Methods and devices using direct coding in point cloud compression

1. A method of encoding a point cloud to generate a bitstream of compressed point cloud data, the point cloud being defined in a tree structure having a plurality of nodes having parent-child relationships and that represent the geometry of a volumetric space recursively split into sub-volumes and containing the points of the point cloud, the method comprising:

traversing the tree to entropy encode patterns of occupancy for sets of child nodes, wherein a pattern of occupancy indicates which of the sub-volumes associated with the respective child nodes contain at least one point, and wherein the traversing includes:

for a current node associated with a sub-volume,

determining, based on occupancy data from another node, that points within the sub-volume associated with the current node are eligible for direct coding;

determining, based on the number of points within the sub-volume associated with the current node, that direct coding is to be applied;

inserting a flag in the bitstream indicating the direct coding is to be applied in association with the current node; and

entropy encoding positional coordinate data for at least some of the points within the sub-volume.

2. The method claimed in claim 1 , wherein determining that the current node is eligible for direct coding includes determining eligibility based on an occupancy pattern for a parent node to the current node.

3. The method claimed in claim 2 , wherein the occupancy pattern for the parent node includes whether sibling nodes to the current node are occupied.

4. The method claimed in claim 1 , wherein determining that the current node is eligible for direct coding includes determining eligibility based on occupancy status of neighbouring nodes to the current node.

5. The method claimed in claim 4 , wherein the neighboring nodes are nodes that are associated with respective sub-volumes that share at least one face with the sub-volume associated with the current node.

6. The method claimed in claim 4 , wherein the neighboring nodes are nodes that are associated with respective sub-volumes that share at least one edge with the sub-volume associated with the current node.

7. The method claimed in claim 4 , wherein the neighboring nodes are nodes that are associated with respective sub-volumes that share at least one vertex with the sub-volume associated with the current node.

8. The method claimed in any claim 1 , wherein determining that the current node is eligible for direct coding includes determining eligibility based on occupancy data for a grandparent node to the current node.

9. The method claimed in claim 8 , wherein the occupancy data for the grandparent node includes whether sibling nodes to a parent node to the current node are occupied.

10. An encoder for encoding a point cloud to generate a bitstream of compressed point cloud data, the point cloud being defined in a tree structure having a plurality of nodes having parent-child relationships and that represent the geometry of a volumetric space recursively split into sub-volumes and containing the points of the point cloud, the encoder comprising:

a processor;

memory; and

an encoding application containing instructions executable by the processor that, when executed, are to cause the processor to:

traverse the tree to entropy encode patterns of occupancy for sets of child nodes, wherein a pattern of occupancy indicates which of the sub-volumes associated with the respective child nodes contain at least one point, and wherein the traversing includes:

for a current node associated with a sub-volume,

determine, based on occupancy data from another node, that points within the sub-volume associated with the current node are eligible for direct coding;

determine, based on the number of points within the sub-volume associated with the current node, that direct coding is to be applied;

insert a flag in the bitstream indicating the direct coding is to be applied in association with the current node; and

entropy encode positional coordinate data for at least some of the points within the sub-volume.

11. A method of decoding a bitstream of compressed point cloud data to produce a reconstructed point cloud, the point cloud being defined in a tree structure having a plurality of nodes having parent-child relationships and that represent the geometry of a volumetric space recursively split into sub-volumes and containing the points of the point cloud, the method comprising:

traversing the tree to entropy decode patterns of occupancy for sets of child nodes, wherein a pattern of occupancy indicates which of the sub-volumes associated with the respective child nodes contain at least one point, and wherein the traversing includes:

for a current node associated with a sub-volume,

determining, based on occupancy data from another node, that points within the sub-volume associated with the current node are eligible for direct coding;

decoding a flag from the bitstream, wherein the decoded flag indicates that direct coding was used for the current node; and

based on the decoded flag, entropy decoding positional coordinate data for points within the sub-volume.

12. The method claimed in claim 11 , wherein determining that the current node is eligible for direct coding includes determining eligibility based on an occupancy pattern for a parent node to the current node.

13. The method claimed in claim 12 , wherein the occupancy pattern for the parent node includes whether sibling nodes to the current node are occupied.

14. The method claimed in claim 11 , wherein determining that the current node is eligible for direct coding includes determining eligibility based on occupancy status of neighbouring nodes to the current node.

15. The method claimed in claim 14 , wherein the neighboring nodes are nodes that are associated with respective sub-volumes that share at least one face with the sub-volume associated with the current node.

16. The method claimed in claim 14 , wherein the neighboring nodes are nodes that are associated with respective sub-volumes that share at least one edge with the sub-volume associated with the current node.

17. The method claimed in claim 14 , wherein the neighboring nodes are nodes that are associated with respective sub-volumes that share at least one vertex with the sub-volume associated with the current node.

18. The method claimed in claim 11 , wherein determining that the current node is eligible for direct coding includes determining eligibility based on occupancy data for a grandparent node to the current node.

19. The method claimed in claim 18 , wherein the occupancy data for the grandparent node includes whether sibling nodes to a parent node to the current node are occupied.

20. A decoder for decoding a bitstream of compressed point cloud data to produce a reconstructed point cloud, the point cloud being defined in a tree structure having a plurality of nodes having parent-child relationships and that represent the geometry of a volumetric space recursively split into sub-volumes and containing the points of the point cloud, the decoder comprising:

a processor;

memory; and

a decoding application containing instructions executable by the processor that, when executed, are to cause the processor to:

traverse the tree to entropy decode patterns of occupancy for sets of child nodes, wherein a pattern of occupancy indicates which of the sub-volumes associated with the respective child nodes contain at least one point, and wherein the traversing includes:

for a current node associated with a sub-volume,

determine, based on occupancy data from another node, that points within the sub-volume associated with the current node are eligible for direct coding;

decode a flag from the bitstream, wherein the decoded flag indicates that direct coding was used for the current node; and

based on the decoded flag, entropy decode positional coordinate data for points within the sub-volume.