Method and apparatus of encoding/decoding point cloud geometry data captured by a spinning sensors head

A method of decoding a point cloud from a bitstream of encoded point cloud data representing a physical object, each point of the point cloud being associated with spherical coordinates representing an azimuthal angle responsive to a capture angle of a sensor of a spinning sensor head that captured the point and a radius responsive of a distance of the point from a referential, the method comprising:

• decoding an elementary azimuthal step (ϕstep) from the bitstream;
• obtaining a decoded radius (rdec) of a point of the point cloud from a decoded residual radius (rres,dec) decoded from the bitstream;
• obtaining a scaled elementary azimuthal step (S(ϕstep, rdec)) associated with a point of the point cloud, the scaled elementary azimuthal step (S(ϕstep, rdec)) being equal to first data (D1) greater than the elementary azimuthal step (ϕstep) in response to second data (D2), depending on the decoded radius (rdec) of the point, being strictly lower than a threshold (TH), and the scaled elementary azimuthal step (S(ϕstep, rdec)) being equal to the elementary azimuthal step (ϕstep) in response to the second data (D2), depending on the decoded radius (rdec) of the point, being equal to or greater than the threshold (TH);
• decoding a number (ms) of scaled elementary azimuthal steps from the bitstream;
• decoding a decoded residual azimuthal angle (ϕres,dec) from the bitstream;
• and
• obtaining a decoded azimuthal angle (ϕdec) from the decoded residual azimuthal angle (ϕres,dec) and a predicted azimuthal angle derived from the number (ms) of scaled elementary azimuthal steps and the scaled elementary azimuthal step (S(ϕstep, rdec)).

An apparatus of encoding a point cloud into a bitstream of encoded point cloud data representing a physical object, each point of the point cloud being associated with spherical coordinates representing an azimuthal angle responsive to a capture angle of a sensor of a spinning sensor head that captured the point and a radius responsive of a distance of the point from a referential, the apparatus comprising one or more processors configured to:

• obtain a scaled elementary azimuthal step associated with a point of the point cloud, the scaled elementary azimuthal step being equal to first data greater than an elementary azimuthal step in response to second data is strictly lower than a threshold, and the scaled elementary azimuthal step being equal to the elementary azimuthal step in response to the second data being equal to or greater than the threshold, the elementary azimuthal step being derived from frequencies and rotation speed at which a spinning sensor head captured the point cloud, and the second data depending on a decoded radius of the point obtained by encoding and decoding a radius associated with the point;
• encode, in the bitstream, a number of scaled elementary azimuthal steps obtained from an azimuthal angle of the point, a prediction of the azimuthal angle and the scaled elementary azimuthal step;
• and
• encode, in the bitstream, an residual azimuthal angle of the point between the azimuthal angle of the point and a predicted azimuthal angle derived from the number of scaled elementary azimuthal steps and the scaled elementary azimuthal step.