Point cloud encoding method and decoding method using rotation matrixes, encoder, and decoder

A point cloud decoding apparatus comprising:

• a memory containing instructions;
• and
• a processor, in communication with the memory and upon execution of the instructions, is configured to:
• reconstruct a point cloud comprising one or more patches, wherein the one or more patches comprise a current patch, wherein the reconstructing process comprises:
• parsing a bitstream to obtain one or more syntax elements, wherein the one or more syntax elements comprise information indicating a transform matrix of the current patch, a tangent axis of the current patch, and a bitangent axis of the current patch;
• obtaining, by pre-projecting the current patch from a three-dimensional space to a two-dimensional space, size information of a minimum bounding rectangle corresponding to the two-dimensional space of the current patch, wherein the size information comprises an index of the relationship between the sizes of the sides of the minimum bounding rectangle;
• determining, based on the size information, whether the tangent axis is the same as a reference tangent axis or a reference bitangent axis;
• and
• transforming second coordinates (x2, y2) of a second point of the current patch in a second coordinate system to first coordinates (x1, y1) of a first point of the current patch in a first coordinate system,
• wherein the first coordinates (x1, y1) of the first point of the current patch in the first coordinate system are obtained based on the second coordinates (x2, y2) of the second point of the current patch in the second coordinate system, the transform matrix, the tangent axis, and the bitangent axis, and
• wherein the transform matrix is selected, based on the information indicating the transform matrix, from a plurality of transform matrices which correspond to different rotation angles.

A non-transitory computer-readable media storing computer instructions that when executed by one or more processors, cause the one or more processors to perform the steps of:

• projecting a current patch from a three-dimensional space to a two-dimensional space;
• transforming first coordinates (x1, y1) of a point of the current patch in a first coordinate system to second coordinates (x2, y2) of the point of the current patch in a second coordinate system, wherein the second coordinates (x2, y2) of the point of the current patch are obtained based on the first coordinates (x1, y1) of the point of the current patch and a selected transform matrix, to obtain an occupancy map of the current patch;
• obtaining, by pre-projecting the current patch from a three-dimensional space to a two-dimensional space, size information of a minimum bounding rectangle corresponding to the two-dimensional space of the current patch, wherein the size information comprises an index of the relationship between the sizes of the sides of the minimum bounding rectangle;
• obtaining a tangent axis of the current patch and a bitangent axis of the current patch, wherein the selected transform matrix is selected from a plurality of transform matrices which correspond to different rotation angles, wherein a size of an occupancy map of a point cloud depends on the minimum bounding rectangle of the occupancy map of each patch of a plurality of patches of the point cloud;
• generating one or more syntax elements indicating the selected transform matrix for the current patch, the tangent axis of the current patch, the bitangent axis of the current patch and the size information of the minimum bounding rectangle;
• encoding the syntax element into a bitstream;
• and
• storing the bitstream for communication toward a point cloud decoder.

A non-transitory computer-readable media storing computer instructions that when executed by one or more processors, cause the one or more processors to perform the steps of:

• reconstructing a point cloud comprising one or more patches, wherein the one or more patches comprise a current patch, wherein a reconstructing process comprises:
• parsing a bitstream to obtain one or more syntax elements, wherein the one or more syntax elements comprise information indicating a transform matrix of the current patch, a tangent axis of the current patch, a bitangent axis of the current patch;
• obtaining, by pre-projecting the current patch from a three-dimensional space to a two-dimensional space, size information of a minimum bounding rectangle corresponding to the two-dimensional space of the current patch, wherein the size information comprises an index of the relationship between the sizes of the sides of the minimum bounding rectangle;
• determining, based on the size information, whether the tangent axis is the same as a reference tangent axis or a reference bitangent axis;
• and
• transforming second coordinates (x2, y2) of a second point of the current patch in a second coordinate system to first coordinates (x1, y1) of a first point of the current patch in a first coordinate system, wherein the first coordinates (x1, y1) of the first point of the current patch in the first coordinate system are obtained based on the second coordinates (x2, y2) of the second point of the current patch in the second coordinate system, the transform matrix, the tangent axis, and the bitangent axis, wherein the transform matrix is selected, based on information indicating the transform matrix, from a plurality of transform matrices which correspond to different rotation angles.

A non-transitory storage medium comprising a bitstream encoded by performing the steps of:

• projecting a current patch from a three-dimensional space to a two-dimensional space;
• transforming first coordinates (x1, y1) of a point of the current patch in a first coordinate system to second coordinates (x2, y2) of the point of the current patch in a second coordinate system, wherein the second coordinates (x2, y2) of the point of the current patch are obtained based on the first coordinates (x1, y1) of the point of the current patch and a selected transform matrix, to obtain an occupancy map of the current patch;
• obtaining, by pre-projecting the current patch from a three-dimensional space to a two-dimensional space, size information of a minimum bounding rectangle corresponding to the two-dimensional space of the current patch, wherein the size information comprises an index of the relationship between the sizes of the sides of the minimum bounding rectangle;
• obtaining a tangent axis of the current patch and a bitangent axis of the current patch, wherein the selected transform matrix is selected from a plurality of transform matrices which correspond to different rotation angles, wherein a size of an occupancy map of a point cloud depends on the minimum bounding rectangle of the occupancy map of each patch of a plurality of patches of the point cloud;
• generating one or more syntax elements indicating the selected transform matrix for the current patch, the tangent axis of the current patch, the bitangent axis of the current patch, and the size information of the minimum bounding rectangle;
• and
• encoding the syntax element into the bitstream.