Patent Publication Number: US-2021168400-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/JP2019/036844 filed on Sep. 19, 2019, claiming the benefit of priority of U.S. Provisional Patent Application No. 62/734,657 filed on Sep. 21, 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: combining first point cloud data and second point cloud data to generate third point cloud data; and encoding the third point cloud data to generate encoded data, wherein the encoded data includes identification information indicating whether each of three-dimensional points included in the third point cloud data belongs to the first point cloud data or the second point cloud data. 
     A three-dimensional data decoding method according to an aspect of the present disclosure includes: decoding encoded data to obtain third point cloud data and identification information, the third point cloud data being generated by combining first point cloud data and second point cloud data, the identification information indicating whether each of three-dimensional points included in the third point cloud data belongs to the first point cloud data or the second point cloud data; and separating the first point cloud data and the second point cloud data from the third point cloud data, using the identification information. 
     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 diagram illustrating a basic structure of ISOBMFF according to Embodiment 2; 
         FIG. 15  is a diagram illustrating a protocol stack according to Embodiment 2; 
         FIG. 16  is a diagram illustrating structures of an encoder and a multiplexer according to Embodiment 3; 
         FIG. 17  is a diagram illustrating a structure example of encoded data according to Embodiment 3; 
         FIG. 18  is a diagram illustrating a structure example of encoded data and a NAL unit according to Embodiment 3; 
         FIG. 19  is a diagram illustrating a semantics example of pcc_nal_unit_type according to Embodiment 3; 
         FIG. 20  is a diagram illustrating an example of a transmitting order of NAL units according to Embodiment 3; 
         FIG. 21  is a block diagram showing a first encoder according to Embodiment 4; 
         FIG. 22  is a block diagram showing a first decoder according to Embodiment 4; 
         FIG. 23  is a block diagram showing a divider according to Embodiment 4; 
         FIG. 24  is a diagram illustrating an example of dividing slices and tiles according to Embodiment 4; 
         FIG. 25  is a diagram illustrating dividing pattern examples of slices and tiles according to Embodiment 4; 
         FIG. 26  is a diagram illustrating an example of dependency relationships according to Embodiment 4; 
         FIG. 27  is a diagram illustrating an example of decoding order of data according to Embodiment 4; 
         FIG. 28  is a flowchart of an encoding process according to Embodiment 4; 
         FIG. 29  is a block diagram of a combiner according to Embodiment 4; 
         FIG. 30  is a diagram illustrating a structural example of encoded data and NAL units according to Embodiment 4; 
         FIG. 31  is a flowchart of an encoding process according to Embodiment 4; 
         FIG. 32  is a flowchart of a decoding process according to Embodiment 4; 
         FIG. 33  is a flowchart of an encoding process according to Embodiment 4; 
         FIG. 34  is a flowchart of a decoding process according to Embodiment 4; 
         FIG. 35  is a diagram showing a concept of generation of a tree structure and an occupancy code from point cloud data of a plurality of frames according to Embodiment 5; 
         FIG. 36  is a diagram showing an example of frame combining according to Embodiment 5; 
         FIG. 37  is a diagram showing an example of combining of a plurality of frames according to Embodiment 5; 
         FIG. 38  is a flowchart of a three-dimensional data encoding process according to Embodiment 5; 
         FIG. 39  is a flowchart of an encoding process according to Embodiment 5; 
         FIG. 40  is a flowchart of a three-dimensional data decoding process according to Embodiment 5; 
         FIG. 41  is a flowchart of a decoding and dividing process according to Embodiment 5; 
         FIG. 42  is a block diagram showing an encoder according to Embodiment 5; 
         FIG. 43  is a block diagram showing a divider according to Embodiment 5; 
         FIG. 44  is a block diagram showing a geometry information encoder according to Embodiment 5; 
         FIG. 45  is a block diagram showing an attribute information encoder according to Embodiment 5; 
         FIG. 46  is a flowchart of a process of encoding point cloud data according to Embodiment 5; 
         FIG. 47  is a flowchart of an encoding process according to Embodiment 5; 
         FIG. 48  is a block diagram showing a decoder according to Embodiment 5; 
         FIG. 49  is a block diagram showing a geometry information decoder according to Embodiment 5; 
         FIG. 50  is a block diagram showing an attribute information decoder according to Embodiment 5; 
         FIG. 51  is a block diagram showing a combiner according to Embodiment 5; 
         FIG. 52  is a flowchart of a process of decoding point cloud data according to Embodiment 5; 
         FIG. 53  is a flowchart of a decoding process according to Embodiment 5; 
         FIG. 54  is a diagram showing an example of pattern of frame combining according to Embodiment 5; 
         FIG. 55  is a diagram showing a configuration example of PCC frames according to Embodiment 5; 
         FIG. 56  is a diagram showing a configuration of encoded geometry information according to Embodiment 5; 
         FIG. 57  is a diagram showing a syntax example of a header of encoded geometry information according to Embodiment 5; 
         FIG. 58  is a diagram showing a syntax example of a payload of encoded geometry information according to Embodiment 5; 
         FIG. 59  is a diagram showing an example of leaf node information according to Embodiment 5; 
         FIG. 60  is a diagram showing an example of the leaf node information according to Embodiment 5; 
         FIG. 61  is a diagram showing an example of bit map information according to Embodiment 5; 
         FIG. 62  is a diagram showing a configuration of encoded attribute information according to Embodiment 5; 
         FIG. 63  is a diagram showing a syntax example of a header of encoded attribute information according to Embodiment 5; 
         FIG. 64  is a diagram showing a syntax example of a payload of encoded attribute information according to Embodiment 5; 
         FIG. 65  is a diagram showing a configuration of encoded data according to Embodiment 5; 
         FIG. 66  is a diagram showing an order of transmission and a data reference relationship according to Embodiment 5; 
         FIG. 67  is a diagram showing an order of transmission and a data reference relationship according to Embodiment 5; 
         FIG. 68  is a diagram showing an order of transmission and a data reference relationship according to Embodiment 5; 
         FIG. 69  is a diagram showing an example in which part of frames is decoded according to Embodiment 5; 
         FIG. 70  is a diagram showing an order of transmission and a data reference relationship according to Embodiment 5; 
         FIG. 71  is a diagram showing an order of transmission and a data reference relationship according to Embodiment 5; 
         FIG. 72  is a diagram showing an order of transmission and a data reference relationship according to Embodiment 5; 
         FIG. 73  is a diagram showing an order of transmission and a data reference relationship according to Embodiment 5; 
         FIG. 74  is a flowchart of an encoding process according to Embodiment 5; and 
         FIG. 75  is a flowchart of a decoding process according to Embodiment 5. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     A three-dimensional data encoding method according to an aspect of the present disclosure includes: combining first point cloud data and second point cloud data to generate third point cloud data; and encoding the third point cloud data to generate encoded data, wherein the encoded data includes identification information indicating whether each of three-dimensional points included in the third point cloud data belongs to the first point cloud data or the second point cloud data. 
     Accordingly, the three-dimensional data encoding method can improve coding efficiency by encoding pieces of point cloud data all at once. 
     For example, the first point cloud data and the second point cloud data may be point cloud data having different times. 
     For example, the first point cloud data and the second point cloud data may be point cloud data of a same object and having different times. 
     For example, the encoded data may include geometry information and attribute information of each of the three-dimensional points included in the third point cloud data, and the identification information may be included in the attribute information. 
     For example, the encoded data may include geometry information in which a position of each of the three-dimensional points included in the third point cloud data is expressed using an N-ary tree, N being an integer greater than or equal to 2. 
     A three-dimensional data decoding method according to an aspect of the present disclosure includes: decoding encoded data to obtain third point cloud data and identification information, the third point cloud data being generated by combining first point cloud data and second point cloud data, the identification information indicating whether each of three-dimensional points included in the third point cloud data belongs to the first point cloud data or the second point cloud data; and separating the first point cloud data and the second point cloud data from the third point cloud data, using the identification information. 
     Accordingly, the three-dimensional data decoding method can decode encoded data the coding efficiency of which has been improved by having pieces of point cloud data encoded all at once. 
     For example, the first point cloud data and the second point cloud data may be point cloud data having different times. 
     For example, the first point cloud data and the second point cloud data may be point cloud data of a same subject and having different times. 
     For example, the encoded data may include geometry information and attribute information of each of the three-dimensional points included in the third point cloud data, and the identification information may be included in the attribute information. 
     For example, the encoded data may include geometry information in which a position of each of the three-dimensional points included in the third point cloud data is expressed using an N-ary tree, N being an integer greater than or equal to 2. 
     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: combines first point cloud data and second point cloud data to generate third point cloud data; and encodes the third point cloud data to generate encoded data, wherein the encoded data includes identification information indicating whether each of three-dimensional points included in the third point cloud data belongs to the first point cloud data or the second point cloud data. 
     Accordingly, the three-dimensional data encoding device can improve coding efficiency by encoding pieces or point cloud data all at once. 
     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 encoded data to obtain third point cloud data and identification information, the third point cloud data being generated by combining first point cloud data and second point cloud data, the identification information indicating whether each of three-dimensional points included in the third point cloud data belongs to the first point cloud data or the second point cloud data; and separates the first point cloud data and the second point cloud data from the third point cloud data, using the identification information. 
     Accordingly, the three-dimensional data decoding device can decode encoded data the coding efficiency of which has been improved by having pieces of point cloud data encoded all at once. 
     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. 
     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/EC14496-12. 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. 14  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. 15  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 Codec, Carriage of Codec2) is desirably prescribed, since a plurality of PCC codecs are stored in the NAL unit. 
     Embodiment 3 
     In this embodiment, 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. 16  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. 17  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. 17  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. 17  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. 17  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. 18  is a diagram showing an example of encoded data and a NAL unit. 
     For example, as shown in  FIG. 18 , 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 pec_nal_unit_type, which is identification information for the encoded data.  FIG. 19  is a diagram showing a semantics example of pec_nal_unit_type. 
     As shown in  FIG. 19 , when pec_codec_type is codec 1 (Codec: first encoding method), values 0 to 10 of pec_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 reservedin codec 1. 
     When pec_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 reservedin codec2. 
     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. 20  is a diagram showing examples of the order of transmission of NAL units.  FIG. 20  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. 20  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. 20 , 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 pec_nal_unit_type. 
     Embodiment 4 
     For HEVC encoding, in order to enable parallel processing in a decoding device, there are slice-based or tile-based data division tools, for example. However, there is no such tool for point cloud compression (PCC) encoding. 
     In PCC, various data division methods are possible, depending on the parallel processing, the compression efficiency, and the compression algorithm. Here, definitions of a slice and a tile, a data structure, and transmission and reception methods will be described. 
       FIG. 21  is a block diagram showing a configuration of first encoder  4910  included in a three-dimensional data encoding device according to this embodiment. First encoder  4910  generates encoded data (encoded stream) by encoding point cloud data in a first encoding method (geometry-based PCC (GPCC)). First encoder  4910  includes divider  4911 , a plurality of geometry information encoders  4912 , a plurality of attribute information encoders  4913 , additional information encoder  4914 , and multiplexer  4915 . 
     Divider  4911  generates a plurality of pieces of divided data by dividing point cloud data. Specifically, divider  4911  generates a plurality of pieces of divided data by dividing a space of point cloud data into a plurality of subspaces. Here, a subspace is a combination of tiles or slices, or a combination of tiles and slices. More specifically, point cloud data includes geometry information, attribute information, and additional information. Divider  4911  divides geometry information into a plurality of pieces of divided geometry information, and divides attribute information into a plurality of pieces of divided attribute information. Divider  4911  also generates additional information concerning the division. 
     The plurality of geometry information encoders  4912  generate a plurality of pieces of encoded geometry information by encoding a plurality of pieces of divided geometry information. For example, the plurality of geometry information encoders  4912  processes a plurality of pieces of divided geometry information in parallel. 
     The plurality of attribute information encoders  4913  generate a plurality of pieces of encoded attribute information by encoding a plurality of pieces of divided attribute information. For example, the plurality of attribute information encoders  4913  process a plurality of pieces of divided attribute information in parallel. 
     Additional information encoder  4914  generates encoded additional information by encoding additional information included in the point cloud data and additional information concerning the data division generated in the division by divider  4911 . 
     Multiplexer  4915  generates encoded data (encoded stream) by multiplexing a plurality of pieces of encoded geometry information, a plurality of pieces of encoded attribute information, and encoded additional information, and transmits the generated encoded data. The encoded additional information is used for decoding. 
     Note that, although  FIG. 21  shows an example in which there are two geometry information encoders  4912  and two attribute information encoders  4913 , the number of geometry information encoders  4912  and the number of attribute information encoders  4913  may be one, or three or more. The plurality of pieces of divided data may be processed in parallel in the same chip, such as by a plurality of cores of a CPU, processed in parallel by cores of a plurality of chips, or processed in parallel by a plurality of cores of a plurality of chips. 
       FIG. 22  is a block diagram showing a configuration of first decoder  4920 . First decoder  4920  reproduces point cloud data by decoding encoded data (encoded stream) generated by encoding the point cloud data in the first encoding method (GPCC). First decoder  4920  includes demultiplexer  4921 , a plurality of geometry information decoders  4922 , a plurality of attribute information decoders  4923 , additional information decoder  4924 , and combiner  4925 . 
     Demultiplexer  4921  generates a plurality of pieces of encoded geometry information, a plurality of pieces of encoded attribute information, and encoded additional information by demultiplexing encoded data (encoded stream). 
     The plurality of geometry information decoders  4922  generate a plurality of pieces of divided geometry information by decoding a plurality of pieces of encoded geometry information. For example, the plurality of geometry information decoders  4922  process a plurality of pieces of encoded geometry information in parallel. 
     The plurality of attribute information decoders  4923  generate a plurality of pieces of divided attribute information by decoding a plurality of pieces of encoded attribute information. For example, the plurality of attribute information decoders  4923  process a plurality of pieces of encoded attribute information in parallel. 
     Additional information decoder  4924  generates additional information by decoding encoded additional information. 
     Combiner  4925  generates geometry information by combining a plurality of pieces of divided geometry information using additional information. Combiner  4925  generates attribute information by combining a plurality of pieces of divided attribute information using additional information. 
     Note that, although  FIG. 22  shows an example in which there are two geometry information decoders  4922  and two attribute information decoders  4923 , the number of geometry information decoders  4922  and the number of attribute information decoders  4923  may be one, or three or more. The plurality of pieces of divided data may be processed in parallel in the same chip, such as by a plurality of cores of a CPU, processed in parallel by cores of a plurality of chips, or processed in parallel by a plurality of cores of a plurality of chips. 
     Next, a configuration of divider  4911  will be described.  FIG. 23  is a block diagram showing divider  4911 . Divider  4911  includes slice divider  4931 , geometry information tile divider (geometry tile divider)  4932 , attribute information tile divider (attribute tile divider)  4933 . 
     Slice divider  4931  generates a plurality of pieces of slice geometry information by dividing geometry information (position (geometry)) into slices. Slice divider  4931  also generates a plurality of pieces of slice attribute information by dividing attribute information (attribute) into slices. Slice divider  4931  also outputs slice additional information (slice metadata) including information concerning the slice division and information generated in the slice division. 
     Geometry information tile divider  4932  generates a plurality of pieces of divided geometry information (a plurality of pieces of tile geometry information) by dividing a plurality of pieces of slice geometry information into tiles. Geometry information tile divider  4932  also outputs geometry tile additional information (geometry tile metadata) including information concerning the tile division of geometry information and information generated in the tile division of geometry information. 
     Attribute information tile divider  4933  generates a plurality of pieces of divided attribute information (a plurality of pieces of tile attribute information) by dividing a plurality of pieces of slice attribute information into tiles. Attribute information tile divider  4933  also outputs attribute tile additional information (attribute tile metadata) including information concerning the tile division of attribute information and information generated in the tile division of attribute information. 
     Note that the number of slices or tiles generated by division is equal to or greater than 1. That is, the slice division or tile division may not be performed. 
     Although an example in which tile division is performed after slice division has been shown here, slice division may be performed after tile division. Alternatively, other units of division may be defined in addition to slice and tile, and the division may be performed based on three or more units of division. 
     Hereinafter, the dividing method for point cloud data will be described.  FIG. 24  is a diagram illustrating an example of slice and tile dividing. 
     First, the method for slice dividing will be described. Divider  4911  divides three-dimensional point cloud data into arbitrary point clouds on a slice-by-slice basis. In slice dividing, divider  4911  does not divide the geometry information and the attribute information constituting points, but collectively divides the geometry information and the attribute information. That is, divider  4911  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 dividing 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, divider  4911  generates slice additional information, which is additional information related to the number of divisions and the dividing 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. Divider  4911  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. 24  illustrates the example in which division is performed with an octree structure, the number of divisions and the dividing method may be any number and any method. 
     Also, divider  4911  may divide geometry information and attribute information with different dividing methods, or may divide geometry information and attribute information with the same dividing method. Additionally, divider  4911  may divide a plurality of slices into tiles with different dividing methods, or may divide a plurality of slices into tiles with the same dividing method. 
     Furthermore, divider  4911  generates tile additional information related to the number of divisions and the dividing 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, divider  4911  may use a predetermined method, or may adaptively switch methods to be used according to point cloud data. 
     At the time of slice dividing, divider  4911  divides a three-dimensional space by collectively handling geometry information and attribute information. For example, divider  4911  determines the shape of an object, and divides a three-dimensional space into slices according to the shape of the object. For example, divider  4911  extracts objects such as trees or buildings, and performs division on an object-by-object basis. For example, divider  4911  performs slice dividing so that the entirety of one or a plurality of objects are included in one slice. Alternatively, divider  4911  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, divider  4911  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, divider  4911  separately divides geometry information and attribute information. For example, divider  4911  divides slices into tiles according to the data amount or the processing amount. For example, divider  4911  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, divider  4911  divides slices into tiles. When the data amount of the slice is less than the threshold value, divider  4911  does not divide slices into tiles. 
     For example, divider  4911  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, divider  4911  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, divider  4911  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. 25  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 dividing method are the same for G slice and A slice. In tile dividing, the number of divisions and the dividing method for G slice are different from the number of divisions and the dividing method for A slice. Additionally, the same number of divisions and dividing method are used among a plurality of G slices. The same number of divisions and dividing method are used among a plurality of A slices. 
     In Pattern  2 , in slice dividing, the number of divisions and the dividing method are the same for G slice and A slice. In tile dividing, the number of divisions and the dividing method for G slice are different from the number of divisions and the dividing method for A slice. Additionally, the number of divisions and the dividing method are different among a plurality of G slices. The number of divisions and the dividing method are different among a plurality of A slices. 
     Next, a method of encoding divided data will be described. The three-dimensional data encoding device (first encoder  4910 ) encodes each piece of divided data. When encoding attribute information, the three-dimensional data encoding device generates, as additional information, dependency information that indicates on which configuration information (geometry information, additional information, or other attribute information) the encoding is based. That is, the dependency information indicates configuration information on a reference destination (dependency destination). In this case, the three-dimensional data encoding device generates dependency information based on configuration information corresponding to a pattern of division of attribute information. Note that the three-dimensional data encoding device may generate dependency information based on configuration information for a plurality of patterns of division of attribute information. 
     The dependency information may be generated by the three-dimensional data encoding device, and the generated dependency information may be transmitted to a three-dimensional data decoding device. Alternatively, the three-dimensional data decoding device may generate dependency information, and the three-dimensional data encoding device may transmit no dependency information. Alternatively, a dependency used by the three-dimensional data encoding device may be previously determined, and the three-dimensional data encoding device may transmit no dependency information. 
       FIG. 26  is a diagram showing an example of the dependency between data. In the drawing, the destination of an arrow indicates a dependency destination, and the source of an arrow indicates a dependency source. The three-dimensional data decoding device first decodes data concerning a dependency destination and then decodes data concerning a dependency source. Data indicated by a solid line in the drawing is data that is actually transmitted, and data indicated by a dotted line is data that is not transmitted. 
     In the drawing, G denotes geometry information, and A denotes attribute information. G s1  denotes geometry information concerning slice number 1, and G s2  denotes geometry information concerning slice number 2. G s1t1  denotes geometry information concerning slice number 1 and tile number 1, G s1t2  denotes geometry information concerning slice number 1 and tile number 2, G s2t1  denotes geometry information concerning slice number 2 and tile number 1, and G s2t2  denotes geometry information concerning slice number 2 and tile number 2. Similarly, A s1  denotes attribute information concerning slice number 1, and A s2  denotes attribute information concerning slice number 2. A s1t1  denotes attribute information concerning slice number 1 and tile number 1, A s1t2  denotes attribute information concerning slice number 1 and tile number 2, A s2t1  denotes attribute information concerning slice number 2 and tile number 1, and A s2t2  denotes attribute information concerning slice number 2 and tile number 2. 
     M slice  denotes slice additional information, MG tile  denotes geometry tile additional information, and MA tile  denotes attribute tile additional information. D s1t1  denotes dependency information for attribute information A s1t1 , and D s2t1  denotes dependency information for attribute information A s2t1 . 
     The three-dimensional data encoding device may rearrange data in the order of decoding so that the three-dimensional data decoding device does not need to rearrange data. Note 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. 27  is a diagram showing an example of the order of decoding of data. In the example in  FIG. 27 , data is decoded in order from left to right. When there is a dependency between data to be decoded, the three-dimensional data decoding device first decodes data on the dependency destination. For example, the three-dimensional data encoding device transmits the data after rearranging the data in that order. Note that the order can be any order as far as the data concerning the dependency destination is first decoded. The three-dimensional data encoding device may transmit additional information and dependency information before transmitting data. 
       FIG. 28  is a flowchart showing a flow of a process performed by the three-dimensional data encoding device. First, the three-dimensional data encoding device encodes a plurality of slices or tiles of data as described above (S 4901 ). The three-dimensional data encoding device then rearrange the data so that the data concerning the dependency destination comes first as shown in  FIG. 27  (S 4902 ). The three-dimensional data encoding device then multiplexes the rearranged data (into a NAL unit) (S 4903 ). 
     Next, a configuration of combiner  4925  included in first decoder  4920  will be described.  FIG. 29  is a block diagram showing a configuration of combiner  4925 . Combiner  4925  includes geometry information tile combiner (geometry tile combiner)  4941 , attribute information tile combiner (attribute tile combiner)  4942 , and slice combiner  4943 . 
     Geometry information tile combiner  4941  generates a plurality of pieces of slice geometry information by combining a plurality of pieces of divided geometry information using geometry tile additional information. Attribute information tile combiner  4942  generates a plurality of pieces of slice attribute information by combining a plurality of pieces of divided attribute information using attribute tile additional information. 
     Slice combiner  4943  generates geometry information by combining a plurality of pieces of slice geometry information using slice additional information. Slice combiner  4943  also generates attribute information by combining a plurality of pieces of slice attribute information using slice additional information. 
     Note that the number of slices or tiles generated by division is equal to or greater than 1. That is, the slice division or tile division may not be performed. 
     Furthermore, although an example in which tile division is performed after slice division has been shown here, slice division may be performed after tile division. Alternatively, other units of division may be defined in addition to slice and tile, and the division may be performed based on three or more units of division. 
     Next, a configuration of encoded data divided into slices or tiles, and a method of storing (multiplexing) encoded data into a NAL unit will be described.  FIG. 30  is a diagram showing a configuration of encoded data and a method of storing encoded data into a NAL unit. 
     Encoded data (divided geometry information and divided attribute information) is stored in a payload of a NAL unit. 
     Encoded data includes a header and a payload. The header includes identification information for identifying data included in the payload. The identification information includes a type (slice_type, tile_type) of slice division or tile division, index information (slice_idx, tile_idx) for identifying a slice or tile, geometry information on data (slice or tile), or an address (address) of data, for example. The index information for identifying a slice is referred to also as a slice index (SliceIndex). The index information for identifying a tile is referred to also as a tile index (TileIndex). The type of division may be a scheme based on an object shape, a scheme based on map information or geometry information, or a scheme based on a data amount or processing amount, for example. 
     All or part of the information described above may be stored in one of the header of the divided geometry information and the header of the divided attribute information and not be stored in the other. For example, when the same division method is used for the geometry information and the attribute information, the same type of division (slice_type, tile_type) and the same index information (slice_idx, tile_idx) are used for the geometry information and the attribute information. Therefore, these pieces of information may be included in the header of one of the geometry information and the attribute information. For example, when the attribute information depends on the geometry information, the geometry information is processed first. Therefore, the header of the geometry information may include these pieces of information, and the header of the attribute information may not include these pieces of information. In this case, the three-dimensional data decoding device determines that the attribute information concerning the dependency source belongs to the same slice or tile as the slice or tile of the geometry information concerning the dependency destination, for example. 
     The additional information (slice additional information, geometry tile additional information, or attribute tile additional information) concerning the slice division or tile division, dependency information indicating a dependency and the like may be stored in an existing parameter set (GPS, APS, geometry SPS, attribute SPS or the like) and transmitted. When the division method varies with frame, information indicating a division method may be stored in a parameter set (GPS, APS or the like) for each frame. When the division method does not vary in a sequence, information indicating a division method may be stored in a parameter set (geometry SPS or attribute SPS) for each sequence. Furthermore, when the same division method is used for the geometry information and the attribute information, information indicating the division method may be stored in a parameter set (stream PS) for the PCC stream. 
     The information described above may be stored in any of the parameter sets described above, or may be stored in a plurality of parameter sets. Alternatively, a parameter set for tile division or slice division may be defined, and the information described above may be stored in the parameter set. Alternatively, these pieces of information may be stored in the header of encoded data. 
     The header of encoded data includes identification information indicating a dependency. That is, when there is a dependency between data, the header includes identification information that allows the dependency source to refer to the dependency destination. For example, the header of the data of the dependency destination includes identification information for identifying the data. The header of the data of the dependency source includes identification information indicating the dependency destination. Note that the identification information for identifying data, the additional information concerning slice division or tile division, and the identification information indicating a dependency may be omitted if these pieces of information can be identified or derived from other information. 
     Next, a flow of a process of encoding point cloud data and a flow of a process of decoding point cloud data according to this embodiment will be described.  FIG. 31  is a flowchart of a process of encoding point cloud data according to this embodiment. 
     First, the three-dimensional data encoding device determines a division method to be used (S 4911 ). The division method includes a determination of whether to perform slice division or not and a determination of whether to perform tile division. The division method may include the number of slices or tiles in the case where slice division or tile division is performed, and the type of division, for example. The type of division is a scheme based on an object shape, a scheme based on map information or geometry information, or a scheme based on a data amount or processing amount, for example. The division method may be determined in advance. 
     When slice division is to be performed (if Yes in S 4912 ), the three-dimensional data encoding device generates a plurality of pieces of slice geometry information and a plurality of pieces of slice attribute information by collectively dividing the geometry information and the attribute information (S 4913 ). The three-dimensional data encoding device also generates slice additional information concerning the slice division. Note that the three-dimensional data encoding device may independently divide the geometry information and the attribute information. 
     When tile division is to be performed (if Yes in S 4914 ), the three-dimensional data encoding device generates a plurality of pieces of divided geometry information and a plurality of pieces of divided attribute information by independently dividing the plurality of pieces of slice geometry information and the plurality of pieces of slice attribute information (or the geometry information and the attribute information) (S 4915 ). The three-dimensional data encoding device also generates geometry tile additional information and attribute tile additional information concerning the tile division. The three-dimensional data encoding device may collectively divide the slice geometry information and the slice attribute information. 
     The three-dimensional data encoding device then generates a plurality of pieces of encoded geometry information and a plurality of pieces of encoded attribute information by encoding each of the plurality of pieces of divided geometry information and the plurality of pieces of divided attribute information (S 4916 ). The three-dimensional data encoding device also generates dependency information. 
     The three-dimensional data encoding device then generates encoded data (encoded stream) by integrating (multiplexing) the plurality of pieces of encoded geometry information, the plurality of pieces of encoded attribute information and the additional information into a NAL unit (S 4917 ). The three-dimensional data encoding device also transmits the generated encoded data. 
       FIG. 32  is a flowchart of a process of decoding point cloud data according to this embodiment. First, the three-dimensional data decoding device determines the division method by analyzing additional information (slice additional information, geometry tile additional information, and attribute tile additional information) concerning the division method included in encoded data (encoded stream) (S 4921 ). The division method includes a determination of whether to perform slice division or not and a determination of whether to perform tile division or not. The division method may include the number of slices or tiles in the case where slice division or tile division is performed, and the type of division, for example. 
     The three-dimensional data decoding device then generates divided geometry information and divided attribute information by decoding a plurality of pieces of encoded geometry information and a plurality of pieces of encoded attribute information included in the encoded data using dependency information included in the encoded data (S 4922 ). 
     If the additional information indicates that tile division has been performed (if Yes in S 4923 ), the three-dimensional data decoding device generates a plurality of pieces of slice geometry information and a plurality of pieces of slice attribute information by combining the plurality of pieces of divided geometry information and the plurality of pieces of divided attribute information in respective manners based on the geometry tile additional information and the attribute tile additional information (S 4924 ). Note that the three-dimensional data decoding device may combine the plurality of pieces of divided geometry information and the plurality of pieces of divided attribute information in the same manner. 
     If the additional information indicates that slice division has been performed (if Yes in S 4925 ), the three-dimensional data decoding device generates geometry information and attribute information by combining the plurality of pieces of slice geometry information and the plurality of pieces of slice attribute information (the plurality of pieces of divided geometry information and the plurality of pieces of divided attribute information) in the same manner based on the slice additional information (S 4926 ). Note that the three-dimensional data decoding device may combine the plurality of pieces of slice geometry information and the plurality of pieces of slice attribute information in different manners. 
     As described above, the three-dimensional data encoding device according to this embodiment performs the process shown in  FIG. 33 . First, the three-dimensional data encoding device divides data into a plurality of pieces of divided data (tiles, for example) that are included in a plurality of subspaces (slices, for example) generated by dividing a target space including a plurality of three-dimensional points and each of which includes one or more three-dimensional points. Here, the divided data is a collection of one or more pieces of data including one or more three-dimensional points that is included in a subspace. The divided data can also be regarded as a space and may include a space including no three-dimensional point. One subspace may include a plurality of pieces of divided data, or one subspace may include one piece of divided data. Note that a plurality of subspaces or one subspace may be set in a target space. 
     The three-dimensional data encoding device then generates a plurality of pieces of encoded data each associated with a different one of the plurality of pieces of divided data by encoding each of the plurality of pieces of divided data (S 4931 ). The three-dimensional data encoding device generates a bitstream including the plurality of pieces of encoded data and a plurality of pieces of control information (the header shown in  FIG. 30 , for example) each associated with a different one of the plurality of pieces of encoded data (S 4932 ). In each of the plurality of pieces of control information, a first identifier (slice_idx, for example) that indicates a subspace associated with the piece of encoded data associated with the piece of control information and a second identifier (tile_idx, for example) that indicates a piece of divided data associated with the piece of encoded data associated with the piece of control information are stored. 
     With such a configuration, the three-dimensional data decoding device that decodes the bitstream generated by the three-dimensional data encoding device can easily reproduce the target space by combining the plurality of pieces of divided data using the first identifier and the second identifier. Therefore, the processing amount of the three-dimensional data decoding device can be reduced. 
     For example, in the encoding described above, the three-dimensional data encoding device encodes the geometry information and the attribute information on the three-dimensional points included in each of the plurality of pieces of divided data. Each of the plurality of pieces of encoded data includes encoded data of the geometry information and the encoded data of the attribute information. Each of the plurality of pieces of control information includes the control information for the encoded data of the geometry information and the control information for the encoded data of the attribute information. The first identifier and the second identifier are stored in the control information for the encoded data of the geometry information. 
     For example, in the bitstream, each of the plurality of pieces of control information is arranged to precede the encoded data associated with the control information. 
     One or more subspaces are set in a target space including a plurality of three-dimensional points, and each subspace includes one or more pieces of divided data each including one or more three-dimensional points. The three-dimensional data encoding device generates a plurality of pieces of encoded data each associated with a different one of a plurality of pieces of divided data by encoding each of the plurality of pieces of divided data, and generates a bitstream including the plurality of pieces of encoded data and a plurality of pieces of control information each associated with a different one of the plurality of pieces of encoded data, and each of the plurality of pieces of control information may store the first identifier that indicates a subspace associated with the piece of encoded data associated with the piece of control information and the second identifier that indicates a piece of divided data associated with the piece of encoded data associated with the piece of control information. 
     For example, the three-dimensional data encoding device includes a processor and memory, and the processor performs the processes described above using the memory. 
     The three-dimensional data decoding device according to this embodiment performs the process shown in  FIG. 34 . First, from a bitstream including a plurality of pieces of encoded data generated by encoding of each of a plurality of pieces of divided data (tiles, for example) that are included in a plurality of subspaces (slices, for example) generated by dividing a target space including a plurality of three-dimensional points and each of which includes one or more three-dimensional points, and a plurality of pieces of control information (the header shown in  FIG. 30 , for example) for each of the plurality of pieces of encoded data, the three-dimensional data decoding device obtains the first identifier (slice_idx, for example) that indicates a subspace associated with the piece of encoded data associated with the piece of control information and the second identifier (tile_idx, for example) that indicates a piece of divided data associated with the piece of encoded data associated with the piece of control information, which are included in the plurality of pieces of control information (S 4941 ). The three-dimensional data decoding device then reproduces the plurality of pieces of divided data by decoding the plurality of pieces of encoded data (S 4942 ). The three-dimensional data decoding device then reproduces the target space by combining the plurality of pieces of divided data using the first identifier and the second identifier (S 4943 ). For example, the three-dimensional data decoding device reproduces the plurality of subspaces by combining the plurality of pieces of divided data using the second identifier, and reproduces the target space (the plurality of three-dimensional points) by combining the plurality of subspaces using the first identifier. Note that the three-dimensional data decoding device may obtain encoded data of a desired subspace or desired divided data from the bitstream using at least one of the first identifier and the second identifier, and selectively or preferentially decode the obtained encoded data. 
     With such a configuration, the three-dimensional data decoding device can easily reproduce the target space by combining the plurality of pieces of divided data using the first identifier and the second identifier. Therefore, the processing amount of the three-dimensional data decoding device can be reduced. 
     For example, each of a plurality of pieces of encoded data is generated by encoding geometry information and attribute information on a three-dimensional point included in an associated piece of divided data, and includes encoded data of the geometry information and encoded data of the attribute information. Each of the plurality of pieces of control information includes control information for the encoded data of the geometry information and control information for the encoded data of the attribute information. The first identifier and the second identifier are stored in the control information for the encoded data of the geometry information. 
     For example, in the bitstream, the control information is arranged to precede the associated encoded data. 
     For example, the three-dimensional data decoding device includes a processor and memory, and the processor performs the processes described above using the memory. 
     Embodiment 5 
     In encoding of geometry information using neighborhood dependency, the coding efficiency can be improved as the density of a point cloud increases. In this embodiment, the three-dimensional data encoding device collectively encodes point cloud data of successive frames by combining the point cloud data of the successive frames. In this process, the three-dimensional data encoding device generates encoded data additionally including information for identifying a frame to which each leaf node included in the combined point cloud data belongs. 
     Here, point cloud data of successive frames are likely to be similar to each other. That is, occupancy codes for successive frames are likely to have a common higher-level part. In other words, occupancy codes for successive frames can share a higher-level part if the successive frames are collectively encoded. 
     By encoding an index of a frame, a determination of to which frame a point cloud belongs is made at a leaf node. 
       FIG. 35  is a diagram showing a concept of generation of a tree structure and an occupancy code from point cloud data of N point cloud compression (PCC) frames. In this drawing, a point in a hollow arrow indicates a point that belongs to a PCC frame. First, a frame index for identifying a frame is assigned to a point that belongs to each PCC frame. 
     Points belonging to the N frames are then converted into a tree structure, and an occupancy code is generated. Specifically, to which leaf node in the tree structure each point belongs is determined. In the drawing, the tree structure represents a set of nodes. The determination of to which node a point belongs is made beginning with the highest-level node. The determination result for each node is encoded into an occupancy code. The occupancy code is common among the N frames. 
     A node can include points belonging to different frames to which different frame indices are assigned. When the octree has a low resolution, a node can include points belonging to the same frame to which the same frame index is assigned. 
     In a lowest-level node (leaf node), points belonging to a plurality of frames can be mixed (duplicated). 
     As for the tree structure and the occupancy code, a higher-level part of the tree structure and occupancy codes in the higher-level part can be a common component for all the frames, and a lower-level part of the tree structure and occupancy codes in the lower-level part can be an individual component for each frame or can be partially a common component and partially an individual component. 
     For example, at a lowest-level node, such as a leaf node, zero or more points having a frame index are generated, and information indicating the number of points and information on the frame index of each point are generated. These pieces of information can be regarded as individual information for frames. 
       FIG. 36  is a diagram showing an example of frame combining. As shown in part (a) of  FIG. 36 , if a tree structure is generated by combining a plurality of frames, the density of the points of the frames included in the same node increases. In addition, if the tree structure is shared, the data amount of the occupancy codes can be reduced. In this way, the coding efficiency can be improved. 
     As shown in part (b) of  FIG. 36 , as the individual components of the occupancy codes in the tree structure become denser, the effectiveness of the arithmetic encoding increases, so that the coding efficiency can be improved. 
     In the following, combining of a plurality of PCC frames associated with different times will be described as an example. However, the description holds true for a case where there is not a plurality of frames, that is, frame combining is not performed (N=1). Furthermore, the plurality of pieces of point cloud data to be combined is not limited to a plurality of frames, that is, a plurality of pieces of point cloud data on the same object associated with different time points. That is, the method described below can be applied to combining of a plurality of pieces of point cloud data associated with different spaces or different times and spaces. The method described below can also be applied to combining of point cloud data or point cloud files of different contents. 
       FIG. 37  is a diagram showing an example of combining of a plurality of PCC frames associated with different times.  FIG. 37  shows an example in which an automobile obtains point cloud data with a sensor such as LiDAR while the automobile is moving. A dotted line indicates an effective range of the sensor in each frame, that is, a range of point cloud data. As the effective range of the sensor increases, the range of the point cloud data also increases. 
     The method of combining and encoding point cloud data is effective for point cloud data, such as point cloud data described below. For example, in the example shown in  FIG. 37 , the automobile is moving, and a frame is identified by 360° scanning of the periphery of the automobile. That is, frame 2, the frame following frame 1, corresponds to another 360° scanning performed when the vehicle has moved in an X direction. 
     In this case, frame 1 and frame 2 partially overlap with each other and therefore can include common point cloud data. Therefore, if frame 1 and frame 2 are combined and encoded, the coding efficiency can be improved. Note that more frames may be able to be combined. However, as the number of frames combined increases, the number of bits required for encoding of the frame indices assigned to the lead nodes increases. 
     Alternatively, point cloud data may be obtained by sensors at different positions. In that case, each piece of point cloud data obtained at a different position can be used as a frame. That is, the plurality of frames may be point cloud data obtained by a single sensor or point cloud data obtained by a plurality of sensors. Furthermore, objects may be partially or totally the same or may be different in the plurality of frames. 
     Next, a flow of a three-dimensional data encoding process according to this embodiment will be described.  FIG. 38  is a flowchart of the three-dimensional data encoding process. According to the combined frame count N, which is the number of frames to be combined, the three-dimensional data encoding device reads point cloud data of all the N frames. 
     First, the three-dimensional data encoding device determines the combined frame count N (S 5401 ). For example, the combined frame count Nis specified by a user. 
     The three-dimensional data encoding device then obtains point cloud data (S 5402 ). The three-dimensional data encoding device then records frame indices of the obtained point cloud data (S 5403 ). 
     When the N frames have not been processed (if No in S 5404 ), the three-dimensional data encoding device specifies next point cloud data (S 5405 ), and performs step S 5402  and the following processing on the specified point cloud data. 
     On the other hand, when the N frames have been processed (if Yes in S 5404 ), the three-dimensional data encoding device combines the N frames and encodes the resulting, combined frame (S 5406 ). 
       FIG. 39  is a flowchart of the encoding process (S 5406 ). First, the three-dimensional data encoding device generates common information that is common to the N frames (S 5411 ). For example, the common information includes an occupancy code and information indicating the combined frame count N. 
     The three-dimensional data encoding device then generates individual information that is individual information on each frame (S 5412 ). For example, the individual information includes the number of points included in a leaf node, and the frame indices of the points included in the leaf node. 
     The three-dimensional data encoding device then combines the common information and the individual information, and generates encoded data by encoding the combined information (S 5413 ). The three-dimensional data encoding device then generates additional information (metadata) concerning the frame combining, and encodes the generated additional information (S 5414 ). 
     Next, a flow of a three-dimensional data decoding process according to this embodiment will be described.  FIG. 40  is a flowchart of the three-dimensional data decoding process. 
     First, the three-dimensional data decoding device obtains the combined frame count N from a bitstream (S 5421 ). The three-dimensional data decoding device then obtains encoded data from the bitstream (S 5422 ). The three-dimensional data decoding device decodes the encoded data to obtain point cloud data and frame indices (S 5423 ). Finally, the three-dimensional data decoding device divides the decoded point cloud data using the frame indices (S 5424 ). 
       FIG. 41  is a flowchart of the decoding and dividing process (S 5423  and S 5424 ). First, the three-dimensional data decoding device decodes the encoded data (bitstream) into common information and individual information (that is, obtains common information and individual information from the encoded data) (S 5431 ). 
     The three-dimensional data decoding device then determines whether to decode a single frame or to decode a plurality of frames (S 432 ). For example, whether to decode a single frame or to decode a plurality of frames may be externally specified. Here, the plurality of frames may be all the frames combined or some of the frames combined. For example, the three-dimensional data decoding device may determine to decode a particular frame required by an application, and not to decode the frames that are not required. Alternatively, when real-time decoding is required, the three-dimensional data decoding device may determine to decode a single frame of the plurality of frames combined. 
     When decoding a single frame (if Yes in S 5432 ), the three-dimensional data decoding device extracts individual information associated with the frame index of the specified single frame from the decoded individual information, and decodes the extracted individual information to reproduce point cloud data of the specified frame corresponding to the frame index (S 5433 ). 
     On the other hand, when decoding a plurality of frames (if No in S 5432 ), the three-dimensional data decoding device extracts individual information associated with the frame indices of the specified plurality of frames (or all the frames), and decodes the extracted individual information to reproduce point cloud data of the specified plurality of frames (S 5434 ). The three-dimensional data decoding device then divides the decoded point cloud data (individual information) based on the frame indices (S 5435 ). That is, the three-dimensional data decoding device divides the decoded point cloud data into the plurality of frames. 
     Note that the three-dimensional data decoding device may collectively decode data of all the frames combined and then divide the decoded data into frames, or collectively decode data of an arbitrary part of the frames combined and divide the decoded data into frames. Furthermore, the three-dimensional data decoding device may separately decode data of a previously determined unit frame composed of a plurality of frames. 
     In the following, a configuration of the three-dimensional data encoding device according to this embodiment will be described.  FIG. 42  is a block diagram showing a configuration of encoder  5410  included in the three-dimensional data encoding device according to this embodiment. Encoder  5410  generates encoded data (encoded stream) by encoding point cloud data (point cloud). Encoder  5410  includes divider  5411 , a plurality of geometry information encoders  5412 , a plurality of attribute information encoders  5413 , additional information encoder  5414 , and multiplexer  5415 . 
     Divider  5411  generates a plurality of pieces of divided data of a plurality of frames by dividing point cloud data of a plurality of frames. Specifically, divider  5411  generates a plurality of pieces of divided data by dividing a space of point cloud data of each frame into a plurality of subspaces. Here, a subspace is a tile, a slice, or a combination of a tile and a slice. More specifically, point cloud data includes geometry information, attribute information (color, reflectance or the like), and additional information. A frame number is also input to divider  5411 . Divider  5411  divides geometry information of each frame into a plurality of pieces of divided geometry information, and divides attribute information of each frame into a plurality of pieces of divided attribute information. Divider  5411  also generates additional information concerning the division. 
     For example, divider  5411  divides a point cloud into tiles. Divider  5411  then divides the resulting tiles into slices. 
     The plurality of geometry information encoders  5412  generates a plurality of pieces of encoded geometry information by encoding a plurality of pieces of divided geometry information. For example, geometry information encoder  5412  encodes divided geometry information using an N-ary tree, such as an octree. Specifically, in the case of an octree, a target space is divided into eight nodes (subspaces), and 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 a predetermined node becomes equal to or less than a threshold. For example, the plurality of geometry information encoders  5412  process the plurality of pieces of divided geometry information in parallel. 
     Attribute information encoder  4632  generates encoded attribute information, 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 target point (target 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 target 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 geometry information or 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. 
     Attribute information encoders  5413  generate pieces of encoded attribute information by encoding pieces of divided attribute information. For example, attribute information encoders  5413  process pieces of divided geometry information in parallel. 
     Additional information encoder  5414  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  5411 . 
     Multiplexer  5415  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. 
       FIG. 43  is a block diagram showing divider  5411 . Divider  5411  includes tile divider  5421  and slice divider  5422 . 
     Tile divider  5421  generates a plurality of pieces of tile geometry information by dividing geometry information (position (geometry)) of each of a plurality of frames into tiles. Tile divider  5421  also generates a plurality of pieces of tile attribute information by dividing attribute information (attribute) of a plurality of frames into tiles. Tile divider  5421  outputs tile additional information (tile metadata) including information concerning the tile division and information generated in the tile division. 
     Slice divider  5422  generates a plurality of pieces of divided geometry information (a plurality of pieces of slice geometry information) by dividing a plurality of pieces of tile geometry information into slices. Slice divider  5422  also generates a plurality of pieces of divided attribute information (a plurality of pieces of slice attribute information) by dividing a plurality of pieces of tile attribute information into slices. Slice divider  5422  outputs slice additional information (slice metadata) including information concerning the slice division and information generated in the slice division. 
     In the dividing process, divider  5411  uses a frame number (frame index) to indicate coordinates of an origin, attribute information or the like. 
       FIG. 44  is a block diagram showing geometry information encoder  5412 . Geometry information encoder  5412  includes frame index generator  5431  and entropy encoder  5432 . 
     Frame index generator  5431  determines a value of a frame index based on a frame number, and adds the determined frame index to geometry information. Entropy encoder  5432  generates encoded geometry information by entropy-encoding divided geometry information with a frame index added thereto. 
       FIG. 45  is a block diagram showing attribute information encoder  5413 . Attribute information encoder  5413  includes frame index generator  5441  and entropy encoder  5442 . 
     Frame index generator  5441  determines a value of a frame index based on a frame number, and adds the determined frame index to attribute information. Entropy encoder  5442  generates encoded attribute information by entropy-encoding divided attribute information with a frame index added thereto. 
     The following describes procedures of a point cloud data encoding process and a point cloud data decoding process according to the present embodiment.  FIG. 46  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 5441 ). 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. 
     When tile division is performed (YES in S 5442 ), 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 5443 ). Besides, the three-dimensional data encoding device generates tile additional information regarding the tile division. 
     When slice division is performed (YES in S 5444 ), 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 5445 ). Also, the three-dimensional data encoding device generates geometry slice additional information and attribute slice additional information regarding the slice division. 
     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 as frame indexes (S 5446 ). 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 5447 ). Additionally, the three-dimensional data encoding device transmits the generated encoded data. 
       FIG. 47  is a flowchart of the encoding process (S 5446 ). First, the three-dimensional data encoding device encodes divided geometry information (S 5451 ). The three-dimensional data encoding device then encodes a frame index for the divided geometry information (S 5452 ). 
     When there is divided attribute information (if Yes in S 5453 ), the three-dimensional data encoding device encodes the divided attribute information (S 5454 ), and encodes a frame index for the divided attribute information (S 5455 ). On the other hand, when there is no divided attribute information (if No in S 5453 ), the three-dimensional data encoding device does not perform encoding of any divided attribute information and encoding of a frame index for any divided attribute information. Note that the frame index may be stored in any one or both of the divided geometry information and the divided attribute information. 
     Note that the three-dimensional data encoding device may encode attribute information using a frame index or without using a frame index. That is, the three-dimensional data encoding device may identify a frame to which each point belongs using a frame index and perform encoding on a frame basis, or may encode the points belonging to all the frames without identifying the frames. 
     In the following, a configuration of the three-dimensional data decoding device according to this embodiment will be described.  FIG. 48  is a block diagram showing a configuration of decoder  5450 . Decoder  5450  reproduces point cloud data by decoding encoded data (encoded stream) generated by encoding the point cloud data. Decoder  5450  includes demultiplexer  5451 , a plurality of geometry information decoders  5452 , a plurality of attribute information decoders  5453 , additional information decoder  5454 , and combiner  5455 . 
     Demultiplexer  5451  generates a plurality of pieces of encoded geometry information, a plurality of pieces of encoded attribute information, and encoded additional information by demultiplexing encoded data (encoded stream). 
     The plurality of geometry information decoders  5452  generate a plurality of pieces of divided geometry information by decoding a plurality of pieces of encoded geometry information. For example, the plurality of geometry information decoders  5452  process a plurality of pieces of encoded geometry information in parallel. 
     The plurality of attribute information decoders  5453  generate a plurality of pieces of divided attribute information by decoding a plurality of pieces of encoded attribute information. For example, the plurality of attribute information decoders  5453  process a plurality of pieces of encoded attribute information in parallel. 
     The plurality of additional information decoders  5454  generate additional information by decoding encoded additional information. 
     Combiner  5455  generates geometry information by combining a plurality of pieces of divided geometry information using additional information. Combiner  5455  generates attribute information by combining a plurality of pieces of divided attribute information using additional information. Combiner  5455  also divides geometry information and attribute information into geometry information of a plurality of frames and attribute information of a plurality of frames using frame indices. 
       FIG. 49  is a block diagram showing geometry information decoder  5452 . Geometry information decoder  5452  includes entropy decoder  5461  and frame index obtainer  5462 . Entropy decoder  5461  generates divided geometry information by entropy-decoding encoded geometry information. Frame index obtainer  5462  obtains a frame index from divided geometry information. 
       FIG. 50  is a block diagram showing attribute information decoder  5453 . Attribute information decoder  5453  includes entropy decoder  5471  and frame index obtainer  5472 . Entropy decoder  5471  generates divided attribute information by entropy-decoding encoded attribute information. Frame index obtainer  5472  obtains a frame index from divided attribute information. 
       FIG. 51  is a diagram showing a configuration of combiner  5455 . Combiner  5455  generates geometry information by combining a plurality of pieces of divided geometry information. Combiner  5455  generates attribute information by combining a plurality of pieces of divided attribute information. Combiner  5455  also divides geometry information and attribute information into geometry information of a plurality of frames and attribute information of a plurality of frames using frame indices. 
       FIG. 52  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 (slice additional information and tile additional information) regarding a division method included in encoded data (an encoded stream) (S 5461 ). 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 5462 ). 
     When the additional information indicates that slice division has been performed (YES in S 5463 ), 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, based on the slice additional information (S 5464 ). Here, the pieces of divided geometry information, the pieces of divided attribute information, the pieces of tile geometry information, and the pieces of tile attribute information include frame indexes. 
     When the additional information indicates that tile division has been performed (YES in S 5465 ), 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), based on tile additional information (S 5466 ). Here, the pieces of tile geometry information, the pieces of tile attribute information, the geometry information, and the attribute information include frame indexes. 
       FIG. 53  is a flowchart of the decoding process (S 5464  and S 5466 ). First, the three-dimensional data decoding device decodes divided geometry information (slice geometry information) (S 5471 ). The three-dimensional data decoding device then decodes a frame index for the divided geometry information (S 5472 ). 
     When there is divided attribute information (if Yes in S 5473 ), the three-dimensional data decoding device decodes the divided attribute information (S 5474 ), and decodes a frame index for the divided attribute information (S 5475 ). On the other hand, when there is no divided attribute information (if No in S 5473 ), the three-dimensional data decoding device does not perform decoding of any divided attribute information and decoding of a frame index for any divided attribute information. 
     Note that the three-dimensional data decoding device may decode attribute information using a frame index or without using a frame index. 
     In the following, a unit of encoding in frame combining will be described.  FIG. 54  is a diagram showing an example of a pattern of frame combining. The example in this drawing is an example in which PCC frames are a time series, and data is generated and encoded in real time. 
     Part (a) of  FIG. 54  shows a case where four frames are always combined. The three-dimensional data encoding device waits until data of four frames is generated, and then generates encoded data. 
     Part (b) of  FIG. 54  shows a case where the number of frames to be combined adaptively varies. For example, the three-dimensional data encoding device changes the number of frames to be combined in order to adjust the code amount of encoded data in a rate control. 
     Note that, if frame combining can be useless, the three-dimensional data encoding device may not combine frames. The three-dimensional data encoding device may also determine whether to combine frames or not. 
     Part (c) of  FIG. 54  shows an example of a case where a plurality of frames combined partially overlap with a plurality of frames to be combined next. This example is useful when real-time processing or low delay is required, such as when each piece of data is transmitted as soon as the data is encoded. 
       FIG. 55  is a diagram showing a configuration example of PCC frames. The three-dimensional data encoding device may configure frames to be combined in such a manner that the frames include at least a data unit that can be singly decoded. For example, when all the PCC frames are intra-encoded, and the PCC frames can be singly decoded as shown in part (a) of  FIG. 55 , any of the patterns described above can be applied. 
     When a random access unit, such as group of frames (GOF), is set, such as when inter-prediction is applied, for example, as shown in part (b) of  FIG. 55 , the three-dimensional data encoding device may combine data based on the GOF unit as a minimum unit. 
     Note that the three-dimensional data encoding device may collectively encode common information and individual information or separately encode common information and individual information. Furthermore, the three-dimensional data encoding device may use a common data structure or different data structures for common information and individual information. 
     The three-dimensional data encoding device may compare occupancy codes for a plurality of frames after an occupancy code is generated for each frame. For example, the three-dimensional data encoding device may determine whether there is a large common part between occupancy codes for a plurality of frames based on a predetermined criterion, and generate common information if there is a large common part. Alternatively, based on whether there is a large common part between occupancy codes, the three-dimensional data encoding device may determine whether to combine frames, which frames are to be combined, or the number of frames to be combined. 
     Next, a configuration of encoded geometry information will be described.  FIG. 56  is a diagram showing a configuration of encoded geometry information. Encoded geometry information includes a header and a payload. 
       FIG. 57  is a diagram showing a syntax example of a header (Geometry_header) of encoded geometry information. The header of encoded geometry information includes a GPS index (gps_idx), offset information (offset), other information (other_geometry_information), a frame combining flag (combine_frame_flag), and a combined frame count (number_of_combine_frame). 
     The GPS index indicates an identifier (ID) of a parameter set (GPS) associated with encoded geometry information. GPS is a parameter set of encoded geometry information of one frame or a plurality of frames. Note that, when there is a parameter set for each frame, the header may indicate identifiers of a plurality of parameter sets. 
     The offset information indicates an offset position for obtaining combined data. The other information indicates other information concerning geometry information (a difference value of a quantization parameter (QPdelta), for example). The frame combining flag indicates whether frame combining has been performed for encoded data or not. The combined frame count indicates the number of frames combined. 
     Note that part or all of the information described above may be described in SPS or GPS. Note that SPS means a parameter set based on a sequence (a plurality of frames) as a unit, and is a parameter set commonly used for encoded geometry information and encoded attribute information. 
       FIG. 58  is a diagram showing a syntax example of a payload (Geometry_data) of encoded geometry information. The payload of encoded geometry information includes common information and leaf node information. 
     Common information is data of one or more frames combined, and includes an occupancy code (occupancy_Code) or the like. 
     Leaf node information (combine_information) is information on each leaf node. Leaf node information may be indicated for each frame as a loop of the number of frames. 
     As a method of indicating a frame index of a point included in a lead node, any of method 1 and method 2 can be used.  FIG. 59  is a diagram showing an example of the leaf node information in the case of method 1. The leaf node information shown in  FIG. 59  includes the three-dimensional point count (NumberOfPoints) that indicates the number of points included in a node, and a frame index (FrameIndex) for each point. 
       FIG. 60  is a diagram showing an example of the leaf node information in the case of method 2. In the example shown in  FIG. 60 , the leaf node information includes bit map information (bitmapIsFramePointsFlag) that indicates frame indices of a plurality of points with a bit map.  FIG. 61  is a diagram showing an example of the bit map information. In this example, the bit map indicates that the lead node includes three-dimensional points of frame indices 1, 3, and 5. 
     Note that, when the quantization resolution is low, there may be duplicated points in the same frame. In that case, the three-dimensional point count (NumberOfPoints) may be shared, and the number of three-dimensional points in each frame and the total number of three-dimensional points in a plurality of frames may be indicated. 
     When lossy compression is used, the three-dimensional data encoding device may delete a duplicated point to reduce the information amount. The three-dimensional data encoding device may delete a duplicated point before frame combining or after frame combining. 
     Next, a configuration of encoded attribute information will be described.  FIG. 62  is a diagram showing a configuration of encoded attribute information. The encoded attribute information includes a header and a payload. 
       FIG. 63  is a diagram showing a syntax example of a header (Attribute_header) of encoded attribute information. The header of the encoded attribute information includes an APS index (aps_idx), offset information (offset), other information (other_attribute_information), a frame combining flag (combine_frame_flag), and a combined frame count (number_of_combine_frame). 
     The APS index indicates an identifier (ID) of a parameter set (APS) associated with encoded attribute information. APS is a parameter set of encoded attribute information of one frame or a plurality of frames. Note that, when there is a parameter set for each frame, the header may indicate identifiers of a plurality of parameter sets. 
     The offset information indicates an offset position for obtaining combined data. The other information indicates other information concerning attribute information (a difference value of a quantization parameter (QPdelta), for example). The frame combining flag indicates whether frame combining has been performed for encoded data or not. The combined frame count indicates the number of frames combined. 
     Note that all or part of the information described above may be described in SPS or APS. 
       FIG. 64  is a diagram showing a syntax example of a payload (Attribute_data) of encoded attribute information. The payload of encoded attribute information includes leaf node information (combine_information). For example, a configuration of the leaf node information is the same as that of the leaf node information included in the payload of the encoded geometry information. That is, the leaf node information (frame index) may be included in the attribute information. 
     The leaf node information may be stored in one of the encoded geometry information and the encoded attribute information and not included in the other. In that case, the leaf node information (frame index) stored in one of the encoded geometry information and the encoded attribute information is referred to when decoding the other information. Furthermore, information indicating a reference destination may be included in the encoded geometry information or the encoded attribute information. 
     Next, an example of the order of transmission of encoded data and an example of the order of decoding of encoded data will be described.  FIG. 65  is a diagram showing a configuration of encoded data. The encoded data includes a header and a payload. 
       FIGS. 66 to 68  are diagrams showing an order of data transmission and a data reference relationship. In these drawings, G(1) or the like denotes encoded geometry information, GPS(1) or the like denotes a parameter set for encoded geometry information, and SPS denotes a parameter set for a sequence (a plurality of frames). A numeral in parentheses indicates a value of a frame index. Note that the three-dimensional data encoding device may transmit data in an order of decoding. 
       FIG. 66  is a diagram showing an example of the order of transmission in a case where frame combining is not performed.  FIG. 67  is a diagram showing an example of a case where frame combining is performed and metadata (a parameter set) is added to each PCC frame.  FIG. 68  is a diagram showing an example of a case where frame combining is performed and metadata (a parameter set) is added on a basis of frames combined. 
     In the header of data of frames combined, an identifier of metadata of a reference destination is stored, in order to obtain metadata of the frames. As shown in  FIG. 68 , metadata of a plurality of frames can be brought together. Any parameters common to the plurality of frames combined can be brought together as one parameter. Parameters that are not common to frames indicate values for respective frames. 
     Information on each frame (a parameter that is not common to frames) is a timestamp that indicates a time point of generation of frame data, a time point of encoding of frame data, or a time point of decoding of frame data, for example. Information on each frame may include information from a sensor that has obtained the frame data (such as sensor speed, sensor acceleration, sensor position information, sensor orientation, or other sensor information). 
       FIG. 69  is a diagram showing an example in which part of the frames is decoded in the example shown in  FIG. 67 . As shown in  FIG. 69 , if there is no dependency between frames in the data of the frames combined, the three-dimensional data decoding device can separately decode each piece of data. 
     When point cloud data has attribute information, the three-dimensional data encoding device can combine attribute information of frames. Attribute information is encoded and decoded by referring to geometry information. The geometry information referred to may be geometry information before frame combining or geometry information after frame combining. The combined frame count for geometry information and the combined frame count for attribute information may be common (the same) or independent (different). 
       FIGS. 70 to 73  are diagrams showing an order of data transmission and a data reference relationship.  FIGS. 70 and 71  show an example in which geometry information of four frames and attribute information of four frames are combined. In  FIG. 70 , metadata (a parameter set) is added to each PCC frame. In  FIG. 71 , metadata (a parameter set) is added on a basis of frames combined. In these drawings, A(1) or the like denotes encoded attribute information, APS(1) or the like denotes a parameter set for encoded attribute information, and APS(1) or the like denotes a parameter set for encoded attribute information. A numeral in parentheses indicates a value of a frame index. 
       FIG. 72  shows an example in which geometry information of four frames are combined, and attribute information are not combined. As shown in  FIG. 72 , geometry information of frames may be combined, and attribute information of frames may not be combined. 
       FIG. 73  shows an example in which frame combining and tile division are combined. When tile division is performed as shown in  FIG. 73 , the header of each piece of tile geometry information includes information such as a GPS index (gps_idx) and a combined frame count (number_of_combine_frame). The header of each piece of tile geometry information also includes a tile index (tile_idx) for identifying a tile. 
     As described above, the three-dimensional data encoding device according to this embodiment performs the process shown in  FIG. 74 . First, the three-dimensional data encoding device combines first point cloud data and second point cloud data to generate third point cloud data (S 5481 ). The three-dimensional data encoding device then encodes the third point cloud data to generate encoded data (S 5482 ). The encoded data includes identification information (a frame index, for example) that indicates whether each of the plurality of three-dimensional points included in the third point cloud data belongs to the first point cloud data or the second point cloud data. 
     With such a configuration, the three-dimensional data encoding device collectively encodes a plurality of pieces of point cloud data, so that the coding efficiency can be improved. 
     For example, the first point cloud data and the second point cloud data are point cloud data (PCC frames, for example) associated with different time points. For example, the first point cloud data and the second point cloud data are point cloud data (PCC frames, for example) on the same object associated with different time points. 
     The encoded data includes geometry information and attribute information on each of the plurality of three-dimensional points included in the third point cloud data, and the identification information is included in the attribute information. 
     For example, the encoded data includes geometry information (an occupancy code, for example) that represents the position of each of the plurality of three-dimensional points included in the third point cloud data using an N-ary tree (N represents an integer equal to or greater than 2). 
     For example, the three-dimensional data encoding device includes a processor and memory, and the processor performs the process described above using the memory. 
     The three-dimensional data decoding device according to this embodiment performs the process shown in  FIG. 75 . First, the three-dimensional data decoding device decodes encoded data to obtain third point cloud data generated by combining first point cloud data and second point cloud data, and identification information that indicates whether each of a plurality of three-dimensional points included in the third point cloud data belongs to the first point cloud data or the second point cloud data (S 5491 ). The three-dimensional data decoding device then separates the third point cloud data into the first point cloud data and the second point cloud data using the identification information (S 5492 ). 
     With such a configuration, the three-dimensional data decoding device can decode data encoded with an improved coding efficiency by collectively encoding a plurality of pieces of point cloud data. 
     For example, the first point cloud data and the second point cloud data are point cloud data (PCC frames, for example) associated with different time points. For example, the first point cloud data and the second point cloud data are point cloud data (PCC frames, for example) on the same object associated with different time points. 
     The encoded data includes geometry information and attribute information on each of the plurality of three-dimensional points included in the third point cloud data, and the identification information is included in the attribute information. 
     For example, the encoded data includes geometry information (an occupancy code, for example) that represents the position of each of the plurality of three-dimensional points included in the third point cloud data using an N-ary tree (N represents an integer equal to or greater than 2). 
     For example, the three-dimensional data decoding device includes a processor and memory, and the processor performs the process described above 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.