell and the neighboring cells of the cell, wherein each one of the angles is defined by the point representative of the particular sub-cell and the two points representative of two cells of the neighboring cells, the point representative of the particular sub-cell corresponding to a vertex of the each one of the angles, determining an angular measure for the each one of the angle, determining a sum of the angular measures of the plurality of angles for the particular sub-cell, determining a difference between 2π and the sum of the angular measures, wherein the surface smoothness measure is determined based on the sum of the angular measures if a scaled difference between 2π and the sum of the angular measures is greater than the sum of the areas, and wherein the surface smoothness measure is determined based on the sum of areas if the scaled difference is not greater than the sum of the areas; and determining a plurality of cells as neighboring cells for the cell; forming a plurality of triangles in response to the particular sub-cell and the neighboring cells of the cell, wherein each one of the triangles is defined by a point representative of the particular sub-cell and two points representative of two cells of the neighboring cells, determining an area for the each one of the triangles, determining a sum of the areas of the plurality of triangles for the particular sub-cell; forming a plurality of angles in response to the particular sub-cell and the neighboring cells of the cell, wherein each one of the angles is defined by the point representative of the particular sub-cell and the two points representative of two cells of the neighboring cells, the point representative of the particular sub-cell corresponding to a vertex of the each one of the angles, determining an angular measure for the each one of the angle, determining a sum of the angular measures of the plurality of angles for the particular sub-cell, determining a difference between 2π and the sum of the angular measures, wherein the surface smoothness measure is determined based on the sum of the angular measures if a scaled difference between 2π and the sum of the angular measures is greater than the sum of the areas, and wherein the surface smoothness measure is determined based on the sum of areas if the scaled difference is not greater than the sum of the areas; and determining a traversal order of the sub-cells of the cell in response to the surface smoothness measures of the sub-cells, determining a bit for the each one of the sub-cells, wherein the bit indicates whether a corresponding sub-cell is empty, forming a bit string using the determined bits for the sub-cells in response to the traversal order, and entropy coding the bit string into the bistream.