Context determination for planar mode in octree-based point cloud coding
Method and devices for coding point cloud data using a planar coding mode. The planar coding mode may be signaled using in a planar mode flag to signal that a volume is planar. A planar volume has all of its occupied child nodes on one side of a plane bisecting the volume. A planar position flag may signal which side of the volume is occupied. Entropy coding may be used to code the planar mode flag and/or the planar position flag. Context determination for coding may take into account one or more of whether a parent volume containing the volume is planar in occupancy, occupancy of a neighbouring volume at a parent depth, distance between the volume and a closest already-coded occupied volume at a same depth as the volume, plane position, if any, of the closest already-coded occupied volume, and a position of the volume within the parent volume.
1. A method of encoding a point cloud to generate a bitstream of compressed point cloud data representing a three-dimensional location of an object, the point cloud being located within a volumetric space recursively split into sub-volumes and containing points of the point cloud, wherein a volume is partitioned into a first set of child sub-volumes and a second set of child sub-volumes, the first set of child sub-volumes being positioned in a first plane and the second set of child sub-volumes being positioned in a second plane parallel to the first plane, and wherein an occupancy bit associated with each respective child sub-volume indicates whether that respective child sub-volume contains at least one of the points, both the first plane and the second plane being orthogonal to an axis, the method comprising:
determining whether the volume is planar based on whether all child sub-volumes containing at least one point are positioned in either the first set or the second set;
entropy encoding in the bitstream a planar mode flag to signal whether the volume is planar, wherein entropy encoding includes determining a context for coding the planar mode flag based, in part, on one or more of:
(a) whether a parent volume containing the volume is planar in occupancy,
(b) occupancy of a neighbouring volume at a parent depth, the neighbouring volume being adjacent the volume and having a face in common with the parent volume, or
(c) a distance between the volume and a closest already-coded occupied volume at a same depth as the volume and having a same position on the axis as the volume;
encoding occupancy bits for at least some of the child sub-volumes; and
outputting the bitstream of compressed point cloud data.
2. The method claimed in claim 1 , wherein the parent volume containing the volume is planar in occupancy if a parent planar mode flag indicates that the parent volume is planar.
3. The method claimed in claim 1 , wherein the distance is near or far and is based on calculating a distance metric and comparing it to a threshold.
4. The method claimed in claim 1 , wherein determining the context for coding the planar mode flag is based on a combination of (a), (b) and (c).
5. The method claimed in claim 1 , wherein determining whether the volume is planar includes determining that the volume is planar and, as a result, entropy encoding a plane position flag to signal whether the at least one point is positioned in the first set or the second set.
6. The method claimed in claim 5 , wherein entropy encoding the plane position flag includes determining a context for coding the plane position flag based, in part, on one or more of:
(a′) occupancy of the neighbouring volume at the parent depth;
(b′) the distance between the volume and the closest already-coded occupied volume;
(c′) a plane position, if any, of the closest already-coded occupied volume; or
(d′) a position of the volume within the parent volume.
7. The method claimed in claim 6 , wherein the distance is near, not too far, or far and is based on calculating a distance metric and comparing it to a first threshold and a second threshold.
8. The method claimed in claim 6 , wherein determining the context for coding the plane position flag is based on a combination of three or more of (a′), (b′), (c′), and (d′).
9. A method of decoding a bitstream of compressed point cloud data to produce a reconstructed point cloud representing a three-dimensional location of a physical object, the point cloud being located within a volumetric space recursively split into sub-volumes and containing points of the point cloud, wherein a volume is partitioned into a first set of child sub-volumes and a second set of child sub-volumes, the first set of child sub-volumes being positioned in a first plane and the second set of child sub-volumes being positioned in a second plane parallel to the first plane, and wherein an occupancy bit associated with each respective child sub-volume indicates whether that respective child sub-volume contains at least one of the points, both the first plane and the second plane being orthogonal to an axis, the method comprising:
reconstructing the points of the point cloud by reconstructing the occupancy bits by
entropy decoding from the bitstream a planar mode flag that indicates whether the volume is planar, wherein the volume is planar if all child sub-volumes containing at least one point are positioned in either the first set or the second set, wherein entropy decoding includes determining a context for decoding the planar mode flag based, in part, on one or more of:
(a) whether a parent volume containing the volume is planar in occupancy,
(b) occupancy of a neighbouring volume at a parent depth, the neighbouring volume being adjacent the volume and having a face in common with the parent volume, or
(c) a distance between the volume and a closest already-coded occupied volume at a same depth as the volume and having a same position on the axis as the volume; and
reconstructing occupancy bits for the child sub-volumes.
10. The method claimed in claim 9 , wherein the parent volume containing the volume is planar in occupancy if a parent planar mode flag indicates that the parent volume is planar.
11. The method claimed in claim 9 , wherein the distance is near or far and is based on calculating a distance metric and comparing it to a threshold.
12. The method claimed in claim 9 , wherein determining the context for coding the planar mode flag is based on a combination of (a), (b) and (c).
13. The method claimed in claim 9 , wherein determining whether the volume is planar includes determining that the volume is planar and, as a result, entropy encoding a plane position flag to signal whether the at least one point is positioned in the first set or the second set.
14. The method claimed in claim 13 , wherein entropy encoding the plane position flag includes determining a context for coding the plane position flag based, in part, on one or more of:
(a′) occupancy of the neighbouring volume at the parent depth;
(b′) the distance between the volume and the closest already-coded occupied volume;
(c′) a plane position, if any, of the closest already-coded occupied volume; or
(d′) a position of the volume within the parent volume.
15. The method claimed in claim 14 , wherein the distance is near, not too far, or far and is based on calculating a distance metric and comparing it to a first threshold and a second threshold.
16. The method claimed in claim 14 , wherein determining the context for coding the plane position flag is based on a combination of three or more of (a′), (b′), (c′), and (d′).
17. An encoder for encoding a point cloud to generate a bitstream of compressed point cloud data representing a three-dimensional location of an object, the point cloud being located within a volumetric space recursively split into sub-volumes and containing points of the point cloud, wherein a volume is partitioned into a first set of child sub-volumes and a second set of child sub-volumes, the first set of child sub-volumes being positioned in a first plane and the second set of child sub-volumes being positioned in a second plane parallel to the first plane, and wherein an occupancy bit associated with each respective child sub-volume indicates whether that respective child sub-volume contains at least one of the points, both the first plane and the second plane being orthogonal to an axis, the encoder comprising:
a processor;
memory; and
an encoding application containing instructions executable by the processor that, when executed, cause the processor to:
determine whether the volume is planar based on whether all child sub-volumes containing at least one point are positioned in either the first set or the second set;
entropy encode in the bitstream a planar mode flag to signal whether the volume is planar, wherein entropy encoding includes determining a context for coding the planar mode flag based, in part, on one or more of:
(a) whether a parent volume containing the volume is planar in occupancy,
(b) occupancy of a neighbouring volume at a parent depth, the neighbouring volume being adjacent the volume and having a face in common with the parent volume, or
(c) a distance between the volume and a closest already-coded occupied volume at a same depth as the volume and having a same position on the axis as the volume;
encode occupancy bits for at least some of the child sub-volumes; and
output the bitstream of compressed point cloud data.
18. A decoder for decoding a bitstream of compressed point cloud data to produce a reconstructed point cloud representing a three-dimensional location of a physical object, the point cloud being located within a volumetric space recursively split into sub-volumes and containing points of the point cloud, wherein a volume is partitioned into a first set of child sub-volumes and a second set of child sub-volumes, the first set of child sub-volumes being positioned in a first plane and the second set of child sub-volumes being positioned in a second plane parallel to the first plane, and wherein an occupancy bit associated with each respective child sub-volume indicates whether that respective child sub-volume contains at least one of the points, both the first plane and the second plane being orthogonal to an axis, the decoder comprising:
a processor;
memory; and
a decoding application containing instructions executable by the processor that, when executed, cause the processor to reconstruct the points of the point cloud by reconstructing the occupancy bits by:
entropy decoding from the bitstream a planar mode flag that indicates whether the volume is planar, wherein the volume is planar if all child sub-volumes containing at least one point are positioned in either the first set or the second set, wherein entropy decoding includes determining a context for decoding the planar mode flag based, in part, on one or more of:
(a) whether a parent volume containing the volume is planar in occupancy,
(b) occupancy of a neighbouring volume at a parent depth, the neighbouring volume being adjacent the volume and having a face in common with the parent volume, or
(c) a distance between the volume and a closest already-coded occupied volume at a same depth as the volume and having a same position on the axis as the volume; and
reconstructing occupancy bits for the child sub-volumes.
19. A non-transitory processor-readable medium storing processor-executable instructions to encode a point cloud to generate a bitstream of compressed point cloud data representing a three-dimensional location of an object, the point cloud being located within a volumetric space recursively split into sub-volumes and containing points of the point cloud, wherein a volume is partitioned into a first set of child sub-volumes and a second set of child sub-volumes, the first set of child sub-volumes being positioned in a first plane and the second set of child sub-volumes being positioned in a second plane parallel to the first plane, and wherein an occupancy bit associated with each respective child sub-volume indicates whether that respective child sub-volume contains at least one of the points, both the first plane and the second plane being orthogonal to an axis, wherein the processor-executable instructions, when executed by a processor, are to cause the processor to:
determine whether the volume is planar based on whether all child sub-volumes containing at least one point are positioned in either the first set or the second set;
entropy encode in the bitstream a planar mode flag to signal whether the volume is planar, wherein entropy encoding includes determining a context for coding the planar mode flag based, in part, on one or more of:
(a) whether a parent volume containing the volume is planar in occupancy,
(b) occupancy of a neighbouring volume at a parent depth, the neighbouring volume being adjacent the volume and having a face in common with the parent volume, or
(c) a distance between the volume and a closest already-coded occupied volume at a same depth as the volume and having a same position on the axis as the volume;
encode occupancy bits for at least some of the child sub-volumes; and
output the bitstream of compressed point cloud data.
20. A non-transitory processor-readable medium storing processor-executable instructions to decode a bitstream of compressed point cloud data to produce a reconstructed point cloud representing a three-dimensional location of a physical object, the point cloud being located within a volumetric space recursively split into sub-volumes and containing points of the point cloud, wherein a volume is partitioned into a first set of child sub-volumes and a second set of child sub-volumes, the first set of child sub-volumes being positioned in a first plane and the second set of child sub-volumes being positioned in a second plane parallel to the first plane, and wherein an occupancy bit associated with each respective child sub-volume indicates whether that respective child sub-volume contains at least one of the points, both the first plane and the second plane being orthogonal to an axis, wherein the processor-executable instructions, when executed by a processor, cause the processor to:
reconstruct the points of the point cloud by reconstructing the occupancy bits by:
entropy decoding from the bitstream a planar mode flag that indicates whether the volume is planar, wherein the volume is planar if all child sub-volumes containing at least one point are positioned in either the first set or the second set, wherein entropy decoding includes determining a context for decoding the planar mode flag based, in part, on one or more of:
(a) whether a parent volume containing the volume is planar in occupancy,
(b) occupancy of a neighbouring volume at a parent depth, the neighbouring volume being adjacent the volume and having a face in common with the parent volume, or
(c) a distance between the volume and a closest already-coded occupied volume at a same depth as the volume and having a same position on the axis as the volume; and
reconstructing occupancy bits for the child sub-volumes.