Patent Publication Number: US-2021168392-A1

Title: Three-dimensional data encoding method, three-dimensional data decoding method, three-dimensional data encoding device, and three-dimensional data decoding device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. continuation application of PCT International Patent Application Number PCT/JP2019/034002 filed on Aug. 29, 2019, claiming the benefit of priority of U.S. Provisional Patent Application No. 62/724,856 filed on Aug. 30, 2018, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a three-dimensional data encoding method, a three-dimensional data decoding method, a three-dimensional data encoding device, and a three-dimensional data decoding device. 
     2. Description of the Related Art 
     Devices or services utilizing three-dimensional data are expected to find their widespread use in a wide range of fields, such as computer vision that enables autonomous operations of cars or robots, map information, monitoring, infrastructure inspection, and video distribution. Three-dimensional data is obtained through various means including a distance sensor such as a rangefinder, as well as a stereo camera and a combination of a plurality of monocular cameras. 
     Methods of representing three-dimensional data include a method known as a point cloud scheme that represents the shape of a three-dimensional structure by a point cloud in a three-dimensional space. In the point cloud scheme, the positions and colors of a point cloud are stored. While point cloud is expected to be a mainstream method of representing three-dimensional data, a massive amount of data of a point cloud necessitates compression of the amount of three-dimensional data by encoding for accumulation and transmission, as in the case of a two-dimensional moving picture (examples include Moving Picture Experts Group-4 Advanced Video Coding (MPEG-4 AVC) and High Efficiency Video Coding (HEVC) standardized by MPEG). 
     Meanwhile, point cloud compression is partially supported by, for example, an open-source library (Point Cloud Library) for point cloud-related processing. 
     Furthermore, a technique for searching for and displaying a facility located in the surroundings of the vehicle by using three-dimensional map data is known (for example, see International Publication WO 2014/020663). 
     SUMMARY 
     There has been a demand for improving coding efficiency in encoding and decoding three-dimensional data. 
     The present disclosure provides a three-dimensional data encoding method, a three-dimensional data decoding method, a three-dimensional data encoding device, or a three-dimensional data decoding device that is capable of improving coding efficiency. 
     A three-dimensional data encoding method according to an aspect of the present disclosure includes: encoding subspaces obtained by dividing a current space which includes three-dimensional points, to generate pieces of encoded data; and generating a bitstream including the pieces of encoded data and first information indicating a shape of each of the subspaces. 
     A three-dimensional data decoding method according to an aspect of the present disclosure includes: decoding pieces of encoded data included in a bitstream and generated by encoding subspaces obtained by dividing a current space which includes three-dimensional points, to restore the subspaces; and restoring the current space by combining the subspaces using first information which is included in the bitstream and indicates a shape of each of the subspaces. 
     The present disclosure can provide a three-dimensional data encoding method, a three-dimensional data decoding method, a three-dimensional data encoding device, or a three-dimensional data decoding device that is capable of improving coding efficiency. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other objects, advantages and features of the disclosure will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the present disclosure. 
         FIG. 1  is a diagram illustrating a configuration of a three-dimensional data encoding and decoding system according to Embodiment 1; 
         FIG. 2  is a diagram illustrating a structure example of point cloud data according to Embodiment 1; 
         FIG. 3  is a diagram illustrating a structure example of a data file indicating the point cloud data according to Embodiment 1; 
         FIG. 4  is a diagram illustrating types of the point cloud data according to Embodiment 1; 
         FIG. 5  is a diagram illustrating a structure of a first encoder according to Embodiment 1; 
         FIG. 6  is a block diagram illustrating the first encoder according to Embodiment 1; 
         FIG. 7  is a diagram illustrating a structure of a first decoder according to Embodiment 1; 
         FIG. 8  is a block diagram illustrating the first decoder according to Embodiment 1; 
         FIG. 9  is a diagram illustrating a structure of a second encoder according to Embodiment 1; 
         FIG. 10  is a block diagram illustrating the second encoder according to Embodiment 1; 
         FIG. 11  is a diagram illustrating a structure of a second decoder according to Embodiment 1; 
         FIG. 12  is a block diagram illustrating the second decoder according to Embodiment 1; 
         FIG. 13  is a diagram illustrating a protocol stack related to PCC encoded data according to Embodiment 1; 
         FIG. 14  is a block diagram of an encoder according to Embodiment 1; 
         FIG. 15  is a block diagram of a decoder according to Embodiment 1; 
         FIG. 16  is a flowchart of encoding processing according to Embodiment 1; 
         FIG. 17  is a flowchart of decoding processing according to Embodiment 1; 
         FIG. 18  is a diagram illustrating a basic structure of ISOBMFF according to Embodiment 2; 
         FIG. 19  is a diagram illustrating a protocol stack according to Embodiment 2; 
         FIG. 20  is a diagram illustrating an example where a NAL unit is stored in a file for codec 1 according to Embodiment 2; 
         FIG. 21  is a diagram illustrating an example where a NAL unit is stored in a file for codec 2 according to Embodiment 2; 
         FIG. 22  is a diagram illustrating a structure of a first multiplexer according to Embodiment 2; 
         FIG. 23  is a diagram illustrating a structure of a first demultiplexer according to Embodiment 2; 
         FIG. 24  is a diagram illustrating a structure of a second multiplexer according to Embodiment 2; 
         FIG. 25  is a diagram illustrating a structure of a second demultiplexer according to Embodiment 2; 
         FIG. 26  is a flowchart of processing performed by the first multiplexer according to Embodiment 2; 
         FIG. 27  is a flowchart of processing performed by the second multiplexer according to Embodiment 2; 
         FIG. 28  is a flowchart of processing performed by the first demultiplexer and the first decoder according to Embodiment 2; 
         FIG. 29  is a flowchart of processing performed by the second demultiplexer and the second decoder according to Embodiment 2; 
         FIG. 30  is a diagram illustrating structures of an encoder and a third multiplexer according to Embodiment 3; 
         FIG. 31  is a diagram illustrating structures of a third demultiplexer and a decoder according to Embodiment 3; 
         FIG. 32  is a flowchart of processing performed by the third multiplexer according to Embodiment 3; 
         FIG. 33  is a flowchart of processing performed by the third demultiplexer and the decoder according to Embodiment 3; 
         FIG. 34  is a flowchart of processing performed by a three-dimensional data storage device according to Embodiment 3; 
         FIG. 35  is a flowchart of processing performed by a three-dimensional data acquisition device according to Embodiment 3; 
         FIG. 36  is a diagram illustrating structures of an encoder and a multiplexer according to Embodiment 4; 
         FIG. 37  is a diagram illustrating a structure example of encoded data according to Embodiment 4; 
         FIG. 38  is a diagram illustrating a structure example of encoded data and a NAL unit according to Embodiment 4; 
         FIG. 39  is a diagram illustrating a semantics example of pcc_nal_unit_type according to Embodiment 4; 
         FIG. 40  is a diagram illustrating an example of a transmitting order of NAL units according to Embodiment 4; 
         FIG. 41  is a flowchart of processing performed by a three-dimensional data encoding device according to Embodiment 4; 
         FIG. 42  is a flowchart of processing performed by a three-dimensional data decoding device according to Embodiment 4; 
         FIG. 43  is a flowchart of multiplexing processing according to Embodiment 4; 
         FIG. 44  is a flowchart of demultiplexing processing according to Embodiment 4; 
         FIG. 45  is a flowchart of processing performed by a three-dimensional data encoding device according to Embodiment 4; 
         FIG. 46  is a flowchart of processing performed by a three-dimensional data decoding device according to Embodiment 4; 
         FIG. 47  is a diagram illustrating an example of dividing slices and tiles according to Embodiment 5; 
         FIG. 48  is a diagram illustrating dividing pattern examples of slices and tiles according to Embodiment 5; 
         FIG. 49  is a block diagram of a first encoder according to Embodiment 6; 
         FIG. 50  is a block diagram of a first decoder according to Embodiment 6; 
         FIG. 51  is a diagram illustrating examples of a tile shape according to Embodiment 6; 
         FIG. 52  is a diagram illustrating an example of tiles and slices according to Embodiment 6; 
         FIG. 53  is a block diagram of a divider according to Embodiment 6; 
         FIG. 54  is a diagram illustrating an example of a map in a top view of point cloud data according to Embodiment 6; 
         FIG. 55  is a diagram illustrating an example of tile division according to Embodiment 6; 
         FIG. 56  is a diagram illustrating an example of tile division according to Embodiment 6; 
         FIG. 57  is a diagram illustrating an example of tile division according to Embodiment 6; 
         FIG. 58  is a diagram illustrating an example of data of tiles stored in a server according to Embodiment 6; 
         FIG. 59  is a diagram illustrating a system regarding tile division according to Embodiment 6; 
         FIG. 60  is a diagram illustrating an example of slice division according to Embodiment 6; 
         FIG. 61  is a diagram illustrating an example of dependency relationships according to Embodiment 6; 
         FIG. 62  is a diagram illustrating an example of decoding order of data according to Embodiment 6; 
         FIG. 63  is a diagram illustrating an example of encoded data of tiles according to Embodiment 6; 
         FIG. 64  is a block diagram of a combiner according to Embodiment 6; 
         FIG. 65  is a diagram illustrating a structural example of encoded data and NAL units according to Embodiment 6; 
         FIG. 66  is a flowchart of an encoding process according to Embodiment 6; 
         FIG. 67  is a flowchart of a decoding process according to Embodiment 6; 
         FIG. 68  is a diagram illustrating an example of syntax of tile additional information according to Embodiment 6; 
         FIG. 69  is a block diagram of an encoding and decoding system according to Embodiment 6; 
         FIG. 70  is a diagram illustrating an example of syntax of slice additional information according to Embodiment 6; 
         FIG. 71  is a flowchart of an encoding process according to Embodiment 6; 
         FIG. 72  is a flowchart of a decoding process according to Embodiment 6; 
         FIG. 73  is a flowchart of an encoding process according to Embodiment 6; and 
         FIG. 74  is a flowchart of a decoding process according to Embodiment 6. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     A three-dimensional data encoding method according to an aspect of the present disclosure includes: encoding subspaces obtained by dividing a current space which includes three-dimensional points, to generate pieces of encoded data; and generating a bitstream which includes the pieces of encoded data and first information indicating a shape of each of the subspaces. 
     Accordingly, the three-dimensional data encoding method can select an arbitrary shape from a plurality of types of subspace shapes, and thus can improve coding efficiency. 
     For example, the shape may be a two-dimensional shape or a three-dimensional shape of each of the subspaces. 
     For example, the shape may be rectangular or circular. 
     For example, the bitstream includes second information indicating whether the subspaces overlap. 
     Accordingly, the three-dimensional data encoding method can cause subspaces to overlap, and thus can generate subspaces without making the shape of the subspaces complex. 
     For example, the bitstream may include third information indicating whether a division method used to obtain the subspaces is a division method using a top view. 
     For example, the bitstream may include fourth information indicating at least one of a height, a width, a depth, or a radius of each of the subspaces. 
     For example, the bitstream includes fifth information indicating a position of each of the subspaces. 
     For example, the bitstream may include sixth information indicating a total number of the subspaces. 
     For example, the bitstream may include seventh information indicating an interval between the subspaces. 
     A three-dimensional data decoding method according to an aspect of the present disclosure includes: decoding pieces of encoded data included in a bitstream and generated by encoding subspaces obtained by dividing a current space which includes three-dimensional points, to restore the subspaces; and restoring the current space by combining the subspaces using first information which is included in the bitstream and indicates a shape of each of the subspaces. 
     Accordingly, the three-dimensional data decoding method can decode a bitstream generated by selecting an arbitrary shape from a plurality of types of subspace shapes and for which coding efficiency has been improved. 
     For example, the shape may be a two-dimensional shape or a three-dimensional shape of each of the subspaces. 
     For example, the shape may be rectangular or circular. 
     For example, the bitstream may include second information indicating whether the subspaces overlap, and, in the restoring of the current space, the subspaces may be combined by further using the second information. 
     For example, the bitstream may include third information indicating whether a division method used to obtain the subspaces is a division method using a top view, and, in the restoring of the current space, when the third information indicates that the division method used to obtain the subspaces is the division method using the top view, the subspaces may be combined using the first information. 
     For example, the bitstream may include fourth information indicating at least one of a height, a width, a depth, or a radius of each of the subspaces, and, in the restoring of the current space, the subspaces may be combined by further using the fourth information. 
     For example, the bitstream may includes fifth information indicating a position of each of the subspaces, and, in the restoring of the current space, the subspaces may be combined by further using the fifth information. 
     For example, the bitstream may include sixth information indicating a total number of the subspaces, and, in the restoring of the current space, the subspaces are combined by further using the sixth information. 
     For example, the bitstream may include seventh information indicating an interval between the subspaces, and, in the restoring of the current space, the subspaces may be combined by further using the seventh information. 
     Furthermore, a three-dimensional data encoding device according to an aspect of the present disclosure includes: a processor; and memory, wherein, using the memory, the processor: encodes subspaces obtained by dividing a current space which includes three-dimensional points, to generate pieces of encoded data; and generates a bitstream which includes the pieces of encoded data and first information indicating a shape of each of the subspaces. 
     Accordingly, the three-dimensional data encoding device can select an arbitrary shape from a plurality of types of subspace shapes, and thus can improve coding efficiency. 
     Furthermore, a three-dimensional data decoding device according to an aspect of the present disclosure includes: a processor; and memory, wherein, using the memory, the processor: decodes pieces of encoded data included in a bitstream and generated by encoding subspaces obtained by dividing a current space which includes three-dimensional points, to restore the subspaces; and restores the current space by combining the subspaces using first information which is included in the bitstream and indicates a shape of each of the subspaces. 
     Accordingly, the three-dimensional data decoding device can decode a bitstream generated by selecting an arbitrary shape from a plurality of types of subspace shapes and for which coding efficiency has been improved. 
     Note that these general or specific aspects may be implemented as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be implemented as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium. 
     The following describes embodiments with reference to the drawings. Note that the following embodiments show exemplary embodiments of the present disclosure. The numerical values, shapes, materials, structural components, the arrangement and connection of the structural components, steps, the processing order of the steps, etc. shown in the following embodiments are mere examples, and thus are not intended to limit the present disclosure. Of the structural components described in the following embodiments, structural components not recited in any one of the independent claims that indicate the broadest concepts will be described as optional structural components. 
     Embodiment 1 
     When using encoded data of a point cloud in a device or for a service in practice, required information for the application is desirably transmitted and received in order to reduce the network bandwidth. However, conventional encoding structures for three-dimensional data have no such a function, and there is also no encoding method for such a function. 
     Embodiment 1 described below relates to a three-dimensional data encoding method and a three-dimensional data encoding device for encoded data of a three-dimensional point cloud that provides a function of transmitting and receiving required information for an application, a three-dimensional data decoding method and a three-dimensional data decoding device for decoding the encoded data, a three-dimensional data multiplexing method for multiplexing the encoded data, and a three-dimensional data transmission method for transmitting the encoded data. 
     In particular, at present, a first encoding method and a second encoding method are under investigation as encoding methods (encoding schemes) for point cloud data. However, there is no method defined for storing the configuration of encoded data and the encoded data in a system format. Thus, there is a problem that an encoder cannot perform an MUX process (multiplexing), transmission, or accumulation of data. 
     In addition, there is no method for supporting a format that involves two codecs, the first encoding method and the second encoding method, such as point cloud compression (PCC). 
     With regard to this embodiment, a configuration of PCC-encoded data that involves two codecs, a first encoding method and a second encoding method, and a method of storing the encoded data in a system format will be described. 
     A configuration of a three-dimensional data (point cloud data) encoding and decoding system according to this embodiment will be first described.  FIG. 1  is a diagram showing an example of a configuration of the three-dimensional data encoding and decoding system according to this embodiment. As shown in  FIG. 1 , the three-dimensional data encoding and decoding system includes three-dimensional data encoding system  4601 , three-dimensional data decoding system  4602 , sensor terminal  4603 , and external connector  4604 . 
     Three-dimensional data encoding system  4601  generates encoded data or multiplexed data by encoding point cloud data, which is three-dimensional data. Three-dimensional data encoding system  4601  may be a three-dimensional data encoding device implemented by a single device or a system implemented by a plurality of devices. The three-dimensional data encoding device may include a part of a plurality of processors included in three-dimensional data encoding system  4601 . 
     Three-dimensional data encoding system  4601  includes point cloud data generation system  4611 , presenter  4612 , encoder  4613 , multiplexer  4614 , input/output unit  4615 , and controller  4616 . Point cloud data generation system  4611  includes sensor information obtainer  4617 , and point cloud data generator  4618 . 
     Sensor information obtainer  4617  obtains sensor information from sensor terminal  4603 , and outputs the sensor information to point cloud data generator  4618 . Point cloud data generator  4618  generates point cloud data from the sensor information, and outputs the point cloud data to encoder  4613 . 
     Presenter  4612  presents the sensor information or point cloud data to a user. For example, presenter  4612  displays information or an image based on the sensor information or point cloud data. 
     Encoder  4613  encodes (compresses) the point cloud data, and outputs the resulting encoded data, control information (signaling information) obtained in the course of the encoding, and other additional information to multiplexer  4614 . The additional information includes the sensor information, for example. 
     Multiplexer  4614  generates multiplexed data by multiplexing the encoded data, the control information, and the additional information input thereto from encoder  4613 . A format of the multiplexed data is a file format for accumulation or a packet format for transmission, for example. 
     Input/output unit  4615  (a communication unit or interface, for example) outputs the multiplexed data to the outside. Alternatively, the multiplexed data may be accumulated in an accumulator, such as an internal memory. Controller  4616  (or an application executor) controls each processor. That is, controller  4616  controls the encoding, the multiplexing, or other processing. 
     Note that the sensor information may be input to encoder  4613  or multiplexer  4614 . Alternatively, input/output unit  4615  may output the point cloud data or encoded data to the outside as it is. 
     A transmission signal (multiplexed data) output from three-dimensional data encoding system  4601  is input to three-dimensional data decoding system  4602  via external connector  4604 . 
     Three-dimensional data decoding system  4602  generates point cloud data, which is three-dimensional data, by decoding the encoded data or multiplexed data. Note that three-dimensional data decoding system  4602  may be a three-dimensional data decoding device implemented by a single device or a system implemented by a plurality of devices. The three-dimensional data decoding device may include a part of a plurality of processors included in three-dimensional data decoding system  4602 . 
     Three-dimensional data decoding system  4602  includes sensor information obtainer  4621 , input/output unit  4622 , demultiplexer  4623 , decoder  4624 , presenter  4625 , user interface  4626 , and controller  4627 . 
     Sensor information obtainer  4621  obtains sensor information from sensor terminal  4603 . 
     Input/output unit  4622  obtains the transmission signal, decodes the transmission signal into the multiplexed data (file format or packet), and outputs the multiplexed data to demultiplexer  4623 . 
     Demultiplexer  4623  obtains the encoded data, the control information, and the additional information from the multiplexed data, and outputs the encoded data, the control information, and the additional information to decoder  4624 . 
     Decoder  4624  reconstructs the point cloud data by decoding the encoded data. 
     Presenter  4625  presents the point cloud data to a user. For example, presenter  4625  displays information or an image based on the point cloud data. User interface  4626  obtains an indication based on a manipulation by the user. Controller  4627  (or an application executor) controls each processor. That is, controller  4627  controls the demultiplexing, the decoding, the presentation, or other processing. 
     Note that input/output unit  4622  may obtain the point cloud data or encoded data as it is from the outside. Presenter  4625  may obtain additional information, such as sensor information, and present information based on the additional information. Presenter  4625  may perform a presentation based on an indication from a user obtained on user interface  4626 . 
     Sensor terminal  4603  generates sensor information, which is information obtained by a sensor. Sensor terminal  4603  is a terminal provided with a sensor or a camera. For example, sensor terminal  4603  is a mobile body, such as an automobile, a flying object, such as an aircraft, a mobile terminal, or a camera. 
     Sensor information that can be generated by sensor terminal  4603  includes (1) the distance between sensor terminal  4603  and an object or the reflectance of the object obtained by LIDAR, a millimeter wave radar, or an infrared sensor or (2) the distance between a camera and an object or the reflectance of the object obtained by a plurality of monocular camera images or a stereo-camera image, for example. The sensor information may include the posture, orientation, gyro (angular velocity), position (GPS information or altitude), velocity, or acceleration of the sensor, for example. The sensor information may include air temperature, air pressure, air humidity, or magnetism, for example. 
     External connector  4604  is implemented by an integrated circuit (LSI or IC), an external accumulator, communication with a cloud server via the Internet, or broadcasting, for example. 
     Next, point cloud data will be described.  FIG. 2  is a diagram showing a configuration of point cloud data.  FIG. 3  is a diagram showing a configuration example of a data file describing information of the point cloud data. 
     Point cloud data includes data on a plurality of points. Data on each point includes geometry information (three-dimensional coordinates) and attribute information associated with the geometry information. A set of a plurality of such points is referred to as a point cloud. For example, a point cloud indicates a three-dimensional shape of an object. 
     Geometry information (position), such as three-dimensional coordinates, may be referred to as geometry. Data on each point may include attribute information (attribute) on a plurality of types of attributes. A type of attribute is color or reflectance, for example. 
     One piece of attribute information may be associated with one piece of geometry information, or attribute information on a plurality of different types of attributes may be associated with one piece of geometry information. Alternatively, a plurality of pieces of attribute information on the same type of attribute may be associated with one piece of geometry information. 
     The configuration example of a data file shown in  FIG. 3  is an example in which geometry information and attribute information are associated with each other in a one-to-one relationship, and geometry information and attribute information on N points forming point cloud data are shown. 
     The geometry information is information on three axes, specifically, an x-axis, a y-axis, and a z-axis, for example. The attribute information is RGB color information, for example. A representative data file is ply file, for example. 
     Next, types of point cloud data will be described.  FIG. 4  is a diagram showing types of point cloud data. As shown in  FIG. 4 , point cloud data includes a static object and a dynamic object. 
     The static object is three-dimensional point cloud data at an arbitrary time (a time point). The dynamic object is three-dimensional point cloud data that varies with time. In the following, three-dimensional point cloud data associated with a time point will be referred to as a PCC frame or a frame. 
     The object may be a point cloud whose range is limited to some extent, such as ordinary video data, or may be a large point cloud whose range is not limited, such as map information. 
     There are point cloud data having varying densities. There may be sparse point cloud data and dense point cloud data. 
     In the following, each processor will be described in detail. Sensor information is obtained by various means, including a distance sensor such as LIDAR or a range finder, a stereo camera, or a combination of a plurality of monocular cameras. Point cloud data generator  4618  generates point cloud data based on the sensor information obtained by sensor information obtainer  4617 . Point cloud data generator  4618  generates geometry information as point cloud data, and adds attribute information associated with the geometry information to the geometry information. 
     When generating geometry information or adding attribute information, point cloud data generator  4618  may process the point cloud data. For example, point cloud data generator  4618  may reduce the data amount by omitting a point cloud whose position coincides with the position of another point cloud. Point cloud data generator  4618  may also convert the geometry information (such as shifting, rotating or normalizing the position) or render the attribute information. 
     Note that, although  FIG. 1  shows point cloud data generation system  4611  as being included in three-dimensional data encoding system  4601 , point cloud data generation system  4611  may be independently provided outside three-dimensional data encoding system  4601 . 
     Encoder  4613  generates encoded data by encoding point cloud data according to an encoding method previously defined. In general, there are the two types of encoding methods described below. One is an encoding method using geometry information, which will be referred to as a first encoding method, hereinafter. The other is an encoding method using a video codec, which will be referred to as a second encoding method, hereinafter. 
     Decoder  4624  decodes the encoded data into the point cloud data using the encoding method previously defined. 
     Multiplexer  4614  generates multiplexed data by multiplexing the encoded data in an existing multiplexing method. The generated multiplexed data is transmitted or accumulated. Multiplexer  4614  multiplexes not only the PCC-encoded data but also another medium, such as a video, an audio, subtitles, an application, or a file, or reference time information. Multiplexer  4614  may further multiplex attribute information associated with sensor information or point cloud data. 
     Multiplexing schemes or file formats include ISOBMFF, MPEG-DASH, which is a transmission scheme based on ISOBMFF, MMT, MPEG-2 TS Systems, or RMP, for example. 
     Demultiplexer  4623  extracts PCC-encoded data, other media, time information and the like from the multiplexed data. 
     Input/output unit  4615  transmits the multiplexed data in a method suitable for the transmission medium or accumulation medium, such as broadcasting or communication. Input/output unit  4615  may communicate with another device over the Internet or communicate with an accumulator, such as a cloud server. 
     As a communication protocol, http, ftp, TCP, UDP or the like is used. The pull communication scheme or the push communication scheme can be used. 
     A wired transmission or a wireless transmission can be used. For the wired transmission, Ethernet (registered trademark), USB, RS-232C, HDMI (registered trademark), or a coaxial cable is used, for example. For the wireless transmission, wireless LAN, Wi-Fi (registered trademark), Bluetooth (registered trademark), or a millimeter wave is used, for example. 
     As a broadcasting scheme, DVB-T2, DVB-S2, DVB-C2, ATSC3.0, or ISDB-S3 is used, for example. 
       FIG. 5  is a diagram showing a configuration of first encoder  4630 , which is an example of encoder  4613  that performs encoding in the first encoding method.  FIG. 6  is a block diagram showing first encoder  4630 . First encoder  4630  generates encoded data (encoded stream) by encoding point cloud data in the first encoding method. First encoder  4630  includes geometry information encoder  4631 , attribute information encoder  4632 , additional information encoder  4633 , and multiplexer  4634 . 
     First encoder  4630  is characterized by performing encoding by keeping a three-dimensional structure in mind. First encoder  4630  is further characterized in that attribute information encoder  4632  performs encoding using information obtained from geometry information encoder  4631 . The first encoding method is referred to also as geometry-based PCC (GPCC). 
     Point cloud data is PCC point cloud data like a PLY file or PCC point cloud data generated from sensor information, and includes geometry information (position), attribute information (attribute), and other additional information (metadata). The geometry information is input to geometry information encoder  4631 , the attribute information is input to attribute information encoder  4632 , and the additional information is input to additional information encoder  4633 . 
     Geometry information encoder  4631  generates encoded geometry information (compressed geometry), which is encoded data, by encoding geometry information. For example, geometry information encoder  4631  encodes geometry information using an N-ary tree structure, such as an octree. Specifically, in the case of an octree, a current space is divided into eight nodes (subspaces), 8-bit information (occupancy code) that indicates whether each node includes a point cloud or not is generated. A node including a point cloud is further divided into eight nodes, and 8-bit information that indicates whether each of the eight nodes includes a point cloud or not is generated. This process is repeated until a predetermined level is reached or the number of the point clouds included in each node becomes equal to or less than a threshold. 
     Attribute information encoder  4632  generates encoded attribute information (compressed attribute), which is encoded data, by encoding attribute information using configuration information generated by geometry information encoder  4631 . For example, attribute information encoder  4632  determines a reference point (reference node) that is to be referred to in encoding a current point (current node) to be processed based on the octree structure generated by geometry information encoder  4631 . For example, attribute information encoder  4632  refers to a node whose parent node in the octree is the same as the parent node of the current node, of peripheral nodes or neighboring nodes. Note that the method of determining a reference relationship is not limited to this method. 
     The process of encoding attribute information may include at least one of a quantization process, a prediction process, and an arithmetic encoding process. In this case, “refer to” means using a reference node for calculating a predicted value of attribute information or using a state of a reference node (occupancy information that indicates whether a reference node includes a point cloud or not, for example) for determining a parameter of encoding. For example, the parameter of encoding is a quantization parameter in the quantization process or a context or the like in the arithmetic encoding. 
     Additional information encoder  4633  generates encoded additional information (compressed metadata), which is encoded data, by encoding compressible data of additional information. 
     Multiplexer  4634  generates encoded stream (compressed stream), which is encoded data, by multiplexing encoded geometry information, encoded attribute information, encoded additional information, and other additional information. The generated encoded stream is output to a processor in a system layer (not shown). 
     Next, first decoder  4640 , which is an example of decoder  4624  that performs decoding in the first encoding method, will be described.  FIG. 7  is a diagram showing a configuration of first decoder  4640 .  FIG. 8  is a block diagram showing first decoder  4640 . First decoder  4640  generates point cloud data by decoding encoded data (encoded stream) encoded in the first encoding method in the first encoding method. First decoder  4640  includes demultiplexer  4641 , geometry information decoder  4642 , attribute information decoder  4643 , and additional information decoder  4644 . 
     An encoded stream (compressed stream), which is encoded data, is input to first decoder  4640  from a processor in a system layer (not shown). 
     Demultiplexer  4641  separates encoded geometry information (compressed geometry), encoded attribute information (compressed attribute), encoded additional information (compressed metadata), and other additional information from the encoded data. 
     Geometry information decoder  4642  generates geometry information by decoding the encoded geometry information. For example, geometry information decoder  4642  restores the geometry information on a point cloud represented by three-dimensional coordinates from encoded geometry information represented by an N-ary structure, such as an octree. 
     Attribute information decoder  4643  decodes the encoded attribute information based on configuration information generated by geometry information decoder  4642 . For example, attribute information decoder  4643  determines a reference point (reference node) that is to be referred to in decoding a current point (current node) to be processed based on the octree structure generated by geometry information decoder  4642 . For example, attribute information decoder  4643  refers to a node whose parent node in the octree is the same as the parent node of the current node, of peripheral nodes or neighboring nodes. Note that the method of determining a reference relationship is not limited to this method. 
     The process of decoding attribute information may include at least one of an inverse quantization process, a prediction process, and an arithmetic decoding process. In this case, “refer to” means using a reference node for calculating a predicted value of attribute information or using a state of a reference node (occupancy information that indicates whether a reference node includes a point cloud or not, for example) for determining a parameter of decoding. For example, the parameter of decoding is a quantization parameter in the inverse quantization process or a context or the like in the arithmetic decoding. 
     Additional information decoder  4644  generates additional information by decoding the encoded additional information. First decoder  4640  uses additional information required for the decoding process for the geometry information and the attribute information in the decoding, and outputs additional information required for an application to the outside. 
     Next, second encoder  4650 , which is an example of encoder  4613  that performs encoding in the second encoding method, will be described.  FIG. 9  is a diagram showing a configuration of second encoder  4650 .  FIG. 10  is a block diagram showing second encoder  4650 . 
     Second encoder  4650  generates encoded data (encoded stream) by encoding point cloud data in the second encoding method. Second encoder  4650  includes additional information generator  4651 , geometry image generator  4652 , attribute image generator  4653 , video encoder  4654 , additional information encoder  4655 , and multiplexer  4656 . 
     Second encoder  4650  is characterized by generating a geometry image and an attribute image by projecting a three-dimensional structure onto a two-dimensional image, and encoding the generated geometry image and attribute image in an existing video encoding scheme. The second encoding method is referred to as video-based PCC (VPCC). 
     Point cloud data is PCC point cloud data like a PLY file or PCC point cloud data generated from sensor information, and includes geometry information (position), attribute information (attribute), and other additional information (metadata). 
     Additional information generator  4651  generates map information on a plurality of two-dimensional images by projecting a three-dimensional structure onto a two-dimensional image. 
     Geometry image generator  4652  generates a geometry image based on the geometry information and the map information generated by additional information generator  4651 . The geometry image is a distance image in which distance (depth) is indicated as a pixel value, for example. The distance image may be an image of a plurality of point clouds viewed from one point of view (an image of a plurality of point clouds projected onto one two-dimensional plane), a plurality of images of a plurality of point clouds viewed from a plurality of points of view, or a single image integrating the plurality of images. 
     Attribute image generator  4653  generates an attribute image based on the attribute information and the map information generated by additional information generator  4651 . The attribute image is an image in which attribute information (color (RGB), for example) is indicated as a pixel value, for example. The image may be an image of a plurality of point clouds viewed from one point of view (an image of a plurality of point clouds projected onto one two-dimensional plane), a plurality of images of a plurality of point clouds viewed from a plurality of points of view, or a single image integrating the plurality of images. 
     Video encoder  4654  generates an encoded geometry image (compressed geometry image) and an encoded attribute image (compressed attribute image), which are encoded data, by encoding the geometry image and the attribute image in a video encoding scheme. Note that, as the video encoding scheme, any well-known encoding method can be used. For example, the video encoding scheme is AVC or HEVC. 
     Additional information encoder  4655  generates encoded additional information (compressed metadata) by encoding the additional information, the map information and the like included in the point cloud data. 
     Multiplexer  4656  generates an encoded stream (compressed stream), which is encoded data, by multiplexing the encoded geometry image, the encoded attribute image, the encoded additional information, and other additional information. The generated encoded stream is output to a processor in a system layer (not shown). 
     Next, second decoder  4660 , which is an example of decoder  4624  that performs decoding in the second encoding method, will be described.  FIG. 11  is a diagram showing a configuration of second decoder  4660 .  FIG. 12  is a block diagram showing second decoder  4660 . Second decoder  4660  generates point cloud data by decoding encoded data (encoded stream) encoded in the second encoding method in the second encoding method. Second decoder  4660  includes demultiplexer  4661 , video decoder  4662 , additional information decoder  4663 , geometry information generator  4664 , and attribute information generator  4665 . 
     An encoded stream (compressed stream), which is encoded data, is input to second decoder  4660  from a processor in a system layer (not shown). 
     Demultiplexer  4661  separates an encoded geometry image (compressed geometry image), an encoded attribute image (compressed attribute image), an encoded additional information (compressed metadata), and other additional information from the encoded data. 
     Video decoder  4662  generates a geometry image and an attribute image by decoding the encoded geometry image and the encoded attribute image in a video encoding scheme. Note that, as the video encoding scheme, any well-known encoding method can be used. For example, the video encoding scheme is AVC or HEVC. 
     Additional information decoder  4663  generates additional information including map information or the like by decoding the encoded additional information. 
     Geometry information generator  4664  generates geometry information from the geometry image and the map information. Attribute information generator  4665  generates attribute information from the attribute image and the map information. 
     Second decoder  4660  uses additional information required for decoding in the decoding, and outputs additional information required for an application to the outside. 
     In the following, a problem with the PCC encoding scheme will be described.  FIG. 13  is a diagram showing a protocol stack relating to PCC-encoded data.  FIG. 13  shows an example in which PCC-encoded data is multiplexed with other medium data, such as a video (HEVC, for example) or an audio, and transmitted or accumulated. 
     A multiplexing scheme and a file format have a function of multiplexing various encoded data and transmitting or accumulating the data. To transmit or accumulate encoded data, the encoded data has to be converted into a format for the multiplexing scheme. For example, with HEVC, a technique for storing encoded data in a data structure referred to as a NAL unit and storing the NAL unit in ISOBMFF is prescribed. 
     At present, a first encoding method (Codec1) and a second encoding method (Codec2) are under investigation as encoding methods for point cloud data. However, there is no method defined for storing the configuration of encoded data and the encoded data in a system format. Thus, there is a problem that an encoder cannot perform an MUX process (multiplexing), transmission, or accumulation of data. 
     Note that, in the following, the term “encoding method” means any of the first encoding method and the second encoding method unless a particular encoding method is specified. 
     In the following, a way of defining a NAL unit according to this embodiment will be described. For example, with a conventional codec, such as HEVC, a NAL unit in one format is defined for one codec. However, there has been no method that supports a format that involves two codecs, that is, the first encoding method and the second encoding method, such as PCC (such a codec will be referred to as a PCC codec, hereinafter). 
     First, encoder  4670  having the functions of both first encoder  4630  and second encoder  4650  described above and decoder  4680  having the functions of both first decoder  4640  and second decoder  4660  described above will be described. 
       FIG. 14  is a block diagram showing encoder  4670  according to this embodiment. Encoder  4670  includes first encoder  4630  and second encoder  4650  described above and multiplexer  4671 . Multiplexer  4671  multiplexes encoded data generated by first encoder  4630  and encoded data generated by second encoder  4650 , and outputs the resulting encoded data. 
       FIG. 15  is a block diagram showing decoder  4680  according to this embodiment. Decoder  4680  includes first decoder  4640  and second decoder  4660  described above and demultiplexer  4681 . Demultiplexer  4681  extracts encoded data generated using the first encoding method and encoded data generated using second encoding method from the input encoded data. Demultiplexer  4681  outputs the encoded data generated using the first encoding method to first decoder  4640 , and outputs the encoded data generated using the second encoding method to second decoder  4660 . 
     With the configuration described above, encoder  4670  can encode point cloud data by selectively using the first encoding method or the second encoding method. Decoder  4680  can decode encoded data encoded using the first encoding method, encoded data using the second encoding method, and encoded data encoded using both the first encoding method and the second encoding method. 
     For example, encoder  4670  may change the encoding method (between the first encoding method and the second encoding method) on a point-cloud-data basis or on a frame basis. Alternatively, encoder  4670  may change the encoding method on the basis of an encodable unit. 
     For example, encoder  4670  generates encoded data (encoded stream) including the identification information for a PCC codec. 
     Demultiplexer  4681  in decoder  4680  identifies data using the identification information for a PCC codec, for example. When the data is data encoded in the first encoding method, demultiplexer  4681  outputs the data to first decoder  4640 . When the data is data encoded in the second encoding method, demultiplexer  4681  outputs the data to second decoder  4660 . 
     Encoder  4670  may transmit, as the control information, information indicating whether both the encoding methods are used or any one of the encoding methods is used, in addition to the identification information for the PCC codec. 
     Next, an encoding process according to this embodiment will be described.  FIG. 16  is a flowchart showing an encoding process according to this embodiment. Using the identification information for a PCC codec allows an encoding process ready for a plurality of codecs. 
     First, encoder  4670  encodes PCC data in both or one of the codecs, that is, the first encoding method and the second encoding method (S 4681 ). 
     When the codec used is the second encoding method (if “second encoding method” in S 4682 ), encoder  4670  sets pcc_codec_type in the NAL unit header to a value that indicates that data included in the payload of the NAL unit is data encoded in the second encoding method (S 4683 ). Encoder  4670  then sets pcc_nal_unit_type in the NAL unit header to the identifier of the NAL unit for the second encoding method (S 4684 ). Encoder  4670  then generates a NAL unit having the set NAL unit header and including the encoded data in the payload. Encoder  4670  then transmits the generated NAL unit (S 4685 ). 
     On the other hand, when the codec used is the first encoding method (if “first encoding method” in S 4682 ). Encoder  4670  sets pcc_codec_type in the NAL unit header to a value that indicates that data included in the payload of the NAL unit is data encoded in the first encoding method (S 4686 ). Encoder  4670  then sets pcc_nal_unit_type in the NAL unit header to the identifier of the NAL unit for the first encoding method (S 4687 ). Encoder  4670  then generates a NAL unit having the set NAL unit header and including the encoded data in the payload. Encoder  4670  then transmits the generated NAL unit (S 4685 ). 
     Next, a decoding process according to this embodiment will be described.  FIG. 17  is a flowchart showing a decoding process according to this embodiment. Using the identification information for a PCC codec allows a decoding process ready for a plurality of codecs. 
     First, decoder  4680  receives a NAL unit (S 4691 ). For example, the NAL unit is the NAL unit generated in the process by encoder  4670  described above. 
     Decoder  4680  then determines whether pcc_codec_type in the NAL unit header indicates the first encoding method or the second encoding method (S 4692 ). 
     When pcc_codec_type indicates the second encoding method (if “second encoding method” in S 4692 ), decoder  4680  determines that the data included in the payload of the NAL unit is data encoded in the second encoding method (S 4693 ). Decoder  4680  then identifies the data based on the determination that pcc_nal_unit_type in the NAL unit header is the identifier of the NAL unit for the second encoding method (S 4694 ). Decoder  4680  then decodes the PCC data in a decoding process for the second encoding method (S 4695 ). 
     On the other hand, when pcc_codec_type indicates the first encoding method (if “first encoding method” in S 4692 ), decoder  4680  determines that the data included in the payload of the NAL unit is data encoded in the first encoding method (S 4696 ). Decoder  4680  then identifies the data based on the determination that pcc_nal_unit_type in the NAL unit header is the identifier of the NAL unit for the first encoding method (S 4697 ). Decoder  4680  then decodes the PCC data in a decoding process for the first encoding method (S 4698 ). 
     As described above, the three-dimensional data encoding device according to an aspect of the present disclosure generates an encoded stream by encoding three-dimensional data (point cloud data, for example), and stores information indicating the encoding method used for the encoding among the first encoding method and the second encoding method (identification information for the codec, for example) in the control information (a parameter set, for example) for the encoded stream. 
     With such a configuration, the three-dimensional data decoding device can determine the encoding method used for the encoding from the information stored in the control information, when decoding the encoded stream generated by the three-dimensional data encoding device. Therefore, the three-dimensional data decoding device can correctly decode the encoded stream even when a plurality of encoding methods are used. 
     The three-dimensional data includes geometry information, for example. In the encoding described above, the three-dimensional data encoding device encodes the geometry information. In the storage described above, the three-dimensional data encoding device stores the information indicating the encoding method used for the encoding of the geometry information among the first encoding method and the second encoding method in the control information for the geometry information. 
     The three-dimensional data includes geometry information and attribute information, for example. In the encoding described above, the three-dimensional data encoding device encodes the geometry information and the attribute information. In the storage described above, the three-dimensional data encoding device stores the information indicating the encoding method used for the encoding of the geometry information among the first encoding method and the second encoding method in the control information for the geometry information, and stores the information indicating the encoding method used for the encoding of the attribute information among the first encoding method and the second encoding method in the control information for the attribute information. 
     With such a configuration, different encoding methods can be used for the geometry information and the attribute information, and therefore, the coding efficiency can be improved. 
     For example, the three-dimensional data encoding method further includes storing the encoded stream in one or more units (NAL units, for example). 
     For example, the unit includes information (pcc_nal_unit_type, for example) indicating the type of data included in the unit that has a format that is common to the first encoding method and the second encoding method and is independently defined for the first encoding method and the second encoding method. 
     For example, the unit includes information (codec1_nal_unit_type or codec2_nal_unit_type, for example) indicating the type of data included in the unit that has different formats for the first encoding method and the second encoding method and is independently defined for the first encoding method and the second encoding method. 
     For example, the unit includes information (pcc_nal_unit_type, for example) indicating the type of data included in the unit that has a format that is common to the first encoding method and the second encoding method and is commonly defined for the first encoding method and the second encoding method. 
     For example, the three-dimensional data encoding device includes a processor and a memory, and the processor performs the processes described above using the memory. 
     The three-dimensional data decoding device according to this embodiment determines the encoding method used for encoding of an encoded stream obtained by encoding of three-dimensional data based on the information indicating the encoding method used for the encoding of the three-dimensional data among the first encoding method and the second encoding method (identification information for the codec, for example) included in the control information (a parameter set, for example) for the encoded stream, and decodes the encoded stream using the determined encoding method. 
     With such a configuration, the three-dimensional data decoding device can determine the encoding method used for the encoding from the information stored in the control information, when decoding the encoded stream. Therefore, the three-dimensional data decoding device can correctly decode the encoded stream even when a plurality of encoding methods are used. 
     The three-dimensional data includes geometry information, and the encoded stream includes encoded data of the geometry information, for example. In the determination described above, the three-dimensional data decoding device determines the encoding method used for the encoding of the geometry information based on the information indicating the encoding method used for the encoding of the geometry information among the first encoding method and the second encoding method included in the control information for the geometry information included in the encoded stream. In the decoding described above, the three-dimensional data decoding device decodes the encoded data of the geometry information using the determined encoding method used for the encoding of the geometry information. 
     The three-dimensional data includes geometry information and attribute information, and the encoded stream includes encoded data of the geometry information and encoded data of the attribute information, for example. In the determination described above, the three-dimensional data decoding device determines the encoding method used for the encoding of the geometry information based on the information indicating the encoding method used for the encoding of the geometry information among the first encoding method and the second encoding method included in the control information for the geometry information included in the encoded stream, and determines the encoding method used for the encoding of the attribute information based on the information indicating the encoding method used for the encoding of the attribute information among the first encoding method and the second encoding method included in the control information for the attribute information included in the encoded stream. In the decoding described above, the three-dimensional data decoding device decodes the encoded data of the geometry information using the determined encoding method used for the encoding of the geometry information, and decodes the encoded data of the attribute information using the determined encoding method used for the encoding of the attribute information. 
     With such a configuration, different encoding methods can be used for the geometry information and the attribute information, and therefore, the coding efficiency can be improved. 
     For example, the encoded stream is stored in one or more units (NAL units, for example), and the three-dimensional data decoding device further obtains the encoded stream from the one or more units. 
     For example, the unit includes information (pcc_nal_unit_type, for example) indicating the type of data included in the unit that has a format that is common to the first encoding method and the second encoding method and is independently defined for the first encoding method and the second encoding method. 
     For example, the unit includes information (codec1_nal_unit_type or codec2_nal_unit_type, for example) indicating the type of data included in the unit that has different formats for the first encoding method and the second encoding method and is independently defined for the first encoding method and the second encoding method. 
     For example, the unit includes information (pcc_nal_unit_type, for example) indicating the type of data included in the unit that has a format that is common to the first encoding method and the second encoding method and is commonly defined for the first encoding method and the second encoding method. 
     For example, the three-dimensional data decoding device includes a processor and a memory, and the processor performs the processes described above using the memory. 
     Embodiment 2 
     In Embodiment 2, a method of storing the NAL unit in an ISOBMFF file will be described. 
     ISOBMFF is a file format standard prescribed in ISO/IEC14496-12. ISOBMFF is a standard that does not depend on any medium, and prescribes a format that allows various media, such as a video, an audio, and a text, to be multiplexed and stored. 
     A basic structure (file) of ISOBMFF will be described. A basic unit of ISOBMFF is a box. A box is formed by type, length, and data, and a file is a set of various types of boxes. 
       FIG. 18  is a diagram showing a basic structure (file) of ISOBMFF. A file in ISOBMFF includes boxes, such as ftyp that indicates the brand of the file by four-character code (4CC), moov that stores metadata, such as control information (signaling information), and mdat that stores data. 
     A method for storing each medium in the ISOBMFF file is separately prescribed. For example, a method of storing an AVC video or an HEVC video is prescribed in ISO/IEC14496-15. Here, it can be contemplated to expand the functionality of ISOBMFF and use ISOBMFF to accumulate or transmit PCC-encoded data. However, there has been no convention for storing PCC-encoded data in an ISOBMFF file. In this embodiment, a method of storing PCC-encoded data in an ISOBMFF file will be described. 
       FIG. 19  is a diagram showing a protocol stack in a case where a common PCC codec NAL unit in an ISOBMFF file. Here, a common PCC codec NAL unit is stored in an ISOBMFF file. Although the NAL unit is common to PCC codecs, a storage method for each codec (Carriage of Codec1, Carriage of Codec2) is desirably prescribed, since a plurality of PCC codecs are stored in the NAL unit. 
     Next, a method of storing a common PCC NAL unit that supports a plurality of PCC codecs in an ISOBMFF file will be described.  FIG. 20  is a diagram showing an example in which a common PCC NAL unit is stored in an ISOBMFF file for the storage method for codec 1 (Carriage of Codec1).  FIG. 21  is a diagram showing an example in which a common PCC NAL unit is stored in an ISOBMFF file for the storage method for codec 2 (Carriage of Codec2). 
     Here, ftyp is information that is important for identification of the file format, and a different identifier of ftyp is defined for each codec. When PCC-encoded data encoded in the first encoding method (encoding scheme) is stored in the file, ftyp is set to pcc1. When PCC-encoded data encoded in the second encoding method is stored in the file, ftyp is set to pcc2. 
     Here, pcc1 indicates that PCC codec 1 (first encoding method) is used. pcc2 indicates that PCC codec2 (second encoding method) is used. That is, pcc1 and pcc2 indicate that the data is PCC (encoded three-dimensional data (point cloud data)), and indicate the PCC codec (first encoding method or second encoding method). 
     In the following, a method of storing a NAL unit in an ISOBMFF file will be described. The multiplexer analyzes the NAL unit header, and describes pcc1 in ftyp of ISOBMFF if pcc_codec_type=Codec1. 
     The multiplexer analyzes the NAL unit header, and describes pcc2 in ftyp of ISOBMFF if pcc_codec_type=Codec2. 
     If pcc_nal_unit_type is metadata, the multiplexer stores the NAL unit in moov or mdat in a predetermined manner, for example. If pcc_nal_unit_type is data, the multiplexer stores the NAL unit in moov or mdat in a predetermined manner, for example. 
     For example, the multiplexer may store the NAL unit size in the NAL unit, as with HEVC. 
     According to this storage method, the demultiplexer (a system layer) can determine whether the PCC-encoded data is encoded in the first encoding method or the second encoding method by analyzing ftyp included in the file. Furthermore, as described above, by determining whether the PCC-encoded data is encoded in the first encoding method or the second encoding method, the encoded data encoded in any one of the encoding methods can be extracted from the data including both the encoded data encoded in the encoding methods. Therefore, when transmitting the encoded data, the amount of data transmitted can be reduced. In addition, according to this storage method, different data (file) formats do not need to be set for the first encoding method and the second encoding method, and a common data format can be used for the first encoding method and the second encoding method. 
     Note that, when the identification information for the codec, such as ftyp of ISOBMFF, is indicated in the metadata of the system layer, the multiplexer can store a NAL unit without pcc_nal_unit_type in the ISOBMFF file. 
     Next, configurations and operations of the multiplexer of the three-dimensional data encoding system (three-dimensional data encoding device) according to this embodiment and the demultiplexer of the three-dimensional data decoding system (three-dimensional data decoding device) according to this embodiment will be described. 
       FIG. 22  is a diagram showing a configuration of first multiplexer  4710 . First multiplexer  4710  includes file converter  4711  that generates multiplexed data (file) by storing encoded data generated by first encoder  4630  and control information (NAL unit) in an ISOBMFF file. First multiplexer  4710  is included in multiplexer  4614  shown in  FIG. 1 , for example. 
       FIG. 23  is a diagram showing a configuration of first demultiplexer  4720 . First demultiplexer  4720  includes file inverse converter  4721  that obtains encoded data and control information (NAL unit) from multiplexed data (file) and outputs the obtained encoded data and control information to first decoder  4640 . First demultiplexer  4720  is included in demultiplexer  4623  shown in  FIG. 1 , for example. 
       FIG. 24  is a diagram showing a configuration of second multiplexer  4730 . Second multiplexer  4730  includes file converter  4731  that generates multiplexed data (file) by storing encoded data generated by second encoder  4650  and control information (NAL unit) in an ISOBMFF file. Second multiplexer  4730  is included in multiplexer  4614  shown in  FIG. 1 , for example. 
       FIG. 25  is a diagram showing a configuration of second demultiplexer  4740 . Second demultiplexer  4740  includes file inverse converter  4741  that obtains encoded data and control information (NAL unit) from multiplexed data (file) and outputs the obtained encoded data and control information to second decoder  4660 . Second demultiplexer  4740  is included in demultiplexer  4623  shown in  FIG. 1 , for example. 
       FIG. 26  is a flowchart showing a multiplexing process by first multiplexer  4710 . First, first multiplexer  4710  analyzes pcc_codec_type in the NAL unit header, thereby determining whether the codec used is the first encoding method or the second encoding method (S 4701 ). 
     When pcc_codec_type represents the second encoding method (if “second encoding method” in S 4702 ), first multiplexer  4710  does not process the NAL unit (S 4703 ). 
     On the other hand, when pcc_codec_type represents the first encoding method (if “first encoding method” in S 4702 ), first multiplexer  4710  describes pcc1 in ftyp (S 4704 ). That is, first multiplexer  4710  describes information indicating that data encoded in the first encoding method is stored in the file in ftyp. 
     First multiplexer  4710  then analyzes pcc_nal_unit_type in the NAL unit header, and stores the data in a box (moov or mdat, for example) in a predetermined manner suitable for the data type represented by pcc_nal_unit_type (S 4705 ). First multiplexer  4710  then creates an ISOBMFF file including the ftyp described above and the box described above (S 4706 ). 
       FIG. 27  is a flowchart showing a multiplexing process by second multiplexer  4730 . First, second multiplexer  4730  analyzes pcc_codec_type in the NAL unit header, thereby determining whether the codec used is the first encoding method or the second encoding method (S 4711 ). 
     When pcc_codec_type represents the second encoding method (if “second encoding method” in S 4712 ), second multiplexer  4730  describes pcc2 in ftyp (S 4713 ). That is, second multiplexer  4730  describes information indicating that data encoded in the second encoding method is stored in the file in ftyp. 
     Second multiplexer  4730  then analyzes pcc_nal_unit_type in the NAL unit header, and stores the data in a box (moov or mdat, for example) in a predetermined manner suitable for the data type represented by pcc_nal_unit_type (S 4714 ). Second multiplexer  4730  then creates an ISOBMFF file including the ftyp described above and the box described above (S 4715 ). 
     On the other hand, when pcc_codec_type represents the first encoding method (if “first encoding method” in S 4712 ), second multiplexer  4730  does not process the NAL unit (S 4716 ). 
     Note that the process described above is an example in which PCC data is encoded in any one of the first encoding method and the second encoding method. First multiplexer  4710  and second multiplexer  4730  store a desired NAL unit in a file by identifying the codec type of the NAL unit. Note that, when the identification information for the PCC codec is included in a location other than the NAL unit header, first multiplexer  4710  and second multiplexer  4730  may identify the codec type (first encoding method or second encoding method) based on the identification information for the PCC codec included in the location other than the NAL unit header in step S 4701  or S 4711 . 
     When storing data in a file in step S 4706  or S 4714 , first multiplexer  4710  and second multiplexer  4730  may store the data in the file after deleting pcc_nal_unit_type from the NAL unit header. 
       FIG. 28  is a flowchart showing a process performed by first demultiplexer  4720  and first decoder  4640 . First, first demultiplexer  4720  analyzes ftyp in an ISOBMFF file (S 4721 ). When the codec represented by ftyp is the second encoding method (pcc2) (if “second encoding method” in S 4722 ), first demultiplexer  4720  determines that the data included in the payload of the NAL unit is data encoded in the second encoding method (S 4723 ). First demultiplexer  4720  also transmits the result of the determination to first decoder  4640 . First decoder  4640  does not process the NAL unit (S 4724 ). 
     On the other hand, when the codec represented by ftyp is the first encoding method (pcc1) (if “first encoding method” in S 4722 ), first demultiplexer  4720  determines that the data included in the payload of the NAL unit is data encoded in the first encoding method (S 4725 ). First demultiplexer  4720  also transmits the result of the determination to first decoder  4640 . 
     First decoder  4640  identifies the data based on the determination that pcc_nal_unit_type in the NAL unit header is the identifier of the NAL unit for the first encoding method (S 4726 ). First decoder  4640  then decodes the PCC data using a decoding process for the first encoding method (S 4727 ). 
       FIG. 29  is a flowchart showing a process performed by second demultiplexer  4740  and second decoder  4660 . First, second demultiplexer  4740  analyzes ftyp in an ISOBMFF file (S 4731 ). When the codec represented by ftyp is the second encoding method (pcc2) (if “second encoding method” in S 4732 ), second demultiplexer  4740  determines that the data included in the payload of the NAL unit is data encoded in the second encoding method (S 4733 ). Second demultiplexer  4740  also transmits the result of the determination to second decoder  4660 . 
     Second decoder  4660  identifies the data based on the determination that pcc_nal_unit_type in the NAL unit header is the identifier of the NAL unit for the second encoding method (S 4734 ). Second decoder  4660  then decodes the PCC data using a decoding process for the second encoding method (S 4735 ). 
     On the other hand, when the codec represented by ftyp is the first encoding method (pcc1) (if “first encoding method” in S 4732 ), second demultiplexer  4740  determines that the data included in the payload of the NAL unit is data encoded in the first encoding method (S 4736 ). Second demultiplexer  4740  also transmits the result of the determination to second decoder  4660 . Second decoder  4660  does not process the NAL unit (S 4737 ). 
     As described above, for example, since the codec type of the NAL unit is identified in first demultiplexer  4720  or second demultiplexer  4740 , the codec type can be identified in an early stage. Furthermore, a desired NAL unit can be input to first decoder  4640  or second decoder  4660 , and an unwanted NAL unit can be removed. In this case, the process of first decoder  4640  or second decoder  4660  analyzing the identification information for the codec may be unnecessary. Note that a process of referring to the NAL unit type again and analyzing the identification information for the codec may be performed by first decoder  4640  or second decoder  4660 . 
     Furthermore, if pcc_nal_unit_type is deleted from the NAL unit header by first multiplexer  4710  or second multiplexer  4730 , first demultiplexer  4720  or second demultiplexer  4740  can output the NAL unit to first decoder  4640  or second decoder  4660  after adding pcc_nal_unit_type to the NAL unit. 
     Embodiment 3 
     In Embodiment 3, a multiplexer and a demultiplexer that correspond to encoder  4670  and decoder  4680  ready for a plurality of codecs described above with regard to Embodiment 1 will be described.  FIG. 30  is a diagram showing configurations of encoder  4670  and third multiplexer  4750  according to this embodiment. 
     Encoder  4670  encodes point cloud data in both or one of the first encoding method and the second encoding method. Encoder  4670  may change the encoding method (between the first encoding method and the second encoding method) on a point-cloud-data basis or on a frame basis. Alternatively, encoder  4670  may change the encoding method on the basis of an encodable unit. 
     Encoder  4670  generates encoded data (encoded stream) including the identification information for a PCC codec. 
     Third multiplexer  4750  includes file converter  4751 . File converter  4751  converts a NAL unit output from encoder  4670  into a PCC data file. File converter  4751  analyzes the codec identification information included in the NAL unit header, and determines whether the PCC-encoded data is data encoded in the first encoding method, data encoded in the second encoding method, or data encoded in both the encoding methods. File converter  4751  describes a brand name that allows codec identification in ftyp. For example, when indicating the data is encoded in both the encoding methods, pcc3 is described in ftyp. 
     Note that, when encoder  4670  describes the PCC codec identification information in a location other than the NAL unit, file converter  4751  may determine the PCC codec (encoding method) based on the identification information. 
       FIG. 31  is a diagram showing configurations of third demultiplexer  4760  and decoder  4680  according to this embodiment. 
     Third demultiplexer  4760  includes file inverse converter  4761 . File inverse converter  4761  analyzes ftyp included in a file, and determines whether the PCC-encoded data is data encoded in the first encoding method, data encoded in the second encoding method, or data encoded in both the encoding methods. 
     When the PCC-encoded data is data encoded in any one of the encoding methods, the data is input to an appropriate one of first decoder  4640  and second decoder  4660 , and is not input to the other decoder. When the PCC-encoded data is data encoded in both the encoding methods, the data is input to decoder  4680  ready for both the encoding methods. 
     Decoder  4680  decodes the PCC-encoded data in both or one of the first encoding method and the second encoding method. 
       FIG. 32  is a flowchart showing a process performed by third multiplexer  4750  according to this embodiment. 
     First, third multiplexer  4750  analyzes pcc_codec_type in the NAL unit header, thereby determining whether the codec(s) used is the first encoding method, the second encoding method, or both the first encoding method and the second encoding method (S 4741 ). 
     When the second encoding method is used (if Yes in S 4742  and “second encoding method” in S 4743 ), third multiplexer  4750  describes pcc2 in ftyp (S 4744 ). That is, third multiplexer  4750  describes information indicating that data encoded in the second encoding method is stored in the file in ftyp. 
     Third multiplexer  4750  then analyzes pcc_nal_unit_type in the NAL unit header, and stores the data in a box (moov or mdat, for example) in a predetermined manner suitable for the data type represented by pcc_nal_unit_type (S 4745 ). Third multiplexer  4750  then creates an ISOBMFF file including the ftyp described above and the box described above (S 4746 ). 
     When the first encoding method is used (if Yes in S 4742  and “first encoding method” in S 4743 ), third multiplexer  4750  describes pcc1 in ftyp (S 4747 ). That is, third multiplexer  4750  describes information indicating that data encoded in the first encoding method is stored in the file in ftyp. 
     Third multiplexer  4750  then analyzes pcc_nal_unit_type in the NAL unit header, and stores the data in a box (moov or mdat, for example) in a predetermined manner suitable for the data type represented by pcc_nal_unit_type (S 4748 ). Third multiplexer  4750  then creates an ISOBMFF file including the ftyp described above and the box described above (S 4746 ). 
     When both the first encoding method and the second encoding method are used (if No in S 4742 ), third multiplexer  4750  describes pcc3 in ftyp (S 4749 ). That is, third multiplexer  4750  describes information indicating that data encoded in both the encoding methods is stored in the file in ftyp. 
     Third multiplexer  4750  then analyzes pcc_nal_unit_type in the NAL unit header, and stores the data in a box (moov or mdat, for example) in a predetermined manner suitable for the data type represented by pcc_nal_unit_type (S 4750 ). Third multiplexer  4750  then creates an ISOBMFF file including the ftyp described above and the box described above (S 4746 ). 
       FIG. 33  is a flowchart showing a process performed by third demultiplexer  4760  and decoder  4680 . First, third demultiplexer  4760  analyzes ftyp included in an ISOBMFF file (S 4761 ). When the codec represented by ftyp is the second encoding method (pcc2) (if Yes in S 4762  and “second encoding method” in S 4763 ), third demultiplexer  4760  determines that the data included in the payload of the NAL unit is data encoded in the second encoding method (S 4764 ). Third demultiplexer  4760  also transmits the result of the determination to decoder  4680 . 
     Decoder  4680  identifies the data based on the determination that pcc_nal_unit_type in the NAL unit header is the identifier of the NAL unit for the second encoding method (S 4765 ). Decoder  4680  then decodes the PCC data using a decoding process for the second encoding method (S 4766 ). 
     When the codec represented by ftyp is the first encoding method (pcc1) (if Yes in S 4762  and “first encoding method” in S 4763 ), third demultiplexer  4760  determines that the data included in the payload of the NAL unit is data encoded in the first encoding method (S 4767 ). Third demultiplexer  4760  also transmits the result of the determination to decoder  4680 . 
     Decoder  4680  identifies the data based on the determination that pcc_nal_unit_type in the NAL unit header is the identifier of the NAL unit for the first encoding method (S 4768 ). Decoder  4680  then decodes the PCC data using a decoding process for the first encoding method (S 4769 ). 
     When ftyp indicates that both the encoding methods are used (pcc3) (if No in S 4762 ), third demultiplexer  4760  determines that the data included in the payload of the NAL unit is data encoded in both the first encoding method and the second encoding method (S 4770 ). Third demultiplexer  4760  also transmits the result of the determination to decoder  4680 . 
     Decoder  4680  identifies the data based on the determination that pcc_nal_unit_type in the NAL unit header is the identifier of the NAL unit for the codecs described in pcc_codec_type (S 4771 ). Decoder  4680  then decodes the PCC data using decoding processes for both the encoding methods (S 4772 ). That is, decoder  4680  decodes the data encoded in the first encoding method using a decoding process for the first encoding method, and decodes the data encoded in the second encoding method using a decoding process for the second encoding method. 
     In the following, variations of this embodiment will be described. As types of brands represented by ftyp, the types described below can be indicated by the identification information. Furthermore, a combination of a plurality of the types described below can also be indicated by the identification information. 
     The identification information may indicate whether the original data object yet to be PCC-encoded is a point cloud whose range is limited or a large point cloud whose range is not limited, such as map information. 
     The identification information may indicate whether the original data yet to be PCC-encoded is a static object or a dynamic object. 
     As described above, the identification information may indicate whether the PCC-encoded data is data encoded in the first encoding method or data encoded in the second encoding method. 
     The identification information may indicate an algorithm used in the PCC encoding. Here, the “algorithm” means an encoding method that can be used in the first encoding method or the second encoding method, for example. 
     The identification information may indicate a differentiation between methods of storing the PCC-encoded data into an ISOBMFF file. For example, the identification information may indicate whether the storage method used is a storage method for accumulation or a storage method for real-time transmission, such as dynamic streaming. 
     Although an example in which ISOBMFF is used as a file format has been described in Embodiments 2 and 3, other formats can also be used. For example, the method according to this embodiment can also be used when PCC-encoded data is stored in MPEG-2 TS Systems, MPEG-DASH, MMT, or RMP. 
     Although an example in which metadata, such as the identification information, is stored in ftyp has been shown above, metadata can also be stored in a location other than ftyp. For example, the metadata may be stored in moov. 
     As described above, a three-dimensional data storing device (or three-dimensional data multiplexing device or three-dimensional data encoding device) performs the process shown in  FIG. 34 . 
     First, the three-dimensional data storing device (which includes first multiplexer  4710 , second multiplexer  4730  or third multiplexer  4750 , for example) acquires one or more units (NAL units, for example) that store an encoded stream, which is encoded point cloud data (S 4781 ). The three-dimensional data storing device then stores the one or more units in a file (an ISOBMFF file, for example) (S 4782 ). In the storage (S 4782 ), the three-dimensional data storing device also stores information indicating that the data stored in the file is encoded point cloud data (pcc1, pcc2, or pcc3, for example) in the control information (ftyp, for example) (referred to also as signaling information) for the file. 
     With such a configuration, a device that processes the file generated by the three-dimensional data storing device can quickly determine whether the data stored in the file is encoded point cloud data or not by referring to the control information for the file. Therefore, the processing amount of the device can be reduced, or the processing speed of the device can be increased. 
     For example, the information indicates the encoding method used for the encoding of the point cloud data among the first encoding method and the second encoding method. Note that the fact that the data stored in the file is encoded point cloud data and the encoding method used for the encoding of the point cloud data among the first encoding method and the second encoding method may be indicated by a single piece of information or different pieces of information. 
     With such a configuration, a device that processes the file generated by the three-dimensional data storing device can quickly determine the codec used for the data stored in the file by referring to the control information for the file. Therefore, the processing amount of the device can be reduced, or the processing speed of the device can be increased. 
     For example, the first encoding method is a method (GPCC) that encodes geometry information that represents the position of point cloud data as an N-ary tree (N represents an integer equal to or greater than 2) and encodes attribute information using the geometry information, and the second encoding method is a method (VPCC) that generates a two-dimensional image from point cloud data and encodes the two-dimensional image in a video encoding method. 
     For example, the file described above is in conformity with ISOBMFF (ISO-based media file format). 
     For example, the three-dimensional data storing device includes a processor and a memory, and the processor performs the processes described above using the memory. 
     As described above, a three-dimensional data acquisition device (or three-dimensional data demultiplexing device or three-dimensional data decoding device) performs the process shown in  FIG. 35 . 
     The three-dimensional data acquisition device (which includes first demultiplexer  4720 , second demultiplexer  4740 , or third demultiplexer  4760 , for example) acquires a file (an ISOBMFF file, for example) that stores one or more units (NAL units, for example) that store an encoded stream, which is encoded point cloud data (S 4791 ). The three-dimensional data acquisition device acquires the one or more units from the file (S 4792 ). The control information (ftyp, for example) for the file includes information indicating that the data stored in the file is encoded point cloud data (pcc1, pcc2, or pcc3, for example). 
     For example, the three-dimensional data acquisition device determines whether the data stored in the file is encoded point cloud data or not by referring to the information. When the three-dimensional data acquisition device determines that the data stored in the file is encoded point cloud data, the three-dimensional data acquisition device generates point cloud data by decoding the encoded point cloud data included in the one or more units. Alternatively, when the three-dimensional data acquisition device determines that the data stored in the file is encoded point cloud data, the three-dimensional data acquisition device outputs information indicating that the data included in the one or more units is encoded point cloud data to a processor in a subsequent stage (first decoder  4640 , second decoder  4660 , or decoder  4680 , for example) (or notifies a processor in a subsequent stage that the data included in the one or more units is encoded point cloud data). 
     With such a configuration, the three-dimensional data acquisition device can quickly determine whether the data stored in the file is encoded point cloud data or not by referring to the control information for the file. Therefore, the processing amount of the three-dimensional data acquisition device or a device in a subsequent stage can be reduced, or the processing speed of the three-dimensional data acquisition device or a device in a subsequent stage can be increased. 
     For example, the information represents the encoding method used for the encoding among the first encoding method and the second encoding method. Note that the fact that the data stored in the file is encoded point cloud data and the encoding method used for the encoding of the point cloud data among the first encoding method and the second encoding method may be indicated by a single piece of information or different pieces of information. 
     With such a configuration, the three-dimensional data acquisition device can quickly determine the codec used for the data stored in the file by referring to the control information for the file. Therefore, the processing amount of the three-dimensional data acquisition device or a device in a subsequent stage can be reduced, or the processing speed of the three-dimensional data acquisition device or a device in a subsequent stage can be increased. 
     For example, based on the information, the three-dimensional data acquisition device acquires the data encoded in any one of the first encoding method and the second encoding method from the encoded point cloud data including the data encoded in the first encoding method and the data encoded in the second encoding method. 
     For example, the first encoding method is a method (GPCC) that encodes geometry information that represents the position of point cloud data as an N-ary tree (N represents an integer equal to or greater than 2) and encodes attribute information using the geometry information, and the second encoding method is a method (VPCC) that generates a two-dimensional image from point cloud data and encodes the two-dimensional image in a video encoding method. 
     For example, the file described above is in conformity with ISOBMFF (ISO-based media file format). 
     For example, the three-dimensional data acquisition device includes a processor and a memory, and the processor performs the processes described above using the memory. 
     Embodiment 4 
     In Embodiment 4, types of the encoded data (geometry information (geometry), attribute information (attribute), and additional information (metadata)) generated by first encoder  4630  or second encoder  4650  described above, a method of generating additional information (metadata), and a multiplexing process in the multiplexer will be described. The additional information (metadata) may be referred to as a parameter set or control information (signaling information). 
     In this embodiment, the dynamic object (three-dimensional point cloud data that varies with time) described above with reference to  FIG. 4  will be described, for example. However, the same method can also be used for the static object (three-dimensional point cloud data associated with an arbitrary time point). 
       FIG. 36  is a diagram showing configurations of encoder  4801  and multiplexer  4802  in a three-dimensional data encoding device according to this embodiment. Encoder  4801  corresponds to first encoder  4630  or second encoder  4650  described above, for example. Multiplexer  4802  corresponds to multiplexer  4634  or  4656  described above. 
     Encoder  4801  encodes a plurality of PCC (point cloud compression) frames of point cloud data to generate a plurality of pieces of encoded data (multiple compressed data) of geometry information, attribute information, and additional information. 
     Multiplexer  4802  integrates a plurality of types of data (geometry information, attribute information, and additional information) into a NAL unit, thereby converting the data into a data configuration that takes data access in the decoding device into consideration. 
       FIG. 37  is a diagram showing a configuration example of the encoded data generated by encoder  4801 . Arrows in the drawing indicate a dependence involved in decoding of the encoded data. The source of an arrow depends on data of the destination of the arrow. That is, the decoding device decodes the data of the destination of an arrow, and decodes the data of the source of the arrow using the decoded data. In other words, “a first entity depends on a second entity” means that data of the second entity is referred to (used) in processing (encoding, decoding, or the like) of data of the first entity. 
     First, a process of generating encoded data of geometry information will be described. Encoder  4801  encodes geometry information of each frame to generate encoded geometry data (compressed geometry data) for each frame. The encoded geometry data is denoted by G(i). i denotes a frame number or a time point of a frame, for example. 
     Furthermore, encoder  4801  generates a geometry parameter set (GPS(i)) for each frame. The geometry parameter set includes a parameter that can be used for decoding of the encoded geometry data. The encoded geometry data for each frame depends on an associated geometry parameter set. 
     The encoded geometry data formed by a plurality of frames is defined as a geometry sequence. Encoder  4801  generates a geometry sequence parameter set (referred to also as geometry sequence PS or geometry SPS) that stores a parameter commonly used for a decoding process for the plurality of frames in the geometry sequence. The geometry sequence depends on the geometry SPS. 
     Next, a process of generating encoded data of attribute information will be described. Encoder  4801  encodes attribute information of each frame to generate encoded attribute data (compressed attribute data) for each frame. The encoded attribute data is denoted by A(i).  FIG. 37  shows an example in which there are attribute X and attribute Y, and encoded attribute data for attribute X is denoted by AX(i), and encoded attribute data for attribute Y is denoted by AY(i). 
     Furthermore, encoder  4801  generates an attribute parameter set (APS(i)) for each frame. The attribute parameter set for attribute X is denoted by AXPS(i), and the attribute parameter set for attribute Y is denoted by AYPS(i). The attribute parameter set includes a parameter that can be used for decoding of the encoded attribute information. The encoded attribute data depends on an associated attribute parameter set. 
     The encoded attribute data formed by a plurality of frames is defined as an attribute sequence. Encoder  4801  generates an attribute sequence parameter set (referred to also as attribute sequence PS or attribute SPS) that stores a parameter commonly used for a decoding process for the plurality of frames in the attribute sequence. The attribute sequence depends on the attribute SPS. 
     In the first encoding method, the encoded attribute data depends on the encoded geometry data. 
       FIG. 37  shows an example in which there are two types of attribute information (attribute X and attribute Y). When there are two types of attribute information, for example, two encoders generate data and metadata for the two types of attribute information. For example, an attribute sequence is defined for each type of attribute information, and an attribute SPS is generated for each type of attribute information. 
     Note that, although  FIG. 37  shows an example in which there is one type of geometry information, and there are two types of attribute information, the present invention is not limited thereto. There may be one type of attribute information or three or more types of attribute information. In such cases, encoded data can be generated in the same manner. If the point cloud data has no attribute information, there may be no attribute information. In such a case, encoder  4801  does not have to generate a parameter set associated with attribute information. 
     Next, a process of generating encoded data of additional information (metadata) will be described. Encoder  4801  generates a PCC stream PS (referred to also as PCC stream PS or stream PS), which is a parameter set for the entire PCC stream. Encoder  4801  stores a parameter that can be commonly used for a decoding process for one or more geometry sequences and one or more attribute sequences in the stream PS. For example, the stream PS includes identification information indicating the codec for the point cloud data and information indicating an algorithm used for the encoding, for example. The geometry sequence and the attribute sequence depend on the stream PS. 
     Next, an access unit and a GOF will be described. In this embodiment, concepts of access unit (AU) and group of frames (GOF) are newly introduced. 
     An access unit is a basic unit for accessing data in decoding, and is formed by one or more pieces of data and one or more pieces of metadata. For example, an access unit is formed by geometry information and one or more pieces of attribute information associated with a same time point. A GOF is a random access unit, and is formed by one or more access units. 
     Encoder  4801  generates an access unit header (AU header) as identification information indicating the top of an access unit. Encoder  4801  stores a parameter relating to the access unit in the access unit header. For example, the access unit header includes a configuration of or information on the encoded data included in the access unit. The access unit header further includes a parameter commonly used for the data included in the access unit, such as a parameter relating to decoding of the encoded data. 
     Note that encoder  4801  may generate an access unit delimiter that includes no parameter relating to the access unit, instead of the access unit header. The access unit delimiter is used as identification information indicating the top of the access unit. The decoding device identifies the top of the access unit by detecting the access unit header or the access unit delimiter. 
     Next, generation of identification information for the top of a GOF will be described. As identification information indicating the top of a GOF, encoder  4801  generates a GOF header. Encoder  4801  stores a parameter relating to the GOF in the GOF header. For example, the GOF header includes a configuration of or information on the encoded data included in the GOF. The GOF header further includes a parameter commonly used for the data included in the GOF, such as a parameter relating to decoding of the encoded data. 
     Note that encoder  4801  may generate a GOF delimiter that includes no parameter relating to the GOF, instead of the GOF header. The GOF delimiter is used as identification information indicating the top of the GOF. The decoding device identifies the top of the GOF by detecting the GOF header or the GOF delimiter. 
     In the PCC-encoded data, the access unit is defined as a PCC frame unit, for example. The decoding device accesses a PCC frame based on the identification information for the top of the access unit. 
     For example, the GOF is defined as one random access unit. The decoding device accesses a random access unit based on the identification information for the top of the GOF. For example, if PCC frames are independent from each other and can be separately decoded, a PCC frame can be defined as a random access unit. 
     Note that two or more PCC frames may be assigned to one access unit, and a plurality of random access units may be assigned to one GOF. 
     Encoder  4801  may define and generate a parameter set or metadata other than those described above. For example, encoder  4801  may generate supplemental enhancement information (SEI) that stores a parameter (an optional parameter) that is not always used for decoding. 
     Next, a configuration of encoded data and a method of storing encoded data in a NAL unit will be described. 
     For example, a data format is defined for each type of encoded data.  FIG. 38  is a diagram showing an example of encoded data and a NAL unit. 
     For example, as shown in  FIG. 38 , encoded data includes a header and a payload. The encoded data may include length information indicating the length (data amount) of the encoded data, the header, or the payload. The encoded data may include no header. 
     The header includes identification information for identifying the data, for example. The identification information indicates a data type or a frame number, for example. 
     The header includes identification information indicating a reference relationship, for example. The identification information is stored in the header when there is a dependence relationship between data, for example, and allows an entity to refer to another entity. For example, the header of the entity to be referred to includes identification information for identifying the data. The header of the referring entity includes identification information indicating the entity to be referred to. 
     Note that, when the entity to be referred to or the referring entity can be identified or determined from other information, the identification information for identifying the data or identification information indicating the reference relationship can be omitted. 
     Multiplexer  4802  stores the encoded data in the payload of the NAL unit. The NAL unit header includes pcc_nal_unit_type, which is identification information for the encoded data.  FIG. 39  is a diagram showing a semantics example of pcc_nal_unit_type. 
     As shown in  FIG. 39 , when pcc_codec_type is codec 1 (Codec1: first encoding method), values 0 to 10 of pcc_nal_unit_type are assigned to encoded geometry data (Geometry), encoded attribute X data (AttributeX), encoded attribute Y data (AttributeY), geometry PS (Geom. PS), attribute XPS (AttrX. S), attribute YPS (AttrY. PS), geometry SPS (Geometry Sequence PS), attribute X SPS (AttributeX Sequence PS), attribute Y SPS (AttributeY Sequence PS), AU header (AU Header), and GOF header (GOF Header) in codec 1. Values of 11 and greater are reserved in codec 1. 
     When pcc_codec_type is codec 2 (Codec2: second encoding method), values of 0 to 2 of pcc_nal_unit_type are assigned to data A (DataA), metadata A (MetaDataA), and metadata B (MetaDataB) in the codec. Values of 3 and greater are reserved in codec 2. 
     Next, an order of transmission of data will be described. In the following, restrictions on the order of transmission of NAL units will be described. 
     Multiplexer  4802  transmits NAL units on a GOF basis or on an AU basis. Multiplexer  4802  arranges the GOF header at the top of a GOF, and arranges the AU header at the top of an AU. 
     In order to allow the decoding device to decode the next AU and the following AUs even when data is lost because of a packet loss or the like, multiplexer  4802  may arrange a sequence parameter set (SPS) in each AU. 
     When there is a dependence relationship for decoding between encoded data, the decoding device decodes the data of the entity to be referred to and then decodes the data of the referring entity. In order to allow the decoding device to perform decoding in the order of reception without rearranging the data, multiplexer  4802  first transmits the data of the entity to be referred to. 
       FIG. 40  is a diagram showing examples of the order of transmission of NAL units.  FIG. 40  shows three examples, that is, geometry information-first order, parameter-first order, and data-integrated order. 
     The geometry information-first order of transmission is an example in which information relating to geometry information is transmitted together, and information relating to attribute information is transmitted together. In the case of this order of transmission, the transmission of the information relating to the geometry information ends earlier than the transmission of the information relating to the attribute information. 
     For example, according to this order of transmission is used, when the decoding device does not decode attribute information, the decoding device may be able to have an idle time since the decoding device can omit decoding of attribute information. When the decoding device is required to decode geometry information early, the decoding device may be able to decode geometry information earlier since the decoding device obtains encoded data of the geometry information earlier. 
     Note that, although in  FIG. 40  the attribute X SPS and the attribute Y SPS are integrated and shown as the attribute SPS, the attribute X SPS and the attribute Y SPS may be separately arranged. 
     In the parameter set-first order of transmission, a parameter set is first transmitted, and data is then transmitted. 
     As described above, as far as the restrictions on the order of transmission of NAL units are met, multiplexer  4802  can transmit NAL units in any order. For example, order identification information may be defined, and multiplexer  4802  may have a function of transmitting NAL units in a plurality of orders. For example, the order identification information for NAL units is stored in the stream PS. 
     The three-dimensional data decoding device may perform decoding based on the order identification information. The three-dimensional data decoding device may indicate a desired order of transmission to the three-dimensional data encoding device, and the three-dimensional data encoding device (multiplexer  4802 ) may control the order of transmission according to the indicated order of transmission. 
     Note that multiplexer  4802  can generate encoded data having a plurality of functions merged to each other as in the case of the data-integrated order of transmission, as far as the restrictions on the order of transmission are met. For example, as shown in  FIG. 40 , the GOF header and the AU header may be integrated, or AXPS and AYPS may be integrated. In such a case, an identifier that indicates data having a plurality of functions is defined in pcc_nal_unit_type. 
     In the following, variations of this embodiment will be described. There are levels of PSs, such as a frame-level PS, a sequence-level PS, and a PCC sequence-level PS. Provided that the PCC sequence level is a higher level, and the frame level is a lower level, parameters can be stored in the manner described below. 
     The value of a default PS is indicated in a PS at a higher level. If the value of a PS at a lower level differs from the value of the PS at a higher level, the value of the PS is indicated in the PS at the lower level. Alternatively, the value of the PS is not described in the PS at the higher level but is described in the PS at the lower level. Alternatively, information indicating whether the value of the PS is indicated in the PS at the lower level, at the higher level, or at both the levels is indicated in both or one of the PS at the lower level and the PS at the higher level. Alternatively, the PS at the lower level may be merged with the PS at the higher level. If the PS at the lower level and the PS at the higher level overlap with each other, multiplexer  4802  may omit transmission of one of the PSs. 
     Note that encoder  4801  or multiplexer  4802  may divide data into slices or tiles and transmit each of the divided slices or tiles as divided data. The divided data includes information for identifying the divided data, and a parameter used for decoding of the divided data is included in the parameter set. In this case, an identifier that indicates that the data is data relating to a tile or slice or data storing a parameter is defined in pcc_nal_unit_type. 
     In the following, a process relating to order identification information will be described.  FIG. 41  is a flowchart showing a process performed by the three-dimensional data encoding device (encoder  4801  and multiplexer  4802 ) that involves the order of transmission of NAL units. 
     First, the three-dimensional data encoding device determines the order of transmission of NAL units (geometry information-first or parameter set-first) (S 4801 ). For example, the three-dimensional data encoding device determines the order of transmission based on a specification from a user or an external device (the three-dimensional data decoding device, for example). 
     If the determined order of transmission is geometry information-first (if “geometry information-first” in S 4802 ), the three-dimensional data encoding device sets the order identification information included in the stream PS to geometry information-first (S 4803 ). That is, in this case, the order identification information indicates that the NAL units are transmitted in the geometry information-first order. The three-dimensional data encoding device then transmits the NAL units in the geometry information-first order (S 4804 ). 
     On the other hand, if the determined order of transmission is parameter set-first (if “parameter set-first” in S 4802 ), the three-dimensional data encoding device sets the order identification information included in the stream PS to parameter set-first (S 4805 ). That is, in this case, the order identification information indicates that the NAL units are transmitted in the parameter set-first order. The three-dimensional data encoding device then transmits the NAL units in the parameter set-first order (S 4806 ). 
       FIG. 42  is a flowchart showing a process performed by the three-dimensional data decoding device that involves the order of transmission of NAL units. First, the three-dimensional data decoding device analyzes the order identification information included in the stream PS (S 4811 ). 
     If the order of transmission indicated by the order identification information is geometry information-first (if “geometry information-first” in S 4812 ), the three-dimensional data decoding device decodes the NAL units based on the determination that the order of transmission of the NAL units is geometry information-first (S 4813 ). 
     On the other hand, if the order of transmission indicated by the order identification information is parameter set-first (if “parameter set-first” in S 4812 ), the three-dimensional data decoding device decodes the NAL units based on the determination that the order of transmission of the NAL units is parameter set-first (S 4814 ). 
     For example, if the three-dimensional data decoding device does not decode attribute information, in step S 4813 , the three-dimensional data decoding device does not obtain the entire NAL units but can obtain a part of a NAL unit relating to the geometry information and decode the obtained NAL unit to obtain the geometry information. 
     Next, a process relating to generation of an AU and a GOF will be described.  FIG. 43  is a flowchart showing a process performed by the three-dimensional data encoding device (multiplexer  4802 ) that relates to generation of an AU and a GOF in multiplexing of NAL units. 
     First, the three-dimensional data encoding device determines the type of the encoded data (S 4821 ). Specifically, the three-dimensional data encoding device determines whether the encoded data to be processed is AU-first data, GOF-first data, or other data. 
     If the encoded data is GOF-first data (if “GOF-first” in S 4822 ), the three-dimensional data encoding device generates NAL units by arranging a GOF header and an AU header at the top of the encoded data belonging to the GOF (S 4823 ). 
     If the encoded data is AU-first data (if “AU-first” in S 4822 ), the three-dimensional data encoding device generates NAL units by arranging an AU header at the top of the encoded data belonging to the AU (S 4824 ). 
     If the encoded data is neither GOF-first data nor AU-first data (if “other than GOF-first and AU-first” in S 4822 ), the three-dimensional data encoding device generates NAL units by arranging the encoded data to follow the AU header of the AU to which the encoded data belongs ( 4825 ). 
     Next, a process relating to access to an AU and a GOF will be described.  FIG. 44  is a flowchart showing a process performed by the three-dimensional data decoding device that involves accessing to an AU and a GOF in demultiplexing of a NAL unit. 
     First, the three-dimensional data decoding device determines the type of the encoded data included in the NAL unit by analyzing nal_unit_type in the NAL unit (S 4831 ). Specifically, the three-dimensional data decoding device determines whether the encoded data included in the NAL unit is AU-first data, GOF-first data, or other data. 
     If the encoded data included in the NAL unit is GOF-first data (if “GOF-first” in S 4832 ), the three-dimensional data decoding device determines that the NAL unit is a start position of random access, accesses the NAL unit, and starts the decoding process (S 4833 ). 
     If the encoded data included in the NAL unit is AU-first data (if “AU-first” in S 4832 ), the three-dimensional data decoding device determines that the NAL unit is AU-first, accesses the data included in the NAL unit, and decodes the AU (S 4834 ). 
     If the encoded data included in the NAL unit is neither GOF-first data nor AU-first data (if “other than GOF-first and AU-first” in S 4832 ), the three-dimensional data decoding device does not process the NAL unit. 
     As described above, the three-dimensional data encoding device performs the process shown in  FIG. 45 . The three-dimensional data encoding device encodes time-series three-dimensional data (point cloud data on a dynamic object, for example). The three-dimensional data includes geometry information and attribute information associated with each time point. 
     First, the three-dimensional data encoding device encodes the geometry information (S 4841 ). The three-dimensional data encoding device then encodes the attribute information to be processed by referring to the geometry information associated with the same time point as the attribute information to be processed (S 4842 ). Here, as shown in  FIG. 37 , the geometry information and the attribute information associated with the same time point form an access unit (AU). That is, the three-dimensional data encoding device encodes the attribute information to be processed by referring to the geometry information included in the same access unit as the attribute information to be processed. 
     In this way, the three-dimensional data encoding device can take advantage of the access unit to facilitate control of reference in encoding. Therefore, the three-dimensional data encoding device can reduce the processing amount of the encoding process. 
     For example, the three-dimensional data encoding device generates a bitstream including the encoded geometry information (encoded geometry data), the encoded attribute information (encoded attribute data), and information indicating the geometry information of the entity to be referred to when encoding the attribute information to be processed. 
     For example, the bitstream includes a geometry parameter set (geometry PS) that includes control information for the geometry information associated with each time point and an attribute parameter set (attribute PS) that includes control information for the attribute information associated with each time point. 
     For example, the bitstream includes a geometry sequence parameter set (geometry SPS) that includes control information that is common to a plurality of pieces of geometry information associated with different time points and attribute sequence parameter set (attribute SPS) that includes control information that is common to a plurality of pieces of attribute information associated with different time points. 
     For example, the bitstream includes a stream parameter set (stream PS) that includes control information that is common to a plurality of pieces of geometry information associated with different time points and a plurality of pieces of attribute information associated with different time points. 
     For example, the bitstream includes an access unit header (AU header) that includes control information that is common in an access unit. 
     For example, the three-dimensional data encoding device performs encoding in such a manner that groups of frames (GOFs) formed by one or more access units can be independently decoded. That is, the GOF is a random access unit. 
     For example, the bitstream includes a GOF header that includes control information that is common in a GOF. 
     For example, the three-dimensional data encoding device includes a processor and a memory, and the processor performs the processes described above using the memory. 
     As described above, the three-dimensional data decoding device performs the process shown in  FIG. 46 . The three-dimensional data decoding device decodes time-series three-dimensional data (point cloud data on a dynamic object, for example). The three-dimensional data includes geometry information and attribute information associated with each time point. The geometry information and the attribute information associated with the same time point forms an access unit (AU). 
     First, the three-dimensional data decoding device decodes the bitstream to obtain the geometry information (S 4851 ). That is, the three-dimensional data decoding device generates the geometry information by decoding the encoded geometry information (encoded geometry data) included in the bitstream. 
     The three-dimensional data decoding device then decodes the bitstream to obtain the attribute information to be processed by referring to the geometry information associated with the same time point as the attribute information to be processed (S 4852 ). That is, the three-dimensional data decoding device generates the attribute information by decoding the encoded attribute information (encoded attribute data) included in the bitstream. In this process, the three-dimensional data decoding device refers to the decoded geometry information included in the access unit as the attribute information. 
     In this way, the three-dimensional data decoding device can take advantage of the access unit to facilitate control of reference in decoding. Therefore, the three-dimensional data decoding device can reduce the processing amount of the decoding process. 
     For example, the three-dimensional data decoding device obtains, from the bitstream, information indicating the geometry information of the entity to be referred to when decoding the attribute information to be processed, and decodes the attribute information to be processed by referring to the geometry information of the entity to be referred to indicated by the obtained information. 
     For example, the bitstream includes a geometry parameter set (geometry PS) that includes control information for the geometry information associated with each time point and an attribute parameter set (attribute PS) that includes control information for the attribute information associated with each time point. That is, the three-dimensional data decoding device uses the control information included in the geometry parameter set associated with the time point to be intended for processing to decode the geometry information associated with the time point intended for processing, and uses the control information included in the attribute parameter set associated with the time point intended for processing to decode the attribute information associated with the time point intended for processing. 
     For example, the bitstream includes a geometry sequence parameter set (geometry SPS) that includes control information that is common to a plurality of pieces of geometry information associated with different time points and an attribute sequence parameter set (attribute SPS) that includes control information that is common to a plurality of pieces of attribute information associated with different time points. That is, the three-dimensional data decoding device uses the control information included in the geometry sequence parameter set to decode a plurality of pieces of geometry information associated with different time points, and uses the control information included in the attribute sequence parameter set to decode a plurality of pieces of attribute information associated with different time points. 
     For example, the bitstream includes a stream parameter set (stream PS) that includes control information that is common to a plurality of pieces of geometry information associated with different time points and a plurality of pieces of attribute information associated with different time points. That is, the three-dimensional data decoding device uses the control information included in the stream parameter set to decode a plurality of pieces of geometry information associated with different time points and a plurality of pieces of attribute information associated with different time points. 
     For example, the bitstream includes an access unit header (AU header) that includes control information that is common in an access unit. That is, the three-dimensional data decoding device uses the control information included in the access unit header to decode the geometry information and the attribute information included in the access unit. 
     For example, the three-dimensional data decoding device independently decodes groups of frames (GOFs) formed by one or more access units. That is, the GOF is a random access unit. 
     For example, the bitstream includes a GOF header that includes control information that is common in a GOF. That is, the three-dimensional data decoding device decodes the geometry information and the attribute information included in the GOF using the control information included in the GOF header. 
     For example, the three-dimensional data decoding device includes a processor and a memory, and the processor performs the processes described above using the memory. 
     Embodiment 5 
     Hereinafter, the division method for point cloud data will be described.  FIG. 47  is a diagram illustrating an example of slice and tile dividing. 
     First, the method for slice dividing will be described. The three-dimensional data encoding device divides three-dimensional point cloud data into arbitrary point clouds on a slice-by-slice basis. In slice dividing, the three-dimensional data encoding device does not divide the geometry information and the attribute information constituting points, but collectively divides the geometry information and the attribute information. That is, the three-dimensional data encoding device performs slice dividing so that the geometry information and the attribute information of an arbitrary point belong to the same slice. Note that, as long as these are followed, the number of divisions and the division method may be any number and any method. Furthermore, the minimum unit of division is a point. For example, the numbers of divisions of geometry information and attribute information are the same. For example, a three-dimensional point corresponding to geometry information after slice dividing, and a three-dimensional point corresponding to attribute information are included in the same slice. 
     Also, the three-dimensional data encoding device generates slice additional information, which is additional information related to the number of divisions and the division method at the time of slice dividing. The slice additional information is the same for geometry information and attribute information. For example, the slice additional information includes the information indicating the reference coordinate position, size, or side length of a bounding box after division. Also, the slice additional information includes the information indicating the number of divisions, the division type, etc. 
     Next, the method for tile dividing will be described. The three-dimensional data encoding device divides the data divided into slices into slice geometry information (G slice) and slice attribute information (A slice), and divides each of the slice geometry information and the slice attribute information on a tile-by-tile basis. 
     Note that, although  FIG. 47  illustrates the example in which division is performed with an octree structure, the number of divisions and the division method may be any number and any method. 
     Also, the three-dimensional data encoding device may divide geometry information and attribute information with different division methods, or may divide geometry information and attribute information with the same division method. Additionally, the three-dimensional data encoding device may divide a plurality of slices into tiles with different division methods, or may divide a plurality of slices into tiles with the same division method. 
     Furthermore, the three-dimensional data encoding device generates tile additional information related to the number of divisions and the division method at the time of tile dividing. The tile additional information (geometry tile additional information and attribute tile additional information) is separate for geometry information and attribute information. For example, the tile additional information includes the information indicating the reference coordinate position, size, or side length of a bounding box after division. Additionally, the tile additional information includes the information indicating the number of divisions, the division type, etc. 
     Next, an example of the method of dividing point cloud data into slices or tiles will be described. As the method for slice or tile dividing, the three-dimensional data encoding device may use a predetermined method, or may adaptively switch methods to be used according to point cloud data. 
     At the time of slice dividing, the three-dimensional data encoding device divides a three-dimensional space by collectively handling geometry information and attribute information. For example, the three-dimensional data encoding device determines the shape of an object, and divides a three-dimensional space into slices according to the shape of the object. For example, the three-dimensional data encoding device extracts objects such as trees or buildings, and performs division on an object-by-object basis. For example, the three-dimensional data encoding device performs slice dividing so that the entirety of one or a plurality of objects are included in one slice. Alternatively, the three-dimensional data encoding device divides one object into a plurality of slices. 
     In this case, the encoding device may change the encoding method for each slice, for example. For example, the encoding device may use a high-quality compression method for a specific object or a specific part of the object. In this case, the encoding device may store the information indicating the encoding method for each slice in additional information (metadata). 
     Also, the three-dimensional data encoding device may perform slice dividing so that each slice corresponds to a predetermined coordinate space based on map information or geometry information. 
     At the time of tile dividing, the three-dimensional data encoding device separately divides geometry information and attribute information. For example, the three-dimensional data encoding device divides slices into tiles according to the data amount or the processing amount. For example, the three-dimensional data encoding device determines whether the data amount of a slice (for example, the number of three-dimensional points included in a slice) is greater than a predetermined threshold value. When the data amount of the slice is greater than the threshold value, the three-dimensional data encoding device divides slices into tiles. When the data amount of the slice is less than the threshold value, the three-dimensional data encoding device does not divide slices into tiles. 
     For example, the three-dimensional data encoding device divides slices into tiles so that the processing amount or processing time in the decoding device is within a certain range (equal to or less than a predetermined value). Accordingly, the processing amount per tile in the decoding device becomes constant, and distributed processing in the decoding device becomes easy. 
     Additionally, when the processing amount is different between geometry information and attribute information, for example, when the processing amount of geometry information is greater than the processing amount of attribute information, the three-dimensional data encoding device makes the number of divisions of geometry information larger than the number of divisions of attribute information. 
     Furthermore, for example, when geometry information may be decoded and displayed earlier, and attribute information may be slowly decoded and displayed later in the decoding device according to contents, the three-dimensional data encoding device may make the number of divisions of geometry information larger than the number of divisions of attribute information. Accordingly, since the decoding device can increase the parallel number of geometry information, it is possible to make the processing of geometry information faster than the processing of attribute information. 
     Note that the decoding device does not necessarily have to process sliced or tiled data in parallel, and may determine whether or not to process them in parallel according to the number or capability of decoding processors. 
     By performing division with the method as described above, it is possible to achieve adaptive encoding according to contents or objects. Also, parallel processing in decoding processing can be achieved. Accordingly, the flexibility of a point cloud encoding system or a point cloud decoding system is improved. 
       FIG. 48  is a diagram illustrating dividing pattern examples of slices and tiles. DU in the diagram is a data unit (DataUnit), and indicates the data of a tile or a slice. Additionally, each DU includes a slice index (SliceIndex) and a tile index (TileIndex). The top right numerical value of a DU in the diagram indicates the slice index, and the bottom left numerical value of the DU indicates the tile index. 
     In Pattern  1 , in slice dividing, the number of divisions and the division method are the same for G slice and A slice. In tile dividing, the number of divisions and the division method for G slice are different from the number of divisions and the division method for A slice. Additionally, the same number of divisions and division method are used among a plurality of G slices. The same number of divisions and division method are used among a plurality of A slices. 
     In Pattern  2 , in slice dividing, the number of divisions and the division method are the same for G slice and A slice. In tile dividing, the number of divisions and the division method for G slice are different from the number of divisions and the division method for A slice. Additionally, the number of divisions and the division method are different among a plurality of G slices. The number of divisions and the division method are different among a plurality of A slices. 
     Embodiment 6 
     Hereinafter, an example of performing slice division after tile division will be described. An autonomous application for automated driving of a vehicle etc. requires not point cloud data of all areas but point cloud data of an area surrounding a vehicle or an area in a traveling direction of a vehicle. Here, tiles and slices can be used to selectively decode original point cloud data. It is possible to achieve the improvement of coding efficiency or parallel processing by dividing three-dimensional point cloud data into tiles and further dividing the tiles into slices. When data is divided, additional information (metadata) is generated, and the generated additional information is transmitted to a multiplexer. 
       FIG. 49  is a block diagram illustrating a configuration of first encoder  5010  included in a three-dimensional data encoding device according to the present embodiment. First encoder  5010  generates encoded data (encoded stream) by encoding point cloud data using a first encoding method (geometry based PCC (GPCC)). First encoder  5010  includes divider  5011 , geometry information encoders  5012 , attribute information encoders  5013 , additional information encoder  5014 , and multiplexer  5015 . 
     Divider  5011  generates pieces of divided data by dividing point cloud data. Specifically, divider  5011  generates pieces of divided data by dividing a space of point cloud data into subspaces. Here, a subspace is one of a tile and a slice, or a combination of a tile and a slice. More specifically, point cloud data includes geometry information, attribute information, and additional information. Divider  5011  divides geometry information into pieces of divided geometry information and attribute information into pieces of divided attribute information. In addition, divider  5011  generates additional information regarding division. 
     For example, first, divider  5011  divides a point cloud into tiles. Next, divider  5011  further divides the obtained tiles into slices. 
     Geometry information encoders  5012  generate pieces of encoded geometry information by encoding pieces of divided geometry information. For example, geometry information encoders  5012  process pieces of divided geometry information in parallel. 
     Attribute information encoders  5013  generate pieces of encoded attribute information by encoding pieces of divided attribute information. For example, attribute information encoders  5013  process pieces of divided geometry information in parallel. 
     Additional information encoder  5014  generates encoded additional information by encoding additional information included in point cloud data and additional information regarding data division generated at the time of dividing by divider  5011 . 
     Multiplexer  5015  generates encoded data (encoded stream) by multiplexing pieces of encoded geometry information, pieces of encoded attribute information, and encoded additional information, and transmits the generated encoded data. The encoded additional information is also used at the time of decoding. 
     It should be noted that although  FIG. 49  shows two geometry information encoders  5012  and two attribute information encoders  5013  as an example, the number of geometry information encoders  5012  and the number of attribute information encoders  5013  may be one or at least three. Moreover, pieces of divided data may be processed in parallel in identical chips, such as cores in a CPU, in a core of each of chips, or in cores of each of chips. 
     The following describes a decoding process.  FIG. 50  is a block diagram illustrating a configuration of first decoder  5020 . First decoder  5020  restores point cloud data by decoding encoded data (encoded stream) generated by encoding the point cloud data using the first encoding method (GPCC). First decoder  5020  includes demultiplexer  5021 , geometry information decoders  5022 , attribute information decoders  5023 , additional information decoder  5024 , and combiner  5025 . 
     Demultiplexer  5021  generates pieces of encoded geometry information, pieces of encoded attribute information, and encoded additional information by demultiplexing encoded data (encoded stream). 
     Geometry information decoders  5022  generate pieces of divided geometry information by decoding pieces of encoded geometry information. For example, geometry information decoders  5022  process pieces of encoded geometry information in parallel. 
     Attribute information decoders  5023  generate pieces of divided attribute information by decoding pieces of encoded attribute information. For example, attribute information decoders  5023  process pieces of encoded attribute information in parallel. 
     Additional information decoder  5024  generates additional information by decoding encoded additional information. 
     Combiner  5025  generates geometry information by combining pieces of divided geometry information using additional information. Combiner  5025  also generates attribute information by combining pieces of divided attribute information using additional information. For example, first, combiner  5025  generates pieces of point cloud data corresponding to tiles by combing pieces of decoded point cloud data corresponding to slices using slice additional information. Next, combiner  5025  restores original point cloud data by combining pieces of point cloud data corresponding to the tiles using tile additional information. 
     It should be noted that although  FIG. 49  shows two geometry information decoders  5022  and two attribute information decoders  5023  as an example, the number of geometry information decoders  5022  and the number of attribute information decoders  5023  may be one or at least three. Moreover, pieces of divided data may be processed in parallel in identical chips, such as cores in a CPU, in a core of each of chips, or in cores of each of chips. 
     The following describes a method of dividing point cloud data. An autonomous application for automated driving of a vehicle etc. requires not point cloud data of all areas but point cloud data of an area surrounding a vehicle or an area in a traveling direction of a vehicle. 
       FIG. 51  is a diagram illustrating examples of a tile shape. As shown in  FIG. 51 , examples of the tile shape may include various shapes such as a circle, a rectangle, or an ellipse. 
       FIG. 52  is a diagram illustrating an example of tiles and slices. A composition of slices may differ between tiles. For example, a composition of tiles or slices may be optimized based on a data volume. Alternatively, a composition of tiles or slices may be optimized based on decoding speed. 
     Tile division may be performed based on geometry information. In this case, attribute information is divided in the same manner as corresponding geometry information. 
     Moreover, in slice division after tile division, geometry information and attribute information may be divided into slices using different methods. For example, a slice division method in each tile may be selected upon request from an application. A different slice division method or a different tile division method may be used based on a request from an application. 
     For example, divider  5011  divides three-dimensional point cloud data into one or more tiles in a two-dimensional shape obtained by seeing the three-dimensional point cloud data from top, based on position information such as map information. Divider  5011  divides each of the one or more tiles into one or more slices afterward. 
     It should be noted that divider  5011  may divide geometry information (geometry) and attribute information (attribute) into slices using the same method. 
     It should be noted that each of geometry information and attribute information may be of one type or two or more types. In addition, when point cloud data has no attribute information, attribute information may be unnecessary. 
       FIG. 53  is a block diagram of divider  5011 . Divider  5011  includes tile divider  5031 , geometry information slice divider (geometry slice divider)  5032 , and attribute information slice divider (attribute slice divider)  5033 . 
     Tile divider  5031  generates pieces of tile geometry information by dividing geometry information (position (geometry)) into tiles. In addition, tile divider  5031  generates pieces of tile attribute information by dividing attribute information (attribute) into tiles. Additionally, tile divider  5031  outputs tile additional information (tile metadata) including information regarding tile division and information generated in the tile division. 
     Geometry information slice divider  5032  generates pieces of divided geometry information (pieces of slice geometry information) by dividing pieces of tile geometry information into slices. In addition, geometry information slice divider  5032  outputs geometry slice additional information (geometry slice metadata) including information regarding slice division of geometry information and information generated in the slice division of the geometry information. 
     Attribute information slice divider  5033  generates pieces of divided attribute information (pieces of slice attribute information) by dividing pieces of tile attribute information into slices. In addition, attribute information slice divider  5033  outputs attribute slice additional information (attribute slice metadata) including information regarding slice division of attribute information and information generated in the slice division of the attribute information. 
     The following describes examples of a tile shape. An entire three-dimensional map (3D map) is divided into tiles. Data of the tiles are selectively transmitted to a three-dimensional data decoding device. Alternatively, the data of the tiles are transmitted to the three-dimensional data decoding device in decreasing order of importance. A tile shape may be selected from shapes according to a situation. 
       FIG. 54  is a diagram illustrating an example of a map in a top of view of point cloud data obtained by LiDAR. The example shown in  FIG. 54  is point cloud data of a highway and includes an overpass (flyover). 
       FIG. 55  is a diagram illustrating an example of dividing the point cloud data shown in  FIG. 54  into square tiles. It is easy to make such a division into squares in a map server. For a normal road, the height of a tile is set low. The height of tiles is set higher for an overpass than for the normal road so that the tiles contain the overpass. 
       FIG. 56  is a diagram illustrating an example of dividing the point cloud data shown in  FIG. 54  into circular tiles. In this case, neighboring tiles may overlap each other in plan view. When a vehicle requires point cloud data of a surrounding area, the three-dimensional data encoding device transmits, to the vehicle, point cloud data of an area including columns (circles in top view) surrounding the vehicle. 
     As with the example shown in  FIG. 55 , for a normal road, the height of a tile is set low. The height of tiles is set higher for an overpass than for the normal road so that the tiles contain the overpass. 
     The three-dimensional data encoding device may change the height of a tile according to, for example, the shape or height of a road or building. In addition, the three-dimensional data encoding device may change the height of a tile according to position information or area information. Additionally, the three-dimensional data encoding device may change the height of each tile. Alternatively, the three-dimensional data encoding device may change the height of tiles for each zone including the tiles. To put it another way, the three-dimensional data encoding device may set tiles in a zone to the same height. Moreover, tiles having different heights may overlap each other in top view. 
       FIG. 57  is a diagram illustrating an example of tile division when tiles having various shapes, sizes, and heights are used. Any tile may have any shape or size, or a combination of these. 
     For example, in addition to making a division into non-overlapping square tiles and making a division into overlapping circular tiles as described above, the three-dimensional data encoding device may make a division into overlapping square tiles. Moreover, the tile shape need not be a square or a circle, and may be a polygon having three or more vertices, or a shape having no vertices. 
     Furthermore, a tile shape may be of two or more types, and tiles having different shapes may overlap each other. In addition, a tile shape may be of one or more types; and when the same shape is used for divided tiles, the same shape may include shapes different in size or such shapes may overlap each other. 
     For example, a tile to be used is larger for an area including no object such as a road than for an area including an object. Moreover, the three-dimensional data encoding device may adaptively change a tile shape or size according to an object. 
     Furthermore, for example, the three-dimensional data encoding device may set tiles in a traveling direction of an automobile (a vehicle) to a large size because reading of tiles at a great distance ahead of the automobile in the traveling direction is likely to be needed; and set tiles in a side lateral to the automobile to a smaller size than the tiles in the traveling direction because the automobile is less likely to move to the side. 
       FIG. 58  is a diagram illustrating an example of data of tiles stored in a server. For example, point cloud data is divided into tiles and encoded in advance, and the obtained encoded data is stored in a server. A user obtains the data of desired tiles from the server when necessary. Alternatively, the server (the three-dimensional data encoding device) may perform tile division and encoding so that tiles include data desired by the user, in response to an instruction from the user. 
     For example, when a movable body (a vehicle) travels at a high speed, it is conceivable that more extensive point cloud data is needed. For this reason, the server may determine a tile shape and size based on a pre-estimated vehicular speed (e.g., a legal speed on a road, a vehicular speed estimated from the width or shape of a road, or a statistical vehicular speed), and perform tile division. Alternatively, as shown in  FIG. 58 , the server may encode tiles having a shape or size in advance, and store the obtained data. The movable body may obtain data of tiles having an appropriate shape or size according to the traveling direction and speed of the movable body. 
       FIG. 59  is a diagram illustrating an example of a system regarding tile division. As shown in  FIG. 59 , a tile shape and an area may be determined based on the location of an antenna (a base station) that is a means of communication transmitting point cloud data, or on a communication area supported by an antenna. Alternatively, when point cloud data is generated by a sensor such as a camera, a tile shape and an area may be determined based on the location or a target range (a detection range) of the sensor. 
     One tile may be assigned to one antenna or one sensor, or one tile may be assigned to antennas or sensors. In addition, tiles may be assigned to one antenna or one sensor. An antenna or a sensor may be fixed or movable. 
     For example, encoded data divided into tiles may be managed by a server connected to an antenna or a sensor for an area assigned to the tiles. The server may manage the encoded data of the area and tile information of a neighboring area. Pieces of encoded data of tiles may be managed in a centralized server (a cloud) that manages servers each corresponding to a different one of the tiles. Alternatively, instead of providing the servers each corresponding to the different one of the tiles, antennas or sensors may be directly connected to the centralized server. 
     It should be noted that the target range of an antenna or a sensor may change depending on the power of radio waves, differences between devices, and installation conditions, and a tile shape and size may change in conformity with these. Instead of a tile, a slice or a PCC frame may be assigned based on the target range of the antenna or the sensor. 
     The following describes a method of dividing a tile into slices. It is possible to improve the coding efficiency by assigning similar objects to the same slice. 
     For example, the three-dimensional data encoding device may recognize objects (e.g., a road, a building, a tree) using features of point cloud data, and perform slice division by clustering point clouds for each of the objects. 
     Alternatively, the three-dimensional data encoding device may classify objects having the same attribute into groups, and perform slice division by assigning a slice to each of the groups. Here, an attribute is, for example, information regarding motion. Objects are classified into groups according to dynamic information about pedestrians, cars, etc., quasi-dynamic information about accidents, congestion, etc., quasi-static information about traffic controls, roadwork, etc., and static information about road surfaces, structures, etc. 
     It should be noted that slices may have overlapping data. For example, when slice division is performed for each object group, any object may belong to one object group or two or more object groups. 
       FIG. 60  is a diagram illustrating an example of this slice division. For example, a tile is a cuboid in the example shown in  FIG. 60 . It should be noted that a tile may be columnar or have another shape. 
     Point clouds included in a tile are classified into object groups such as road, building, and tree. Then, slice division is performed so that each object group is included in a different one of slices. Subsequently, the slices are encoded separately. 
     The following describes a method of encoding divided data. The three-dimensional data encoding device (first encoder  5010 ) encodes each divided data. When the three-dimensional data encoding device encodes attribute information, the three-dimensional data encoding device generates, as additional information, dependency relationship information indicating based on which composition information (geometry information, additional information, or another attribute information) encoding has been performed. In other words, dependency relationship information indicates, for example, composition information of a reference destination (a dependee). In this case, the three-dimensional data encoding device generates dependency relationship information based on composition information corresponding to a divided shape for attribute information. It should be noted that the three-dimensional data encoding device may generate dependency relationship information based on composition information corresponding to divided shapes. 
     Dependency relationship information may be generated by the three-dimensional data encoding device, and the generated dependency relationship information may be transmitted to the three-dimensional data decoding device. Alternatively, the three-dimensional data decoding device may generate dependency relationship information, and the three-dimensional data encoding device need not transmit dependency relationship information. In addition, a dependency relationship to be used by the three-dimensional data encoding device may be determined in advance, and the three-dimensional data encoding device need not transmit dependency relationship information. 
       FIG. 61  is a diagram illustrating an example of a dependency relationship of each data. The pointed end of an arrow in the figure indicates a dependee, and the other end of the arrow indicates a depender. The three-dimensional data decoding device decodes data in order from dependee to depender. Data indicated by a solid line in the figure is data actually transmitted, and data indicated by a broken line is data not transmitted. 
     In the figure, G denotes geometry information, and A denotes attribute information. Gt 1  denotes geometry information for tile number  1 , and Gt 2  denotes geometry information for tile number  2 . Gt 1   s   1  denotes geometry information for tile number  1  and slice number  1 , Gt 1   s   2  denotes geometry information for tile number  1  and slice number  2 , Gt 2   s   1  denotes geometry information for tile number  2  and slice number  1 , and Gt 2   s   2  denotes geometry information for tile number  2  and slice number  2 . Likewise, At 1  denotes attribute information for tile number  1 , and At 2  denotes attribute information for tile number  2 . At 1   s   1  denotes attribute information for tile number  1  and slice number  1 , At 1   s   2  denotes attribute information for tile number  1  and slice number  2 , At 2   s   1  denotes attribute information for tile number  2  and slice number  1 , and At 2   s   2  denotes attribute information for tile number  2  and slice number  2 . 
     Mtile denotes tile additional information, MGslice denotes geometry slice additional information, and MAslice denotes attribute slice additional information. Dt 1   s   1  denotes dependency relationship information of attribute information At 1   s   1 , and Dt 2   s   1  denotes dependency relationship information of attribute information At 2   s   1 . 
     It should be noted that a different structure resulting from tile division or slice division may be used according to an application etc. 
     The three-dimensional data encoding device may rearrange data in decoding order so that the three-dimensional data decoding device need not rearrange data. It should be noted that the three-dimensional data decoding device may rearrange data, or both the three-dimensional data encoding device and the three-dimensional data decoding device may rearrange data. 
       FIG. 62  is a diagram illustrating an example of decoding order of data. In the example shown in  FIG. 62 , data are decoded in order from the left. The three-dimensional data decoding device decodes, out of data having a dependency relationship with each other, data of a dependee first. For example, the three-dimensional data encoding device rearranges data in this order and transmits the data. It should be noted that any order may be used as long as data of a dependee takes precedence. Moreover, the three-dimensional data encoding device may transmit additional information and dependency relationship information before data. 
     Furthermore, the three-dimensional data decoding device may selectively decode tiles based on a request from an application and information obtained from a NAL unit header.  FIG. 63  is a diagram illustrating an example of encoded data of tiles. For example, decoding order of tiles is optional. In other words, tiles need not have a dependency relationship with each other. 
     The following describes a configuration of combiner  5025  included in first decoder  5020 .  FIG. 64  is a block diagram illustrating a configuration of combiner  5025 . Combiner  5025  includes geometry information slice combiner (geometry slice combiner)  5041 , attribute information slice combiner (attribute slice combiner)  5042 , and tile combiner  5043 . 
     Geometry information slice combiner  5041  generates pieces of tile geometry information by combining pieces of divided geometry information using geometry slice additional information. Attribute information slice combiner  5042  generates pieces of tile attribute information by combining pieces of divided attribute information using attribute slice additional information. 
     Tile combiner  5043  generates geometry information by combining pieces of tile geometry information using tile additional information. Besides, tile combiner  5043  generates attribute information by combining pieces of tile attribute information using tile additional information. 
     It should be noted that the number of divided slices or tiles is at least one. In other words, slice division or tile division need not be performed. 
     The following describes a structure of encoded data subjected to slice division or tile division, and a method of storing encoded data in a NAL unit (a multiplexing method).  FIG. 65  is a diagram illustrating a structure of encoded data and a method of storing encoded data in a NAL unit. 
     Encoded data (divided geometry information or divided attribute information) is stored in a NAL unit payload. 
     Encoded data includes a header and a payload. The header includes identification information for identifying data included in the payload. Examples of the identification information include a type of slice division or tile division (slice_type, tile_type), index information for identifying a slice or a tile (slice_idx, tile_idx), geometry information of data (a slice or tile), or an address of data (address). Index information for identifying a slice is also referred to as a slice index (SliceIndex). Index information for identifying a tile is also referred to as a tile index (TileIndex). A division type indicates, for example, a method based on an object shape as described above, a method based on map information or position information, or a method based on a data volume or an amount of processing. 
     Moreover, the header of the encoded data includes identification information indicating a dependency relationship. To put it another way, when data have a dependency relationship with each other, the header includes identification information for a depender to refer to a dependee. For example, the header of data of a dependee includes identification information for identifying the data. The header of data of a depender includes identification information indicating a dependee. It should be noted that when identification information for identifying data, additional information regarding slice division or tile division, and identification information indicating a dependency relationship are identifiable or derivable from other information, these pieces of information may be omitted. 
     The following describes procedures of a point cloud data encoding process and a point cloud data decoding process according to the present embodiment.  FIG. 66  is a flowchart of a point cloud data encoding process according to the present embodiment. 
     First, the three-dimensional data encoding device determines a division method to be used (S 5011 ). Examples of the division method include tile division and slice division. A division method may include a division number, a division type, etc. when tile division or slice division is performed. A division type indicates, for example, a method based on an object shape as described above, a method based on map information or geometry information, or a method based on a data volume or an amount of processing. It should be noted that a division method may be determined in advance. 
     When tile division is performed (YES in S 5012 ), the three-dimensional data encoding device generates pieces of tile geometry information and pieces of tile attribute information by dividing geometry information and attribute information collectively (S 5013 ). Besides, the three-dimensional data encoding device generates tile additional information regarding the tile division. It should be noted that the three-dimensional data encoding device may divide geometry information and attribute information separately. 
     When slice division is performed (YES in S 5014 ), the three-dimensional data encoding device generates pieces of divided geometry information and pieces of divided attribute information by dividing the pieces of tile geometry information and the pieces of tile attribute information (or the geometry information and the attribute information) separately (S 5015 ). Also, the three-dimensional data encoding device generates geometry slice additional information and attribute slice additional information regarding the slice division. It should be noted that the three-dimensional data encoding device may divide tile geometry information and tile attribute information collectively. 
     Next, the three-dimensional data encoding device generates pieces of encoded geometry information and pieces of encoded attribute information by respectively encoding the pieces of divided geometry information and the pieces of divided attribute information (S 5016 ). In addition, the three-dimensional data encoding device generates dependency relationship information. 
     Finally, the three-dimensional data encoding device generates encoded data (an encoded stream) by storing in NAL units (multiplexing) the pieces of encoded geometry information, the pieces of encoded attribute information, and additional information (S 5017 ). Additionally, the three-dimensional data encoding device transmits the generated encoded data. 
       FIG. 67  is a flowchart of a point cloud data decoding process according to the present embodiment. First, the three-dimensional data decoding device determines a division method by analyzing additional information (tile additional information, geometry slice additional information, attribute slice additional information) regarding a division method included in encoded data (an encoded stream) (S 5021 ). Examples of the division method include tile division and slice division. A division method may include a division number, a division type, etc. when tile division or slice division is performed. 
     Next, the three-dimensional data decoding device generates divided geometry information and divided attribute information by decoding pieces of encoded geometry information and pieces of encoded attribute information included in the encoded data, using dependency relationship information included in the encoded data (S 5022 ). 
     When the additional information indicates that slice division has been performed (YES in S 5023 ), the three-dimensional data decoding device generates pieces of tile geometry information and pieces of tile attribute information by combining pieces of divided geometry information and combining pieces of divided attribute information, using respective methods, based on the geometry slice additional information and the attribute slice additional information (S 5024 ). It should be noted that the three-dimensional data decoding device may combine the pieces of divided geometry information and combine the pieces of divided attribute information, using the same method. 
     When the additional information indicates that tile division has been performed (YES in S 5025 ), the three-dimensional data decoding device generates geometry information and attribute information by combining the pieces of tile geometry information (the pieces of divided geometry information) and combining the pieces of tile attribute information (the pieces of divided attribute information), using the same method, based on tile additional information (S 5026 ). It should be noted that the three-dimensional data decoding device may combine the pieces of tile geometry information and combine the pieces of tile attribute information, using respective methods. 
     The following describes tile additional information. The three-dimensional data encoding device generates tile additional information that is metadata regarding a tile division method, and transmits the generated tile additional information to the three-dimensional data decoding device. 
       FIG. 68  is a diagram illustrating an example of syntax of tile additional information (TileMetaData). As shown in  FIG. 68 , for example, tile additional information includes division method information (type_of_divide), shape information (topview_shape), an overlap flag (tile_overlap_flag), overlap information (type_of_overlap), height information (tile_height), a tile number (tile_number), and tile position information (global_position, relative_position). 
     Division method information (type_of_divide) indicates a tile division method. For example, division method information indicates whether a tile division method is division based on map information, that is, division based on top view (top_view) or another division (other). 
     Shape information (topview_shape) is included in tile additional information when a tile division method is, for example, division based on top view. Shape information indicates a shape in top view of a tile. Examples of the shape include a square and a circle. Moreover, the examples of the shape may include an ellipse, a rectangle, or a polygon other than a quadrangle, or may include a shape other than these. It should be noted that shape information may indicate not only a shape in top view of a tile but also a three-dimensional shape (e.g., a cube, a round column) of a tile. 
     An overlap flag (tile_overlap_flag) indicates whether tiles overlap each other. For example, an overlap flag is included in tile additional information when a tile division method is division based on top view. In this case, the overlap flag indicates whether tiles overlap each other in top view. It should be noted that an overlap flag may indicate whether tiles overlap each other in a three-dimensional space. 
     Overlap information (type_of_overlap) is included in tile additional information when, for example, tiles overlap each other. Overlap information indicates, for example, how tiles overlap each other. For example, overlap information indicates the size of an overlapping region. 
     Height information (tile_height) indicates the height of a tile. It should be noted that height information may include information indicating a tile shape. For example, when the shape of a tile in top view is a rectangle, the information may indicate the length of a side (a vertical length, a horizontal length) of the rectangle. When the shape of a tile in top view is a circle, the information may indicate the diameter or radius of the circle. 
     Moreover, height information may indicate the height of each tile or a height common to tiles. In addition, height types such as roads and overpasses may be set in advance, and height information may indicate the height of each of the height types and a height type of each tile. Alternatively, a height of each height type may be specified in advance, and height information may indicate a height type of each tile. In other words, height information need not indicate a height of each height type. 
     A tile number (tile_number) indicates the number of tiles. It should be noted that tile additional information may include information indicating an interval between tiles. 
     Tile position information (global_position, relative_position) is information for identifying the position of each tile. For example, tile position information indicates the absolute coordinates or relative coordinates of each tile. 
     It should be noted that part or all of the above-mentioned information may be provided for each tile or each group of tiles (e.g., for each frame or group of frames). 
     The three-dimensional data encoding device may include tile additional information in supplemental enhancement information (SEI) and transmit the SEI. Alternatively, the three-dimensional data encoding device may store tile additional information in an existing parameter set (PPS, GPS, or APS, etc.) and transmit the parameter set. 
     For example, when tile additional information changes for each frame, the tile additional information may be stored in a parameter set for each frame (GPS or APS etc.). When tile additional information does not change in a sequence, the tile additional information may be stored in a parameter set for sequence (geometry SPS or attribute SPS). Further, when the same tile division information is used for geometry information and attribute information, tile additional information may be stored in a parameter set for a PCC stream (a stream PS). 
     Moreover, tile additional information may be stored in any one of the above-mentioned parameter sets or in parameter sets. In addition, tile additional information may be stored in the header of encoded data. Additionally, tile additional information may be stored in the header of a NAL unit. 
     Furthermore, part or all of tile additional information may be stored in one of the header of divided geometry information and the header of divided attribute information, and need not be stored in the other. For example, when the same tile additional information is used for geometry information and attribute information, the tile additional information may be included in the header of one of the geometry information and the attribute information. For example, when attribute information depends on geometry information, the geometry information is processed first. For this reason, the tile additional information may be included in the header of the geometry information, and need not be included in the header of the attribute information. In this case, for example, the three-dimensional data decoding device determines that the attribute information of the depender belongs to the same tile as a tile having the geometry information of the dependee. 
     The three-dimensional data decoding device reconstructs point cloud data subjected to tile division, based on tile additional information. When there are pieces of overlapping point cloud data, the three-dimensional data decoding device specifies the pieces of overlapping point cloud data and selects one of the pieces of overlapping point cloud data or merges pieces of point cloud data. 
     Moreover, the three-dimensional data decoding device may perform decoding using tile additional information. For example, when tiles overlap each other, the three-dimensional data decoding device may perform decoding for each tile, perform processing (e.g., smoothing or filtering) using the pieces of decoded data, and generate point cloud data. This makes it possible to perform highly accurate decoding. 
       FIG. 69  is a diagram illustrating a configuration example of a system including the three-dimensional data encoding device and the three-dimensional data decoding device. Tile divider  5051  divides point cloud data including geometry information and attribute information into a first tile and a second tile. In addition, tile divider  5051  transmits tile additional information regarding tile division to decoder  5053  and tile combiner  5054 . 
     Encoder  5052  generates encoded data by encoding the first tile and the second tile. 
     Decoder  5053  restores the first tile and the second tile by decoding the encoded data generated by encoder  5052 . Tile combiner  5054  restores the point cloud data (the geometry information and the attribute information) by combining the first tile and the second tile using the tile additional information. 
     The following describes slice additional information. The three-dimensional data encoding device generates slice additional information that is metadata regarding a slice division method, and transmits the generated slice additional information to the three-dimensional data decoding device. 
       FIG. 70  is a diagram illustrating an example of syntax of slice additional information (SliceMetaData). As shown in  FIG. 70 , for example, slice additional information includes division method information (type_of_divide), an overlap flag (slice_overlap_flag), overlap information (type_of_overlap), a slice number (slice_number), slice position information (global_position, relative_position), and slice size information (slice_bounding_box_size). 
     Division method information (type_of_divide) indicates a slice division method. For example, division method information indicates whether a slice division method is division based on information about an object (object) as shown in  FIG. 60 . It should be noted that slice additional information may include information indicating an object division method. For example, this information indicates whether one object is to be divided into slices or assigned to one slice. In addition, the information may indicate, for example, a division number when one object is divided into slices. 
     An overlap flag (slice_overlap_flag) indicates whether slices overlap each other. Overlap information (type_of_overlap) is included in slice additional information when, for example, slices overlap each other. Overlap information indicates, for example, how slices overlap each other. For example, overlap information indicates the size of an overlapping region. 
     A slice number (slice_number) indicates the number of slices. 
     Slice position information (global_position, relative_position) and slice size information (slice_bounding_box_size) are information about a region of a slice. Slice position information is information for identifying the position of each slice. For example, slice position information indicates the absolute coordinates or relative coordinates of each slice. Slice size information (slice_bounding_box_size) indicates the size of each slice. For example, slice size information indicates the size of a bounding box of each slice. 
     The three-dimensional data encoding device may include slice additional information in SEI and transmit the SEI. Alternatively, the three-dimensional data encoding device may store slice additional information in an existing parameter set (PPS, GPS, or APS, etc.) and transmit the parameter set. 
     For example, when slice additional information changes for each frame, the slice additional information may be stored in a parameter set for each frame (GPS or APS etc.). When slice additional information does not change in a sequence, the slice additional information may be stored in a parameter set for sequence (geometry SPS or attribute SPS). Further, when the same slice division information is used for geometry information and attribute information, slice additional information may be stored in a parameter set for a PCC stream (a stream PS). 
     Moreover, slice additional information may be stored in any one of the above-mentioned parameter sets or in parameter sets. In addition, slice additional information may be stored in the header of encoded data. Additionally, slice additional information may be stored in the header of a NAL unit. 
     Furthermore, part or all of slice additional information may be stored in one of the header of divided geometry information and the header of divided attribute information, and need not be stored in the other. For example, when the same slice additional information is used for geometry information and attribute information, the slice additional information may be included in the header of one of the geometry information and the attribute information. For example, when attribute information depends on geometry information, the geometry information is processed first. For this reason, the slice additional information may be included in the header of the geometry information, and need not be included in the header of the attribute information. In this case, for example, the three-dimensional data decoding device determines that the attribute information of the depender belongs to the same slice as a slice having the geometry information of the dependee. 
     The three-dimensional data decoding device reconstructs point cloud data subjected to slice division, based on slice additional information. When there are pieces of overlapping point cloud data, the three-dimensional data decoding device specifies the pieces of overlapping point cloud data and selects one of the pieces of overlapping point cloud data or merges pieces of point cloud data. 
     Moreover, the three-dimensional data decoding device may perform decoding using slice additional information. For example, when slices overlap each other, the three-dimensional data decoding device may perform decoding for each slice, perform processing (e.g., smoothing or filtering) using the pieces of decoded data, and generate point cloud data. This makes it possible to perform highly accurate decoding. 
       FIG. 71  is a flowchart of a three-dimensional data encoding process including a tile additional information generation process performed by the three-dimensional data encoding device according to the present embodiment. 
     First, the three-dimensional data encoding device determines a division method to be used (S 5031 ). Specifically, the three-dimensional data encoding device determines whether a division method based on top view (top_view) or another method (other) is to be used as a tile division method. In addition, the three-dimensional data encoding device determines a tile shape when the division method based on top view is used. Additionally, the three-dimensional data encoding device determines whether tiles overlap with other tiles. 
     When the tile division method determined in step S 5031  is the division method based on top view (YES in S 5032 ), the three-dimensional data encoding device includes a result of the determination that the tile division method is the division method based on top view (top_view), in tile additional information (S 5033 ). 
     On the other hand, when the tile division method determined in step S 5031  is a method other than the division method based on top view (NO in S 5032 ), the three-dimensional data encoding device includes a result of the determination that the tile division method is the method other than the division method based on top view (top_view), in tile additional information (S 5034 ). 
     Moreover, when a shape in top view of a tile determined in step S 5031  is a square (SQUARE in S 6035 ), the three-dimensional data encoding device includes a result of the determination that the shape in top view of the tile is the square, in the tile additional information (S 5036 ). In contrast, when a shape in top view of a tile determined in step S 5031  is a circle (CIRCLE in S 5035 ), the three-dimensional data encoding device includes a result of the determination that the shape in top view of the tile is the circle, in the tile additional information (S 5037 ). 
     Next, the three-dimensional data encoding device determines whether tiles overlap with other tiles (S 5038 ). When the tiles overlap with the other tiles (YES in S 5038 ), the three-dimensional data encoding device includes a result of the determination that the tiles overlap with the other tiles, in the tile additional information (S 5039 ). On the other hand, when the tiles do not overlap with other tiles (NO in S 5038 ), the three-dimensional data encoding device includes a result of the determination that the tiles do not overlap with the other tiles, in the tile additional information (S 5040 ). 
     Finally, the three-dimensional data encoding device divides the tiles based on the tile division method determined in step S 5031 , encodes each of the tiles, and transmits the generated encoded data and the tile additional information (S 5041 ). 
       FIG. 72  is a flowchart of a three-dimensional data decoding process performed by the three-dimensional data decoding device according to the present embodiment using tile additional information. 
     First, the three-dimensional data decoding device analyzes tile additional information included in a bitstream (S 5051 ). 
     When the tile additional information indicates that tiles do not overlap with other tiles (NO in S 5052 ), the three-dimensional data decoding device generates point cloud data of each tile by decoding the tile (S 5053 ). Finally, the three-dimensional data decoding device reconstructs point cloud data from the point cloud data of each tile, based on a tile division method and a tile shape indicated by the tile additional information (S 5054 ). 
     In contrast, when the tile additional information indicates that tiles overlap with other tiles (YES in S 5052 ), the three-dimensional data decoding device generates point cloud data of each tile by decoding the tile. In addition, the three-dimensional data decoding device identifies overlap portions of the tiles based on the tile additional information (S 5055 ). It should be noted that, regarding the overlap portions, the three-dimensional data decoding device may perform decoding using pieces of overlapping information. Finally, the three-dimensional data decoding device reconstructs point cloud data from the point cloud data of each tile, based on a tile division method, a tile shape, and overlap information indicated by the tile additional information (S 5056 ). 
     The following describes, for example, variations regarding slice. The three-dimensional data encoding device may transmit, as additional information, information indicating a type (a road, a building, a tree, etc.) or attribute (dynamic information, static information, etc.) of an object. Alternatively, a coding parameter may be predetermined according to an object, and the three-dimensional data encoding device may notify the coding parameter to the three-dimensional data decoding device by transmitting a type or attribute of the object. 
     The following methods may be used regarding slice data encoding order and transmitting order. For example, the three-dimensional data encoding device may encode slice data in decreasing order of ease of object recognition or clustering. Alternatively, the three-dimensional data encoding device may encode slice data in the order in which clustering is completed. Moreover, the three-dimensional data encoding device may transmit slice data in the order in which the slice data is encoded. Alternatively, the three-dimensional data encoding device may transmit slice data in decreasing order of priority for decoding in an application. For example, when dynamic information has high priority for decoding, the three-dimensional data encoding device may transmit slice data in the order in which slices are grouped using the dynamic information. 
     Furthermore, when encoded data order is different from the order of priority for decoding, the three-dimensional data encoding device may transmit encoded data after rearranging the encoded data. In addition, when storing encoded data, the three-dimensional data encoding device may store encoded data after rearranging the encoded data. 
     An application (the three-dimensional data decoding device) requests a server (the three-dimensional data encoding device) to transmit slices including desired data. The server may transmit slice data required by the application, and need not transmit slice data unnecessary for the application. 
     An application requests a server to transmit a tile including desired data. The server may transmit tile data required by the application, and need not transmit tile data unnecessary for the application. 
     As stated above, the three-dimensional data encoding device according to the present embodiment performs the process shown in  FIG. 73 . First, the three-dimensional data encoding device encodes subspaces (e.g., tiles) obtained by dividing a current space which includes three-dimensional points, to generate pieces of encoded data (S 5061 ). The three-dimensional data encoding device generates a bitstream including the pieces of encoded data and first information (e.g., topview_shape) indicating a shape of each of the subspaces (S 5062 ). 
     Accordingly, since the three-dimensional data encoding device can select any shape from various types of shapes of subspaces, the three-dimensional data encoding device can improve the coding efficiency. 
     For example, the shape is a two-dimensional shape or a three-dimensional shape of each of the subspaces. For example, the shape is a shape in a top view of the subspace. To put it another way, the first information indicates a shape of the subspace viewed from a specific direction (e.g., an upper direction). In short, the first information indicates a shape in an overhead view of the subspace. For example, the shape is rectangular or circular. 
     For example, the bitstream includes second information (e.g., tile_overlap_flag) indicating whether the subspaces overlap. 
     Accordingly, since the three-dimensional data encoding device allows subspaces to overlap, the three-dimensional data encoding device can generate the subspaces without making a shape of each of the subspaces complex. 
     For example, the bitstream includes third information (e.g., type_of_divide) indicating whether a division method used to obtain the subspaces is a division method using a top view. 
     For example, the bitstream includes fourth information (e.g., tile_height) indicating at least one of a height, a width, a depth, or a radius of each of the subspaces. 
     For example, the bitstream includes fifth information (e.g., global_position or relative_position) indicating a position of each of the subspaces. 
     For example, the bitstream includes sixth information (e.g., tile_number) indicating a total number of the subspaces. 
     For example, the bitstream includes seventh information indicating an interval between the subspaces. 
     For example, the three-dimensional data encoding device includes a processor and memory, and the processor performs the above process using the memory. 
     Moreover, the three-dimensional data decoding device according to the present embodiment performs the process shown in  FIG. 74 . First, the three-dimensional data decoding device decodes pieces of encoded data included in a bitstream and generated by encoding subspaces (e.g., tiles) obtained by dividing a current space which includes three-dimensional points, to restore the subspaces (S 5071 ). The three-dimensional data decoding device restores the current space by combining the subspaces using first information (e.g., topview_shape) which is included in the bitstream and indicates a shape of each of the subspaces (S 5072 ). For example, the three-dimensional data decoding device can determine a position and a range of each of subspaces in a current space by recognizing a shape of the subspace using the first information. The three-dimensional data decoding device can combine the subspaces based on the determined positions and ranges of the subspaces. Accordingly, the three-dimensional data decoding device can combine the subspaces correctly. 
     For example, the shape is a two-dimensional shape or a three-dimensional shape of each of the subspaces. For example, the shape is rectangular or circular. 
     For example, the bitstream includes second information (e.g., tile_overlap_flag) indicating whether the subspaces overlap. In the restoring of the current space, the three-dimensional data decoding device combines the subspaces by further using the second information. For example, the three-dimensional data decoding device determines whether subspaces overlap, using the second information. When the subspaces overlap, the three-dimensional data decoding device identifies overlap regions and performs a predetermined process on the identified regions. 
     For example, the bitstream includes third information (e.g., type_of_divide) indicating whether a division method used to obtain the subspaces is a division method using a top view. In the restoring of the current space, when the third information indicates that the division method used to obtain the subspaces is the division method using the top view, the three-dimensional data decoding device combines the subspaces using the first information. 
     For example, the bitstream includes fourth information (e.g., tile_height) indicating at least one of a height, a width, a depth, or a radius of each of the subspaces. In the restoring of the current space, the three-dimensional data decoding device combines the subspaces by further using the fourth information. For example, the three-dimensional data decoding device can determine a position and a range of each of subspaces in a current space by recognizing a height of the subspace using the fourth information. The three-dimensional data decoding device can combine the subspaces based on the determined positions and ranges of the subspaces. 
     For example, the bitstream includes fifth information (e.g., global_position or relative_position) indicating a position of each of the subspaces. In the restoring of the current space, the three-dimensional data decoding device combines the subspaces by further using the fifth information. For example, the three-dimensional data decoding device can determine a position of each of subspaces in a current space by recognizing a position of the subspace using the fifth information. The three-dimensional data decoding device can combine the subspaces based on the determined positions of the subspaces. 
     For example, the bitstream includes sixth information (e.g., tile_number) indicating a total number of the subspaces. In the restoring of the current space, the three-dimensional data decoding device combines the subspaces by further using the sixth information. 
     For example, the bitstream includes seventh information indicating an interval between the subspaces. In the restoring of the current space, the three-dimensional data decoding device combines the subspaces by further using the seventh information. For example, the three-dimensional data decoding device can determine a position and a range of each of subspaces in a current space by recognizing an interval between the subspaces using the seventh information. The three-dimensional data decoding device can combine the subspaces based on the determined positions and ranges of the subspaces. 
     For example, the three-dimensional data decoding device includes a processor and memory, and the processor performs the above process using the memory. 
     A three-dimensional data encoding device, a three-dimensional data decoding device, and the like according to the embodiments of the present disclosure have been described above, but the present disclosure is not limited to these embodiments. 
     Note that each of the processors included in the three-dimensional data encoding device, the three-dimensional data decoding device, and the like according to the above embodiments is typically implemented as a large-scale integrated (LSI) circuit, which is an integrated circuit (IC). These may take the form of individual chips, or may be partially or entirely packaged into a single chip. 
     Such IC is not limited to an LSI, and thus may be implemented as a dedicated circuit or a general-purpose processor. Alternatively, a field programmable gate array (FPGA) that allows for programming after the manufacture of an LSI, or a reconfigurable processor that allows for reconfiguration of the connection and the setting of circuit cells inside an LSI may be employed. 
     Moreover, in the above embodiments, the structural components may be implemented as dedicated hardware or may be realized by executing a software program suited to such structural components. Alternatively, the structural components may be implemented by a program executor such as a CPU or a processor reading out and executing the software program recorded in a recording medium such as a hard disk or a semiconductor memory. 
     The present disclosure may also be implemented as a three-dimensional data encoding method, a three-dimensional data decoding method, or the like executed by the three-dimensional data encoding device, the three-dimensional data decoding device, and the like. 
     Also, the divisions of the functional blocks shown in the block diagrams are mere examples, and thus a plurality of functional blocks may be implemented as a single functional block, or a single functional block may be divided into a plurality of functional blocks, or one or more functions may be moved to another functional block. Also, the functions of a plurality of functional blocks having similar functions may be processed by single hardware or software in a parallelized or time-divided manner. 
     Also, the processing order of executing the steps shown in the flowcharts is a mere illustration for specifically describing the present disclosure, and thus may be an order other than the shown order. Also, one or more of the steps may be executed simultaneously (in parallel) with another step. 
     A three-dimensional data encoding device, a three-dimensional data decoding device, and the like according to one or more aspects have been described above based on the embodiments, but the present disclosure is not limited to these embodiments. The one or more aspects may thus include forms achieved by making various modifications to the above embodiments that can be conceived by those skilled in the art, as well forms achieved by combining structural components in different embodiments, without materially departing from the spirit of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to a three-dimensional data encoding device and a three-dimensional data decoding device.