Patent Publication Number: US-2022222863-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/JP2020/037595 filed on Oct. 2, 2020, claiming the benefit of priority of U.S. Provisional Patent Application No. 62/910,600 filed on Oct. 4, 2019, 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 Patent Literature (PTL) 1). 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: International Publication WO 2014/020663 
       
    
     SUMMARY 
     There has been a demand for appropriately decoding point cloud data in the encoding and decoding of 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 appropriately decoding point cloud data. 
     A three-dimensional data encoding method according to an aspect of the present disclosure includes: determining a first maximum bit count for encoded data obtained after encoding at least one of (i) a divisional data unit obtained when point cloud data indicating a three-dimensional point cloud is divided or (ii) a point cloud data unit of the point cloud data before the dividing; and generating a bitstream by encoding (i) items of divisional data obtained by dividing the point cloud data or (ii) the point cloud data before the dividing, to satisfy the first maximum bit count determined, wherein the bitstream includes first bit count information indicating the first maximum bit count. 
     A three-dimensional data decoding method according to an aspect of the present disclosure includes: obtaining a bitstream including encoded data and first bit count information, the encoded data being data obtained after encoding at least one of (i) a divisional data unit obtained when point cloud data indicating a three-dimensional point cloud is divided or (ii) a point cloud data unit of the point cloud data before the dividing, the first bit count information indicating a first maximum bit count for the encoded data; judging whether the bitstream obtained satisfies the first maximum bit count indicated by the first bit count information; and decoding the encoded data when the bitstream is judged to satisfy the first maximum bit count. 
     Note that these general and specific aspects may be implemented as a system, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or as any combination of a system, an integrated circuit, a computer program, and a computer-readable recording medium. 
     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 appropriately decoding point cloud data. 
    
    
     
       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 structures of an encoder and a multiplexer according to Embodiment 2; 
         FIG. 15  is a diagram illustrating a structure example of encoded data according to Embodiment 2; 
         FIG. 16  is a diagram illustrating a structure example of encoded data and a NAL unit according to Embodiment 2; 
         FIG. 17  is a diagram illustrating a semantics example of pcc_nal_unit_type according to Embodiment 2; 
         FIG. 18  is a diagram illustrating an example of a transmitting order of NAL units according to Embodiment 2; 
         FIG. 19  is a block diagram of a first encoder according to Embodiment 3; 
         FIG. 20  is a block diagram of a first decoder according to Embodiment 3; 
         FIG. 21  is a block diagram of a divider according to Embodiment 3; 
         FIG. 22  is a diagram illustrating an example of dividing slices and tiles according to Embodiment 3; 
         FIG. 23  is a diagram illustrating dividing pattern examples of slices and tiles according to Embodiment 3; 
         FIG. 24  is a diagram illustrating an example of dependency according to Embodiment 3; 
         FIG. 25  is a diagram illustrating a data decoding order according to Embodiment 3; 
         FIG. 26  is a flowchart of encoding processing according to Embodiment 3; 
         FIG. 27  is a block diagram of a combiner according to Embodiment 3; 
         FIG. 28  is a diagram illustrating a structure example of encoded data and a NAL unit according to Embodiment 3; 
         FIG. 29  is a flowchart of encoding processing according to Embodiment 3; 
         FIG. 30  is a flowchart of decoding processing according to Embodiment 3; 
         FIG. 31  is a diagram illustrating an example of syntax of tile additional information according to Embodiment 4; 
         FIG. 32  is a block diagram of an encoding and decoding system according to Embodiment 4; 
         FIG. 33  is a diagram illustrating an example of syntax of slice additional information according to Embodiment 4; 
         FIG. 34  is a flowchart of an encoding process according to Embodiment 4; 
         FIG. 35  is a flowchart of a decoding process according to Embodiment 4; 
         FIG. 36  is a diagram showing an example of a tree structure according to Embodiment 5; 
         FIG. 37  is a diagram showing an example of a data structure of encoded data on an octree structure according to Embodiment 5; 
         FIG. 38  is a diagram showing a syntax example of a payload according to Embodiment 5; 
         FIG. 39  is a flowchart of a decoding process according to Embodiment 5; 
         FIG. 40  is a diagram showing a relationship between levels and data decoded according to Embodiment 5; 
         FIG. 41  is a schematic diagram showing levels according to Embodiment 5; 
         FIG. 42  is a diagram showing a syntax example of a header according to Embodiment 5; 
         FIG. 43  is a diagram showing a syntax example of the payload according to Embodiment 5; 
         FIG. 44  is a diagram showing a configuration of overall encoded data according to Embodiment 5; 
         FIG. 45  is a diagram showing a configuration of the overall encoded data according to Embodiment 5; 
         FIG. 46  is a diagram showing a syntax example of depth information according to Embodiment 5; 
         FIG. 47  is a diagram showing a syntax example of hierarchical structure metadata according to Embodiment 5; 
         FIG. 48  is a diagram showing a syntax example of the header according to Embodiment 5; 
         FIG. 49  is a diagram showing a configuration of the overall encoded data according to Embodiment 5; 
         FIG. 50  is a diagram showing a syntax example of layer information according to Embodiment 5; 
         FIG. 51  is a diagram showing a syntax example of the hierarchical structure metadata according to Embodiment 5; 
         FIG. 52  is a diagram showing a syntax example of a header of the overall encoded data according to Embodiment 5; 
         FIG. 53  is a diagram showing an example configuration of a bitstream according to Embodiment 5; 
         FIG. 54  is a diagram showing a syntax example of the hierarchical structure metadata according to Embodiment 5; 
         FIG. 55  is a diagram showing a reference relationship between geometry information and attribute information according to Embodiment 5; 
         FIG. 56  is a diagram showing a reference relationship between geometry information and attribute information according to Embodiment 5; 
         FIG. 57  is a diagram showing a reference relationship between geometry information and attribute information according to Embodiment 5; 
         FIG. 58  is a diagram showing an example configuration of a bitstream according to Embodiment 5; 
         FIG. 59  is a diagram showing an example configuration of a three-dimensional data encoding device according to Embodiment 5; 
         FIG. 60  is a diagram showing an example configuration of a three-dimensional data decoding device according to Embodiment 5; 
         FIG. 61  is a diagram showing a basic structure of ISOBMFF according to Embodiment 5; 
         FIG. 62  is a diagram showing a protocol stack in a case where a common PCC codec NAL unit is stored in ISOBMFF according to Embodiment 5; 
         FIG. 63  is a diagram showing a process of transforming a bitstream into a file format according to Embodiment 5; 
         FIG. 64  is a flowchart of a format transforming process according to Embodiment 5; 
         FIG. 65  is a flowchart of a decoding process according to Embodiment 5; 
         FIG. 66  is a diagram showing a process of transforming a bitstream into a file format according to Embodiment 5; 
         FIG. 67  is a diagram showing a syntax example of hierarchical structure metadata according to Embodiment 5; 
         FIG. 68  is a diagram schematically shows a division process according to Embodiment 5; 
         FIG. 69  is a flowchart of a transform process using layer information according to Embodiment 5; 
         FIG. 70  is a flowchart of a transform process that uses no layer information according to Embodiment 5; 
         FIG. 71  is a flowchart of a decoding process for sample data of layer data according to Embodiment 5; 
         FIG. 72  is a diagram showing an example configuration of overall encoded data according to Embodiment 5; 
         FIG. 73  is a diagram showing an example configuration of the overall encoded data according to Embodiment 5; 
         FIG. 74  is a diagram showing a process of transforming a bitstream into a file format according to Embodiment 5; 
         FIG. 75  is a flowchart of a format transforming process according to Embodiment 5; 
         FIG. 76  is a flowchart of a decoding process according to Embodiment 5; 
         FIG. 77  is a diagram showing a syntax example of depth information according to Embodiment 5; 
         FIG. 78  is a diagram showing a syntax example of a sample size box according to Embodiment 5; 
         FIG. 79  is a diagram showing a syntax example of layer information according to Embodiment 5; 
         FIG. 80  is a diagram showing a syntax example of PCCLayerStructureBox according to Embodiment 5; 
         FIG. 81  is a diagram schematically showing an extraction operation according to Embodiment 5; 
         FIG. 82  is a diagram showing an example of a file format according to Embodiment 5; 
         FIG. 83  is a diagram showing an example of an extracted bitstream according to Embodiment 5; 
         FIG. 84  is a diagram showing an example of an extracted bitstream according to Embodiment 5; 
         FIG. 85  is a diagram showing an example of an extracted bitstream according to Embodiment 5; 
         FIG. 86  is a diagram showing an example of a direct mode according to Embodiment 5; 
         FIG. 87  is a flowchart of a three-dimensional data encoding process according to Embodiment 5; 
         FIG. 88  is a flowchart of a three-dimensional data decoding process according to Embodiment 5; 
         FIG. 89  is a block diagram illustrating an example of a configuration of a three-dimensional data encoding device according to Embodiment 6; 
         FIG. 90  is a flowchart illustrating a first example of a three-dimensional data encoding method according to Embodiment 6; 
         FIG. 91  is a block diagram illustrating an example of a configuration of a three-dimensional data decoding device according to Embodiment 6; 
         FIG. 92  is a flowchart illustrating an example of a three-dimensional data decoding method according to Embodiment 6; 
         FIG. 93  is a flowchart illustrating a second example of the three-dimensional data encoding method according to Embodiment 6; 
         FIG. 94  is a diagram illustrating an example of a bounding box according to Embodiment 6; 
         FIG. 95  is a flowchart illustrating another example of the three-dimensional data decoding method according to Embodiment 6; 
         FIG. 96  is a flowchart illustrating a third example of the three-dimensional data encoding method according to Embodiment 6; 
         FIG. 97  illustrates an example of a processing of reducing a bit count according to Embodiment 6; 
         FIG. 98  illustrates another example of the processing of reducing a bit count according to Embodiment 6; 
         FIG. 99  is a flowchart illustrating a fourth example of the three-dimensional data encoding method according to Embodiment 6; 
         FIG. 100  illustrates an example of a processing of increasing a bit count according to Embodiment 6; 
         FIG. 101  illustrates another example of the processing of increasing a bit count according to Embodiment 6; 
         FIG. 102  is a flowchart illustrating a fifth example of the three-dimensional data encoding method according to Embodiment 6; 
         FIG. 103  is a diagram illustrating an example of a combination of conformances according to Embodiment 6; 
         FIG. 104  is a flowchart illustrating a sixth example of the three-dimensional data encoding method according to Embodiment 6; 
         FIG. 105  is a diagram illustrating another example of the combination of conformances according to Embodiment 6; 
         FIG. 106  is a diagram illustrating another example of the combination of conformances according to Embodiment 6; 
         FIG. 107  is a diagram illustrating an example (example 1) of a sequence parameter set (SPS) according to Embodiment 6; 
         FIG. 108  is a diagram illustrating an example (example 2) of the SPS according to Embodiment 6; 
         FIG. 109  is a diagram illustrating an example (example 3) of a geometry parameter set (GPS) according to Embodiment 6; 
         FIG. 110  is a diagram illustrating a configuration of a bitstream according to Embodiment 6; 
         FIG. 111  is a diagram for describing an example in which conformances are changed according to the position of a three-dimensional point cloud according to Embodiment 6; 
         FIG. 112  is a flowchart illustrating another example of a three-dimensional data encoding process according to Embodiment 6; 
         FIG. 113  is a flowchart illustrating another example of a three-dimensional data encoding process according to Embodiment 6; 
         FIG. 114  is a block diagram of a three-dimensional data creation device according to Embodiment 7; 
         FIG. 115  is a flowchart of a three-dimensional data creation method according to Embodiment 7; 
         FIG. 116  is a diagram showing a structure of a system according to Embodiment 7; 
         FIG. 117  is a block diagram of a client device according to Embodiment 7; 
         FIG. 118  is a block diagram of a server according to Embodiment 7; 
         FIG. 119  is a flowchart of a three-dimensional data creation process performed by the client device according to Embodiment 7; 
         FIG. 120  is a flowchart of a sensor information transmission process performed by the client device according to Embodiment 7; 
         FIG. 121  is a flowchart of a three-dimensional data creation process performed by the server according to Embodiment 7; 
         FIG. 122  is a flowchart of a three-dimensional map transmission process performed by the server according to Embodiment 7; 
         FIG. 123  is a diagram showing a structure of a variation of the system according to Embodiment 7; 
         FIG. 124  is a diagram showing a structure of the server and client devices according to Embodiment 7; 
         FIG. 125  is a diagram illustrating a configuration of a server and a client device according to Embodiment 7; 
         FIG. 126  is a flowchart of a process performed by the client device according to Embodiment 7; 
         FIG. 127  is a diagram illustrating a configuration of a sensor information collection system according to Embodiment 7; 
         FIG. 128  is a diagram illustrating an example of a system according to Embodiment 7; 
         FIG. 129  is a diagram illustrating a variation of the system according to Embodiment 7; 
         FIG. 130  is a flowchart illustrating an example of an application process according to Embodiment 7; 
         FIG. 131  is a diagram illustrating the sensor range of various sensors according to Embodiment 7; 
         FIG. 132  is a diagram illustrating a configuration example of an automated driving system according to Embodiment 7; 
         FIG. 133  is a diagram illustrating a configuration example of a bitstream according to Embodiment 7; 
         FIG. 134  is a flowchart of a point cloud selection process according to Embodiment 7; 
         FIG. 135  is a diagram illustrating a screen example for point cloud selection process according to Embodiment 7; 
         FIG. 136  is a diagram illustrating a screen example of the point cloud selection process according to Embodiment 7; and 
         FIG. 137  is a diagram illustrating a screen example of the point cloud selection process according to Embodiment 7. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     A three-dimensional data encoding method according to an aspect of the present disclosure includes: determining a first maximum bit count for encoded data obtained after encoding at least one of (i) a divisional data unit obtained when point cloud data indicating a three-dimensional point cloud is divided or (ii) a point cloud data unit of the point cloud data before the dividing; and generating a bitstream by encoding (i) items of divisional data obtained by dividing the point cloud data or (ii) the point cloud data before the dividing, to satisfy the first maximum bit count determined. The bitstream includes first bit count information indicating the first maximum bit count. 
     Accordingly, in the three-dimensional data encoding method, a bitstream including first bit count information indicating a first maximum bit count for encoded data is generated, and thus a three-dimensional data decoding device can determine whether the encoded data can be decoded appropriately, without having to analyze the bitstream. For this reason, the processing load of the three-dimensional data decoding device can be reduced. 
     For example, the point cloud data may include geometry information of each of three-dimensional points in the three-dimensional point cloud, the first maximum bit count may relate to a bit count after encoding the geometry information, and in the generating, the bitstream may be generated by encoding the geometry information of (i) the items of divisional data obtained by dividing the point cloud data or (ii) the point cloud data before the dividing, to satisfy the first maximum bit count determined. 
     Accordingly, in the three-dimensional data encoding method, a bitstream including first bit count information indicating a first maximum bit count for encoded geometry information is generated, and thus a three-dimensional data decoding device can determine whether the geometry information can be decoded appropriately, without having to analyze the bitstream. 
     For example, the three-dimensional data encoding method may further include: determining a range of a total number of three-dimensional points included in the at least one of the divisional data unit or the point cloud data unit. Furthermore, in the generating, the bitstream may be generated by encoding (i) the items of divisional data obtained by dividing the point cloud data or (ii) the point cloud data before the dividing, to satisfy the first maximum bit count and the range of the total number determined. Moreover, the bitstream may further include range information indicating the range of the total number. For this reason, the processing load of the three-dimensional data decoding device can be reduced. 
     Accordingly, in the three-dimensional data encoding method, a bitstream including range information indicating a range of the number of three-dimensional points of encoded data is generated, and thus a three-dimensional data decoding device can determine whether the geometry information can be decoded appropriately, without having to analyze the bitstream. For this reason, the processing load of the three-dimensional data decoding device can be reduced. 
     For example, the point cloud data may further include attribute information of each of the three-dimensional points in the three-dimensional point cloud. The three-dimensional data encoding method may further include: determining a second maximum bit count after encoding attribute information of a three-dimensional point cloud of at least one of the divisional data unit or the point cloud data unit. In the generating, the bitstream may be generated by: encoding the geometry information of (i) the items of divisional data obtained by dividing the point cloud data or (ii) the point cloud data before the dividing, to satisfy the first maximum bit count determined; and encoding the attribute information of (i) the items of divisional data obtained by dividing of the point cloud data or (ii) the point cloud data before the dividing, to satisfy the second maximum bit count determined. The bitstream may further include second bit count information indicating the second maximum bit count. 
     Accordingly, in the three-dimensional data encoding method, a bitstream including second bit count information indicating a second maximum bit count for encoded attribute information is generated, and thus a three-dimensional data decoding device can determine whether the encoded data can be decoded appropriately, without having to analyze the bitstream. For this reason, the processing load of the three-dimensional data decoding device can be reduced. 
     A three-dimensional data decoding method according to an aspect of the present disclosure includes: obtaining a bitstream including encoded data and first bit count information, the encoded data being data obtained after encoding at least one of (i) a divisional data unit obtained when point cloud data indicating a three-dimensional point cloud is divided or (ii) a point cloud data unit of the point cloud data before the dividing, the first bit count information indicating a first maximum bit count for the encoded data; judging whether the bitstream obtained satisfies the first maximum bit count indicated by the first bit count information; and decoding the encoded data when the bitstream is judged to satisfy the first maximum bit count. 
     Accordingly, in the three-dimensional decoding method, first bit count information indicating the first maximum bit count for encoded data is obtained from the bitstream, and thus point cloud data can be decoded appropriately based on the obtained first bit count information. 
     For example, in the decoding, the encoded data need not be not decoded when the bitstream is judged not to satisfy the first maximum bit count. 
     Accordingly, since decoding processing of encoded data of a bitstream that cannot be appropriately decoded is not performed, processing load can be reduced. 
     For example, the point cloud data may include geometry information of each of three-dimensional points of the three-dimensional point cloud, and the first maximum bit count may relate to a bit count after the geometry information is encoded. 
     Accordingly, in the three-dimensional decoding method, first bit count information indicating the first maximum bit count for encoded geometry information is obtained from the bitstream, and thus point cloud data can be decoded appropriately based on the obtained first bit count information. 
     For example, the bitstream may further include range information indicating a range of a total number of three-dimensional points included in the at least one of the divisional data unit or the point cloud data unit. In the judging, whether the bitstream satisfies the range of the total number indicated in the range information may be further judged. In the decoding: the encoded data may be decoded when the bitstream is judged to satisfy the first maximum bit count and the range of the total number; and the encoded data need not be decoded when the bitstream is judged not to satisfy the first maximum bit count or the range of the total number. 
     Accordingly, in the three-dimensional decoding method, range information indicating a range of the number of three-dimensional points of encoded data is obtained from the bitstream, and thus point cloud data can be decoded appropriately based on the obtained range information. 
     Furthermore, the point cloud data may further include attribute data of each of the three-dimensional points of the three-dimensional point cloud, and the bitstream may further includes second bit count information indicating a second maximum bit count after encoding attribute information of a three-dimensional point cloud of the at least one of the divisional data unit or the point cloud data unit. In the judging, whether the bitstream satisfies the second maximum bit count indicated by the second bit count information may be further judged. Moreover, in the decoding: the encoded data may be decoded when the bitstream is judged to satisfy the first maximum bit count and the second maximum bit count; and the encoded data need not decoded when the bitstream is judged not to satisfy the first maximum bit count or the second maximum bit count. 
     Accordingly, in the three-dimensional decoding method, second bit count information indicating the second maximum bit count for encoded attribute information is obtained from the bitstream, and thus point cloud data can be decoded appropriately based on the obtained second bit count information. 
     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 item of attribute information (in other words, a piece of attribute information or an attribute information item) may be associated with one item of geometry information (in other words, a piece of geometry information or a geometry information item), or attribute information on a plurality of different types of attributes may be associated with one item of geometry information. Alternatively, items of attribute information on the same type of attribute may be associated with one item 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 (target 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 (in other words, a current node or a 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 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 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. 14  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. 15  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. 15  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. 15  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. 15  shows an example in which there is one type of geometry information, and there are two types of attribute information, the present disclosure 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. 16  is a diagram showing an example of encoded data and a NAL unit. 
     For example, as shown in  FIG. 16 , encoded data includes a header and a payload. The encoded data may include length information indicating the length (data amount) of the encoded data, the header, or the payload. The encoded data may include no header. 
     The header includes identification information for identifying the data, for example. The identification information indicates a data type or a frame number, for example. 
     The header includes identification information indicating a reference relationship, for example. The identification information is stored in the header when there is a dependence relationship between data, for example, and allows an entity to refer to another entity. For example, the header of the entity to be referred to includes identification information for identifying the data. The header of the referring entity includes identification information indicating the entity to be referred to. 
     Note that, when the entity to be referred to or the referring entity can be identified or determined from other information, the identification information for identifying the data or identification information indicating the reference relationship can be omitted. 
     Multiplexer  4802  stores the encoded data in the payload of the NAL unit. The NAL unit header includes pcc_nal_unit_type, which is identification information for the encoded data.  FIG. 27  is a diagram showing a semantics example of pcc_nal_unit_type. 
     As shown in  FIG. 17 , when pcc_codec_type is codec 1 (Codec1: first encoding method), values 0 to 10 of pcc_nal_unit_type are assigned to encoded geometry data (Geometry), encoded attribute X data (AttributeX), encoded attribute Y data (AttributeY), geometry PS (Geom. PS), attribute XPS (AttrX. S), attribute YPS (AttrY. PS), geometry SPS (Geometry Sequence PS), attribute X SPS (AttributeX Sequence PS), attribute Y SPS (AttributeY Sequence PS), AU header (AU Header), and GOF header (GOF Header) in codec 1. Values of 11 and greater are reserved in codec 1. 
     When pcc_codec_type is codec 2 (Codec2: second encoding method), values of 0 to 2 of pcc_nal_unit_type are assigned to data A (DataA), metadata A (MetaDataA), and metadata B (MetaDataB) in the codec. Values of 3 and greater are reserved in codec 2. 
     Next, an order of transmission of data will be described. In the following, restrictions on the order of transmission of NAL units will be described. 
     Multiplexer  4802  transmits NAL units on a GOF basis or on an AU basis. Multiplexer  4802  arranges the GOF header at the top of a GOF, and arranges the AU header at the top of an AU. 
     In order to allow the decoding device to decode the next AU and the following AUs even when data is lost because of a packet loss or the like, multiplexer  4802  may arrange a sequence parameter set (SPS) in each AU. 
     When there is a dependence relationship for decoding between encoded data, the decoding device decodes the data of the entity to be referred to and then decodes the data of the referring entity. In order to allow the decoding device to perform decoding in the order of reception without rearranging the data, multiplexer  4802  first transmits the data of the entity to be referred to. 
       FIG. 18  is a diagram showing examples of the order of transmission of NAL units.  FIG. 18  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. 18  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. 18 , 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 divisional data (also referred to as divided data). The divisional data includes information for identifying the divisional data, and a parameter used for decoding of the divisional data is included in the parameter set. In this case, an identifier that indicates that the data is data relating to a tile or slice or data storing a parameter is defined in pcc_nal_unit_type. 
     Embodiment 3 
     Although there are tools for data dividing, such as the slice or the tile, in HEVC encoding in order to make parallel processing in a decoding device possible, there are no such tools yet in PCC (Point Cloud Compression) encoding. 
     In PCC, various data dividing methods can be considered according to parallel processing, compression efficiency, and compression algorithms. Here, the definitions of slice and tile, the data structure, and the transmission/reception methods will be described. 
       FIG. 19  is a block diagram illustrating the configuration of first encoder  4910  included in a three-dimensional data encoding device according to the present embodiment. First encoder  4910  generates encoded data (an encoded stream) by encoding point cloud data with a first encoding method (GPCC (Geometry based PCC)). 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 divisional data by dividing point cloud data. Specifically, divider  4911  generates a plurality of divisional data by dividing the space of point cloud data into a plurality of subspaces. Here, the subspaces are one of tiles and 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 divided geometry information, and divides attribute information into a plurality of divided attribute information. Also, divider  4911  generates additional information about division. 
     A plurality of geometry information encoders  4912  generate a plurality of encoded geometry information by encoding the plurality of divided geometry information. For example, the plurality of geometry information encoders  4912  process the plurality of divided geometry information in parallel. 
     The plurality of attribute information encoders  4913  generate a plurality of encoded attribute information by encoding the plurality of divided attribute information. For example, the plurality of attribute information encoders  4913  process the plurality of divided attribute information in parallel. 
     Additional information encoder  4914  generates encoded additional information by encoding the additional information included in point cloud data, and the additional information about data dividing generated by divider  4911  at the time of division. 
     Multiplexer  4915  generates encoded data (an encoded stream) by multiplexing the plurality of encoded geometry information, the plurality of encoded attribute information, and the encoded additional information, and transmits the generated encoded data. Furthermore, the encoded additional information is used at the time of decoding. 
     Note that, although  FIG. 19  illustrates the example in which the respective numbers of geometry information encoders  4912  and attribute information encoders  4913  are two, the respective numbers of geometry information encoders  4912  and attribute information encoders  4913  may be one, or may be three or more. Furthermore, the plurality of divisional data may be processed in parallel in the same chip, such as a plurality of cores in a CPU, may be processed in parallel by the respective cores of a plurality of chips, or may be processed in parallel by the plurality of cores of a plurality of chips. 
       FIG. 20  is a block diagram illustrating the configuration of first decoder  4920 . First decoder  4920  restores point cloud data by decoding the encoded data (encoded stream) generated by encoding the point cloud data with 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 encoded geometry information, a plurality of encoded attribute information, and encoded additional information by demultiplexing the encoded data (encoded stream). 
     The plurality of geometry information decoders  4922  generate a plurality of divided geometry information by decoding the plurality of encoded geometry information. For example, the plurality of geometry information decoders  4922  process the plurality of encoded geometry information in parallel. 
     The plurality of attribute information decoders  4923  generate a plurality of divided attribute information by decoding the plurality of encoded attribute information. For example, the plurality of attribute information decoders  4923  process the plurality of encoded attribute information in parallel. 
     Additional information decoder  4924  generates additional information by decoding the encoded additional information. 
     Combiner  4925  generates geometry information by combining the plurality of divided geometry information by using the additional information. Combiner  4925  generates attribute information by combining the plurality of divided attribute information by using the additional information. 
     Note that, although  FIG. 20  illustrates the example in which the respective numbers of geometry information decoders  4922  and attribute information decoders  4923  are two, the respective numbers of geometry information decoders  4922  and attribute information decoders  4923  may be one, or may be three or more. Furthermore, the plurality of divisional data may be processed in parallel in the same chip, such as a plurality of cores in a CPU, may be processed in parallel by the respective cores of a plurality of chips, or may be processed in parallel by the plurality of cores of a plurality of chips. 
     Next, the configuration of divider  4911  will be described.  FIG. 21  is a block diagram of divider  4911 . Divider  4911  includes slice divider  4931 , geometry information tile divider (geometry tile divider)  4932 , and attribute information tile divider (attribute tile divider)  4933 . 
     Slice divider  4931  generates a plurality of slice geometry information by dividing geometry information (position or geometry) into slices. Also, slice divider  4931  generates a plurality of slice attribute information by dividing attribute information (attribute) into slices. Furthermore, slice divider  4931  outputs slice additional information (SliceMetaData) including the information related to slice dividing and the information generated in the slice dividing. 
     Geometry information tile divider  4932  generates a plurality of divided geometry information (a plurality of tile geometry information) by dividing the plurality of slice geometry information into tiles. Also, geometry information tile divider  4932  outputs geometry tile additional information (geometry tile metadata) including the information related to tile dividing of geometry information, and the information generated in the tile dividing of the geometry information. 
     Attribute information tile divider  4933  generates a plurality of divided attribute information (a plurality of tile attribute information) by dividing the plurality of slice attribute information into tiles. Also, attribute information tile divider  4933  outputs attribute tile additional information (attribute tile metadata) including the information related to tile dividing of attribute information, and the information generated in the tile dividing of the attribute information. 
     Note that the number of slices or tiles to be divided is one or more. That is, slice or tile dividing may not be performed. 
     Note that, although the example in which tile dividing is performed after slice dividing has been illustrated here, slice dividing may be performed after tile dividing. Furthermore, a new division type may be defined in addition to the slice and the tile, and dividing may be performed with three or more division types. 
     Hereinafter, the dividing method for point cloud data will be described.  FIG. 22  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. 21  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. 23  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, the encoding method for divisional data will be described. The three-dimensional data encoding device (first encoder  4910 ) encodes each of divisional data. When encoding attribute information, the three-dimensional data encoding device generates, as additional information, dependency information indicating based on which configuration information (geometry information, additional information, or other attribute information) encoding has been performed. That is, the dependency information indicates, for example, the configuration information of a reference destination (dependence destination). In this case, the three-dimensional data encoding device generates the dependency information based on the configuration information corresponding to the divided shape of attribute information. Note that the three-dimensional data encoding device may generate the dependency information based on the configuration information corresponding to a plurality of divided shapes. 
     Dependency information may be generated by the three-dimensional data encoding device, and the generated dependency information may be transmitted to the three-dimensional data decoding device. Alternatively, the three-dimensional data decoding device may generate dependency information, and the three-dimensional data encoding device may not transmit the dependency information. Furthermore, the dependency used by the three-dimensional data encoding device may be defined in advance, and the three-dimensional data encoding device may not transmit the dependency information. 
       FIG. 24  is a diagram illustrating an example of dependency of each data. The heads of arrows in the diagram indicate dependence destinations, and the origins of the arrows indicate dependence sources. The three-dimensional data decoding device decodes data in the order of a dependence destination to a dependence source. Additionally, the data indicated by solid lines in the diagram is data that is actually transmitted, and the data indicated by dotted lines is data that is not transmitted. 
     Furthermore, in the diagram, G indicates geometry information, and A indicates attribute information. G s1  indicates the geometry information of slice number 1, and G s2  indicates the geometry information of slice number 2. G s1t1  indicates the geometry information of slice number 1 and tile_number 1, G s1 t2 indicates the geometry information of slice number 1 and tile_number 2, G s2t1  indicates the geometry information of slice number 2 and tile_number 1, and G s2t2  indicates the geometry information of slice number 2 and tile_number 2. Similarly, A s1  indicates the attribute information of slice number 1, and A s2  indicates the attribute information of slice number 2. A s1t1  indicates the attribute information of slice number 1 and tile_number 1, A s1t2  indicates the attribute information of slice number 1 and tile_number 2, A s2t1  indicates the attribute information of slice number 2 and tile_number 1, and A s2t2  indicates the attribute information of slice number 2 and tile_number 2. 
     Mslice indicates slice additional information, MGtile indicates geometry tile additional information, and MAtile indicates attribute tile additional information. D s1t1  indicates the dependency information of attribute information A s1t1 , and D s2t1  indicates the dependency information of attribute information A s2t1 . 
     Additionally, the three-dimensional data encoding device may rearrange data in a decoding order, so that it is unnecessary to rearrange data in the three-dimensional data decoding device. Note that data may be rearranged in the three-dimensional data decoding device, or data may be rearranged in both the three-dimensional data encoding device and the three-dimensional data decoding device. 
       FIG. 25  is a diagram illustrating an example of the data decoding order. In the example of  FIG. 25 , decoding is sequentially performed from the data on the left. For those data in dependency, the three-dimensional data decoding device decodes the data of a dependence destination first. For example, the three-dimensional data encoding device rearranges data in advance to be in this order, and transmits the data. Note that, as long as it is the order in which the data of dependence destinations become first, it may be any kind of order. Additionally, the three-dimensional data encoding device may transmit additional information and dependency information before data. 
       FIG. 26  is a flowchart illustrating the flow of processing by the three-dimensional data encoding device. First, the three-dimensional data encoding device encodes the data of a plurality of slices or tiles as described above (S 4901 ). Next, as illustrated in  FIG. 25 , the three-dimensional data encoding device rearranges the data so that the data of dependence destinations become first (S 4902 ). Next, the three-dimensional data encoding device multiplexes the rearranged data (forms the rearranged data into a NAL unit) (S 4903 ). 
     Next, the configuration of combiner  4925  included in first decoder  4920  will be described.  FIG. 27  is a block diagram illustrating the configuration of combiner  4925 . Combiner  4925  includes geometry information tile combiner (geometry tile combiner)  4941 , attribute information tile combiner (attribute tile combiner)  4942 , and a slice combiner. 
     Geometry information tile combiner  4941  generates a plurality of slice geometry information by combining a plurality of divided geometry information by using geometry tile additional information. Attribute information tile combiner  4942  generates a plurality of slice attribute information by combining a plurality of divided attribute information by using attribute tile additional information. 
     Slice combiner  4943  generates geometry information by combining the plurality of slice geometry information by using slice additional information. Additionally, slice combiner  4943  generates attribute information by combining the plurality of slice attribute information by using slice additional information. 
     Note that the number of slices or tiles to be divided is one or more. That is, slice or tile dividing may not be performed. 
     Furthermore, although the example in which tile dividing is performed after slice dividing has been illustrated here, slice dividing may be performed after tile dividing. Furthermore, a new division type may be defined in addition to the slice and the tile, and dividing may be performed with three or more division types. 
     Next, the configuration of encoded data divided into slices or divided into tiles, and the storing method (multiplexing method) of the encoded data into a NAL unit will be described.  FIG. 28  is a diagram illustrating the configuration of encoded data, and the storing method of the encoded data into a NAL unit. 
     Encoded data (divided geometry information and divided attribute information) is stored in the payload of a NAL unit. 
     Encoded data includes a header and a payload. The header includes identification information for specifying the data included in the payload. This identification information includes, for example, the type of slice dividing or tile dividing (slice_type, tile_type), the index information for specifying slices or tiles (slice_idx, tile_idx), the geometry information of data (slices or tiles), or the address of data, etc. The index information for specifying slices is also written as the slice index (SliceIndex). The index information for specifying tiles is also written as the tile index (TileIndex). Additionally, the type of division is, for example, the technique based on an object shape as described above, the technique based on map information or geometry information, or the technique based on the data amount or processing amount, etc. 
     Note that all or a part of the above-described information may be stored in one of the header of divided geometry information and the header of divided attribute information, and may not be stored in the other. For example, when the same dividing method is used for geometry information and attribute information, the type of division (slice_type, tile_type) and the index information (slice_idx, tile_idx) for the geometry information and the attribute information are the same. Therefore, these information may be included in the header of one of the geometry information and the attribute information. For example, when attribute information depends on geometry information, the geometry information is processed first. Therefore, these information may be included in the header of the geometry information, and these information may not be included in the header of the attribute information. In this case, the three-dimensional data decoding device determines that, for example, the attribute information of a dependence source belongs to the same slice or tile as a slice or tile of the geometry information of a dependence destination. 
     Furthermore, additional information (slice additional information, geometry tile additional information, or attribute tile additional information) related to slice dividing or tile dividing, and dependency information indicating dependency, etc. may be stored and transmitted in an existing parameter set (GPS, APS, geometry SPS, or attribute SPS). When the dividing method is changed for each frame, the information indicating the dividing method may be stored in the parameter set (GPS or APS) for each frame. When the dividing method is not changed within a sequence, the information indicating the dividing method may be stored in the parameter set (geometry SPS or attribute SPS) for each sequence. Furthermore, when the same dividing method is used for geometry information and attribute information, the information indicating the dividing method may be stored in the parameter set of a PCC stream (stream PS). 
     Also, the above-described information may be stored in any of the above-described parameter sets, or may be stored in a plurality of the parameter sets. Additionally, a parameter set for tile dividing or slice dividing may be defined, and the above-described information may be stored in the parameter set. Furthermore, these information may be stored in the header of encoded data. 
     Also, the header of encoded data includes the identification information indicating dependency. That is, when there is dependency between data, the header includes the identification information for referring to a dependence destination from a dependence source. For example, the header of data of a dependence destination includes the identification information for specifying the data. The identification information indicating the dependence destination is included in the header of the data of a dependence source. Note that, when the identification information for specifying data, the additional information related to slice dividing or tile dividing, and the identification information indicating dependency can be identified or derived from other information, these information may be omitted. 
     Next, the flows of encoding processing and decoding processing of point cloud data according to the present embodiment will be described.  FIG. 29  is a flowchart of the encoding processing of point cloud data according to the present embodiment. 
     First, the three-dimensional data encoding device determines the dividing method to be used (S 4911 ). This dividing method includes whether or not to perform slice dividing, and whether or not to perform tile dividing. Also, the dividing method may include the number of divisions and the type of division, etc. in the case of performing slice dividing or tile dividing. The type of division is the technique based on an object shape as described above, the technique based on map information or geometry information, or the technique based on the data amount or processing amount, etc. Note that the dividing method may be defined in advance. 
     When slice dividing is performed (Yes in S 4912 ), the three-dimensional data encoding device generates a plurality of slice geometry information and a plurality of slice attribute information by collectively dividing geometry information and attribute information (S 4913 ). Also, the three-dimensional data encoding device generates slice additional information related to slice dividing. Note that the three-dimensional data encoding device may separately divide geometry information and attribute information. 
     When tile dividing is performed (Yes in S 4914 ), the three-dimensional data encoding device generates a plurality of divided geometry information and a plurality of divided attribute information by separately dividing the plurality of slice geometry information and the plurality of slice attribute information (or geometry information and attribute information) (S 4915 ). Additionally, the three-dimensional data encoding device generates geometry tile additional information and attribute tile additional information related to tile dividing. Note that the three-dimensional data encoding device may collectively divide slice geometry information and slice attribute information. 
     Next, the three-dimensional data encoding device generates a plurality of encoded geometry information and a plurality of encoded attribute information by encoding each of the plurality of divided geometry information and the plurality of divided attribute information (S 4916 ). Also, the three-dimensional data encoding device generates dependency information. 
     Next, the three-dimensional data encoding device generates encoded data (an encoded stream) by forming (multiplexing) the plurality of encoded geometry information, the plurality of encoded attribute information, and additional information into a NAL unit (S 4917 ). Also, the three-dimensional data encoding device transmits the generated encoded data. 
       FIG. 30  is a flowchart of the decoding processing of point cloud data according to the present embodiment. First, the three-dimensional data decoding device determines the dividing method by analyzing additional information (slice additional information, geometry tile additional information, and attribute tile additional information) related to the dividing method included in the encoded data (encoded stream) (S 4921 ). This dividing method includes whether or not to perform slice dividing, and whether or not to perform tile dividing. Additionally, the dividing method may include the number of divisions and the type of division, etc. in the case of performing slice dividing or tile dividing. 
     Next, the three-dimensional data decoding device generates divided geometry information and divided attribute information by decoding a plurality of encoded geometry information and a plurality of encoded attribute information included in the encoded data by using dependency information included in the encoded data (S 4922 ). 
     When it is indicated by the additional information that tile dividing has been performed (Yes in S 4923 ), the three-dimensional data decoding device generates a plurality of slice geometry information and a plurality of slice attribute information by combining a plurality of divided geometry information and a plurality of divided attribute information with respective methods based on geometry tile additional information and attribute tile additional information (S 4924 ). Note that the three-dimensional data decoding device may combine the plurality of divided geometry information and the plurality of divided attribute information with the same method. 
     When it is indicated by the additional information that slice dividing has been performed (Yes in S 4925 ), the three-dimensional data decoding device generates geometry information and attribute information by combining the plurality of slice geometry information and the plurality of slice attribute information (the plurality of divided geometry information and the plurality of divided attribute information) with the same method based on slice additional information (S 4926 ). Note that the three-dimensional data decoding device may combine the plurality of slice geometry information and the plurality of slice attribute information with respective different methods. 
     It is to be noted that attribute information (an identifier, area information, address information, position information, etc.) of a tile or a slice may be stored in other control information instead of SEI. For example, the attribute information may be stored in control information indicating the overall structure of PCC data, or may be stored in control information for each tile or each slice. 
     In addition, when the three-dimensional data encoding device (three-dimensional data transmitting device) transmits the PCC data to another device, the three-dimensional data encoding device may convert control information such as SEI into control information unique to a protocol supported by the system and present the converted control information. 
     For example, when the three-dimensional data encoding device converts PCC data including attribute information into an ISO Base Media File Format (ISOBM), the three-dimensional data encoding device may store SEI in an “mdat box” together with the PCC data, or may store SEI in a “track box” in which control information related to a stream is described. In other words, the three-dimensional data encoding device may store the control information in a table for random access. In addition, when the three-dimensional data encoding device packetizes PCC data and transmits packets of PCC data, the three-dimensional data encoding device may store SEI in packet headers. In this way, attribute information can be obtained in a layer of the system, which makes it easier to access the attribute information, and the tile data or the slice data, and thus makes it possible to accelerate the access. 
     It is to be noted that, in the configuration of the three-dimensional data decoding device, memory manager may determine, in advance, whether information which is necessary for a decoding process is present in memory, and if the information necessary for the decoding process is absent, memory manager may obtain the information necessary for the decoding process from storage or via a network. 
     When the three-dimensional data decoding device obtains PCC data from storage or via a network using Pull in a protocol such as the MPEG-DASH, memory manager may identify attribute information of data necessary for a decoding process based on information obtained from localizer or the like, request the tile or the slice including the identified attribute information, and obtain the necessary data (PCC stream). A tile or a slice including attribute information may be identified by a storage or network side, or may be identified by memory manager. For example, memory manager may obtain SEI from all PCC data in advance, and identify a tile or a slice based on the information. 
     When all PCC data have been transmitted from the storage or via the network using Push in the UDP protocol, or the like, memory manager may obtain desired data by identifying the attribute information of data necessary for a decoding process and a tile or a slice, based on information obtained from localizer, or the like, and by filtering a plurality of tiles or slices to obtain a desired tile or a slice from the PCC data transmitted. 
     In addition, when obtaining data, the three-dimensional data encoding device may determine whether desired data is present, whether real-time processing is possible based on a data size, etc., or a communication state, etc. When the three-dimensional data encoding device determines that it is difficult to obtain the data based on the determination result, the three-dimensional data encoding device may select and obtain another slice or tile whose priority or data amount is different from that of the data. 
     In addition, the three-dimensional data decoding device may transmit information from localizer, or the like to a cloud server, and the cloud server may determine necessary information based on the information. 
     Embodiment 4 
     The following describes tile additional information. The three-dimensional data encoding device generates tile additional information that is metadata regarding a tile division method, and transmits the generated tile additional information to the three-dimensional data decoding device. 
       FIG. 31  is a diagram illustrating an example of syntax of tile additional information (TileMetaData). As shown in  FIG. 31 , for example, tile additional information includes division method information (type_of_divide), shape information (topview_shape), an overlap flag (tile_overlap_flag), overlap information (type_of_overlap), height information (tile_height), a tile_number (tile_number), and tile position information (global_position, relative_position). 
     Division method information (type_of_divide) indicates a tile division method. For example, division method information indicates whether a tile division method is division based on map information, that is, division based on top view (top_view) or another division (other). 
     Shape information (topview_shape) is included in tile additional information when a tile division method is, for example, division based on top view. Shape information indicates a shape in top view of a tile. Examples of the shape include a square and a circle. Moreover, the examples of the shape may include an ellipse, a rectangle, or a polygon other than a quadrangle, or may include a shape other than these. It should be noted that shape information may indicate not only a shape in top view of a tile but also a three-dimensional shape (e.g., a cube, a round column) of a tile. 
     An overlap flag (tile_overlap_flag) indicates whether tiles overlap each other. For example, an overlap flag is included in tile additional information when a tile division method is division based on top view. In this case, the overlap flag indicates whether tiles overlap each other in top view. It should be noted that an overlap flag may indicate whether tiles overlap each other in a three-dimensional space. 
     Overlap information (type_of_overlap) is included in tile additional information when, for example, tiles overlap each other. Overlap information indicates, for example, how tiles overlap each other. For example, overlap information indicates the size of an overlapping region. 
     Height information (tile_height) indicates the height of a tile. It should be noted that height information may include information indicating a tile shape. For example, when the shape of a tile in top view is a rectangle, the information may indicate the length of a side (a vertical length, a horizontal length) of the rectangle. When the shape of a tile in top view is a circle, the information may indicate the diameter or radius of the circle. 
     Moreover, height information may indicate the height of each tile or a height common to tiles. In addition, height types such as roads and overpasses may be set in advance, and height information may indicate the height of each of the height types and a height type of each tile. Alternatively, a height of each height type may be specified in advance, and height information may indicate a height type of each tile. In other words, height information need not indicate a height of each height type. 
     A tile_number (tile_number) indicates the number of tiles. It should be noted that tile additional information may include information indicating an interval between tiles. 
     Tile position information (global_position, relative_position) is information for identifying the position of each tile. For example, tile position information indicates the absolute coordinates or relative coordinates of each tile. 
     It should be noted that part or all of the above-mentioned information may be provided for each tile or each group of tiles (e.g., for each frame or group of frames). 
     The three-dimensional data encoding device may include tile additional information in supplemental enhancement information (SET) and transmit the SEI. Alternatively, the three-dimensional data encoding device may store tile additional information in an existing parameter set (PPS, GPS, or APS, etc.) and transmit the parameter set. 
     For example, when tile additional information changes for each frame, the tile additional information may be stored in a parameter set for each frame (GPS or APS etc.). When tile additional information does not change in a sequence, the tile additional information may be stored in a parameter set for sequence (geometry SPS or attribute SPS). Further, when the same tile division information is used for geometry information and attribute information, tile additional information may be stored in a parameter set for a PCC stream (a stream PS). 
     Moreover, tile additional information may be stored in any one of the above-mentioned parameter sets or in parameter sets. In addition, tile additional information may be stored in the header of encoded data. Additionally, tile additional information may be stored in the header of a NAL unit. 
     Furthermore, part or all of tile additional information may be stored in one of the header of divided geometry information and the header of divided attribute information, and need not be stored in the other. For example, when the same tile additional information is used for geometry information and attribute information, the tile additional information may be included in the header of one of the geometry information and the attribute information. For example, when attribute information depends on geometry information, the geometry information is processed first. For this reason, the tile additional information may be included in the header of the geometry information, and need not be included in the header of the attribute information. In this case, for example, the three-dimensional data decoding device determines that the attribute information of the depender belongs to the same tile as a tile having the geometry information of the dependee. 
     The three-dimensional data decoding device reconstructs point cloud data subjected to tile division, based on tile additional information. When there are pieces of overlapping point cloud data, the three-dimensional data decoding device specifies the pieces of overlapping point cloud data and selects one of the pieces of overlapping point cloud data or merges pieces of point cloud data. 
     Moreover, the three-dimensional data decoding device may perform decoding using tile additional information. For example, when tiles overlap each other, the three-dimensional data decoding device may perform decoding for each tile, perform processing (e.g., smoothing or filtering) using the pieces of decoded data, and generate point cloud data. This makes it possible to perform highly accurate decoding. 
       FIG. 32  is a diagram illustrating a configuration example of a system including the three-dimensional data encoding device and the three-dimensional data decoding device. Tile divider  5051  divides point cloud data including geometry information and attribute information into a first tile and a second tile. In addition, tile divider  5051  transmits tile additional information regarding tile division to decoder  5053  and tile combiner  5054 . 
     Encoder  5052  generates encoded data by encoding the first tile and the second tile. 
     Decoder  5053  restores the first tile and the second tile by decoding the encoded data generated by encoder  5052 . Tile combiner  5054  restores the point cloud data (the geometry information and the attribute information) by combining the first tile and the second tile using the tile additional information. 
     The following describes slice additional information. The three-dimensional data encoding device generates slice additional information that is metadata regarding a slice division method, and transmits the generated slice additional information to the three-dimensional data decoding device. 
       FIG. 33  is a diagram illustrating an example of syntax of slice additional information (SliceMetaData). As shown in  FIG. 33 , for example, slice additional information includes division method information (type_of_divide), an overlap flag (slice_overlap_flag), overlap information (type_of_overlap), a slice number (slice_number), slice position information (global_position, relative_position), and slice size information (slice_bounding_box_size). 
     Division method information (type_of_divide) indicates a slice division method. For example, division method information indicates whether a slice division method is division based on information about an object (object). It should be noted that slice additional information may include information indicating an object division method. For example, this information indicates whether one object is to be divided into slices or assigned to one slice. In addition, the information may indicate, for example, a division number when one object is divided into slices. 
     An overlap flag (slice_overlap_flag) indicates whether slices overlap each other. Overlap information (type_of_overlap) is included in slice additional information when, for example, slices overlap each other. Overlap information indicates, for example, how slices overlap each other. For example, overlap information indicates the size of an overlapping region. 
     A slice number (slice_number) indicates the number of slices. 
     Slice position information (global_position, relative_position) and slice size information (slice_bounding_box_size) are information about a region of a slice. Slice position information is information for identifying the position of each slice. For example, slice position information indicates the absolute coordinates or relative coordinates of each slice. Slice size information (slice_bounding_box_size) indicates the size of each slice. For example, slice size information indicates the size of a bounding box of each slice. 
     The three-dimensional data encoding device may include slice additional information in SEI and transmit the SEI. Alternatively, the three-dimensional data encoding device may store slice additional information in an existing parameter set (PPS, GPS, or APS, etc.) and transmit the parameter set. 
     For example, when slice additional information changes for each frame, the slice additional information may be stored in a parameter set for each frame (GPS or APS etc.). When slice additional information does not change in a sequence, the slice additional information may be stored in a parameter set for sequence (geometry SPS or attribute SPS). Further, when the same slice division information is used for geometry information and attribute information, slice additional information may be stored in a parameter set for a PCC stream (a stream PS). 
     Moreover, slice additional information may be stored in any one of the above-mentioned parameter sets or in parameter sets. In addition, slice additional information may be stored in the header of encoded data. Additionally, slice additional information may be stored in the header of a NAL unit. 
     Furthermore, part or all of slice additional information may be stored in one of the header of divided geometry information and the header of divided attribute information, and need not be stored in the other. For example, when the same slice additional information is used for geometry information and attribute information, the slice additional information may be included in the header of one of the geometry information and the attribute information. For example, when attribute information depends on geometry information, the geometry information is processed first. For this reason, the slice additional information may be included in the header of the geometry information, and need not be included in the header of the attribute information. In this case, for example, the three-dimensional data decoding device determines that the attribute information of the depender belongs to the same slice as a slice having the geometry information of the dependee. 
     The three-dimensional data decoding device reconstructs point cloud data subjected to slice division, based on slice additional information. When there are pieces of overlapping point cloud data, the three-dimensional data decoding device specifies the pieces of overlapping point cloud data and selects one of the pieces of overlapping point cloud data or merges pieces of point cloud data. 
     Moreover, the three-dimensional data decoding device may perform decoding using slice additional information. For example, when slices overlap each other, the three-dimensional data decoding device may perform decoding for each slice, perform processing (e.g., smoothing or filtering) using the pieces of decoded data, and generate point cloud data. This makes it possible to perform highly accurate decoding. 
       FIG. 34  is a flowchart of a three-dimensional data encoding process including a tile additional information generation process performed by the three-dimensional data encoding device according to the present embodiment. 
     First, the three-dimensional data encoding device determines a division method to be used (S 5031 ). Specifically, the three-dimensional data encoding device determines whether a division method based on top view (top_view) or another method (other) is to be used as a tile division method. In addition, the three-dimensional data encoding device determines a tile shape when the division method based on top view is used. Additionally, the three-dimensional data encoding device determines whether tiles overlap with other tiles. 
     When the tile division method determined in step S 5031  is the division method based on top view (YES in S 5032 ), the three-dimensional data encoding device includes a result of the determination that the tile division method is the division method based on top view (top_view), in tile additional information (S 5033 ). 
     On the other hand, when the tile division method determined in step S 5031  is a method other than the division method based on top view (NO in S 5032 ), the three-dimensional data encoding device includes a result of the determination that the tile division method is the method other than the division method based on top view (top_view), in tile additional information (S 5034 ). 
     Moreover, when a shape in top view of a tile determined in step S 5031  is a square (SQUARE in S 5035 ), the three-dimensional data encoding device includes a result of the determination that the shape in top view of the tile is the square, in the tile additional information (S 5036 ). In contrast, when a shape in top view of a tile determined in step S 5031  is a circle (CIRCLE in S 5035 ), the three-dimensional data encoding device includes a result of the determination that the shape in top view of the tile is the circle, in the tile additional information (S 5037 ). 
     Next, the three-dimensional data encoding device determines whether tiles overlap with other tiles (S 5038 ). When the tiles overlap with the other tiles (YES in S 5038 ), the three-dimensional data encoding device includes a result of the determination that the tiles overlap with the other tiles, in the tile additional information (S 5039 ). On the other hand, when the tiles do not overlap with other tiles (NO in S 5038 ), the three-dimensional data encoding device includes a result of the determination that the tiles do not overlap with the other tiles, in the tile additional information (S 5040 ). 
     Finally, the three-dimensional data encoding device divides the tiles based on the tile division method determined in step S 5031 , encodes each of the tiles, and transmits the generated encoded data and the tile additional information (S 5041 ). 
       FIG. 35  is a flowchart of a three-dimensional data decoding process performed by the three-dimensional data decoding device according to the present embodiment using tile additional information. 
     First, the three-dimensional data decoding device analyzes tile additional information included in a bitstream (S 5051 ). 
     When the tile additional information indicates that tiles do not overlap with other tiles (NO in S 5052 ), the three-dimensional data decoding device generates point cloud data of each tile by decoding the tile (S 5053 ). Finally, the three-dimensional data decoding device reconstructs point cloud data from the point cloud data of each tile, based on a tile division method and a tile shape indicated by the tile additional information (S 5054 ). 
     In contrast, when the tile additional information indicates that tiles overlap with other tiles (YES in S 5052 ), the three-dimensional data decoding device generates point cloud data of each tile by decoding the tile. In addition, the three-dimensional data decoding device identifies overlap portions of the tiles based on the tile additional information (S 5055 ). It should be noted that, regarding the overlap portions, the three-dimensional data decoding device may perform decoding using pieces of overlapping information. Finally, the three-dimensional data decoding device reconstructs point cloud data from the point cloud data of each tile, based on a tile division method, a tile shape, and overlap information indicated by the tile additional information (S 5056 ). 
     The following describes, for example, variations regarding slice. The three-dimensional data encoding device may transmit, as additional information, information indicating a type (a road, a building, a tree, etc.) or attribute (dynamic information, static information, etc.) of an object. Alternatively, a coding parameter may be predetermined according to an object, and the three-dimensional data encoding device may notify the coding parameter to the three-dimensional data decoding device by transmitting a type or attribute of the object. 
     The following methods may be used regarding slice data encoding order and transmitting order. For example, the three-dimensional data encoding device may encode slice data in decreasing order of ease of object recognition or clustering. Alternatively, the three-dimensional data encoding device may encode slice data in the order in which clustering is completed. Moreover, the three-dimensional data encoding device may transmit slice data in the order in which the slice data is encoded. Alternatively, the three-dimensional data encoding device may transmit slice data in decreasing order of priority for decoding in an application. For example, when dynamic information has high priority for decoding, the three-dimensional data encoding device may transmit slice data in the order in which slices are grouped using the dynamic information. 
     Furthermore, when encoded data order is different from the order of priority for decoding, the three-dimensional data encoding device may transmit encoded data after rearranging the encoded data. In addition, when storing encoded data, the three-dimensional data encoding device may store encoded data after rearranging the encoded data. 
     An application (the three-dimensional data decoding device) requests a server (the three-dimensional data encoding device) to transmit slices including desired data. The server may transmit slice data required by the application, and need not transmit slice data unnecessary for the application. 
     An application requests a server to transmit a tile including desired data. The server may transmit tile data required by the application, and need not transmit tile data unnecessary for the application. 
     Embodiment 5 
     Encoding of geometry information (geometry) will be described. In encoding of geometry information, the three-dimensional data encoding device divides a region including point cloud data using an octree to transform the point cloud data into a set of occupancy information on a point of each node. The occupancy information is 8-bit information that indicates whether each child node contains a point or not, and whether each child node contains a point or not is indicated by 0 and 1. 
     As methods of division into an octree, there are a method that first produces nodes at smaller depths (of smaller values of depth) according to the breadth-first search method and a method that searches points to the depth of the lowest layer along a branch and then backtracks to search points again along another branch according to the depth-first search method, for example. In encoding, items of occupancy information are arranged and encoded in the orders described above. 
       FIG. 36  is a diagram showing an octree structure of a point cloud divided up to depth=6.  FIG. 37  is a diagram showing an example of a data structure of encoded data on the octree structure according to the breadth-first search method. The encoded data on the point cloud includes a header (header) and a payload (payload). In the payload, items of information (depth #0 to #6) are arranged in sequence on a per depth (depth) basis.  FIG. 38  is a diagram showing a syntax example of the payload. The payload includes an occupancy code for each depth. 
     Next, a hierarchical structure will be described. For example, a plurality of levels (referred to also as hierarchical levels) are defined as shown in  FIG. 36 . Level 2 is a point cloud represented by point cloud data resulting from octree division from depth=0 to a last depth (depth=6), level 1 is a point cloud represented by point cloud data resulting from octree division from depth=0 to depth=5, and level 0 is a point cloud represented by point cloud data resulting from octree division from depth=0 to depth=4. That is, the resolution of the point cloud increases in the order of level 0, level 1, and level 2. In other words, the resolution of the point cloud decreases in the order of level 2, level 1, and level 0. This can also be said that the point cloud data is quantized with 1/2 as the level goes down by 1. In this way, by using the levels, the entire point cloud can be represented by using all the data down to the lowest layer, and point cloud data of low resolution can also be represented by using data of some higher layers from depth=0. Note that depending on the resolution or amount of data handled, various combinations of levels can be adaptively set as required. 
       FIG. 39  is a flowchart of a decoding process of decoding encoded data, which is encoded geometry information, with a desired resolution. First, the three-dimensional data decoding device determines a level of decoding (resolution) and a depth corresponding to the level (S 8801 ). 
     The three-dimensional data decoding device then decodes encoded data at the determined level. Specifically, the three-dimensional data decoding device decodes encoded data at a first depth (depth 0 (depth=0)) (S 8802 ). When the decoding of the encoded data at all the depths to be decoded is not completed (No in S 8803 ), the three-dimensional data decoding device decodes the encoded data at the next depth (S 8804 ). Note that the three-dimensional data decoding device may decode the encoded data at the depth to be decoded by using data at a previous level (or depth). When the decoding of the encoded data at all the depths to be decoded is completed (Yes in S 8803 ), the three-dimensional data decoding device displays the obtained point cloud (S 8805 ). 
     It is also possible that the three-dimensional data decoding device decodes the encoded data at the determined depth but does not decode the encoded data at the remaining depths.  FIG. 40  is a diagram showing a relationship between levels and data decoded.  FIG. 41  is a schematic diagram showing levels. For example, in  FIG. 40 , in order to decode the point cloud at level 0, encoded data at depth #0 to depth #4 needs to be decoded. Therefore, the three-dimensional data decoding device decodes the encoded data up to A. 
     In order to decode the point cloud at level 1, encoded data at depth #0 to depth #5 needs to be decoded. Therefore, the three-dimensional data decoding device decodes the encoded data up to B. In in order to decode the point cloud at level 2 (or all levels), encoded data at depth #0 to depth #6 needs to be decoded. Therefore, the three-dimensional data decoding device decodes the encoded data up to C. 
     By the process described above, the three-dimensional data decoding device can produce data of low resolution. Therefore, when a point cloud of high resolution is not required, the three-dimensional data decoding device can reduce the processing amount by reducing the data amount or skipping part of the decoding process. 
     Alternatively, the three-dimensional data decoding device may display data of low resolution after producing the data of low resolution before decoding the remaining data, and display the remaining data after producing decoded data of high resolution. In this way, the initial delay of decoding and display can be reduced. 
     Here, in order to partially decode the data, the three-dimensional data decoding device needs to determine that the data up to point in time A or B has been obtained or, in other words, determine information on the depths or the boundaries between the depths of the encoded data.  FIG. 42  is a diagram showing a syntax example of the header.  FIG. 43  is a diagram showing a syntax example of the payload. 
     For example, based on the number (numPoint) of the points of the point cloud and a depth count (depth) indicating the number of depths indicated in the header and encoded data (occupancy_code) for each node or leaf stored on a per depth basis indicated by the payload, the three-dimensional data decoding device may sequentially decode the encoded data from the head and analyze the decoded information on occupancy codes to determine the information on the depths or the boundaries between the depths. 
     In this embodiment, a data configuration that facilitates such partial decoding of depth data and division and combining of data will be described. Here, another data structure for a hierarchical structure is defined. Using this data structure allows data division and combining in units of layer data. 
     The three-dimensional data encoding device or three-dimensional data decoding device can reduce the amount of data required to be transmitted by extracting particular required layer data. The three-dimensional data encoding device or three-dimensional data decoding device is also improved in functionality since data division or combining can be performed without decoding encoded data. 
       FIG. 44  is a diagram showing a configuration of encoded data having all geometry information (depth #0 to depth #6) from depth 0 to depth 6. Note that the encoded data is referred to as overall encoded data or a bitstream (encoded bitstream). In this example, overall encoded data does not include information indicating an explicit boundary between items of data of different depths. The three-dimensional data decoding device can obtain the information on the depths or the boundaries between the depths by analyzing an occupancy code (occupancy_code). Here, the number (numPoint) of the points included in the header indicates the total number of the points included in the overall encoded data. The depth count depth indicating the number of depths is “7” in this example. 
       FIG. 45  is a diagram showing a configuration of overall encoded data. The overall encoded data shown in  FIG. 45  includes hierarchical structure metadata, which is metadata indicating a hierarchical structure, in addition to the components shown in  FIG. 44 .  FIG. 46  is a diagram showing a syntax example of depth information (depth_info).  FIG. 47  is a diagram showing an example of depth information stored in hierarchical structure metadata (layer_metadata). 
     The depth information includes the depth count (depth) and length information (length) indicating the length of data at each depth (depth). For example, the length information indicates the difference between the position of the head and the position of the tail of the encoded data at the corresponding depth (referred to also as depth data) in terms of number of bytes or bits. 
     The hierarchical structure metadata including the length information may be transmitted before or after the encoded data. The length information may be stored in the header of the overall encoded data.  FIG. 48  is a diagram showing a syntax example of the header in that case. The header includes the number of points (numPoint) and the depth information (depth_info). 
     As described above, for example, data boundaries between depths are explicitly indicated in the hierarchical structure metadata or header. Note that the three-dimensional data decoding device need not use the hierarchical structure metadata for decoding. In that case, the three-dimensional data decoding device uses the hierarchical structure metadata when dividing or reconstructing layer data. 
     Note that in the configurations shown in  FIG. 44  and  FIG. 45 , all the depth data is continuous, and context information used for entropy encoding is also continuous, rather than being initialized. 
     By using this structure, the three-dimensional data decoding device can easily divide the overall encoded data into items of data at different depths, and therefore can reduce the processing amount. In addition, since divisional data can be transmitted, the amount of transmission can be reduced. 
     Next, a case where a concept of a hierarchy (layers) is introduced will be described.  FIG. 49  is a diagram showing an example configuration of the overall encoded data in this case. In the drawing, depth 0 to depth 4 (depth #0 to depth #4) are defined as layer 0, depth 5 (depth #5) is defined as layer 1, and depth 6 (depth #6) is defined as layer 2. In comparison with the levels (hierarchical levels) described above, the plurality of layers are each defined by one or more depths that do not overlap with each other, while the levels described above are each defined by a plurality of depths from depth 0 to a desired depth. For example, layer 0 includes the same depths as level 0, layer 1 corresponds to the difference between level 1 and level 0, and layer 2 corresponds to the difference between level 2 and level 1. 
     In this case, layer information (layer_info) is added to the overall encoded data.  FIG. 50  is a diagram showing a syntax example of the layer information. The layer information includes a layer count (layer) indicating the number of layers, and a layer depth count (num_depth) indicating the number of depths included in each layer.  FIG. 51  is a diagram showing a syntax example of the hierarchical structure metadata. For example, the hierarchical structure metadata includes layer information (layer_info).  FIG. 52  is a diagram showing a syntax example of the header of the overall encoded data. For example, as shown in  FIG. 52 , the header includes depth information (depth_info). Note that both the layer information and the depth information may be included in the header or the hierarchical structure metadata. Note that the syntax structure shown here is an example and is not limited thereto. The information included in the overall encoded data can be any information from which the three-dimensional data decoding device can obtains the depth count, the layer count, the layer depth count, and the length information. For example, the overall encoded data may include information indicating the length of each layer. 
     When the layer structure is common to a plurality of processing units (such as frames), the whole or a part of these items of information may be included in higher-order metadata, such as a parameter set at the sequence level (such as SPS). 
     Note that the overall encoded data may include a flag that indicates whether the overall encoded data includes the layer information (layer_info) and the depth information (depth_info) or not. The layer information and the depth information may be included in the overall encoded data when the flag is on (a value of 1, for example). Note that a flag may be separately provided for each of the layer information and the depth information. 
     By using this structure, the above-described data can be more easily divided into items of data on a per depth basis or on a per layer basis, so that the processing amount can be reduced. In addition, divisional data can be transmitted, so that the amount of transmission can be reduced. 
     Next, a configuration of the whole of the point cloud data will be described. The point cloud data may have one or more items of attribute information (Attribute), such as color or reflectance, in addition to the geometry information (geometry). The attribute information may also have a hierarchical structure, as with the geometry information. 
     When the attribute information has a hierarchical structure similar to that of the geometry information, the three-dimensional data encoding device stores the information on the hierarchical structure in the hierarchical structure metadata or the data header, as with the geometry information. For example, the three-dimensional data encoding device stores the information on the hierarchical structure in each of an attribute information header and a geometry information header. When storing the information on the hierarchical structure in the hierarchical structure metadata, the three-dimensional data encoding device may store the hierarchical structure metadata in different parameter sets for the geometry information and the attribute information, such as GPS and APS, or in a common parameter set, such as SPS. Alternatively, the three-dimensional data encoding device may store the hierarchical structure metadata in SEI or other metadata. 
       FIG. 53  is a diagram showing an example configuration of the bitstream in the case where the geometry information and the attribute information each have a hierarchical structure, and the information on the hierarchical structure is stored in the hierarchical structure metadata. By using this structure, the above-described data can be more easily divided into items of data on a per layer basis, so that the processing amount can be reduced. In addition, divisional data can be transmitted, so that the amount of transmission can be reduced. In addition, the geometry information and the attribute information can be divided on a per layer basis in the same manner. 
       FIG. 54  is a diagram showing a syntax example of the hierarchical structure metadata. This drawing shows an example of the case where common hierarchical structure metadata is used for the geometry information and the attribute information. 
     The hierarchical structure metadata includes layer information (layer_info), a component count (component), and depth information (depth_info) on each component. The component count indicates the number of components, such as geometry information and attribute information. For example, when the point cloud data includes color and reflectance in addition to geometry information, the component count is 3. Note that the component count of the attribute information may be indicated on the assumption that the geometry information is essentially included. When the component count of the attribute information is indicated in SPS, this information can be omitted. In this way, the data amount is reduced. 
     The layer information (layer_info) indicates the number of layers and the number of depths included in each layer. For example, the hierarchical structure is common to all components. 
     The depth information (depth_info) indicates the depth count and the data length (length information) of each item of depth data. The depth information is set for each component, for example. Note that the whole or a part of the depth information may be common to all components. 
     When an independent hierarchical structure is provided for each component, the hierarchical structure may be generated for each component. Note that although a method of layering on a depth basis has been described herein, the layering may be performed based on temporal information or spatial information. When the layering is performed, the hierarchical structure metadata is indicated in the manner described above. A configuration that has no hierarchical structure may be generated. Information indicating whether the encoded data has a hierarchical structure or not may be included in the header or metadata. In this way, there can be both data having a hierarchical structure and data having no hierarchical structure at the same time. For example, it is possible that the geometry information has a hierarchical structure, and the attribute information has no hierarchical structure. Furthermore, information indicating this may be indicated in the header or the like. 
     Next, a data reference relationship and a dependence relationship between geometry information and attribute information will be described.  FIG. 55 ,  FIG. 56 , and  FIG. 57  are diagrams showing a reference relationship between geometry information and attribute information. 
     When the encoded data has a hierarchical structure, layer 0 is a base layer and is data that can be decoded by itself. On the other hand, layer 1 cannot be decoded by itself and is integrated with the data of layer 0 for decoding. Layer 2 cannot be decoded by itself and is integrated with the data of layer 0 and layer 1 for decoding. When an octree-based encoding method is used, as shown in  FIG. 55 , layer 0 of attribute information is decoded by referring to layer 0 of geometry information. For example, as shown in  FIG. 56 , layer 1 of attribute information is decoded by referring to layer 0 of attribute information and layer 0 and layer 1 of geometry information. When there is a reference relationship or dependence relationship in decoding, the data of the reference destination is first transmitted. By transmitting the data of the reference destination, the three-dimensional data decoding device can decode data in the order of obtaining and can reduce the required capacity of the receiver buffer or otherwise achieve efficient decoding. 
     In the following, a method of storing encoded data in a file format, such as ISOBMFF, will be described.  FIG. 58  is a diagram showing an example configuration of a bitstream.  FIG. 59  is a diagram showing an example configuration of a three-dimensional data encoding device. The three-dimensional data encoding device includes encoder  8801  and file transformer  8802 . Encoder  8801  generates a bitstream including encoded data and control information by encoding point cloud data. File transformer  8802  transforms the bitstream into a file format. 
       FIG. 60  is a diagram showing an example configuration of a three-dimensional data decoding device. The three-dimensional data decoding device includes file inverse transformer  8811  and decoder  8812 . File inverse transformer  8811  transforms a file format into a bitstream including encoded data and control information. Decoder  8812  generates point cloud data by decoding the bitstream. 
       FIG. 61  is a diagram showing a basic structure of ISOBMFF.  FIG. 62  is a diagram showing a protocol stack in a case where a common PCC codec NAL unit is stored in ISOBMFF. Here, what is stored in ISOBMFF is a PCC codec NAL unit. 
     NAL units include NAL units for data and NAL units for metadata. NAL units for data include geometry information slice data (Geometry Slice Data) and attribute information slice data (Attribute Slice Data), for example. NAL units for metadata include SPS, GPS, APS, and SEI, for example. 
     ISO based media file format (ISOBMFF) is a file format standard prescribed in ISO/IEC14496-12. ISOBMFF is a standard that does not depend on any medium, and prescribes a format that allows various media, such as a video, an audio, and a text, to be multiplexed and stored. 
     A basic 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. A file mainly includes boxes, such as ftyp that indicates the brand of the file by 4CC, moov that stores metadata, such as control information, and mdat that stores data. 
     A method for storing each medium in ISOBMFF is separately prescribed. For example, a method of storing an AVC video or an HEVC video is prescribed in ISO/IEC14496-15. It can be contemplated to expand the functionality of ISOBMFF and use ISOBMFF to accumulate or transmit PCC-encoded data. 
     When storing a NAL unit for metadata in ISOBMFF, SEI may be stored in “mdat box” along with PCC data, or may be stored in “track box” that describes control information concerning the stream. When packetizing and transmitting data, SEI may be stored in the packet header. By indicating SEI in a system layer, attribute information, tiles and slice data can be more easily accessed, and the access speed is improved. 
     Next, a first example of a format transform of PCC layer data will be described. The encoding method is a data compression technique. Additional functions are provided by a system format and have a different role than the encoding method. Such additional functions are prescribed in a different standard than the encoding method. To make the format optimal for providing the additional functions, the three-dimensional data encoding device transforms data. In the process, the three-dimensional data encoding device stores, in the encoded data, information that facilitates the transform in advance. In this way, the processing amount involved with the transform can be reduced. 
     In the following, a method of transforming data of each layer and hierarchical structure metadata including layer information into a file format will be described. Slice data, such as geometry information and attribute information, is each stored in a sample of the file format. The sample is stored in mdat. To allow access to sample data, information indicating a data configuration, offset information indicating the location of data, and length information indicating the length of data are stored in metadata, such as a random access table. These items of information may be stored in a different table than the random access table. 
     In the following, a case where slice data is stored in a sample will be described.  FIG. 63  is a diagram showing a process of transforming a bitstream into a file format. The three-dimensional data encoding device stores a geometry information slice and an attribute information slice in a sample (sample) in a one-to-one relationship. Here, a slice includes information (layer data) on all layers. 
     A geometry information sample belongs to a geometry information track (Geometry Track), and an attribute information sample belongs to an attribute information track (Attribute Track). Layer information is stored in metadata for each frame that belongs to a metadata track (Meta Data Track). Information indicating that a geometry information sample and an attribute information sample belong to the same frame, information indicating whether or not an attribute information sample refers to a geometry information sample in the case of the octree-based encoding method, timestamp information common to a geometry information sample and an attribute information sample, or other information may be stored in a metadata sample. 
     Frame units operating at a common timestamp may be referred to as an access unit. Note that layer information (layer_information) may be stored in moov. Here, the layer information includes information on the layer (layer_info) described above, for example. Note that the layer information may include at least part of the other information included in the hierarchical structure metadata or header described above, such as depth information (depth_info). 
     If this method is used, a slice can be stored as a sample as it is, so that the process is easy. 
       FIG. 64  is a flowchart of a format transforming process. First, the three-dimensional data encoding device starts a format transform of encoded data (S 8811 ). The three-dimensional data encoding device then stores one slice including a plurality of layers in one sample (S 8812 ). The three-dimensional data encoding device also stores layer information in metadata (S 8813 ). The three-dimensional data encoding device forms a frame (access unit: AU) (S 8814 ). 
     Next, a partial decoding method using a file format will be described.  FIG. 65  is a flowchart of this decoding process. First, the three-dimensional data decoding device extracts a desired sample by random access (S 8821 ). Specifically, the three-dimensional data decoding device determines the location of a desired sample using metadata included in moov, a random access table and the like, and extracts data of the sample. 
     The three-dimensional data decoding device analyzes layer information metadata (S 8822 ), and extracts layer boundary information in the sample (S 8823 ). Specifically, the three-dimensional data decoding device obtains the number of depths included in each layer in the sample and the data length of each depth, and obtains layer boundary information from the number of depths included in each layer and the data length of each depth. For example, the three-dimensional data decoding device calculates the data length of each layer from the number of depths included in the layer and the data lengths of the depths, and determines a data boundary between the layers based on the calculated data length of the layer. 
     The three-dimensional data decoding device then divides the layer based on the layer boundary information, and decodes desired data (S 8824 ). For example, the three-dimensional data decoding device extracts a particular layer component from the sample. 
     By including the layer information in the metadata in this way, the three-dimensional data decoding device can extract particular information based on the layer information without decoding the encoded data. 
     In the following, a second example of the format transform of PCC layer data will be described. When storing layer data in a sample, the three-dimensional data encoding device may store one item of layer data as one sample or as one sub-sample. 
       FIG. 66  is a diagram showing a process of transforming a bitstream into a file format. The three-dimensional data encoding device stores data for each layer of a geometry information slice and an attribute information slice in a sample in a one-to-one relationship. 
     A geometry information sample belongs to a geometry information track (Geometry Track), and an attribute information sample belongs to an attribute information track (Attribute Track). Layer information is stored in metadata for each frame that belongs to a metadata track (Meta Data Track). There is a track for each layer, and there is a sample belonging to each track. By providing a track for each layer, data can be more easily handled on a per layer basis. 
     In the bitstream of encoded data, slice data includes all items of layer data, and therefore, the three-dimensional data encoding device stores data in samples by dividing the data. When the layer information is indicated in the bitstream, the three-dimensional data encoding device divides slice data based on information indicating the data length of each item of layer data. When no layer information is indicated in the bitstream, the three-dimensional data encoding device calculates layer information while decoding the encoded data. The three-dimensional data encoding device encodes data again and divides the data based on the obtained layer information. 
     By this process, information for each layer can be stored in a track and a sample for the layer. Therefore, the three-dimensional data decoding device can extract data on a per layer basis, so that the data for each layer can be more easily handled. 
       FIG. 67  is a diagram showing a syntax example of hierarchical structure metadata. The hierarchical structure metadata includes layer information (layer_info), a component count (component), and depth information (depth_info) on each component. 
     Note that if header information is included in the sample when a slice is divided into layer data, the three-dimensional data encoding device may copy and add a slice header to all items of divisional data.  FIG. 68  is a diagram schematically shows such a division process. Note that the three-dimensional data encoding device may store a slice header in metadata, rather than in the sample. By copying the header information, the processing of creating a header can be reduced. 
     The three-dimensional data encoding device may add, to the file format, an identifier that indicates whether data to be stored in a sample is layered or not. When the data is layered, an identifier that indicates whether the data includes all layer data or not or whether the data stored in the sample is layer data obtained by layering the data may be added to the file format. The three-dimensional data encoding device may indicate these items of information by a medium type or a box type (type), such as 4CC. In this way, the medium can be more easily identified. 
       FIG. 69  is a flowchart of a transform process using layer information. First, the three-dimensional data encoding device starts a format transform of encoded data (S 8831 ). The three-dimensional data encoding device then divides a slice into information on a per layer basis using layer information metadata (S 8832 ). The three-dimensional data encoding device then stores each of the plurality of items of layer data resulting from the division in one sample (S 8833 ). The three-dimensional data encoding device then stores layer information in metadata (S 8834 ). The three-dimensional data encoding device then forms a frame (AU) (S 8835 ). 
       FIG. 70  is a flowchart of a transform process that uses no layer information. First, the three-dimensional data encoding device starts a format transform of encoded data (S 8841 ). The three-dimensional data encoding device then decodes the data and determines a boundary of layer data (S 8842 ). The three-dimensional data encoding device then encodes the data again and divides the data (S 8843 ). The three-dimensional data encoding device then stores each item of the plurality of items of layer data resulting from the division in one sample (S 8844 ). The three-dimensional data encoding device then stores layer information in metadata (S 8845 ). The three-dimensional data encoding device then forms a frame (AU) (S 8846 ).  FIG. 71  is a flowchart of a decoding process for sample data of layer data. First, the three-dimensional data decoding device extracts a desired sample by random access (S 8851 ). The three-dimensional data decoding device then decodes data included in the extracted sample (S 8852 ). 
     Next, another example of the layer data structure will be described.  FIG. 72  and  FIG. 73  are diagrams showing example configurations of the overall encoded data (PCC data). The hierarchical structure in the examples shown in  FIG. 72  and  FIG. 73  are the same as that in  FIG. 49 . 
       FIG. 72  shows a case where one item of depth data is used as one item of slice data, in which a slice header is assigned for each item of depth data. The slice header includes depthId that identifies the layer of the depth data, layerId that indicates the layer to which the depth belongs, and length that indicates the length of the depth data. The slice header may further include groupId that indicates that data belongs to the same frame. That is, groupId indicates a frame (time) to which the data belongs. 
     When these items of information are included in the slice header, the overall encoded data need not have hierarchical structure metadata. The three-dimensional data encoding device may store a parameter common to all the depths in the header of the slice that transmits the first depth, or may store the parameter in a common header and arrange the parameter ahead of the data of depth #0. Note that the three-dimensional data encoding device may store depthId and groupId in the slice header, and store the number of depths and layerId and length for each depth in the hierarchical structure metadata or the common header. 
     The data of depth #0 can be decoded by itself, and data of the depths other than depth #0 cannot be decoded by itself and depends on other data. The three-dimensional data decoding device determines that data of the depths other than depth #0 cannot be decoded by itself, and decodes depth data to be decoded along with depth data that has the same groupId as the depth data to be decoded and has depthId smaller than depthId of the depth data to be decoded. 
       FIG. 73  shows a case where one item of layer data is used as one item of slice data, in which a slice header is assigned for each item of layer data. The slice header includes layerId, and the depth count (num_depth) indicating the number of depths included in the layer, and the length (length) of the depth data. The slice header may further include groupId that indicates that layer data belongs to the same frame. Note that the slice header may include layerId and groupId, and the number of layers, the number of depths included in each layer, and the length information (length) on each depth may be included in the hierarchical structure metadata. 
     By using this structure, the above-described data can be more easily divided into items of data on a per layer basis, so that the processing amount involved with the division can be reduced. In addition, divisional data can be transmitted, so that the amount of transmission can be reduced. In addition, the geometry information and the attribute information can be divided on a per layer basis in the same manner. 
     Next, a third example of the format transform of PCC layer data will be described. When storing layer data in a sample, the three-dimensional data encoding device may store one item of depth data as one sample or as one sub-sample. 
       FIG. 74  is a diagram showing a process of transforming a bitstream into a file format. The three-dimensional data encoding device stores data for each layer of a geometry information slice and an attribute information slice in a sample in a one-to-one relationship. 
     A geometry information sample belongs to a geometry information track (Geometry Track), and an attribute information sample belongs to an attribute information track (Attribute Track). Layer information is stored in metadata for each frame that belongs to a metadata track (Meta Data Track). There is a track for each layer, and there is a sample belonging to each track. By providing a track for each layer, data can be more easily handled on a per layer basis. 
     In the bitstream of encoded data, slice data is formed for each item of layer data, and therefore, the three-dimensional data encoding device can directly store data in a sample as it is. Therefore, the processing amount can be reduced compared with the case where slice data is not formed for each item of layer data. The layer information is stored in metadata. 
       FIG. 75  is a flowchart of a format transforming process. First, the three-dimensional data encoding device starts a format transform of encoded data (S 8861 ). The three-dimensional data encoding device then stores slice data for each layer in one sample (S 8862 ). The three-dimensional data encoding device then stores layer information in metadata (S 8863 ). The three-dimensional data encoding device then forms a frame (AU) (S 8864 ). 
       FIG. 76  is a flowchart of a decoding process. First, in order to access particular layer data, the three-dimensional data decoding device analyzes metadata and obtains the number of depths belonging to the layer (S 8871 ). Based on the obtained information, the three-dimensional data decoding device then calculates the starting position of the depth data at the head of the layer data and the total layer size (S 8872 ). The three-dimensional data decoding device then decodes the layer data (S 8873 ). 
       FIG. 77  is a diagram showing a syntax example of the depth information.  FIG. 78  is a diagram showing a syntax example of a sample size box (sample_size_box: stsz). The three-dimensional data encoding device may store the size (entry_size) of the layer data of each sample in a sample size box that stores size information on the sample. 
       FIG. 79  is a diagram showing a syntax example of layer information (layer_info).  FIG. 80  is a diagram showing a syntax example of PCCLayerStructureBox. For example, as shown in  FIG. 79  and  FIG. 80 , the three-dimensional data encoding device stores the layer count (layer) and the numbers of depths (num_depth) included in the layers in PCCLayerStructureBox. Note that the three-dimensional data encoding device may store these items of information in the same box or in different boxes. 
     Next, a process of extracting partial data from a file format will be described. Based on the data structure and the hierarchical structure metadata described above in this embodiment, the three-dimensional data decoding device randomly accesses, from the file, a part of data to be decoded to extract the data. The three-dimensional data decoding device can access data and extract desired data based on frame information, layer information, data length information, and the numbers of depths included in layers of the geometry information and attribute information included in the metadata. 
       FIG. 81  is a diagram schematically showing this extraction operation. Transmitter  8821  has a file (file format) of complete data having layer 0 and layer 1, and receiver  8823  has a data file of layer 0. In this state, in order to obtain data of layer 1, receiver  8823  requests transmitter  8821  to transmit a file of layer 1. Extractor  8822  included in transmitter  8821  extracts the file of layer 1 from the file (file format) of the complete data, and provides the file (bitstream) of layer 1 to receiver  8823 . Receiver  8823  integrates the file of layer 0 and the file of layer 1 to generate the file of the complete data.  FIG. 82  is a diagram showing an example of the file (file format) of the complete data.  FIG. 83 ,  FIG. 84 , and  FIG. 85  are diagrams showing examples of the bitstream extracted by extractor  8822 . For example, as shown in  FIG. 83 , extractor  8822  may extract all data from the file format. Alternatively, as shown in  FIG. 84 , extractor  8822  may extract geometry information and need not extract attribute information. Alternatively, as shown in  FIG. 85 , extractor  8822  may extract layer 0 and need not extract layer 1. Alternatively, although not shown, extractor  8822  may re-order data before transmitting the data, for example. 
     By using the data structure and hierarchical structure metadata described in this embodiment, the layer data can be more easily divided, and therefore, a function of obtaining necessary data without obtaining unnecessary data can be implemented. As a result, the transmission band and the transmission delay can be reduced, and the data transmission functionality is improved. 
     Next, a partial decoding process for direct mode data will be described. The direct mode is a method of stopping the octree (Octree) encoding at a certain node in the octree-based encoding and directly encoding the coordinates of a point of a leaf node. For example, the direct mode is used when the points belonging to a node are sparce. By using the direct mode, the data amount can be reduced. 
       FIG. 86  is a diagram showing an example of the direct mode. In  FIG. 86 , the part enclosed by a dotted line includes two leaf points (sparce). For example, if it is determined at an A node at depth=1 that the points are sparce, the coordinates of these two points are directly described in a data region of depth1. The coordinates of the two points are coordinates with respect to the A node, and are coordinates having a resolution at depth=4. That is, the data at depth=1 includes an occupancy code (occupancy_code) at depth=1 and coordinate (B region) data at depth=4 in the direct mode enclosed by the dotted line. 
     Next, such a data decoding method will be described. When decoding depth0 to depth4, the three-dimensional data decoding device performs the decoding process in a normal decoding method. On the other hand, if all items of decoded data need to have the same resolution when partial data of depth0 to depth1 is extracted and decoded, the three-dimensional data decoding device may perform the decoding without using the coordinates at depth4 included in the data of depth 1. When there can be data of high resolution, the three-dimensional data decoding device can perform the decoding using the coordinates at depth4 included in the data of depth1. 
     Next, a data division in the case where the direct mode is used will be described. When extracting and transmitting data of depth0 to depth1, a transmission device may or may not include the information obtained in the direct mode (depth4) in the data of depth 1. 
     The transmission device may determine whether to include the information obtained in the direct mode based on whether the receiving device requires the information or not, and may include the information in the bitstream when the receiving device requires the information and need not include the information in the bitstream when the receiving device does not require the information. In this way, the data amount can be reduced. For example, the transmission device may determine that the information obtained in the direct mode is required when data of the resolutions at depth2 to depth4 can be decoded along with the data of depth0 to depth1, and determine that the information obtained in the direct mode is not required when the data of depth2 to depth4 is not to be decoded. 
     As described above, the three-dimensional data encoding device performs the processes illustrated in  FIG. 87 . The three-dimensional data encoding device sets a hierarchical structure for items of geometry information of three-dimensional points included in point cloud data, the hierarchical structure having depths and layers each having one or more of the depths (S 8881 ). The three-dimensional data encoding device encodes the items of geometry information on a per depth basis to generate items of first encoded data (for example, depth data) each for a different one of the depths (S 8882 ). The three-dimensional data encoding device generates a bitstream including items of second encoded data which are items of encoded data for respective layers, the items of second encoded data each including one or more items of first encoded data of one or more depths included in a layer corresponding to the item of second encoded data (S 8883 ). The bitstream includes an item of first information indicating a data length of each of the items of second encoded data. 
     Accordingly, a three-dimensional data decoder that decodes the bitstream can easily access data of any layer by using the first information. Therefore, the three-dimensional data encoder can reduce the processing amount of the three-dimensional data decoder. 
     For example, the item of first information includes: an item of second information (for example, num_depth) indicating a total number of depths included in each of the layers; and an item of third information (for example, length) indicating a data length of each of the items of first encoded data. 
     For example, the bitstream includes a first header (for example, hierarchical structure metadata or header illustrated in  FIG. 49 ) which is common to the items of second encoded data, and the first header includes the item of first information. 
     For example, the bitstream includes second headers (for example, the slice header illustrated in  FIG. 73 ) each for a different one of the items of second encoded data. The item of first information includes items of fourth information each corresponding to a different one of the items of second encoded data and indicating a data length of the item of second encoded data to which the item of fourth information corresponds. Each of the second headers includes an item of fourth information indicating a data length of an item of second encoded data corresponding to the second header, the item of fourth information being included in the items of fourth information, the item of second encoded data being included in the items of second encoded data. 
     For example, the bitstream includes third headers (for example, the slice header illustrated in  FIG. 72 ) each for a different one of the items of first encoded data. The item of first information includes: an item of second information (for example, num_depth) indicating a total number of depths included in each of the layers; and items of fifth information (for example, length) each corresponding to a different one of the items of first encoded data and indicating a data length of the item of first encoded data to which the fifth information corresponds. Each of the third headers includes an item of fifth information indicating a data length of an item of first encoded data corresponding to the third header, the item of fifth information being included in the items of fifth information, the item of first encoded data being included in the items of first encoded data. 
     For example, the three-dimensional data encoding device further encodes items of attribute information of the three-dimensional points on a per depth basis to generate items of third encoded data each for a different one of the depths. The bitstream includes items of fourth encoded data which are items of encoded data for respective layers, the items of fourth encoded data each including one or more items of third encoded data of one or more depths included in a layer corresponding to the item of fourth encoded data. The bitstream includes an item of sixth information indicating a data length of each of the items of fourth encoded data. 
     For example, the three-dimensional data encoder includes a processor and memory, and the processor performs the above-described processes using the memory. 
     Furthermore, the three-dimensional data decoding device performs the processes illustrated in  FIG. 88 . The three-dimensional data decoding device obtains, from a bitstream including items of second encoded data and an item of first information indicating a data length of each of the items of second encoded data, the item of first information (S 8886 ). The three-dimensional data decoding device obtains at least one item of second encoded data from among the items of second encoded data, using the item of first information (S 8887 ). The three-dimensional data decoding device decodes the at least one item of second encoded data obtained (S 8888 ). The bitstream includes items of first encoded data each for a different one of depths, the items of first encoded data being generated by encoding, on a per depth basis, items of geometry information of three-dimensional points included in point cloud data, for which a hierarchical structure is set, the hierarchical structure having depths and layers each having one or more of the depths. Each of the items of second encoded data corresponds to a different one of the layers and includes, among the items of the first encoded data, one or more items of first encoded data included in a layer corresponding to the second encoded data. 
     Accordingly, the three-dimensional data decoder can easily access data of any layer by using the first information. Therefore, the three-dimensional data decoder can reduce the processing amount. 
     For example, the item of first information includes: an item of second information (for example, num_depth) indicating a total number of depths included in each of the layers; and an item of third information (for example, length) indicating a data length of each of the items of first encoded data. For example, the third-dimensional data decoding device calculates the data length of second encoded data using the item of second information and the item of third information. 
     For example, the bitstream includes a first header (for example, the hierarchical structure metadata or the header illustrated in  FIG. 49 ) which is common to the items of second encoded data, and the first header includes the item of first information. 
     For example, the bitstream includes second headers (for example, the slice header illustrated in  FIG. 73 ) each for a different one of the items of second encoded data. The item of first information includes items of fourth information each corresponding to a different one of the items of second encoded data and indicating a data length of the item of second encoded data to which the item of fourth information corresponds. Each of the second headers includes an item of fourth information indicating a data length of an item of second encoded data corresponding to the second header, the item of fourth information being included in the items of fourth information, the item of second encoded data being included in the items of second encoded data. 
     For example, the bitstream includes third headers (for example, the slice header illustrated in  FIG. 72 ) each for a different one of the items of first encoded data. The item of first information includes: an item of second information (for example, num_depth) indicating a total number of depths included in each of the layers; and items of fifth information (for example, length) each corresponding to a different one of the items of first encoded data and indicating a data length of the item of first encoded data to which the fifth information corresponds. Each of the third headers includes an item of fifth information indicating a data length of an item of first encoded data corresponding to the third header, the item of fifth information being included in the items of fifth information, the item of first encoded data being included in the items of first encoded data. 
     For example, the bitstream includes items of third encoded data each for a different one of the depths, the items of third encoded data being generated by encoding items of attribute information of the three-dimensional points on a per depth basis. The bitstream includes items of fourth encoded data which are items of encoded data for respective layers, the items of fourth encoded data each including one or more items of third encoded data of one or more depths included in a layer corresponding to the item of fourth encoded data. The bitstream includes an item of sixth information indicating a data length of each of the items of fourth encoded data. The three-dimensional data decoding device further: obtains the item of sixth information from the bitstream; obtains at least one item of fourth encoded data from among the items of fourth encoded data, using the item of sixth information; and decodes the at least one item of fourth encoded data obtained. 
     For example, the three-dimensional data decoder includes a processor and memory, and the processor performs the above-described processes using the memory. 
     Embodiment 6 
     Embodiment 6 will be described. 
     Conformance is a predetermined criterion (a criterion defined by a standard, for example) that a three-dimensional point cloud encoded by a three-dimensional data encoding device, that is, a bitstream, or a three-dimensional data decoding device that decodes the bitstream needs to satisfy. Conformance may be referred to also as conformance point or conformity point, or conformity level. The three-dimensional data encoding device selects one conformance from a plurality of previously determined conformances, and encodes a three-dimensional point cloud based on the selected one conformance in a predetermined method. The three-dimensional data decoding device determines whether to decode a bitstream or not based on whether the bitstream is in conformity with the conformance or not and whether the three-dimensional data decoding device supports the decoding of the bitstream in conformity with the predetermined conformance. 
     The three-dimensional data encoding device encodes a three-dimensional point cloud in an arbitrary method (a predetermined process) in such a manner that the bitstream can satisfy the previously determined conformance. As the arbitrary method for the three-dimensional point cloud, the three-dimensional data encoding device may perform a scaling process, quantization, division on a slice or tile basis, offset of a divisional space, or table referencing (code book), for example. The precision level of the three-dimensional point cloud may be adjusted to increase, maintain, or decrease the bit precision. The three-dimensional data encoding device encodes a three-dimensional point cloud to generate a bitstream including information that indicates the conformance satisfied by the bitstream. 
     The three-dimensional data decoding device obtains the information indicating the conformance from the bitstream (a syntax of encoded data, for example), and judges, based on the information indicating the conformance, whether the bitstream of the encoded three-dimensional point cloud satisfies the previously determined conformance or not. When it is judged that the conformance is satisfied, the three-dimensional data decoding device decodes the point cloud data. 
     A combination (set) of conformances may include parameters listed below. A combination of conformances may include any one of the precision of the encoding of the three-dimensional point cloud (that is, the bit count (i.e., the number of bits) of encoded data), the number of three-dimensional points of each divisional data (slice or tile) unit, the number of processing cores available to the three-dimensional data decoding device, the rate of the processor of the three-dimensional data decoding device, an application requirement on the three-dimensional data decoding device (real-time, low power consumption mode, or remote server processing, for example), whether lossless encoding or lossy encoding, and information on a bounding box of a slice, for example. 
     Note that, in this embodiment, the bit precision means the bit count. The bit precision means the precision of hardware processing. 
       FIG. 89  is a block diagram illustrating an example of a configuration of a three-dimensional data encoding device according to Embodiment 6.  FIG. 90  is a flowchart illustrating a first example of a three-dimensional data encoding method according to Embodiment 6. 
     Three-dimensional data encoding device  9600  includes judgment unit  9601 , transformer  9602 , and encoder  9603 . 
     Point cloud data on a three-dimensional point cloud is input to three-dimensional data encoding device  9600 . In this way, three-dimensional data encoding device  9600  obtains point cloud data. 
     Judgment unit  9601  of three-dimensional data encoding device  9600  determines a conformance of encoded data, which is the point cloud data on the three-dimensional point cloud after encoding (S 9601 ). Here, the conformance is determined based on the capability of the relevant equipment (three-dimensional data decoding device), a use case of an application, or the type of the three-dimensional point cloud to be handled, for example. The conformance may be previously determined or adaptively determined. Three-dimensional data encoding device  9600  determines the conformance by selecting one conformance from a combination of conformances. 
     Judgment unit  9601  judges whether the three-dimensional point cloud of the point cloud data satisfies the determined conformance or not (S 9602 ). 
     When it is judged by judgment unit  9601  that the three-dimensional point cloud of the point cloud data does not satisfy the determined conformance (No in S 9602 ), transformer  9602  performs a predetermined processing so that the determined conformance is satisfied (S 9603 ). Transformer  9602  may perform quantization or data division, for example, as the predetermined processing. 
     Following step S 9603 , or when it is judged by judgment unit  9601  that the three-dimensional point cloud of the point cloud data satisfies the determined conformance (Yes in S 9602 ), encoder  9603  generates metadata including a conformance index that indicates the determined conformance (S 9604 ). The conformance index is identification information for identifying one of a combination of a plurality of conformances. 
     Encoder  9603  encodes the point cloud data transformed in step S 9603 , or the point cloud data that is not transformed if the result of the judging in step S 9602  is Yes, to generate a bitstream including the encoded point cloud data and the metadata (S 9605 ). 
       FIG. 91  is a block diagram illustrating an example of a configuration of a three-dimensional data decoding device according to Embodiment 6.  FIG. 92  is a flowchart illustrating an example of a three-dimensional data decoding method according to Embodiment 6. 
     Three-dimensional data decoding device  9610  includes judgment unit  9611  and decoder  9612 . 
     Three-dimensional data decoding device  9610  obtains a bitstream. The bitstream includes encoded point cloud data (encoded data) and metadata including a conformance index. 
     Three-dimensional data decoding device  9610  is a decoding device that is in conformity with at least any of a plurality of previously determined conformances, and can decode a bitstream if the bitstream is data that is in conformity with a conformance supported by three-dimensional data decoding device  9610 . 
     Judgment unit  9611  obtains the conformance index from the metadata (S 9611 ). 
     Judgment unit  9611  judges whether or not the conformance indicated by the conformance index is included in the conformances with which three-dimensional data decoding device  9611  is in conformity (S 9612 ). The conformances with which three-dimensional data decoding device  9610  is in conformity are decoding conditions for three-dimensional data decoding device  9610 . Judgment unit  9611  also judges whether or not the bitstream satisfies the conformance indicated by the conformance index (S 9612 ). In other words, judgment unit  9611  judges whether or not the bitstream satisfies the decoding conditions for three-dimensional data decoding device  9610 . 
     When it is judged by judgment unit  9611  that the bitstream satisfies any conformance with which three-dimensional data decoding device  9610  is in conformity (Yes in S 9612 ), decoder  9612  decodes the encoded point cloud data included in the bitstream (S 9613 ). 
     When it is judged by judgment unit  9611  that the bitstream does not satisfy any conformance with which three-dimensional data decoding device  9610  is in conformity (No in S 9612 ), decoder  9612  skips the decoding of the encoded point cloud data included in the bitstream, and does not decode the point cloud data (S 9614 ). 
     Note that, when the result of the judging in step S 9612  is No, decoder  9612  may directly decode the point cloud data or proceed to a dedicated error process to perform a predetermined processing. Here, the predetermined processing may be a processing in which the quality of the decoding result is judged, and the decoding result is directly displayed (output) if the result of the judging shows that the quality has no problem and is not displayed (output) if the result of the judging shows that the quality is poor. 
     Next, types of restrictions caused by setting conformances will be described. 
     Targets on which a conformance restriction is imposed (referred to as a restriction target) may be two targets, an input point cloud and divisional data. 
     The input point cloud is point cloud data indicating a three-dimensional point cloud input to the three-dimensional data encoding device. The input point cloud is the original point cloud data yet to be divided into slices or tiles. The input point cloud is the same as the point cloud data obtained by dividing the point cloud data into a plurality of pieces of divisional data and then integrating the plurality of pieces of divisional data. When such an input point cloud is a restriction target, the conformance includes the number of three-dimensional points of the input point cloud, the bit precision (bit count), or the like. In that case, the input point cloud that is in conformity with the conformance may be generated by using a sensor that outputs, as the input point cloud, a detection result that is in conformity with the conformance. The input point cloud that is in conformity with the conformance may be generated by the three-dimensional data encoding device performing a predetermined processing on an existing input point cloud so that the existing input point cloud comes in conformity with the conformance. 
     Instead of imposing a restriction on an input point cloud as described above, divisional data may be a restriction target. The divisional data is data obtained by dividing an input point cloud into slices or tiles. When the divisional data is a restriction target, the conformance includes the number of three-dimensional points of each divisional data unit, the bit precision (bit count), or the like. That is, the three-dimensional data encoding device may perform a process of dividing an input point cloud in such a manner that the divisional data obtained by the division of the input point cloud satisfies the conformance. 
     Note that the conformance may be set for both the input point cloud and the divisional data. In that case, when the input point cloud does not satisfy the conformance, the three-dimensional data encoding device divides the input point cloud into a plurality of pieces of divisional data so that each divisional data unit satisfies the conformance. On the other hand, when the input point cloud satisfies the conformance, the three-dimensional data encoding device need not divide the input point cloud into a plurality of pieces of divisional data. That is, when the input point cloud satisfies the conformance, the three-dimensional data encoding device can directly encode the input point cloud without dividing the input point cloud. 
     When the restriction is imposed on the input point cloud, the three-dimensional data encoding device can use the conformance for the input point cloud (the number of three-dimensional points of the input point cloud, the bit count, or the like) as a regulation when generating the input point cloud that is in conformity with the conformance in advance. On the other hand, when the restriction is imposed on the divisional data, the three-dimensional data encoding device can use the conformance as a regulation when dividing the input point cloud that is not in conformity with the input point cloud. 
     For example, with a three-dimensional point cloud used for map data, the number of three-dimensional points to be handled or the distribution range of the three-dimensional point cloud varies with the size or density of the map, and has no upper limit. For such a large-scale three-dimensional point cloud, the method in which a restriction is imposed on divisional data can be used. In other words, by imposing a restriction on a divisional data basis, large-scale point cloud data having no upper limit of the number of three-dimensional points or the bit count can be decoded even by a three-dimensional data decoding device having a limited resource (memory or processing capability). 
     Furthermore, by imposing a restriction on both the input point cloud and the divisional data, this encoding method can be applied to various contents. 
       FIG. 93  is a flowchart illustrating a second example of the three-dimensional data encoding method according to Embodiment 6. This three-dimensional data encoding method is a method in which processes are changed depending on whether the restriction target is an input point cloud or divisional data. 
     The three-dimensional data encoding device judges whether the restriction target is an input point cloud or divisional data (S 9621 ). Whether the restriction target is an input point cloud or divisional data may be determined in advance by a user or may be determined depending on the application of the three-dimensional point cloud. 
     When it is judged that the restriction target is an input point cloud (input point cloud in S 9621 ), the three-dimensional data encoding device restricts the bit precision (bit count) or the point count (i.e., the number of points) of the input point cloud (S 9622 ). Specifically, the three-dimensional data encoding device determines the bit precision or point count as a conformance for the input point cloud. The bit count is the maximum bit count for the encoded data obtained by encoding the point cloud data of the input point cloud. The point count is the range of the number of three-dimensional points included in the input point cloud. 
     The three-dimensional data encoding device judges whether or not the input point cloud falls within the regulation (S 9623 ). That is, the three-dimensional data encoding device judges whether or not the input point cloud satisfies the conformance determined in step S 9622 . 
     When it is judged that the input point cloud does not fall within the regulation (No in S 9623 ), the three-dimensional data encoding device processes the input point cloud so that the input point cloud comes in conformity with the regulation. That is, when the input point cloud does not satisfy the conformance, the three-dimensional data encoding device performs a predetermined processing on the input point cloud so that the input point cloud comes in conformity with the conformance. 
     When it is judged that the input point cloud falls within the regulation (Yes in S 9623 ), the three-dimensional data encoding device encodes the input point cloud judged to fall within the regulation (S 9630 ). The three-dimensional data encoding device also encodes the processed input point cloud, which has been subjected to the predetermined processing in step S 9624  and satisfies the conformance (S 9630 ). 
     Referring back to step S 9621 , when it is judged that the restriction target is divisional data (divisional data in S 9621 ), the three-dimensional data encoding device restricts the bit precision (bit count) or the point count for each piece of divisional data (S 9625 ). Specifically, the three-dimensional data encoding device determines the bit precision or point count as a conformance for each divisional data unit. 
     The three-dimensional data encoding device judges whether or not the input point cloud falls within the regulation (S 9626 ). Step S 9626  is the same processing as step S 9623 . 
     When it is judged that the input point cloud falls within the regulation (Yes in S 9626 ), the three-dimensional data encoding device encodes the input point cloud judged to fall within the regulation (S 9630 ). 
     Step S 9626  does not necessarily have to be performed. 
     When it is judged that the input point cloud does not fall within the regulation (No in S 9626 ), the three-dimensional data encoding device divides the input point cloud into a plurality of pieces of divisional data (S 9627 ). For example, the three-dimensional data encoding device may divide a three-dimensional space in which the input point cloud exists into a plurality of subspaces and determine point cloud data representing the three-dimensional point cloud included in each subspace as a piece of divisional data. The subspace may be a slice or a tile. 
     The three-dimensional data encoding device judges whether or not the divisional data falls within the regulation (S 9628 ). That is, the three-dimensional data encoding device judges whether or not the divisional data satisfies the conformance determined in step S 9625 . 
     When it is judged that the divisional data does not fall within the regulation (No in S 9628 ), the three-dimensional data encoding device processes the divisional data so that the divisional data comes in conformity with the regulation (S 9629 ). That is, when the divisional data does not satisfy the conformance, the three-dimensional data encoding device performs a predetermined processing on the divisional data so that the divisional data satisfies the conformance. 
     When it is judged that the divisional data falls within the regulation (Yes in S 9628 ), the three-dimensional data encoding device encodes the divisional data judged to fall within the regulation (S 9630 ). The three-dimensional data encoding device also encodes the processed divisional data, which has been subjected to the predetermined processing in step S 9629  and satisfies the conformance (S 9630 ). 
     Note that the judging of whether the divisional data satisfies the conformance or not or the predetermined processing for making the divisional data come in conformity with the regulation may be performed for each piece of divisional data. That is, there may be both divisional data that is subjected to the predetermined processing for making the divisional data come in conformity with the regulation and divisional data that is not subjected to the predetermined processing. That is, it is possible that the judging in step S 9628  is performed on each of the plurality of pieces of divisional data, and the predetermined processing (S 9629 ) for making the divisional data come in conformity with the regulation is performed on divisional data of the plurality of pieces of divisional data that does not satisfy the regulation, and the predetermined processing (S 9629 ) for making the divisional data come in conformity with the regulation is not performed on divisional data that satisfies the regulation. 
     When encoding, the three-dimensional data encoding device may add, to the bitstream, metadata including restriction target information that indicates whether the input point cloud or the divisional data is set as the restriction target. 
       FIG. 94  is a diagram illustrating an example of a bounding box. 
     As a restriction method for the bit precision of divisional data, for example, there is a method of determining the size of a bounding box of divisional data. For example, as the size of a bounding box, the height, the width, and the depth may be defined to fall within the same, predetermined N bits. Note that an upper limit (maximum value) of the bit count of each of the height, the width, and the depth may be defined. 
       FIG. 95  is a flowchart illustrating another example of the three-dimensional data decoding method according to Embodiment 6. 
     The three-dimensional data decoding device analyzes the metadata included in the bitstream to obtain the conformance (restriction condition) included in the metadata (S 9631 ). The conformance is the conformance determined when the three-dimensional data encoding device encodes the input point cloud or divisional data. 
     The three-dimensional data decoding device judges whether or not the restriction target is the input point cloud or the divisional data (S 9632 ). 
     When it is judged that the restriction target is the input point cloud (input point cloud in S 9632 ), the three-dimensional data decoding device checks whether or not the bitstream of a unit input point cloud satisfies the decoding condition for the three-dimensional data decoding device (S 9633 ). When the result of the check shows that the bitstream of the unit input point cloud satisfies the decoding condition, the three-dimensional data decoding device decodes the encoded input point cloud included in the bitstream. When the bitstream of the unit input point cloud does not satisfy the decoding condition, the three-dimensional data decoding device need not decode the encoded input point cloud. 
     When it is judged that the restriction target is the divisional data (divisional data in S 9632 ), the three-dimensional data decoding device checks whether or not the bitstream of unit divisional data satisfies the decoding condition (S 9634 ). When the result of the check shows that the bitstream of the unit divisional data satisfies the decoding condition, the three-dimensional data decoding device decodes the encoded divisional data included in the bitstream. When the bitstream of the unit divisional data does not satisfy the decoding condition, the three-dimensional data decoding device need not decode the encoded divisional data. 
     Next, the predetermined processing in a case where a restriction on the bit count for each slice is defined will be described. 
       FIG. 96  is a flowchart illustrating a third example of the three-dimensional data encoding method according to Embodiment 6. This flowchart is an example in a case where a processing of reducing the bit count is performed as the predetermined processing. Note that, although a case where the restriction target is the input point cloud will be described below as an example, the same description applies to a case where the restriction target is the divisional data. That is, the term “input point cloud” can be read as “divisional data”. 
     The three-dimensional data encoding device determines the conformance concerning the bit count of geometry information of the input point cloud (S 9641 ). Specifically, the three-dimensional data encoding device determines, as the conformance, an upper limit of the bit count (a first maximum bit count) of the encoded data obtained by encoding the input point cloud. The first maximum bit count relates to the bit count of the encoded data of geometry information. The geometry information included in the input point cloud indicates the position of each three-dimensional point in the input point cloud. The geometry information is the coordinates of each three-dimensional point, for example. The coordinates may be those in the Cartesian coordinate system or in the polar coordinate system. 
     The three-dimensional data encoding device judges whether or not the bit count of the geometry information of the input point cloud satisfies the conformance determined in step S 9641  (S 9642 ). That is, the three-dimensional data encoding device judges whether or not the bit count of the geometry information of the input point cloud is equal to or smaller than the first maximum bit count. 
     When it is judged that the bit count of the geometry information of the input point cloud does not satisfy the determined conformance (No in S 9642 ), that is, when it is judged that the bit count of the geometry information of the input point cloud is greater than the first maximum bit count, the three-dimensional data encoding device performs, as the predetermined processing, a processing of reducing the bit count of the geometry information of the input point cloud (S 9643 ). 
     When it is judged that the bit count of the geometry information of the input point cloud satisfies the determined conformance (Yes in S 9642 ), the three-dimensional data encoding device encodes the geometry information of the input point cloud (S 9644 ). The three-dimensional data encoding device also encodes the geometry information of the processed input point cloud, which has been subjected to the predetermined processing in step S 9643  and satisfies the conformance (S 9644 ). 
     The three-dimensional data encoding device generates a bitstream by encoding point cloud data in such a manner that the point cloud data satisfies the determined conformance by performing steps S 9642  to S 9644 . Specifically, the three-dimensional data encoding device generates a bitstream by encoding geometry information of a input point cloud in such a manner that the geometry information is equal to or smaller than a determined first maximum bit count. The three-dimensional data encoding device adds, to the bitstream, conformance information indicating the determined conformance. The conformance information is first bit count information indicating the first maximum bit count, for example. The first bit count information may be the first maximum bit count itself or may be identification information for uniquely identifying the first maximum bit count. The identification information is the conformance index, for example. 
     Next, the predetermined processing in step S 9643  in  FIG. 96  will be described. 
       FIG. 97  illustrates an example of the processing of reducing the bit count according to Embodiment 6. 
     In the predetermined processing, position coordinates (x, y, z) may be quantized to reduce the bit count. For example, as shown in  FIG. 97 , when the maximum bit count defined by the conformance is 4, if any of the coordinates (x, y, z) included as the geometry information is 6-bit, the bit count of the geometry information is greater than the maximum bit count defined by the conformance. Therefore, as the predetermined processing performed on the input point cloud so that the conformance is satisfied, 2-bit shift quantization is performed to reduce the bit count of the geometry information by 2 bits. Here, the data to be subjected to the 2-bit shift quantization may be input bits or bits substantially used of all three-dimensional points in the input point cloud. 
       FIG. 98  illustrates another example of the processing of reducing the bit count according to Embodiment 6. 
     In the predetermined processing, data division into slices, tiles or the like may be used to reduce the bit precision on a slice basis, tile basis, or the like. Specifically, when performing slice-based data division of the input point cloud, the three-dimensional data encoding device may reduce the bit precision by shifting the coordinates of the origins of the other slices to coincide with the coordinates of the origin of one slice. 
     When the maximum bit count for each slice is defined as the conformance, if the number of bits of each point cloud (the bit count of the size, that is, the width, the height, and the depth, of the bounding box including a slice) does not satisfy the conformance (that is, the maximum bit count for a slice does not satisfy the conformance), the three-dimensional data encoding device divides the point cloud so that the bit count of the bounding box of the slice satisfies the conformance. The three-dimensional data encoding device can then reduce the bit count by shifting the origin of the bounding box of a divisional slice (slice 2) to coincide with the origin of the bounding box of a divisional slice (slice 1) in  FIG. 98 , thereby making the bit count come in conformity with the conformance. For example, when there is a rule that the upper limit of the bit count of each slice is M bits, if the width of the bounding box forming the input point cloud is N (&gt;M) bits, the width of the bounding box may be divided into int(N/M)+1 pieces having a size of M bits. 
     Note that, although a predetermined processing is described using a two-dimensional space in  FIG. 98 , the predetermined processing may be applied to a three-dimensional space or a space of other dimensions. 
       FIG. 99  is a flowchart illustrating a fourth example of the three-dimensional data encoding method according to Embodiment 6. This flowchart is an example in a case where a processing of increasing the bit count is performed as the predetermined processing. 
     The three-dimensional data encoding device determines the conformance concerning the bit count of geometry information of the input point cloud (S 9651 ). Specifically, the three-dimensional data encoding device determines, as the conformance, an upper limit of the bit count (a first maximum bit count) of the encoded data obtained by encoding the input point cloud. 
     The three-dimensional data encoding device judges whether or not the bit count of the geometry information of the input point cloud satisfies the conformance determined in step S 9651  (S 9652 ). That is, the three-dimensional data encoding device judges whether or not the bit count of the geometry information of the input point cloud is equal to the first maximum bit count. 
     When it is judged that the bit count of the geometry information of the input point cloud does not satisfy the determined conformance (No in S 9652 ), that is, when it is judged that the bit count of the geometry information of the input point cloud is smaller than the first maximum bit count, the three-dimensional data encoding device performs, as the predetermined processing, a processing of increasing the bit count of the geometry information of the input point cloud (S 9653 ). 
     When it is judged that the bit count of the geometry information of the input point cloud satisfies the determined conformance (Yes in S 9652 ), the three-dimensional data encoding device encodes the geometry information of the input point cloud (S 9654 ). The three-dimensional data encoding device also encodes the geometry information of the processed input point cloud, which has been subjected to the predetermined processing in step S 9653  and satisfies the conformance (S 9654 ). 
     Next, the predetermined processing in step S 9653  in  FIG. 99  will be described. 
       FIG. 100  illustrates an example of the processing of increasing the bit count according to Embodiment 6. 
     In the predetermined processing, when the bit count is insufficient, the bit count may be increased by up-sampling or the like. For example, according to this method, the bit count may be increased by padding the position coordinates (x, y, z). 
       FIG. 101  illustrates another example of the processing of increasing the bit count according to Embodiment 6. 
     In the predetermined processing, the bit count may be adjusted by bit shift or by shifting the origin of a point cloud. The bit count for each slice can be increased by inputting a shift value to a data partition, such as a slice or a tile. When combining a plurality of slices (a plurality of pieces of divisional data), the bit count may be increased by shifting the coordinates of different slices from different bitstreams. For example, the bit count may be increased by shifting the origin of the bounding box of a divisional slice (slice 2) to a position where the origin does not overlap with the bounding box of a divisional slice (slice 1) in  FIG. 101 . In this way, the conformance can be satisfied. 
     The conformance may be defined as a combination of the bit count of the geometry information and the number of three-dimensional points. Such an example will be described with reference to  FIG. 102 . Note that the number of three-dimensional points will be sometimes referred to as the number of points included in a point cloud. 
       FIG. 102  is a flowchart illustrating a fifth example of the three-dimensional data encoding method according to Embodiment 6. This flowchart is an example in which the bit count of the geometry information and the range of the number of three-dimensional points in the input point cloud are determined as conformances. Note that the conformances are not limited to the combination of the position precision and the range of the number of three-dimensional points, and may be combinations of other parameters. 
     The three-dimensional data encoding device determines conformances of encoded data, which is encoded point cloud data on a three-dimensional point cloud (S 9661 ). Here, the conformances are the first maximum bit count that defines the bit count of the geometry information and the range of the number of three-dimensional points included in the input point cloud. 
     The three-dimensional data encoding device judges whether or not the input three-dimensional point cloud satisfies the determined conformance concerning the bit count (S 9662 ). That is, the three-dimensional data encoding device judges whether or not the bit count of the geometry information on the input three-dimensional point cloud satisfies (i.e., coincides with) the determined first maximum bit count. 
     When it is judged that the input three-dimensional point cloud does not satisfy the determined conformance concerning the bit count (No in S 9662 ), the three-dimensional data encoding device performs a predetermined processing so that the determined conformance is satisfied (S 9663 ). The predetermined processing is any of the processing described above with reference to  FIG. 97 ,  FIG. 98 ,  FIG. 100 , and  FIG. 101 , for example. 
     When step S 9663  ends, or when it is judged that the input three-dimensional point cloud satisfies the determined conformance concerning the bit count (Yes in S 9662 ), the three-dimensional data encoding device performs the next step S 9664 . 
     The three-dimensional data encoding device judges whether the input three-dimensional point cloud satisfies the determined conformance concerning the range of the number of three-dimensional points (S 9664 ). That is, the three-dimensional data encoding device judges whether or not the number of three-dimensional points of the input three-dimensional point cloud falls within the determined range of the number of three-dimensional points. 
     When it is judged that the input three-dimensional point cloud does not satisfy the determined conformance concerning the range of the number of three-dimensional points (No in S 9664 ), the three-dimensional data encoding device performs a predetermined processing so that the determined conformance is satisfied (S 9665 ). The predetermined processing is any of the processing described above with reference to  FIG. 97 ,  FIG. 98 ,  FIG. 100 , and  FIG. 101 , for example. 
     When step S 9665  ends, or when it is judged that the input three-dimensional point cloud satisfies the determined conformance concerning the range of the number of three-dimensional points (Yes in S 9664 ), the three-dimensional data encoding device performs the next step S 9666 . 
     The three-dimensional data encoding device generates metadata including a conformance index indicating the conformances determined in step S 9661  (S 9666 ). The conformance index is identification information for identifying one of a combination of a plurality of conformances. 
     According to the result of the judging in step S 9662  and step S 9664 , the three-dimensional data encoding device encodes the point cloud data processed in step S 9663 , the point cloud data processed in step S 9665 , the point cloud data processed in steps S 9663  and S 9665 , or the point cloud data that is not processed (that is, the point cloud data that is not subjected to the predetermined processing) to generate a bitstream including the encoded point cloud data and the metadata (S 9667 ). 
     The three-dimensional data encoding device generates a bitstream by encoding point cloud data in such a manner that the point cloud data satisfies both the determined conformances concerning the first maximum bit count and the range of the number of three-dimensional points by performing steps S 9662  to S 9665 . Here, the three-dimensional data encoding device adds, to the bitstream, conformance information indicating the determined conformance. The conformance information are first bit count information indicating the first maximum bit count and range information indicating the range of the number of three-dimensional points, for example. The range information may be a value of the range of the number of three-dimensional points itself or may be identification information for uniquely identifying the range of the number. 
       FIG. 103  is a diagram illustrating an example of a combination of conformances according to Embodiment 6. 
     As shown in this drawing, the combination of conformances may be a combination of the bit count of geometry information and the range of the number of point clouds. In this example, the bit count of geometry information is classified into two cases where the upper limit is 32 bits and where the upper limit is 64 bits. The range of the number point clouds is classified into three cases where the number of points is equal to or smaller than 10000, where the number of points is greater than 10000 and equal to or smaller than 100000, and where the number of points is greater than 100000. Therefore, the combination of conformances is classified into six conformance points, and a conformance index is assigned to each conformance point. That is, by specifying a conformance index represented by any of numerals 1 to 6, a bit count of geometry information and a range of the number of point clouds can be uniquely set. 
     The example described above with reference to  FIG. 102  and  FIG. 103  is an example in a case where the bit count of geometry information for each divisional data unit (slice unit, for example) and the range of the number of point clouds of each divisional data unit are restricted at the same time. 
     The three-dimensional data encoding device selects any one of a plurality of conformance points included in a combination of conformances, and performs encoding so that the selected one conformance point is satisfied. If the selected one conformance point is not satisfied, the three-dimensional data encoding device performs quantization, data division, or integration of divisional data so that the bit count for each piece of divisional data and the number of point clouds of each divisional data unit come in conformity with the conformance point. 
     Note that when the three-dimensional data encoding device tries to satisfy one of the conformance concerning the bit count of the geometry information and the conformance concerning the range of the number of point clouds, the three-dimensional data encoding device may fail to satisfy the other conformance. For example, when the three-dimensional data encoding device divides data in order to satisfy the conformance concerning the bit count, the regulation conformance concerning the range of the number of point clouds may fail to be satisfied since the three-dimensional point cloud is also divided into point clouds. 
     In such a case, the three-dimensional data encoding device may perform a predetermined processing in accordance with the priorities of the regulations. For example, it may be regulated that to meet the restriction concerning the bit count of the geometry information is given the highest priority (essential), and the restriction concerning the range of the number of point clouds should be met as far as possible. That is, in the three-dimensional data encoding method, it is possible that a predetermined processing for satisfying a regulation conformance given a higher priority is performed, while a predetermined processing for satisfying a regulation conformance given a lower priority is not performed. 
     When the processing rate is given a higher priority, such as in a low delay mode, to meet the restriction concerning the bit count may be given a higher priority than to meet the restriction concerning the range of the number of point clouds. From the viewpoint of encoding efficiency, to meet the restriction concerning the number of point clouds may be given a higher priority than to meet the restriction concerning the bit count. In this way, the priorities of meeting the restriction concerning the bit count and the restriction concerning the range of the number of point clouds may be set in accordance with the purpose. 
     The conformance may be a regulation for the bit count or the size of the bounding box of divisional data, a regulation for the number of pieces of divisional data, or a combination of these regulations. 
     The conformance may be defined by a combination of the bit count of geometry information and a frame rate. Such an example will be described with reference to  FIG. 104 . 
       FIG. 104  is a flowchart illustrating a sixth example of the three-dimensional data encoding method according to Embodiment 6. This flowchart is an example in which the bit count of geometry information and the frame rate of an input point cloud are determined as conformances. 
     The three-dimensional data encoding device determines conformances of encoded data, which is encoded point cloud data on a three-dimensional point cloud (S 9671 ). The conformances determined here are the first maximum bit count that defines the bit count of the geometry information and the frame rate of the input point cloud. 
     The three-dimensional data encoding device judges whether or not the input three-dimensional point cloud satisfies the determined conformance concerning the bit count (S 9672 ). That is, the three-dimensional data encoding device judges whether or not the bit count of the geometry information on the input three-dimensional point cloud satisfies (i.e., coincides with) the determined first maximum bit count, and whether or not the frame rate of the input three-dimensional point cloud is less than or equal to the determined frame rate. 
     When it is judged that the input three-dimensional point cloud does not satisfy the determined conformance concerning the bit count (No in S 9672 ), the three-dimensional data encoding device performs a predetermined processing so that the determined conformance is satisfied (S 9673 ). The predetermined processing is any of the processing described above with reference to  FIG. 97 ,  FIG. 98 ,  FIG. 100 , and  FIG. 101 , for example. 
     When step S 9673  ends, or when it is judged that the input three-dimensional point cloud satisfies the determined conformance concerning the range of the number of three-dimensional points (Yes in S 9672 ), the three-dimensional data encoding device performs the next step S 9674 . 
     The three-dimensional data encoding device generates metadata including a conformance index indicating the conformances determined in step S 9671  (S 9674 ). The conformance index is identification information for identifying one of a combination of a plurality of conformances. 
     According to the result of the judging in step S 9672 , the three-dimensional data encoding device encodes the point cloud data processed in step S 9673  or the point cloud data that is not processed (that is, the point cloud data that is not subjected to the predetermined processing) to generate a bitstream including the encoded point cloud data and the metadata (S 9675 ). 
     As described above, for example, the conformance may be determined based on a hardware requirement that can be transformed into a need of an application in terms of the number of frames per unit time (second) (frame rate/fps) required for the hardware (the three-dimensional data encoding device/the three-dimensional data decoding device). In such a case, one frame may be regarded as a 360-degree capturing of LiDAR. The combination of conformances may be a combination of other parameters. The conformance may be defined by the frame rate on a divisional data (slice) basis. 
       FIG. 105  is a diagram illustrating another example of the combination of conformances according to Embodiment 6. 
     As shown in this drawing, the combination of conformances may be a combination of the bit count of geometry information and a frame rate. In this example, the bit count of geometry information is classified into three cases where the upper limit is 16 bits, where the upper limit is 32 bits, and where the upper limit is 64 bits. The frame rate is classified into three cases where the frame rate is less than 60 fps, where the frame rate is less than 10 fps, and where the frame rate is less than 1 fps. Therefore, the combination of conformances is classified into nine conformance points, and a conformance index is assigned to each conformance. That is, by specifying a conformance index represented by any of numerals 1 to 9, a bit count of geometry information and a frame rate can be uniquely set. 
     Although an example has been described above in which a conformance is set in the encoding process and decoding process for geometry information, a conformance can also be set in the encoding process and decoding process for attribute information, as in the encoding process and decoding process for geometry information. Note that the conformance applied to attribute information can be not only a regulation of attribute part information such as color or reflectance but also a regulation of information concerning geometry information associated with a point cloud for the purpose of prediction or compression. Prediction of attribute information using a hierarchical structure such as LoD or RAHT requires geometry information on a three-dimensional point cloud, in order to implement a function of searching for a subsample or a neighbor point within a predetermined distance. Therefore, the conformance for regulating attribute information may include a parameter based on such geometry information. 
     The conformance for regulating attribute information may include an upper limit of the number of bits of information representing color. The conformance may be the bit count of RGB information. The bit count of RGB information indicates whether the color of the point cloud is in an 8-bit representation, in a 12-bit representation, or in a 16-bit representation. Reflectance can also be regulated in the same manner. 
       FIG. 106  is a diagram illustrating another example of the combination of conformances according to Embodiment 6. 
     As shown in this drawing, the combination of conformances may be a combination of the bit count of color and an attribute transformation parameter. In this example, the bit count of color is classified into three cases where the upper limit is 8 bits, where the upper limit is 12 bits, and where the upper limit is 16 bits. The attribute transformation parameter indicates the number of layers of a LoD hierarchical structure used for prediction, for example. The attribute transformation parameter is classified into three cases where the number of layers is less than 10, where the number of layers is less than 5, and where the number of layers is 1. Therefore, the combination of conformances is classified into nine conformance points, and a conformance index is assigned to each conformance. That is, by specifying a conformance index represented by any of numerals 1 to 9, a bit count of color and an attribute transformation parameter can be uniquely set. 
     A conformance may be set for attribute information. That is, point cloud data may include attribute information on each three-dimensional point of a three-dimensional point cloud, in addition to geometry information. The three-dimensional data encoding device determines, as a conformance for encoded data, a second maximum bit count that defines the bit count of encoded attribute information of point cloud data of a three-dimensional point cloud. The three-dimensional data encoding device generates a bitstream by encoding attribute information so as to be less than or equal to the second maximum bit count. The bitstream may include second bit count information indicating the second maximum bit count. 
     A syntax of the conformance index will be described. 
       FIG. 107  is a diagram illustrating an example (example 1) of a sequence parameter set (SPS) according to Embodiment 6.  FIG. 108  is a diagram illustrating an example (example 2) of the SPS according to Embodiment 6.  FIG. 109  is a diagram illustrating an example (example 3) of a geometry parameter set (GPS) according to Embodiment 6.  FIG. 110  is a diagram illustrating a configuration of a bitstream according to Embodiment 6. 
     As shown in  FIG. 107 , the conformance index may be included in SPS as a part of an available parameter profile_idc, profile_compatibility_flags, or level_idc. 
     Alternatively, as shown in  FIG. 108 , depending on the description or use scenario, in order to further expand a large number of difference profiles, levels, and conformances for the encoding and decoding process for G-PCC, the conformance index may be set as an independent parameter in SPS. That is, the conformance index may be set in header  9621  in  FIG. 110 . 
     Alternatively, as shown in  FIG. 109 , the conformance index may be set to be included in a header of each slice such as a Geometry slice header (GPS). That is, the conformance index may be set in header  9622  or  9623  in  FIG. 110 . 
     This means that each slice can have a different conformance index in order to adapt to a different type of three-dimensional point cloud or data on a different area. In addition, encoding processes or decoding processes adapted to different processor types, such as CPU and GPU ASIC, can be performed.  FIG. 111  is a diagram for describing an example in which conformances are changed according to the position of a three-dimensional point cloud according to Embodiment 6. 
       FIG. 111  shows an example in which three-dimensional point cloud  9631  for an indoor and three-dimensional point cloud  9632  for an outdoor are obtained, and three-dimensional area  9633 , which is a part of three-dimensional point cloud  9632  for an outdoor, corresponds to three-dimensional point cloud  9631  for an indoor. Three-dimensional point cloud  9631  for an indoor and three-dimensional point cloud  9632  for an outdoor are data obtained with different sensors, and therefore are different in density of the point cloud, for example. 
     Three-dimensional point cloud  9631  for an indoor is a point cloud measured indoors, such as in an office, and therefore cannot be obtained with an outdoor sensor. That is, three-dimensional point cloud  9632  for an outdoor does not include three-dimensional point cloud  9631  for an indoor. 
     As described above, three-dimensional point cloud  9631  for an indoor and three-dimensional point cloud  9632  for an outdoor are point cloud data that are generated with different precisions and different densities and are independent from each other. Therefore, an independent conformance may be set for each of three-dimensional point clouds  9631  and  9632 , and the conformances may be changed depending on whether the three-dimensional point cloud is three-dimensional point cloud  9631  or three-dimensional point cloud  9632 . 
     The two pieces of data may be combined by changing the precision of three-dimensional point  9632  for an outdoor to increasing the scale so that three-dimensional point cloud  9631  for an indoor is included. The point cloud for an indoor may be shifted using a different slice origin value. 
     As described above, the three-dimensional data encoding device according to an aspect of the present embodiment performs the process shown in  FIG. 112 . The three-dimensional data encoding device determines a first maximum bit count for encoded data obtained after encoding at least one of (i) a divisional data unit obtained when point cloud data indicating a three-dimensional point cloud is divided or (ii) a point cloud data unit of the point cloud data before the dividing (S 9681 ). The three-dimensional data encoding device generates a bitstream by encoding (i) items of divisional data obtained by dividing the point cloud data or (ii) the point cloud data before the dividing, to satisfy the first maximum bit count determined (S 9682 ). The bitstream includes first bit count information indicating the first maximum bit count. 
     Accordingly, in the three-dimensional data encoding method, a bitstream including first bit count information indicating a first maximum bit count for encoded data is generated, and thus a three-dimensional data decoding device can determine whether the encoded data can be decoded appropriately, without having to analyze the bitstream. For this reason, the processing load of the three-dimensional data decoding device can be reduced. 
     For example, the point cloud data includes geometry information of each of three-dimensional points in the three-dimensional point cloud. The first maximum bit count relates to a bit count after encoding the geometry information. In the generating (S 9682 ), the bitstream is generated by encoding the geometry information of (i) the items of divisional data obtained by dividing the point cloud data or (ii) the point cloud data before the dividing, to satisfy the first maximum bit count determined. 
     Accordingly, in the three-dimensional data encoding method, a bitstream including first bit count information indicating a first maximum bit count for encoded geometry information is generated, and thus a three-dimensional data decoding device can determine whether the geometry information can be decoded appropriately, without having to analyze the bitstream. 
     For example, the three-dimensional data encoding device further determines a range of a total number of three-dimensional points included in the at least one of the divisional data unit or the point cloud data unit. In the generating (S 9682 ), the bitstream is generated by encoding (i) the items of divisional data obtained by dividing the point cloud data or (ii) the point cloud data before the dividing, to satisfy the first maximum bit count and the range of the total number determined. The bitstream further includes range information indicating the range of the total number. 
     Accordingly, in the three-dimensional data encoding method, a bitstream including range information indicating a range of the number of three-dimensional points of encoded data is generated, and thus a three-dimensional data decoding device can determine whether the geometry information can be decoded appropriately, without having to analyze the bitstream. For this reason, the processing load of the three-dimensional data decoding device can be reduced. 
     For example, the point cloud data includes attribute information of each of the three-dimensional points in the three-dimensional point cloud. The three-dimensional data encoding device further determines a second maximum bit count after encoding attribute information of a three-dimensional point cloud of at least one of the divisional data unit or the point cloud data unit. In the generating (S 9682 ), the bitstream is generated by: encoding the geometry information of (i) the items of divisional data obtained by dividing the point cloud data or (ii) the point cloud data before the dividing, to satisfy the first maximum bit count determined; and encoding the attribute information of (i) the items of divisional data obtained by dividing of the point cloud data or (ii) the point cloud data before the dividing, to satisfy the second maximum bit count determined. The bitstream further includes second bit count information indicating the second maximum bit count. 
     Accordingly, in the three-dimensional data encoding method, a bitstream including second bit count information indicating a second maximum bit count for encoded attribute information is generated, and thus a three-dimensional data decoding device can determine whether the encoded data can be decoded appropriately, without having to analyze the bitstream. For this reason, the processing load of the three-dimensional data decoding device can be reduced. 
     For example, the three-dimensional data encoding device includes a processor and memory, and, using the memory, the processor performs the processes described above. 
     Furthermore, the three-dimensional data decoding device according to an aspect of the present embodiment performs the process shown in  FIG. 113 . The three-dimensional data decoding device obtains a bitstream including encoded data and first bit count information, the encoded data being data obtained after encoding at least one of (i) a divisional data unit obtained when point cloud data indicating a three-dimensional point cloud is divided or (ii) a point cloud data unit of the point cloud data before the dividing, the first bit count information indicating a first maximum bit count for the encoded data (S 9691 ). The three-dimensional data decoding device judges whether the bitstream obtained satisfies the first maximum bit count indicated by the first bit count information (S 9692 ). The three-dimensional data decoding device decodes the encoded data when the bitstream is judged to satisfy the first maximum bit count (S 9693 ). 
     Accordingly, in the three-dimensional decoding method, first bit count information indicating the first maximum bit count for encoded data is obtained from the bitstream, and thus point cloud data can be decoded appropriately based on the obtained first bit count information. 
     For example, in the decoding (S 9693 ), the three-dimensional decoding device does not decode the encoded data when the bitstream is judged not to satisfy the first maximum bit count. 
     Accordingly, since decoding processing of encoded data of a bitstream that cannot be appropriately decoded is not performed, processing load can be reduced. 
     Furthermore, the point cloud data includes geometry information of each of three-dimensional points of the three-dimensional point cloud. The first maximum bit count relates to a bit count after the geometry information is encoded. 
     Accordingly, in the three-dimensional decoding method, first bit count information indicating the first maximum bit count for encoded geometry information is obtained from the bitstream, and thus point cloud data can be decoded appropriately based on the obtained first bit count information. 
     Furthermore, the bitstream further includes range information indicating a range of a total number of three-dimensional points included in the at least one of the divisional data unit or the point cloud data unit. In the judging (S 9692 ), the three-dimensional data decoding device further judges whether the bitstream satisfies the range of the total number indicated in the range information. In the decoding (S 9693 ), the encoded data is decoded when the bitstream is judged to satisfy the first maximum bit count and the range of the total number; and the encoded data is not decoded when the bitstream is judged not to satisfy the first maximum bit count or the range of the total number. 
     Accordingly, in the three-dimensional decoding method, range information indicating a range of the number of three-dimensional points of encoded data is obtained from the bitstream, and thus point cloud data can be decoded appropriately based on the obtained range information. 
     For example, the point cloud data further includes attribute data of each of the three-dimensional points of the three-dimensional point cloud. The bitstream further includes second bit count information indicating a second maximum bit count after encoding attribute information of a three-dimensional point cloud of the at least one of the divisional data unit or the point cloud data unit. In the judging (S 9692 ), whether the bitstream satisfies the second maximum bit count indicated by the second bit count information is further judged. In the decoding (S 9693 ); the encoded data is decoded when the bitstream is judged to satisfy the first maximum bit count and the second maximum bit count; and the encoded data is not decoded when the bitstream is judged not to satisfy the first maximum bit count or the second maximum bit count. 
     Accordingly, in the three-dimensional decoding method, second bit count information indicating the second maximum bit count for encoded attribute information is obtained from the bitstream, and thus point cloud data can be decoded appropriately based on the obtained second bit count information. 
     For example, the three-dimensional decoding device includes a processor and memory, and, using the memory, the processor performs the processes described above. 
     Embodiment 7 
     The following describes the structure of three-dimensional data creation device  810  according to the present embodiment.  FIG. 114  is a block diagram of an exemplary structure of three-dimensional data creation device  810  according to the present embodiment. Such three-dimensional data creation device  810  is equipped, for example, in a vehicle. Three-dimensional data creation device  810  transmits and receives three-dimensional data to and from an external cloud-based traffic monitoring system, a preceding vehicle, or a following vehicle, and creates and stores three-dimensional data. 
     Three-dimensional data creation device  810  includes data receiver  811 , communication unit  812 , reception controller  813 , format converter  814 , a plurality of sensors  815 , three-dimensional data creator  816 , three-dimensional data synthesizer  817 , three-dimensional data storage  818 , communication unit  819 , transmission controller  820 , format converter  821 , and data transmitter  822 . 
     Data receiver  811  receives three-dimensional data  831  from a cloud-based traffic monitoring system or a preceding vehicle. Three-dimensional data  831  includes, for example, information on a region undetectable by sensors  815  of the own vehicle, such as a point cloud, visible light video, depth information, sensor position information, and speed information. 
     Communication unit  812  communicates with the cloud-based traffic monitoring system or the preceding vehicle to transmit a data transmission request, etc. to the cloud-based traffic monitoring system or the preceding vehicle. 
     Reception controller  813  exchanges information, such as information on supported formats, with a communications partner via communication unit  812  to establish communication with the communications partner. 
     Format converter  814  applies format conversion, etc. on three-dimensional data  831  received by data receiver  811  to generate three-dimensional data  832 . Format converter  814  also decompresses or decodes three-dimensional data  831  when three-dimensional data  831  is compressed or encoded. 
     A plurality of sensors  815  are a group of sensors, such as visible light cameras and infrared cameras, that obtain information on the outside of the vehicle and generate sensor information  833 . Sensor information  833  is, for example, three-dimensional data such as a point cloud (point group data), when sensors  815  are laser sensors such as LiDARs. Note that a single sensor may serve as a plurality of sensors  815 . 
     Three-dimensional data creator  816  generates three-dimensional data  834  from sensor information  833 . Three-dimensional data  834  includes, for example, information such as a point cloud, visible light video, depth information, sensor position information, and speed information. 
     Three-dimensional data synthesizer  817  synthesizes three-dimensional data  834  created on the basis of sensor information  833  of the own vehicle with three-dimensional data  832  created by the cloud-based traffic monitoring system or the preceding vehicle, etc., thereby forming three-dimensional data  835  of a space that includes the space ahead of the preceding vehicle undetectable by sensors  815  of the own vehicle. 
     Three-dimensional data storage  818  stores generated three-dimensional data  835 , etc. 
     Communication unit  819  communicates with the cloud-based traffic monitoring system or the following vehicle to transmit a data transmission request, etc. to the cloud-based traffic monitoring system or the following vehicle. 
     Transmission controller  820  exchanges information such as information on supported formats with a communications partner via communication unit  819  to establish communication with the communications partner. Transmission controller  820  also determines a transmission region, which is a space of the three-dimensional data to be transmitted, on the basis of three-dimensional data formation information on three-dimensional data  832  generated by three-dimensional data synthesizer  817  and the data transmission request from the communications partner. 
     More specifically, transmission controller  820  determines a transmission region that includes the space ahead of the own vehicle undetectable by a sensor of the following vehicle, in response to the data transmission request from the cloud-based traffic monitoring system or the following vehicle. Transmission controller  820  judges, for example, whether a space is transmittable or whether the already transmitted space includes an update, on the basis of the three-dimensional data formation information to determine a transmission region. For example, transmission controller  820  determines, as a transmission region, a region that is: a region specified by the data transmission request; and a region, corresponding three-dimensional data  835  of which is present. Transmission controller  820  then notifies format converter  821  of the format supported by the communications partner and the transmission region. 
     Of three-dimensional data  835  stored in three-dimensional data storage  818 , format converter  821  converts three-dimensional data  836  of the transmission region into the format supported by the receiver end to generate three-dimensional data  837 . Note that format converter  821  may compress or encode three-dimensional data  837  to reduce the data amount. 
     Data transmitter  822  transmits three-dimensional data  837  to the cloud-based traffic monitoring system or the following vehicle. Such three-dimensional data  837  includes, for example, information on a blind spot, which is a region hidden from view of the following vehicle, such as a point cloud ahead of the own vehicle, visible light video, depth information, and sensor position information. 
     Note that an example has been described in which format converter  814  and format converter  821  perform format conversion, etc., but format conversion may not be performed. 
     With the above structure, three-dimensional data creation device  810  obtains, from an external device, three-dimensional data  831  of a region undetectable by sensors  815  of the own vehicle, and synthesizes three-dimensional data  831  with three-dimensional data  834  that is based on sensor information  833  detected by sensors  815  of the own vehicle, thereby generating three-dimensional data  835 . Three-dimensional data creation device  810  is thus capable of generating three-dimensional data of a range undetectable by sensors  815  of the own vehicle. 
     Three-dimensional data creation device  810  is also capable of transmitting, to the cloud-based traffic monitoring system or the following vehicle, etc., three-dimensional data of a space that includes the space ahead of the own vehicle undetectable by a sensor of the following vehicle, in response to the data transmission request from the cloud-based traffic monitoring system or the following vehicle. 
     The following describes the steps performed by three-dimensional data creation device  810  of transmitting three-dimensional data to a following vehicle.  FIG. 115  is a flowchart showing exemplary steps performed by three-dimensional data creation device  810  of transmitting three-dimensional data to a cloud-based traffic monitoring system or a following vehicle. 
     First, three-dimensional data creation device  810  generates and updates three-dimensional data  835  of a space that includes space on the road ahead of the own vehicle (S 801 ). More specifically, three-dimensional data creation device  810  synthesizes three-dimensional data  834  created on the basis of sensor information  833  of the own vehicle with three-dimensional data  831  created by the cloud-based traffic monitoring system or the preceding vehicle, etc., for example, thereby forming three-dimensional data  835  of a space that also includes the space ahead of the preceding vehicle undetectable by sensors  815  of the own vehicle. 
     Three-dimensional data creation device  810  then judges whether any change has occurred in three-dimensional data  835  of the space included in the space already transmitted (S 802 ). 
     When a change has occurred in three-dimensional data  835  of the space included in the space already transmitted due to, for example, a vehicle or a person entering such space from outside (Yes in S 802 ), three-dimensional data creation device  810  transmits, to the cloud-based traffic monitoring system or the following vehicle, the three-dimensional data that includes three-dimensional data  835  of the space in which the change has occurred (S 803 ). 
     Three-dimensional data creation device  810  may transmit three-dimensional data in which a change has occurred, at the same timing of transmitting three-dimensional data that is transmitted at a predetermined time interval, or may transmit three-dimensional data in which a change has occurred soon after the detection of such change. Stated differently, three-dimensional data creation device  810  may prioritize the transmission of three-dimensional data of the space in which a change has occurred to the transmission of three-dimensional data that is transmitted at a predetermined time interval. 
     Also, three-dimensional data creation device  810  may transmit, as three-dimensional data of a space in which a change has occurred, the whole three-dimensional data of the space in which such change has occurred, or may transmit only a difference in the three-dimensional data (e.g., information on three-dimensional points that have appeared or vanished, or information on the displacement of three-dimensional points). 
     Three-dimensional data creation device  810  may also transmit, to the following vehicle, meta-data on a risk avoidance behavior of the own vehicle such as hard breaking warning, before transmitting three-dimensional data of the space in which a change has occurred. This enables the following vehicle to recognize at an early stage that the preceding vehicle is to perform hard braking, etc., and thus to start performing a risk avoidance behavior at an early stage such as speed reduction. 
     When no change has occurred in three-dimensional data  835  of the space included in the space already transmitted (No in S 802 ), or after step S 803 , three-dimensional data creation device  810  transmits, to the cloud-based traffic monitoring system or the following vehicle, three-dimensional data of the space included in the space having a predetermined shape and located ahead of the own vehicle by distance L (S 804 ). 
     The processes of step S 801  through step S 804  are repeated, for example at a predetermined time interval. 
     When three-dimensional data  835  of the current space to be transmitted includes no difference from the three-dimensional map, three-dimensional data creation device  810  may not transmit three-dimensional data  837  of the space. 
     In the present embodiment, a client device transmits sensor information obtained through a sensor to a server or another client device. 
     A structure of a system according to the present embodiment will first be described.  FIG. 116  is a diagram showing the structure of a transmission/reception system of a three-dimensional map and sensor information according to the present embodiment. This system includes server  901 , and client devices  902 A and  902 B. Note that client devices  902 A and  902 B are also referred to as client device  902  when no particular distinction is made therebetween. 
     Client device  902  is, for example, a vehicle-mounted device equipped in a mobile object such as a vehicle. Server  901  is, for example, a cloud-based traffic monitoring system, and is capable of communicating with the plurality of client devices  902 . 
     Server  901  transmits the three-dimensional map formed by a point cloud to client device  902 . Note that a structure of the three-dimensional map is not limited to a point cloud, and may also be another structure expressing three-dimensional data such as a mesh structure. 
     Client device  902  transmits the sensor information obtained by client device  902  to server  901 . The sensor information includes, for example, at least one of information obtained by LiDAR, a visible light image, an infrared image, a depth image, sensor position information, or sensor speed information. 
     The data to be transmitted and received between server  901  and client device  902  may be compressed in order to reduce data volume, and may also be transmitted uncompressed in order to maintain data precision. When compressing the data, it is possible to use a three-dimensional compression method on the point cloud based on, for example, an octree structure. It is possible to use a two-dimensional image compression method on the visible light image, the infrared image, and the depth image. The two-dimensional image compression method is, for example, MPEG-4 AVC or HEVC standardized by MPEG. 
     Server  901  transmits the three-dimensional map managed by server  901  to client device  902  in response to a transmission request for the three-dimensional map from client device  902 . Note that server  901  may also transmit the three-dimensional map without waiting for the transmission request for the three-dimensional map from client device  902 . For example, server  901  may broadcast the three-dimensional map to at least one client device  902  located in a predetermined space. Server  901  may also transmit the three-dimensional map suited to a position of client device  902  at fixed time intervals to client device  902  that has received the transmission request once. Server  901  may also transmit the three-dimensional map managed by server  901  to client device  902  every time the three-dimensional map is updated. 
     Client device  902  sends the transmission request for the three-dimensional map to server  901 . For example, when client device  902  wants to perform the self-location estimation during traveling, client device  902  transmits the transmission request for the three-dimensional map to server  901 . 
     Note that in the following cases, client device  902  may send the transmission request for the three-dimensional map to server  901 . Client device  902  may send the transmission request for the three-dimensional map to server  901  when the three-dimensional map stored by client device  902  is old. For example, client device  902  may send the transmission request for the three-dimensional map to server  901  when a fixed period has passed since the three-dimensional map is obtained by client device  902 . 
     Client device  902  may also send the transmission request for the three-dimensional map to server  901  before a fixed time when client device  902  exits a space shown in the three-dimensional map stored by client device  902 . For example, client device  902  may send the transmission request for the three-dimensional map to server  901  when client device  902  is located within a predetermined distance from a boundary of the space shown in the three-dimensional map stored by client device  902 . When a movement path and a movement speed of client device  902  are understood, a time when client device  902  exits the space shown in the three-dimensional map stored by client device  902  may be predicted based on the movement path and the movement speed of client device  902 . 
     Client device  902  may also send the transmission request for the three-dimensional map to server  901  when an error during alignment of the three-dimensional data and the three-dimensional map created from the sensor information by client device  902  is at least at a fixed level. 
     Client device  902  transmits the sensor information to server  901  in response to a transmission request for the sensor information from server  901 . Note that client device  902  may transmit the sensor information to server  901  without waiting for the transmission request for the sensor information from server  901 . For example, client device  902  may periodically transmit the sensor information during a fixed period when client device  902  has received the transmission request for the sensor information from server  901  once. Client device  902  may determine that there is a possibility of a change in the three-dimensional map of a surrounding area of client device  902  having occurred, and transmit this information and the sensor information to server  901 , when the error during alignment of the three-dimensional data created by client device  902  based on the sensor information and the three-dimensional map obtained from server  901  is at least at the fixed level. 
     Server  901  sends a transmission request for the sensor information to client device  902 . For example, server  901  receives position information, such as GPS information, about client device  902  from client device  902 . Server  901  sends the transmission request for the sensor information to client device  902  in order to generate a new three-dimensional map, when it is determined that client device  902  is approaching a space in which the three-dimensional map managed by server  901  contains little information, based on the position information about client device  902 . Server  901  may also send the transmission request for the sensor information, when wanting to (i) update the three-dimensional map, (ii) check road conditions during snowfall, a disaster, or the like, or (iii) check traffic congestion conditions, accident/incident conditions, or the like. 
     Client device  902  may set an amount of data of the sensor information to be transmitted to server  901  in accordance with communication conditions or bandwidth during reception of the transmission request for the sensor information to be received from server  901 . Setting the amount of data of the sensor information to be transmitted to server  901  is, for example, increasing/reducing the data itself or appropriately selecting a compression method. 
       FIG. 117  is a block diagram showing an example structure of client device  902 . Client device  902  receives the three-dimensional map formed by a point cloud and the like from server  901 , and estimates a self-location of client device  902  using the three-dimensional map created based on the sensor information of client device  902 . Client device  902  transmits the obtained sensor information to server  901 . 
     Client device  902  includes data receiver  1011 , communication unit  1012 , reception controller  1013 , format converter  1014 , sensors  1015 , three-dimensional data creator  1016 , three-dimensional image processor  1017 , three-dimensional data storage  1018 , format converter  1019 , communication unit  1020 , transmission controller  1021 , and data transmitter  1022 . 
     Data receiver  1011  receives three-dimensional map  1031  from server  901 . Three-dimensional map  1031  is data that includes a point cloud such as a WLD or a SWLD. Three-dimensional map  1031  may include compressed data or uncompressed data. 
     Communication unit  1012  communicates with server  901  and transmits a data transmission request (e.g., transmission request for three-dimensional map) to server  901 . 
     Reception controller  1013  exchanges information, such as information on supported formats, with a communications partner via communication unit  1012  to establish communication with the communications partner. 
     Format converter  1014  performs a format conversion and the like on three-dimensional map  1031  received by data receiver  1011  to generate three-dimensional map  1032 . Format converter  1014  also performs a decompression or decoding process when three-dimensional map  1031  is compressed or encoded. Note that format converter  1014  does not perform the decompression or decoding process when three-dimensional map  1031  is uncompressed data. 
     Sensors  1015  are a group of sensors, such as LiDARs, visible light cameras, infrared cameras, or depth sensors that obtain information about the outside of a vehicle equipped with client device  902 , and generate sensor information  1033 . Sensor information  1033  is, for example, three-dimensional data such as a point cloud (point group data) when sensors  1015  are laser sensors such as LiDARs. Note that a single sensor may serve as sensors  1015 . 
     Three-dimensional data creator  1016  generates three-dimensional data  1034  of a surrounding area of the own vehicle based on sensor information  1033 . For example, three-dimensional data creator  1016  generates point cloud data with color information on the surrounding area of the own vehicle using information obtained by LiDAR and visible light video obtained by a visible light camera. 
     Three-dimensional image processor  1017  performs a self-location estimation process and the like of the own vehicle, using (i) the received three-dimensional map  1032  such as a point cloud, and (ii) three-dimensional data  1034  of the surrounding area of the own vehicle generated using sensor information  1033 . Note that three-dimensional image processor  1017  may generate three-dimensional data  1035  about the surroundings of the own vehicle by merging three-dimensional map  1032  and three-dimensional data  1034 , and may perform the self-location estimation process using the created three-dimensional data  1035 . 
     Three-dimensional data storage  1018  stores three-dimensional map  1032 , three-dimensional data  1034 , three-dimensional data  1035 , and the like. 
     Format converter  1019  generates sensor information  1037  by converting sensor information  1033  to a format supported by a receiver end. Note that format converter  1019  may reduce the amount of data by compressing or encoding sensor information  1037 . Format converter  1019  may omit this process when format conversion is not necessary. Format converter  1019  may also control the amount of data to be transmitted in accordance with a specified transmission range. 
     Communication unit  1020  communicates with server  901  and receives a data transmission request (transmission request for sensor information) and the like from server  901 . 
     Transmission controller  1021  exchanges information, such as information on supported formats, with a communications partner via communication unit  1020  to establish communication with the communications partner. 
     Data transmitter  1022  transmits sensor information  1037  to server  901 . Sensor information  1037  includes, for example, information obtained through sensors  1015 , such as information obtained by LiDAR, a luminance image obtained by a visible light camera, an infrared image obtained by an infrared camera, a depth image obtained by a depth sensor, sensor position information, and sensor speed information. 
     A structure of server  901  will be described next.  FIG. 118  is a block diagram showing an example structure of server  901 . Server  901  transmits sensor information from client device  902  and creates three-dimensional data based on the received sensor information. Server  901  updates the three-dimensional map managed by server  901  using the created three-dimensional data. Server  901  transmits the updated three-dimensional map to client device  902  in response to a transmission request for the three-dimensional map from client device  902 . 
     Server  901  includes data receiver  1111 , communication unit  1112 , reception controller  1113 , format converter  1114 , three-dimensional data creator  1116 , three-dimensional data merger  1117 , three-dimensional data storage  1118 , format converter  1119 , communication unit  1120 , transmission controller  1121 , and data transmitter  1122 . 
     Data receiver  1111  receives sensor information  1037  from client device  902 . Sensor information  1037  includes, for example, information obtained by LiDAR, a luminance image obtained by a visible light camera, an infrared image obtained by an infrared camera, a depth image obtained by a depth sensor, sensor position information, sensor speed information, and the like. 
     Communication unit  1112  communicates with client device  902  and transmits a data transmission request (e.g., transmission request for sensor information) and the like to client device  902 . 
     Reception controller  1113  exchanges information, such as information on supported formats, with a communications partner via communication unit  1112  to establish communication with the communications partner. 
     Format converter  1114  generates sensor information  1132  by performing a decompression or decoding process when the received sensor information  1037  is compressed or encoded. Note that format converter  1114  does not perform the decompression or decoding process when sensor information  1037  is uncompressed data. 
     Three-dimensional data creator  1116  generates three-dimensional data  1134  of a surrounding area of client device  902  based on sensor information  1132 . For example, three-dimensional data creator  1116  generates point cloud data with color information on the surrounding area of client device  902  using information obtained by LiDAR and visible light video obtained by a visible light camera. 
     Three-dimensional data merger  1117  updates three-dimensional map  1135  by merging three-dimensional data  1134  created based on sensor information  1132  with three-dimensional map  1135  managed by server  901 . 
     Three-dimensional data storage  1118  stores three-dimensional map  1135  and the like. 
     Format converter  1119  generates three-dimensional map  1031  by converting three-dimensional map  1135  to a format supported by the receiver end. Note that format converter  1119  may reduce the amount of data by compressing or encoding three-dimensional map  1135 . Format converter  1119  may omit this process when format conversion is not necessary. Format converter  1119  may also control the amount of data to be transmitted in accordance with a specified transmission range. 
     Communication unit  1120  communicates with client device  902  and receives a data transmission request (transmission request for three-dimensional map) and the like from client device  902 . 
     Transmission controller  1121  exchanges information, such as information on supported formats, with a communications partner via communication unit  1120  to establish communication with the communications partner. 
     Data transmitter  1122  transmits three-dimensional map  1031  to client device  902 . Three-dimensional map  1031  is data that includes a point cloud such as a WLD or a SWLD. Three-dimensional map  1031  may include one of compressed data and uncompressed data. 
     An operational flow of client device  902  will be described next.  FIG. 119  is a flowchart of an operation when client device  902  obtains the three-dimensional map. 
     Client device  902  first requests server  901  to transmit the three-dimensional map (point cloud, etc.) (S 1001 ). At this point, by also transmitting the position information about client device  902  obtained through GPS and the like, client device  902  may also request server  901  to transmit a three-dimensional map relating to this position information. 
     Client device  902  next receives the three-dimensional map from server  901  (S 1002 ). When the received three-dimensional map is compressed data, client device  902  decodes the received three-dimensional map and generates an uncompressed three-dimensional map (S 1003 ). 
     Client device  902  next creates three-dimensional data  1034  of the surrounding area of client device  902  using sensor information  1033  obtained by sensors  1015  (S 1004 ). Client device  902  next estimates the self-location of client device  902  using three-dimensional map  1032  received from server  901  and three-dimensional data  1034  created using sensor information  1033  (S 1005 ). 
       FIG. 120  is a flowchart of an operation when client device  902  transmits the sensor information. Client device  902  first receives a transmission request for the sensor information from server  901  (S 1011 ). Client device  902  that has received the transmission request transmits sensor information  1037  to server  901  (S 1012 ). Note that client device  902  may generate sensor information  1037  by compressing each item of information using a compression method suited to each piece (item) of information, when sensor information  1033  includes a plurality of pieces of information obtained by sensors  1015 . 
     An operational flow of server  901  will be described next.  FIG. 121  is a flowchart of an operation when server  901  obtains the sensor information. Server  901  first requests client device  902  to transmit the sensor information (S 1021 ). Server  901  next receives sensor information  1037  transmitted from client device  902  in accordance with the request (S 1022 ). Server  901  next creates three-dimensional data  1134  using the received sensor information  1037  (S 1023 ). Server  901  next reflects the created three-dimensional data  1134  in three-dimensional map  1135  (S 1024 ). 
       FIG. 122  is a flowchart of an operation when server  901  transmits the three-dimensional map. Server  901  first receives a transmission request for the three-dimensional map from client device  902  (S 1031 ). Server  901  that has received the transmission request for the three-dimensional map transmits the three-dimensional map to client device  902  (S 1032 ). At this point, server  901  may extract a three-dimensional map of a vicinity of client device  902  along with the position information about client device  902 , and transmit the extracted three-dimensional map. Server  901  may compress the three-dimensional map formed by a point cloud using, for example, an octree structure compression method, and transmit the compressed three-dimensional map. 
     The following describes variations of the present embodiment. 
     Server  901  creates three-dimensional data  1134  of a vicinity of a position of client device  902  using sensor information  1037  received from client device  902 . Server  901  next calculates a difference between three-dimensional data  1134  and three-dimensional map  1135 , by matching the created three-dimensional data  1134  with three-dimensional map  1135  of the same area managed by server  901 . Server  901  determines that a type of anomaly has occurred in the surrounding area of client device  902 , when the difference is greater than or equal to a predetermined threshold. For example, it is conceivable that a large difference occurs between three-dimensional map  1135  managed by server  901  and three-dimensional data  1134  created based on sensor information  1037 , when land subsidence and the like occurs due to a natural disaster such as an earthquake. 
     Sensor information  1037  may include information indicating at least one of a sensor type, a sensor performance, and a sensor model number. Sensor information  1037  may also be appended with a class ID and the like in accordance with the sensor performance. For example, when sensor information  1037  is obtained by LiDAR, it is conceivable to assign identifiers to the sensor performance. A sensor capable of obtaining information with precision in units of several millimeters is class  1 , a sensor capable of obtaining information with precision in units of several centimeters is class  2 , and a sensor capable of obtaining information with precision in units of several meters is class  3 . Server  901  may estimate sensor performance information and the like from a model number of client device  902 . For example, when client device  902  is equipped in a vehicle, server  901  may determine sensor specification information from a type of the vehicle. In this case, server  901  may obtain information on the type of the vehicle in advance, and the information may also be included in the sensor information. Server  901  may change a degree of correction with respect to three-dimensional data  1134  created using sensor information  1037 , using the obtained sensor information  1037 . For example, when the sensor performance is high in precision (class  1 ), server  901  does not correct three-dimensional data  1134 . When the sensor performance is low in precision (class  3 ), server  901  corrects three-dimensional data  1134  in accordance with the precision of the sensor. For example, server  901  increases the degree (intensity) of correction with a decrease in the precision of the sensor. 
     Server  901  may simultaneously send the transmission request for the sensor information to the plurality of client devices  902  in a certain space. Server  901  does not need to use all of the sensor information for creating three-dimensional data  1134  and may, for example, select sensor information to be used in accordance with the sensor performance, when having received a plurality of pieces of sensor information from the plurality of client devices  902 . For example, when updating three-dimensional map  1135 , server  901  may select high-precision sensor information (class  1 ) from among the received plurality of pieces of sensor information, and create three-dimensional data  1134  using the selected sensor information. 
     Server  901  is not limited to only being a server such as a cloud-based traffic monitoring system, and may also be another (vehicle-mounted) client device.  FIG. 123  is a diagram of a system structure in this case. 
     For example, client device  902 C sends a transmission request for sensor information to client device  902 A located nearby, and obtains the sensor information from client device  902 A. Client device  902 C then creates three-dimensional data using the obtained sensor information of client device  902 A, and updates a three-dimensional map of client device  902 C. This enables client device  902 C to generate a three-dimensional map of a space that can be obtained from client device  902 A, and fully utilize the performance of client device  902 C. For example, such a case is conceivable when client device  902 C has high performance. 
     In this case, client device  902 A that has provided the sensor information is given rights to obtain the high-precision three-dimensional map generated by client device  902 C. Client device  902 A receives the high-precision three-dimensional map from client device  902 C in accordance with these rights. 
     Server  901  may send the transmission request for the sensor information to the plurality of client devices  902  (client device  902 A and client device  902 B) located nearby client device  902 C. When a sensor of client device  902 A or client device  902 B has high performance, client device  902 C is capable of creating the three-dimensional data using the sensor information obtained by this high-performance sensor. 
       FIG. 124  is a block diagram showing a functionality structure of server  901  and client device  902 . Server  901  includes, for example, three-dimensional map compression/decoding processor  1201  that compresses and decodes the three-dimensional map and sensor information compression/decoding processor  1202  that compresses and decodes the sensor information. 
     Client device  902  includes three-dimensional map decoding processor  1211  and sensor information compression processor  1212 . Three-dimensional map decoding processor  1211  receives encoded data of the compressed three-dimensional map, decodes the encoded data, and obtains the three-dimensional map. Sensor information compression processor  1212  compresses the sensor information itself instead of the three-dimensional data created using the obtained sensor information, and transmits the encoded data of the compressed sensor information to server  901 . With this structure, client device  902  does not need to internally store a processor that performs a process for compressing the three-dimensional data of the three-dimensional map (point cloud, etc.), as long as client device  902  internally stores a processor that performs a process for decoding the three-dimensional map (point cloud, etc.). This makes it possible to limit costs, power consumption, and the like of client device  902 . 
     As stated above, client device  902  according to the present embodiment is equipped in the mobile object, and creates three-dimensional data  1034  of a surrounding area of the mobile object using sensor information  1033  that is obtained through sensor  1015  equipped in the mobile object and indicates a surrounding condition of the mobile object. Client device  902  estimates a self-location of the mobile object using the created three-dimensional data  1034 . Client device  902  transmits the obtained sensor information  1033  to server  901  or another client device  902 . 
     This enables client device  902  to transmit sensor information  1033  to server  901  or the like. This makes it possible to further reduce the amount of transmission data compared to when transmitting the three-dimensional data. Since there is no need for client device  902  to perform processes such as compressing or encoding the three-dimensional data, it is possible to reduce the processing amount of client device  902 . As such, client device  902  is capable of reducing the amount of data to be transmitted or simplifying the structure of the device. 
     Client device  902  further transmits the transmission request for the three-dimensional map to server  901  and receives three-dimensional map  1031  from server  901 . In the estimating of the self-location, client device  902  estimates the self-location using three-dimensional data  1034  and three-dimensional map  1032 . 
     Sensor information  1033  includes at least one of information obtained by a laser sensor, a luminance image, an infrared image, a depth image, sensor position information, or sensor speed information. 
     Sensor information  1033  includes information that indicates a performance of the sensor. 
     Client device  902  encodes or compresses sensor information  1033 , and in the transmitting of the sensor information, transmits sensor information  1037  that has been encoded or compressed to server  901  or another client device  902 . This enables client device  902  to reduce the amount of data to be transmitted. 
     For example, client device  902  includes a processor and memory. The processor performs the above processes using the memory. 
     Server  901  according to the present embodiment is capable of communicating with client device  902  equipped in the mobile object, and receives sensor information  1037  that is obtained through sensor  1015  equipped in the mobile object and indicates a surrounding condition of the mobile object. Server  901  creates three-dimensional data  1134  of a surrounding area of the mobile object using the received sensor information  1037 . 
     With this, server  901  creates three-dimensional data  1134  using sensor information  1037  transmitted from client device  902 . This makes it possible to further reduce the amount of transmission data compared to when client device  902  transmits the three-dimensional data. Since there is no need for client device  902  to perform processes such as compressing or encoding the three-dimensional data, it is possible to reduce the processing amount of client device  902 . As such, server  901  is capable of reducing the amount of data to be transmitted or simplifying the structure of the device. 
     Server  901  further transmits a transmission request for the sensor information to client device  902 . 
     Server  901  further updates three-dimensional map  1135  using the created three-dimensional data  1134 , and transmits three-dimensional map  1135  to client device  902  in response to the transmission request for three-dimensional map  1135  from client device  902 . 
     Sensor information  1037  includes at least one of information obtained by a laser sensor, a luminance image, an infrared image, a depth image, sensor position information, or sensor speed information. 
     Sensor information  1037  includes information that indicates a performance of the sensor. 
     Server  901  further corrects the three-dimensional data in accordance with the performance of the sensor. This enables the three-dimensional data creation method to improve the quality of the three-dimensional data. 
     In the receiving of the sensor information, server  901  receives a plurality of pieces of sensor information  1037  received from a plurality of client devices  902 , and selects sensor information  1037  to be used in the creating of three-dimensional data  1134 , based on a plurality of pieces of information that each indicates the performance of the sensor included in the plurality of pieces of sensor information  1037 . This enables server  901  to improve the quality of three-dimensional data  1134 . 
     Server  901  decodes or decompresses the received sensor information  1037 , and creates three-dimensional data  1134  using sensor information  1132  that has been decoded or decompressed. This enables server  901  to reduce the amount of data to be transmitted. 
     For example, server  901  includes a processor and memory. The processor performs the above processes using the memory. 
     The following will describe a variation of the present embodiment.  FIG. 125  is a diagram illustrating a configuration of a system according to the present embodiment. The system illustrated in  FIG. 125  includes server  2001 , client device  2002 A, and client device  2002 B. 
     Client device  2002 A and client device  2002 B are each provided in a mobile object such as a vehicle, and transmit sensor information to server  2001 . Server  2001  transmits a three-dimensional map (a point cloud) to client device  2002 A and client device  2002 B. 
     Client device  2002 A includes sensor information obtainer  2011 , storage  2012 , and data transmission possibility determiner  2013 . It should be noted that client device  2002 B has the same configuration. Additionally, when client device  2002 A and client device  2002 B are not particularly distinguished below, client device  2002 A and client device  2002 B are also referred to as client device  2002 . 
       FIG. 126  is a flowchart illustrating operation of client device  2002  according to the present embodiment. 
     Sensor information obtainer  2011  obtains a variety of sensor information using sensors (a group of sensors) provided in a mobile object. In other words, sensor information obtainer  2011  obtains sensor information obtained by the sensors (the group of sensors) provided in the mobile object and indicating a surrounding state of the mobile object. Sensor information obtainer  2011  also stores the obtained sensor information into storage  2012 . This sensor information includes at least one of information obtained by LiDAR, a visible light image, an infrared image, or a depth image. Additionally, the sensor information may include at least one of sensor position information, speed information, obtainment time information, or obtainment location information. Sensor position information indicates a position of a sensor that has obtained sensor information. Speed information indicates a speed of the mobile object when a sensor obtained sensor information. Obtainment time information indicates a time when a sensor obtained sensor information. Obtainment location information indicates a position of the mobile object or a sensor when the sensor obtained sensor information. 
     Next, data transmission possibility determiner  2013  determines whether the mobile object (client device  2002 ) is in an environment in which the mobile object can transmit sensor information to server  2001  (S 2002 ). For example, data transmission possibility determiner  2013  may specify a location and a time at which client device  2002  is present using GPS information etc., and may determine whether data can be transmitted. Additionally, data transmission possibility determiner  2013  may determine whether data can be transmitted, depending on whether it is possible to connect to a specific access point. 
     When client device  2002  determines that the mobile object is in the environment in which the mobile object can transmit the sensor information to server  2001  (YES in S 2002 ), client device  2002  transmits the sensor information to server  2001  (S 2003 ). In other words, when client device  2002  becomes capable of transmitting sensor information to server  2001 , client device  2002  transmits the sensor information held by client device  2002  to server  2001 . For example, an access point that enables high-speed communication using millimeter waves is provided in an intersection or the like. When client device  2002  enters the intersection, client device  2002  transmits the sensor information held by client device  2002  to server  2001  at high speed using the millimeter-wave communication. 
     Next, client device  2002  deletes from storage  2012  the sensor information that has been transmitted to server  2001  (S 2004 ). It should be noted that when sensor information that has not been transmitted to server  2001  meets predetermined conditions, client device  2002  may delete the sensor information. For example, when an obtainment time of sensor information held by client device  2002  precedes a current time by a certain time, client device  2002  may delete the sensor information from storage  2012 . In other words, when a difference between the current time and a time when a sensor obtained sensor information exceeds a predetermined time, client device  2002  may delete the sensor information from storage  2012 . Besides, when an obtainment location of sensor information held by client device  2002  is separated from a current location by a certain distance, client device  2002  may delete the sensor information from storage  2012 . In other words, when a difference between a current position of the mobile object or a sensor and a position of the mobile object or the sensor when the sensor obtained sensor information exceeds a predetermined distance, client device  2002  may delete the sensor information from storage  2012 . Accordingly, it is possible to reduce the capacity of storage  2012  of client device  2002 . 
     When client device  2002  does not finish obtaining sensor information (NO in S 2005 ), client device  2002  performs step S 2001  and the subsequent steps again. Further, when client device  2002  finishes obtaining sensor information (YES in S 2005 ), client device  2002  completes the process. 
     Client device  2002  may select sensor information to be transmitted to server  2001 , in accordance with communication conditions. For example, when high-speed communication is available, client device  2002  preferentially transmits sensor information (e.g., information obtained by LiDAR) of which the data size held in storage  2012  is large. Additionally, when high-speed communication is not readily available, client device  2002  transmits sensor information (e.g., a visible light image) which has high priority and of which the data size held in storage  2012  is small. Accordingly, client device  2002  can efficiently transmit sensor information held in storage  2012 , in accordance with network conditions 
     Client device  2002  may obtain, from server  2001 , time information indicating a current time and location information indicating a current location. Moreover, client device  2002  may determine an obtainment time and an obtainment location of sensor information based on the obtained time information and location information. In other words, client device  2002  may obtain time information from server  2001  and generate obtainment time information using the obtained time information. Client device  2002  may also obtain location information from server  2001  and generate obtainment location information using the obtained location information. 
     For example, regarding time information, server  2001  and client device  2002  perform clock synchronization using a means such as the Network Time Protocol (NTP) or the Precision Time Protocol (PTP). This enables client device  2002  to obtain accurate time information. What&#39;s more, since it is possible to synchronize clocks between server  2001  and client devices  2002 , it is possible to synchronize times included in pieces of sensor information obtained by separate client devices  2002 . As a result, server  2001  can handle sensor information indicating a synchronized time. It should be noted that a means of synchronizing clocks may be any means other than the NTP or PTP. In addition, GPS information may be used as the time information and the location information. 
     Server  2001  may specify a time or a location and obtain pieces of sensor information from client devices  2002 . For example, when an accident occurs, in order to search for a client device in the vicinity of the accident, server  2001  specifies an accident occurrence time and an accident occurrence location and broadcasts sensor information transmission requests to client devices  2002 . Then, client device  2002  having sensor information obtained at the corresponding time and location transmits the sensor information to server  2001 . In other words, client device  2002  receives, from server  2001 , a sensor information transmission request including specification information specifying a location and a time. When sensor information obtained at a location and a time indicated by the specification information is stored in storage  2012 , and client device  2002  determines that the mobile object is present in the environment in which the mobile object can transmit the sensor information to server  2001 , client device  2002  transmits, to server  2001 , the sensor information obtained at the location and the time indicated by the specification information. Consequently, server  2001  can obtain the pieces of sensor information pertaining to the occurrence of the accident from client devices  2002 , and use the pieces of sensor information for accident analysis etc. 
     It should be noted that when client device  2002  receives a sensor information transmission request from server  2001 , client device  2002  may refuse to transmit sensor information. Additionally, client device  2002  may set in advance which pieces of sensor information can be transmitted. Alternatively, server  2001  may inquire of client device  2002  each time whether sensor information can be transmitted. 
     A point may be given to client device  2002  that has transmitted sensor information to server  2001 . This point can be used in payment for, for example, gasoline expenses, electric vehicle (EV) charging expenses, a highway toll, or rental car expenses. After obtaining sensor information, server  2001  may delete information for specifying client device  2002  that has transmitted the sensor information. For example, this information is a network address of client device  2002 . Since this enables the anonymization of sensor information, a user of client device  2002  can securely transmit sensor information from client device  2002  to server  2001 . Server  2001  may include servers. For example, by servers sharing sensor information, even when one of the servers breaks down, the other servers can communicate with client device  2002 . Accordingly, it is possible to avoid service outage due to a server breakdown. 
     A specified location specified by a sensor information transmission request indicates an accident occurrence location etc., and may be different from a position of client device  2002  at a specified time specified by the sensor information transmission request. For this reason, for example, by specifying, as a specified location, a range such as within XX meters of a surrounding area, server  2001  can request information from client device  2002  within the range. Similarly, server  2001  may also specify, as a specified time, a range such as within N seconds before and after a certain time. As a result, server  2001  can obtain sensor information from client device  2002  present for a time from t−N to t+N and in a location within XX meters from absolute position S. When client device  2002  transmits three-dimensional data such as LiDAR, client device  2002  may transmit data created immediately after time t. 
     Server  2001  may separately specify information indicating, as a specified location, a location of client device  2002  from which sensor information is to be obtained, and a location at which sensor information is desirably obtained. For example, server  2001  specifies that sensor information including at least a range within YY meters from absolute position S is to be obtained from client device  2002  present within XX meters from absolute position S. When client device  2002  selects three-dimensional data to be transmitted, client device  2002  selects one or more pieces of three-dimensional data so that the one or more pieces of three-dimensional data include at least the sensor information including the specified range. Each of the one or more pieces of three-dimensional data is a random-accessible unit of data. In addition, when client device  2002  transmits a visible light image, client device  2002  may transmit pieces of temporally continuous image data including at least a frame immediately before or immediately after time t. 
     When client device  2002  can use physical networks such as 5G, Wi-Fi, or modes in 5G for transmitting sensor information, client device  2002  may select a network to be used according to the order of priority notified by server  2001 . Alternatively, client device  2002  may select a network that enables client device  2002  to ensure an appropriate bandwidth based on the size of transmit data. Alternatively, client device  2002  may select a network to be used, based on data transmission expenses etc. A transmission request from server  2001  may include information indicating a transmission deadline, for example, performing transmission when client device  2002  can start transmission by time t. When server  2001  cannot obtain sufficient sensor information within a time limit, server  2001  may issue a transmission request again. 
     Sensor information may include header information indicating characteristics of sensor data along with compressed or uncompressed sensor data. Client device  2002  may transmit header information to server  2001  via a physical network or a communication protocol that is different from a physical network or a communication protocol used for sensor data. For example, client device  2002  transmits header information to server  2001  prior to transmitting sensor data. Server  2001  determines whether to obtain the sensor data of client device  2002 , based on a result of analysis of the header information. For example, header information may include information indicating a point cloud obtainment density, an elevation angle, or a frame rate of LiDAR, or information indicating, for example, a resolution, an SN ratio, or a frame rate of a visible light image. Accordingly, server  2001  can obtain the sensor information from client device  2002  having the sensor data of determined quality. 
     As stated above, client device  2002  is provided in the mobile object, obtains sensor information that has been obtained by a sensor provided in the mobile object and indicates a surrounding state of the mobile object, and stores the sensor information into storage  2012 . Client device  2002  determines whether the mobile object is present in an environment in which the mobile object is capable of transmitting the sensor information to server  2001 , and transmits the sensor information to server  2001  when the mobile object is determined to be present in the environment in which the mobile object is capable of transmitting the sensor information to server  2001 . 
     Additionally, client device  2002  further creates, from the sensor information, three-dimensional data of a surrounding area of the mobile object, and estimates a self-location of the mobile object using the three-dimensional data created. 
     Besides, client device  2002  further transmits a transmission request for a three-dimensional map to server  2001 , and receives the three-dimensional map from server  2001 . In the estimating, client device  2002  estimates the self-location using the three-dimensional data and the three-dimensional map. It should be noted that the above process performed by client device  2002  may be realized as an information transmission method for use in client device  2002 . 
     In addition, client device  2002  may include a processor and memory. Using the memory, the processor may perform the above process. 
     Next, a sensor information collection system according to the present embodiment will be described.  FIG. 127  is a diagram illustrating a configuration of the sensor information collection system according to the present embodiment. As illustrated in  FIG. 127 , the sensor information collection system according to the present embodiment includes terminal  2021 A, terminal  2021 B, communication device  2022 A, communication device  2022 B, network  2023 , data collection server  2024 , map server  2025 , and client device  2026 . It should be noted that when terminal  2021 A and terminal  2021 B are not particularly distinguished, terminal  2021 A and terminal  2021 B are also referred to as terminal  2021 . Additionally, when communication device  2022 A and communication device  2022 B are not particularly distinguished, communication device  2022 A and communication device  2022 B are also referred to as communication device  2022 . 
     Data collection server  2024  collects data such as sensor data obtained by a sensor included in terminal  2021  as position-related data in which the data is associated with a position in a three-dimensional space. 
     Sensor data is data obtained by, for example, detecting a surrounding state of terminal  2021  or an internal state of terminal  2021  using a sensor included in terminal  2021 . Terminal  2021  transmits, to data collection server  2024 , one or more pieces of sensor data collected from one or more sensor devices in locations at which direct communication with terminal  2021  is possible or at which communication with terminal  2021  is possible by the same communication system or via one or more relay devices. 
     Data included in position-related data may include, for example, information indicating an operating state, an operating log, a service use state, etc. of a terminal or a device included in the terminal. In addition, the data include in the position-related data may include, for example, information in which an identifier of terminal  2021  is associated with a position or a movement path etc. of terminal  2021 . 
     Information indicating a position included in position-related data is associated with, for example, information indicating a position in three-dimensional data such as three-dimensional map data. The details of information indicating a position will be described later. 
     Position-related data may include at least one of the above-described time information or information indicating an attribute of data included in the position-related data or a type (e.g., a model number) of a sensor that has created the data, in addition to position information that is information indicating a position. The position information and the time information may be stored in a header area of the position-related data or a header area of a frame that stores the position-related data. Further, the position information and the time information may be transmitted and/or stored as metadata associated with the position-related data, separately from the position-related data. 
     Map server  2025  is connected to, for example, network  2023 , and transmits three-dimensional data such as three-dimensional map data in response to a request from another device such as terminal  2021 . Besides, as described in the aforementioned embodiments, map server  2025  may have, for example, a function of updating three-dimensional data using sensor information transmitted from terminal  2021 . 
     Data collection server  2024  is connected to, for example, network  2023 , collects position-related data from another device such as terminal  2021 , and stores the collected position-related data into a storage of data collection server  2024  or a storage of another server. In addition, data collection server  2024  transmits, for example, metadata of collected position-related data or three-dimensional data generated based on the position-related data, to terminal  2021  in response to a request from terminal  2021 . 
     Network  2023  is, for example, a communication network such as the Internet. Terminal  2021  is connected to network  2023  via communication device  2022 . Communication device  2022  communicates with terminal  2021  using one communication system or switching between communication systems. 
     Communication device  2022  is a communication satellite that performs communication using, for example, (1) a base station compliant with Long-Term Evolution (LTE) etc., (2) an access point (AP) for Wi-Fi or millimeter-wave communication etc., (3) a low-power wide-area (LPWA) network gateway such as SIGFOX, LoRaWAN, or Wi-SUN, or (4) a satellite communication system such as DVB-S2. 
     It should be noted that a base station may communicate with terminal  2021  using a system classified as an LPWA network such as Narrowband Internet of Things (NB IoT) or LTE-M, or switching between these systems. 
     Here, although, in the example given, terminal  2021  has a function of communicating with communication device  2022  that uses two types of communication systems, and communicates with map server  2025  or data collection server  2024  using one of the communication systems or switching between the communication systems and between communication devices  2022  to be a direct communication partner; a configuration of the sensor information collection system and terminal  2021  is not limited to this. For example, terminal  2021  need not have a function of performing communication using communication systems, and may have a function of performing communication using one of the communication systems. Terminal  2021  may also support three or more communication systems. Additionally, each terminal  2021  may support a different communication system. 
     Terminal  2021  includes, for example, the configuration of client device  902  illustrated in  FIG. 117 . Terminal  2021  estimates a self-location etc. using received three-dimensional data. Besides, terminal  2021  associates sensor data obtained from a sensor and position information obtained by self-location estimation to generate position-related data. 
     Position information appended to position-related data indicates, for example, a position in a coordinate system used for three-dimensional data. For example, the position information is coordinate values represented using a value of a latitude and a value of a longitude. Here, terminal  2021  may include, in the position information, a coordinate system serving as a reference for the coordinate values and information indicating three-dimensional data used for location estimation, along with the coordinate values. Coordinate values may also include altitude information. 
     The position information may be associated with a data unit or a space unit usable for encoding the above three-dimensional data. Such a unit is, for example, WLD, GOS, SPC, VLM, or VXL. Here, the position information is represented by, for example, an identifier for identifying a data unit such as the SPC corresponding to position-related data. It should be noted that the position information may include, for example, information indicating three-dimensional data obtained by encoding a three-dimensional space including a data unit such as the SPC or information indicating a detailed position within the SPC, in addition to the identifier for identifying the data unit such as the SPC. The information indicating the three-dimensional data is, for example, a file name of the three-dimensional data. 
     As stated above, by generating position-related data associated with position information based on location estimation using three-dimensional data, the system can give more accurate position information to sensor information than when the system appends position information based on a self-location of a client device (terminal  2021 ) obtained using a GPS to sensor information. As a result, even when another device uses the position-related data in another service, there is a possibility of more accurately determining a position corresponding to the position-related data in an actual space, by performing location estimation based on the same three-dimensional data. 
     It should be noted that although the data transmitted from terminal  2021  is the position-related data in the example given in the present embodiment, the data transmitted from terminal  2021  may be data unassociated with position information. In other words, the transmission and reception of three-dimensional data or sensor data described in the other embodiments may be performed via network  2023  described in the present embodiment. 
     Next, a different example of position information indicating a position in a three-dimensional or two-dimensional actual space or in a map space will be described. The position information appended to position-related data may be information indicating a relative position relative to a keypoint in three-dimensional data. Here, the keypoint serving as a reference for the position information is encoded as, for example, SWLD, and notified to terminal  2021  as three-dimensional data. 
     The information indicating the relative position relative to the keypoint may be, for example, information that is represented by a vector from the keypoint to the point indicated by the position information, and indicates a direction and a distance from the keypoint to the point indicated by the position information. Alternatively, the information indicating the relative position relative to the keypoint may be information indicating an amount of displacement from the keypoint to the point indicated by the position information along each of the x axis, the y axis, and the z axis. Additionally, the information indicating the relative position relative to the keypoint may be information indicating a distance from each of three or more keypoints to the point indicated by the position information. It should be noted that the relative position need not be a relative position of the point indicated by the position information represented using each keypoint as a reference, and may be a relative position of each keypoint represented with respect to the point indicated by the position information. Examples of position information based on a relative position relative to a keypoint include information for identifying a keypoint to be a reference, and information indicating the relative position of the point indicated by the position information and relative to the keypoint. When the information indicating the relative position relative to the keypoint is provided separately from three-dimensional data, the information indicating the relative position relative to the keypoint may include, for example, coordinate axes used in deriving the relative position, information indicating a type of the three-dimensional data, and/or information indicating a magnitude per unit amount (e.g., a scale) of a value of the information indicating the relative position. 
     The position information may include, for each keypoint, information indicating a relative position relative to the keypoint. When the position information is represented by relative positions relative to keypoints, terminal  2021  that intends to identify a position in an actual space indicated by the position information may calculate candidate points of the position indicated by the position information from positions of the keypoints each estimated from sensor data, and may determine that a point obtained by averaging the calculated candidate points is the point indicated by the position information. Since this configuration reduces the effects of errors when the positions of the keypoints are estimated from the sensor data, it is possible to improve the estimation accuracy for the point in the actual space indicated by the position information. Besides, when the position information includes information indicating relative positions relative to keypoints, if it is possible to detect any one of the keypoints regardless of the presence of keypoints undetectable due to a limitation such as a type or performance of a sensor included in terminal  2021 , it is possible to estimate a value of the point indicated by the position information. 
     A point identifiable from sensor data can be used as a keypoint. Examples of the point identifiable from the sensor data include a point or a point within a region that satisfies a predetermined keypoint detection condition, such as the above-described three-dimensional feature or feature of visible light data is greater than or equal to a threshold value. 
     Moreover, a marker etc. placed in an actual space may be used as a keypoint. In this case, the maker may be detected and located from data obtained using a sensor such as LiDAR or a camera. For example, the marker may be represented by a change in color or luminance value (degree of reflection), or a three-dimensional shape (e.g., unevenness). Coordinate values indicating a position of the marker, or a two-dimensional bar code or a bar code etc. generated from an identifier of the marker may be also used. 
     Furthermore, a light source that transmits an optical signal may be used as a marker. When a light source of an optical signal is used as a marker, not only information for obtaining a position such as coordinate values or an identifier but also other data may be transmitted using an optical signal. For example, an optical signal may include contents of service corresponding to the position of the marker, an address for obtaining contents such as a URL, or an identifier of a wireless communication device for receiving service, and information indicating a wireless communication system etc. for connecting to the wireless communication device. The use of an optical communication device (a light source) as a marker not only facilitates the transmission of data other than information indicating a position but also makes it possible to dynamically change the data. 
     Terminal  2021  finds out a correspondence relationship of keypoints between mutually different data using, for example, a common identifier used for the data, or information or a table indicating the correspondence relationship of the keypoints between the data. When there is no information indicating a correspondence relationship between keypoints, terminal  2021  may also determine that when coordinates of a keypoint in three-dimensional data are converted into a position in a space of another three-dimensional data, a keypoint closest to the position is a corresponding keypoint. 
     When the position information based on the relative position described above is used, terminal  2021  that uses mutually different three-dimensional data or services can identify or estimate a position indicated by the position information with respect to a common keypoint included in or associated with each three-dimensional data. As a result, terminal  2021  that uses the mutually different three-dimensional data or the services can identify or estimate the same position with higher accuracy. 
     Even when map data or three-dimensional data represented using mutually different coordinate systems are used, since it is possible to reduce the effects of errors caused by the conversion of a coordinate system, it is possible to coordinate services based on more accurate position information. 
     Hereinafter, an example of functions provided by data collection server  2024  will be described. Data collection server  2024  may transfer received position-related data to another data server. When there are data servers, data collection server  2024  determines to which data server received position-related data is to be transferred, and transfers the position-related data to a data server determined as a transfer destination. 
     Data collection server  2024  determines a transfer destination based on, for example, transfer destination server determination rules preset to data collection server  2024 . The transfer destination server determination rules are set by, for example, a transfer destination table in which identifiers respectively associated with terminals  2021  are associated with transfer destination data servers. 
     Terminal  2021  appends an identifier associated with terminal  2021  to position-related data to be transmitted, and transmits the position-related data to data collection server  2024 . Data collection server  2024  determines a transfer destination data server corresponding to the identifier appended to the position-related data, based on the transfer destination server determination rules set out using the transfer destination table etc.; and transmits the position-related data to the determined data server. The transfer destination server determination rules may be specified based on a determination condition set using a time, a place, etc. at which position-related data is obtained. Here, examples of the identifier associated with transmission source terminal  2021  include an identifier unique to each terminal  2021  or an identifier indicating a group to which terminal  2021  belongs. 
     The transfer destination table need not be a table in which identifiers associated with transmission source terminals are directly associated with transfer destination data servers. For example, data collection server  2024  holds a management table that stores tag information assigned to each identifier unique to terminal  2021 , and a transfer destination table in which the pieces of tag information are associated with transfer destination data servers. Data collection server  2024  may determine a transfer destination data server based on tag information, using the management table and the transfer destination table. Here, the tag information is, for example, control information for management or control information for providing service assigned to a type, a model number, an owner of terminal  2021  corresponding to the identifier, a group to which terminal  2021  belongs, or another identifier. Moreover, in the transfer destination able, identifiers unique to respective sensors may be used instead of the identifiers associated with transmission source terminals  2021 . Furthermore, the transfer destination server determination rules may be set by client device  2026 . 
     Data collection server  2024  may determine data servers as transfer destinations, and transfer received position-related data to the data servers. According to this configuration, for example, when position-related data is automatically backed up or when, in order that position-related data is commonly used by different services, there is a need to transmit the position-related data to a data server for providing each service, it is possible to achieve data transfer as intended by changing a setting of data collection server  2024 . As a result, it is possible to reduce the number of steps necessary for building and changing a system, compared to when a transmission destination of position-related data is set for each terminal  2021 . 
     Data collection server  2024  may register, as a new transfer destination, a data server specified by a transfer request signal received from a data server; and transmit position-related data subsequently received to the data server, in response to the transfer request signal. 
     Data collection server  2024  may store position-related data received from terminal  2021  into a recording device, and transmit position-related data specified by a transmission request signal received from terminal  2021  or a data server to request source terminal  2021  or the data server in response to the transmission request signal. 
     Data collection server  2024  may determine whether position-related data is suppliable to a request source data server or terminal  2021 , and transfer or transmit the position-related data to the request source data server or terminal  2021  when determining that the position-related data is suppliable. 
     When data collection server  2024  receives a request for current position-related data from client device  2026 , even if it is not a timing for transmitting position-related data by terminal  2021 , data collection server  2024  may send a transmission request for the current position-related data to terminal  2021 , and terminal  2021  may transmit the current position-related data in response to the transmission request. 
     Although terminal  2021  transmits position information data to data collection server  2024  in the above description, data collection server  2024  may have a function of managing terminal  2021  such as a function necessary for collecting position-related data from terminal  2021  or a function used when collecting position-related data from terminal  2021 . 
     Data collection server  2024  may have a function of transmitting, to terminal  2021 , a data request signal for requesting transmission of position information data, and collecting position-related data. 
     Management information such as an address for communicating with terminal  2021  from which data is to be collected or an identifier unique to terminal  2021  is registered in advance in data collection server  2024 . Data collection server  2024  collects position-related data from terminal  2021  based on the registered management information. Management information may include information such as types of sensors included in terminal  2021 , the number of sensors included in terminal  2021 , and communication systems supported by terminal  2021 . 
     Data collection server  2024  may collect information such as an operating state or a current position of terminal  2021  from terminal  2021 . 
     Registration of management information may be instructed by client device  2026 , or a process for the registration may be started by terminal  2021  transmitting a registration request to data collection server  2024 . Data collection server  2024  may have a function of controlling communication between data collection server  2024  and terminal  2021 . 
     Communication between data collection server  2024  and terminal  2021  may be established using a dedicated line provided by a service provider such as a mobile network operator (MNO) or a mobile virtual network operator (MVNO), or a virtual dedicated line based on a virtual private network (VPN). According to this configuration, it is possible to perform secure communication between terminal  2021  and data collection server  2024 . 
     Data collection server  2024  may have a function of authenticating terminal  2021  or a function of encrypting data to be transmitted and received between data collection server  2024  and terminal  2021 . Here, the authentication of terminal  2021  or the encryption of data is performed using, for example, an identifier unique to terminal  2021  or an identifier unique to a terminal group including terminals  2021 , which is shared in advance between data collection server  2024  and terminal  2021 . Examples of the identifier include an international mobile subscriber identity (IMSI) that is a unique number stored in a subscriber identity module (SIM) card. An identifier for use in authentication and an identifier for use in encryption of data may be identical or different. 
     The authentication or the encryption of data between data collection server  2024  and terminal  2021  is feasible when both data collection server  2024  and terminal  2021  have a function of performing the process. The process does not depend on a communication system used by communication device  2022  that performs relay. Accordingly, since it is possible to perform the common authentication or encryption without considering whether terminal  2021  uses a communication system, the user&#39;s convenience of system architecture is increased. However, the expression “does not depend on a communication system used by communication device  2022  that performs relay” means a change according to a communication system is not essential. In other words, in order to improve the transfer efficiency or ensure security, the authentication or the encryption of data between data collection server  2024  and terminal  2021  may be changed according to a communication system used by a relay device. 
     Data collection server  2024  may provide client device  2026  with a User Interface (UI) that manages data collection rules such as types of position-related data collected from terminal  2021  and data collection schedules. Accordingly, a user can specify, for example, terminal  2021  from which data is to be collected using client device  2026 , a data collection time, and a data collection frequency. Additionally, data collection server  2024  may specify, for example, a region on a map from which data is to be desirably collected, and collect position-related data from terminal  2021  included in the region. 
     When the data collection rules are managed on a per terminal  2021  basis, client device  2026  presents, on a screen, a list of terminals  2021  or sensors to be managed. The user sets, for example, a necessity for data collection or a collection schedule for each item in the list. 
     When a region on a map from which data is to be desirably collected is specified, client device  2026  presents, on a screen, a two-dimensional or three-dimensional map of a region to be managed. The user selects the region from which data is to be collected on the displayed map. Examples of the region selected on the map include a circular or rectangular region having a point specified on the map as the center, or a circular or rectangular region specifiable by a drag operation. Client device  2026  may also select a region in a preset unit such as a city, an area or a block in a city, or a main road, etc. Instead of specifying a region using a map, a region may be set by inputting values of a latitude and a longitude, or a region may be selected from a list of candidate regions derived based on inputted text information. Text information is, for example, a name of a region, a city, or a landmark. 
     Moreover, data may be collected while the user dynamically changes a specified region by specifying one or more terminals  2021  and setting a condition such as within 100 meters of one or more terminals  2021 . 
     When client device  2026  includes a sensor such as a camera, a region on a map may be specified based on a position of client device  2026  in an actual space obtained from sensor data. For example, client device  2026  may estimate a self-location using sensor data, and specify, as a region from which data is to be collected, a region within a predetermined distance from a point on a map corresponding to the estimated location or a region within a distance specified by the user. Client device  2026  may also specify, as the region from which the data is to be collected, a sensing region of the sensor, that is, a region corresponding to obtained sensor data. Alternatively, client device  2026  may specify, as the region from which the data is to be collected, a region based on a location corresponding to sensor data specified by the user. Either client device  2026  or data collection server  2024  may estimate a region on a map or a location corresponding to sensor data. 
     When a region on a map is specified, data collection server  2024  may specify terminal  2021  within the specified region by collecting current position information of each terminal  2021 , and may send a transmission request for position-related data to specified terminal  2021 . When data collection server  2024  transmits information indicating a specified region to terminal  2021 , determines whether terminal  2021  is present within the specified region, and determines that terminal  2021  is present within the specified region, rather than specifying terminal  2021  within the region, terminal  2021  may transmit position-related data. 
     Data collection server  2024  transmits, to client device  2026 , data such as a list or a map for providing the above-described User Interface (UI) in an application executed by client device  2026 . Data collection server  2024  may transmit, to client device  2026 , not only the data such as the list or the map but also an application program. Additionally, the above UI may be provided as contents created using HTML displayable by a browser. It should be noted that part of data such as map data may be supplied from a server, such as map server  2025 , other than data collection server  2024 . 
     When client device  2026  receives an input for notifying the completion of an input such as pressing of a setup key by the user, client device  2026  transmits the inputted information as configuration information to data collection server  2024 . Data collection server  2024  transmits, to each terminal  2021 , a signal for requesting position-related data or notifying position-related data collection rules, based on the configuration information received from client device  2026 , and collects the position-related data. 
     Next, an example of controlling operation of terminal  2021  based on additional information added to three-dimensional or two-dimensional map data will be described. 
     In the present configuration, object information that indicates a position of a power feeding part such as a feeder antenna or a feeder coil for wireless power feeding buried under a road or a parking lot is included in or associated with three-dimensional data, and such object information is provided to terminal  2021  that is a vehicle or a drone. 
     A vehicle or a drone that has obtained the object information to get charged automatically moves so that a position of a charging part such as a charging antenna or a charging coil included in the vehicle or the drone becomes opposite to a region indicated by the object information, and such vehicle or a drone starts to charge itself. It should be noted that when a vehicle or a drone has no automatic driving function, a direction to move in or an operation to perform is presented to a driver or an operator by using an image displayed on a screen, audio, etc. When a position of a charging part calculated based on an estimated self-location is determined to fall within the region indicated by the object information or a predetermined distance from the region, an image or audio to be presented is changed to a content that puts a stop to driving or operating, and the charging is started. 
     Object information need not be information indicating a position of a power feeding part, and may be information indicating a region within which placement of a charging part results in a charging efficiency greater than or equal to a predetermined threshold value. A position indicated by object information may be represented by, for example, the central point of a region indicated by the object information, a region or a line within a two-dimensional plane, or a region, a line, or a plane within a three-dimensional space. 
     According to this configuration, since it is possible to identify the position of the power feeding antenna unidentifiable by sensing data of LiDAR or an image captured by the camera, it is possible to highly accurately align a wireless charging antenna included in terminal  2021  such as a vehicle with a wireless power feeding antenna buried under a road. As a result, it is possible to increase a charging speed at the time of wireless charging and improve the charging efficiency. 
     Object information may be an object other than a power feeding antenna. For example, three-dimensional data includes, for example, a position of an AP for millimeter-wave wireless communication as object information. Accordingly, since terminal  2021  can identify the position of the AP in advance, terminal  2021  can steer a directivity of beam to a direction of the object information and start communication. As a result, it is possible to improve communication quality such as increasing transmission rates, reducing the duration of time before starting communication, and extending a communicable period. 
     Object information may include information indicating a type of an object corresponding to the object information. In addition, when terminal  2021  is present within a region in an actual space corresponding to a position in three-dimensional data of the object information or within a predetermined distance from the region, the object information may include information indicating a process to be performed by terminal  2021 . 
     Object information may be provided by a server different from a server that provides three-dimensional data. When object information is provided separately from three-dimensional data, object groups in which object information used by the same service is stored may be each provided as separate data according to a type of a target service or a target device. 
     Three-dimensional data used in combination with object information may be point cloud data of WLD or keypoint data of SWLD. 
     In the three-dimensional data encoding device, when attribute information of a current three-dimensional point to be encoded is layer-encoded using Levels of Detail (LoDs), the three-dimensional data decoding device may decode the attribute information in layers down to LoD required by the three-dimensional data decoding device and need not decode the attribute information in layers not required. For example, when the total number of LoDs for the attribute information in a bitstream generated by the three-dimensional data encoding device is N, the three-dimensional data decoding device may decode M LoDs (M&lt;N), i.e., layers from the uppermost layer LoD0 to LoD(M−1), and need not decode the remaining LoDs, i.e., layers down to LoD(N−1). With this, while reducing the processing load, the three-dimensional data decoding device can decode the attribute information in layers from LoD0 to LoD(M−1) required by the three-dimensional data decoding device. 
       FIG. 128  is a diagram illustrating the foregoing use case. In the example shown in  FIG. 128 , a server stores a three-dimensional map obtained by encoding three-dimensional geometry information and attribute information. The server (the three-dimensional data encoding device) broadcasts the three-dimensional map to client devices (the three-dimensional data decoding devices: for example, vehicles, drones, etc.) in an area managed by the server, and each client device uses the three-dimensional map received from the server to perform a process for identifying the self-position of the client device or a process for displaying map information to a user or the like who operates the client device. 
     The following describes an example of the operation in this case. First, the server encodes the geometry information of the three-dimensional map using an octree structure or the like. Then, the sever layer-encodes the attribute information of the three-dimensional map using N LoDs established based on the geometry information. The server stores a bitstream of the three-dimensional map obtained by the layer-encoding. 
     Next, in response to a send request for the map information from the client device in the area managed by the server, the server sends the bitstream of the encoded three-dimensional map to the client device. 
     The client device receives the bitstream of the three-dimensional map sent from the server, and decodes the geometry information and the attribute information of the three-dimensional map in accordance with the intended use of the client device. For example, when the client device performs highly accurate estimation of the self-position using the geometry information and the attribute information in N LoDs, the client device determines that a decoding result to the dense three-dimensional points is necessary as the attribute information, and decodes all the information in the bitstream. 
     Moreover, when the client device displays the three-dimensional map information to a user or the like, the client device determines that a decoding result to the sparse three-dimensional points is necessary as the attribute information, and decodes the geometry information and the attribute information in M LoDs (M&lt;N) starting from an upper layer LoD0. 
     In this way, the processing load of the client device can be reduced by changing LoDs for the attribute information to be decoded in accordance with the intended use of the client device. 
     In the example shown in  FIG. 128 , for example, the three-dimensional map includes geometry information and attribute information. The geometry information is encoded using the octree. The attribute information is encoded using N LoDs. 
     Client device A performs highly accurate estimation of the self-position. In this case, client device A determines that all the geometry information and all the attribute information are necessary, and decodes all the geometry information and all the attribute information constructed from N LoDs in the bitstream. 
     Client device B displays the three-dimensional map to a user. In this case, client device B determines that the geometry information and the attribute information in M LoDs (M&lt;N) are necessary, and decodes the geometry information and the attribute information constructed from M LoDs in the bitstream. 
     It is to be noted that the server may broadcast the three-dimensional map to the client devices, or multicast or unicast the three-dimensional map to the client devices. 
     The following describes a variation of the system according to the present embodiment. In the three-dimensional data encoding device, when attribute information of a current three-dimensional point to be encoded is layer-encoded using LoDs, the three-dimensional data encoding device may encode the attribute information in layers down to LoD required by the three-dimensional data decoding device and need not encode the attribute information in layers not required. For example, when the total number of LoDs is N, the three-dimensional data encoding device may generate a bitstream by encoding M LoDs (M&lt;N), i.e., layers from the uppermost layer LoD0 to LoD(M−1), and not encoding the remaining LoDs, i.e., layers down to LoD(N−1). With this, in response to a request from the three-dimensional data decoding device, the three-dimensional data encoding device can provide a bitstream in which the attribute information from LoD0 to LoD(M−1) required by the three-dimensional data decoding device is encoded. 
       FIG. 129  is a diagram illustrating the foregoing use case. In the example shown in  FIG. 129 , a server stores a three-dimensional map obtained by encoding three-dimensional geometry information and attribute information. The server (the three-dimensional data encoding device) unicasts, in response to a request from the client device, the three-dimensional map to a client device (the three-dimensional data decoding device: for example, a vehicle, a drone, etc.) in an area managed by the server, and the client device uses the three-dimensional map received from the server to perform a process for identifying the self-position of the client device or a process for displaying map information to a user or the like who operates the client device. 
     The following describes an example of the operation in this case. First, the server encodes the geometry information of the three-dimensional map using an octree structure, or the like. Then, the sever generates a bitstream of three-dimensional map A by layer-encoding the attribute information of the three-dimensional map using N LoDs established based on the geometry information, and stores the generated bitstream in the server. The sever also generates a bitstream of three-dimensional map B by layer-encoding the attribute information of the three-dimensional map using M LoDs (M&lt;N) established based on the geometry information, and stores the generated bitstream in the server. 
     Next, the client device requests the server to send the three-dimensional map in accordance with the intended use of the client device. For example, when the client device performs highly accurate estimation of the self-position using the geometry information and the attribute information in N LoDs, the client device determines that a decoding result to the dense three-dimensional points is necessary as the attribute information, and requests the server to send the bitstream of three-dimensional map A. Moreover, when the client device displays the three-dimensional map information to a user or the like, the client device determines that a decoding result to the sparse three-dimensional points is necessary as the attribute information, and requests the server to send the bitstream of three-dimensional map B including the geometry information and the attribute information in M LoDs (M&lt;N) starting from an upper layer LoD0. Then, in response to the send request for the map information from the client device, the server sends the bitstream of encoded three-dimensional map A or B to the client device. 
     The client device receives the bitstream of three-dimensional map A or B sent from the server in accordance with the intended use of the client device, and decodes the received bitstream. In this way, the server changes a bitstream to be sent, in accordance with the intended use of the client device. With this, it is possible to reduce the processing load of the client device. 
     In the example shown in  FIG. 129 , the server stores three-dimensional map A and three-dimensional map B. The server generates three-dimensional map A by encoding the geometry information of the three-dimensional map using, for example, an octree structure, and encoding the attribute information of the three-dimensional map using N LoDs. In other words, NumLoD included in the bitstream of three-dimensional map A indicates N. 
     The server also generates three-dimensional map B by encoding the geometry information of the three-dimensional map using, for example, an octree structure, and encoding the attribute information of the three-dimensional map using M LoDs. In other words, NumLoD included in the bitstream of three-dimensional map B indicates M. 
     Client device A performs highly accurate estimation of the self-position. In this case, client device A determines that all the geometry information and all the attribute information are necessary, and requests the server to send three-dimensional map A including all the geometry information and the attribute information constructed from N LoDs. Client device A receives three-dimensional map A, and decodes all the geometry information and the attribute information constructed from N LoDs. 
     Client device B displays the three-dimensional map to a user. In this case, client device B determines that all the geometry information and the attribute information in M LoDs (M&lt;N) are necessary, and requests the server to send three-dimensional map B including all the geometry information and the attribute information constructed from M LoDs. Client device B receives three-dimensional map B, and decodes all the geometry information and the attribute information constructed from M LoDs. 
     It is to be noted that in addition to three-dimensional map B, the server (the three-dimensional data encoding device) may generate three-dimensional map C in which attribute information in the remaining N-M LoDs is encoded, and send three-dimensional map C to client device B in response to the request from client device B. Moreover, client device B may obtain the decoding result of N LoDs using the bitstreams of three-dimensional maps B and C. 
     Hereinafter, an example of an application process will be described.  FIG. 130  is a flowchart illustrating an example of the application process. When an application operation is started, a three-dimensional data demultiplexing device obtains an ISOBMFF file including point cloud data and a plurality of pieces of encoded data (S 7301 ). For example, the three-dimensional data demultiplexing device may obtain the ISOBMFF file through communication, or may read the ISOBMFF file from the accumulated data. 
     Next, the three-dimensional data demultiplexing device analyzes the general configuration information in the ISOBMFF file, and specifies the data to be used for the application (S 7302 ). For example, the three-dimensional data demultiplexing device obtains data that is used for processing, and does not obtain data that is not used for processing. 
     Next, the three-dimensional data demultiplexing device extracts one or more pieces of data to be used for the application, and analyzes the configuration information on the data (S 7303 ). 
     When the type of the data is encoded data (encoded data in S 7304 ), the three-dimensional data demultiplexing device converts the ISOBMFF to an encoded stream, and extracts a timestamp (S 7305 ). Additionally, the three-dimensional data demultiplexing device refers to, for example, the flag indicating whether or not the synchronization between data is aligned to determine whether or not the synchronization between data is aligned, and may perform a synchronization process when not aligned. 
     Next, the three-dimensional data demultiplexing device decodes the data with a predetermined method according to the timestamp and the other instructions, and processes the decoded data (S 7306 ). 
     On the other hand, when the type of the data is RAW data (RAW data in S 7304 ), the three-dimensional data demultiplexing device extracts the data and timestamp (S 7307 ). Additionally, the three-dimensional data demultiplexing device may refer to, for example, the flag indicating whether or not the synchronization between data is aligned to determine whether or not the synchronization between data is aligned, and may perform a synchronization process when not aligned. Next, the three-dimensional data demultiplexing device processes the data according to the timestamp and the other instructions (S 7308 ). 
     For example, an example will be described in which the sensor signals obtained by a beam LiDAR, a FLASH LiDAR, and a camera are encoded and multiplexed with respective different encoding schemes.  FIG. 131  is a diagram illustrating examples of the sensor ranges of a beam LiDAR, a FLASH LiDAR, and a camera. For example, the beam LiDAR detects all directions in the periphery of a vehicle (sensor), and the FLASH LiDAR and the camera detect the range in one direction (for example, the front) of the vehicle. 
     In the case of an application that integrally handles a LiDAR point cloud, the three-dimensional data demultiplexing device refers to the general configuration information, and extracts and decodes the encoded data of the beam LiDAR and the FLASH LiDAR. Additionally, the three-dimensional data demultiplexing device does not extract camera images. 
     According to the timestamps of the beam LiDAR and the FLASH LiDAR, the three-dimensional data demultiplexing device simultaneously processes the respective encoded data of the time of the same timestamp. 
     For example, the three-dimensional data demultiplexing device may present the processed data with a presentation device, may synthesize the point cloud data of the beam LiDAR and the FLASH LiDAR, or may perform a process such as rendering. 
     Additionally, in the case of an application that performs calibration between data, the three-dimensional data demultiplexing device may extract sensor geometry information, and use the sensor geometry information in the application. 
     For example, the three-dimensional data demultiplexing device may select whether to use beam LiDAR information or FLASH LiDAR information in the application, and may switch the process according to the selection result. 
     In this manner, since it is possible to adaptively change the obtaining of data and the encoding process according to the process of the application, the processing amount and the power consumption can be reduced. 
     Hereinafter, a use case in automated driving will be described.  FIG. 132  is a diagram illustrating a configuration example of an automated driving system. This automated driving system includes cloud server  7350 , and edge  7360  such as an in-vehicle device or a mobile device. Cloud server  7350  includes demultiplexer  7351 , decoders  7352 A,  7352 B, and  7355 , point cloud data synthesizer  7353 , large data accumulator  7354 , comparator  7356 , and encoder  7357 . Edge  7360  includes sensors  7361 A and  7361 B, point cloud data generators  7362 A and  7362 B, synchronizer  7363 , encoders  7364 A and  7364 B, multiplexer  7365 , update data accumulator  7366 , demultiplexer  7367 , decoder  7368 , filter  7369 , self-position estimator  7370 , and driving controller  7371 . 
     In this system, edge  7360  downloads large data, which is large point-cloud map data accumulated in cloud server  7350 . Edge  7360  performs a self-position estimation process of edge  7360  (a vehicle or a terminal) by matching the large data with the sensor information obtained by edge  7360 . Additionally, edge  7360  uploads the obtained sensor information to cloud server  7350 , and updates the large data to the latest map data. 
     Additionally, in various applications that handle point cloud data in the system, point cloud data with different encoding methods are handled. 
     Cloud server  7350  encodes and multiplexes large data. Specifically, encoder  7357  performs encoding by using a third encoding method suitable for encoding a large point cloud. Additionally, encoder  7357  multiplexes encoded data. Large data accumulator  7354  accumulates the data encoded and multiplexed by encoder  7357 . 
     Edge  7360  performs sensing. Specifically, point cloud data generator  7362 A generates first point cloud data (geometry information (geometry) and attribute information) by using the sensing information obtained by sensor  7361 A. Point cloud data generator  7362 B generates second point cloud data (geometry information and attribute information) by using the sensing information obtained by sensor  7361 B. The generated first point cloud data and second point cloud data are used for the self-position estimation or vehicle control of automated driving, or for map updating. In each process, a part of information of the first point cloud data and the second point cloud data may be used. 
     Edge  7360  performs the self-position estimation. Specifically, edge  7360  downloads large data from cloud server  7350 . Demultiplexer  7367  obtains encoded data by demultiplexing the large data in a file format. Decoder  7368  obtains large data, which is large point-cloud map data, by decoding the obtained encoded data. 
     Self-position estimator  7370  estimates the self-position in the map of a vehicle by matching the obtained large data with the first point cloud data and the second point cloud data generated by point cloud data generators  7362 A and  7362 B. Additionally, driving controller  7371  uses the matching result or the self-position estimation result for driving control. 
     Note that self-position estimator  7370  and driving controller  7371  may extract specific information, such as geometry information, of the large data, and may perform processes by using the extracted information. Additionally, filter  7369  performs a process such as correction or decimation on the first point cloud data and the second point cloud data. Self-position estimator  7370  and driving controller  7371  may use the first point cloud data and second point cloud data on which the process has been performed. Additionally, self-position estimator  7370  and driving controller  7371  may use the sensor signals obtained by sensors  7361 A and  7361 B. 
     Synchronizer  7363  performs time synchronization and geometry correction between a plurality of sensor signals or the pieces of data of a plurality of pieces of point cloud data. Additionally, synchronizer  7363  may correct the geometry information on the sensor signal or point cloud data to match the large data, based on geometry correction information on the large data and sensor data generated by the self-position estimation process. 
     Note that synchronization and geometry correction may be performed not by edge  7360 , but by cloud server  7350 . In this case, edge  7360  may multiplex the synchronization information and the geometry information to transmit the synchronization information and the geometry information to cloud server  7350 . 
     Edge  7360  encodes and multiplexes the sensor signal or point cloud data. Specifically, the sensor signal or point cloud data is encoded by using a first encoding method or a second encoding method suitable for encoding each signal. For example, encoder  7364 A generates first encoded data by encoding first point cloud data by using the first encoding method. Encoder  7364 B generates second encoded data by encoding second point cloud data by using the second encoding method. 
     Multiplexer  7365  generates a multiplexed signal by multiplexing the first encoded data, the second encoded data, the synchronization information, and the like. Update data accumulator  7366  accumulates the generated multiplexed signal. Additionally, update data accumulator  7366  uploads the multiplexed signal to cloud server  7350 . 
     Cloud server  7350  synthesizes the point cloud data. Specifically, demultiplexer  7351  obtains the first encoded data and the second encoded data by demultiplexing the multiplexed signal uploaded to cloud server  7350 . Decoder  7352 A obtains the first point cloud data (or sensor signal) by decoding the first encoded data. Decoder  7352 B obtains the second point cloud data (or sensor signal) by decoding the second encoded data. 
     Point cloud data synthesizer  7353  synthesizes the first point cloud data and the second point cloud data with a predetermined method. When the synchronization information and the geometry correction information are multiplexed in the multiplexed signal, point cloud data synthesizer  7353  may perform synthesis by using these pieces of information. 
     Decoder  7355  demultiplexes and decodes the large data accumulated in large data accumulator  7354 . Comparator  7356  compares the point cloud data generated based on the sensor signal obtained by edge  7360  with the large data held by cloud server  7350 , and determines the point cloud data that needs to be updated. Comparator  7356  updates the point cloud data that is determined to need to be updated of the large data to the point cloud data obtained from edge  7360 . 
     Encoder  7357  encodes and multiplexes the updated large data, and accumulates the obtained data in large data accumulator  7354 . 
     As described above, the signals to be handled may be different, and the signals to be multiplexed or encoding methods may be different, according to the usage or applications to be used. Even in such a case, flexible decoding and application processes are enabled by multiplexing data of various encoding schemes by using the present embodiment. Additionally, even in a case where the encoding schemes of signals are different, by conversion to an encoding scheme suitable for demultiplexing, decoding, data conversion, encoding, and multiplexing processing, it becomes possible to build various applications and systems, and to offer of flexible services. 
     Hereinafter, an example of decoding and application of divisional data will be described. First, the information on divisional data will be described.  FIG. 133  is a diagram illustrating a configuration example of a bitstream. The general information of divisional data indicates, for each divisional data, the sensor ID (sensor_id) and data ID (data_id) of the divisional data. Note that the data ID is also indicated in the header of each encoded data. 
     Note that, as in  FIG. 31 , the general information of divisional data illustrated in  FIG. 133  includes, in addition to the sensor ID, at least one of the sensor information (Sensor), the version (Version) of the sensor, the maker name (Maker) of the sensor, the mount information (Mount Info.) of the sensor, and the position coordinates of the sensor (World Coordinate). Accordingly, the three-dimensional data decoding device can obtain the information on various sensors from the configuration information. 
     The general information of divisional data may be stored in SPS, GPS, or APS, which is the metadata, or may be stored in SEI, which is the metadata not required for encoding. Additionally, at the time of multiplexing, the three-dimensional data encoding device stores the SEI in a file of ISOBMFF. The three-dimensional data decoding device can obtain desired divisional data based on the metadata. 
     In  FIG. 133 , SPS is the metadata of the entire encoded data, GPS is the metadata of the geometry information, APS is the metadata for each attribute information, G is encoded data of the geometry information for each divisional data, and A1, etc. are encoded data of the attribute information for each divisional data. 
     Next, an application example of divisional data will be described. An example of application will be described in which an arbitrary point cloud is selected, and the selected point cloud is presented.  FIG. 134  is a flowchart of a point cloud selection process performed by this application.  FIG. 135  to  FIG. 137  are diagrams illustrating screen examples of the point cloud selection process. 
     As illustrated in  FIG. 135 , the three-dimensional data decoding device that performs the application includes, for example, a UI unit that displays an input UI (user interface)  8661  for selecting an arbitrary point cloud. Input UI  8661  includes presenter  8662  that presents the selected point cloud, and an operation unit (buttons  8663  and  8664 ) that receives operations by a user. After a point cloud is selected in UI  8661 , the three-dimensional data decoding device obtains desired data from accumulator  8665 . 
     First, based on an operation by the user on input UI  8661 , the point cloud information that the user wants to display is selected (S 8631 ). Specifically, by selecting button  8663 , the point cloud based on sensor  1  is selected. By selecting button  8664 , the point cloud based on sensor  2  is selected. Alternatively, by selecting both button  8663  and button  8664 , the point cloud based on sensor  1  and the point cloud based on sensor  2  are selected. Note that it is an example of the selection method of point cloud, and it is not limited to this. 
     Next, the three-dimensional data decoding device analyzes the general information of divisional data included in the multiplexed signal (bitstream) or encoded data, and specifies the data ID (data_id) of the divisional data constituting the selected point cloud from the sensor ID (sensor_id) of the selected sensor (S 8632 ). Next, the three-dimensional data decoding device extracts, from the multiplexed signal, the encoded data including the specified and desired data ID, and decodes the extracted encoded data to decode the point cloud based on the selected sensor (S 8633 ). Note that the three-dimensional data decoding device does not decode the other encoded data. 
     Lastly, the three-dimensional data decoding device presents (for example, displays) the decoded point cloud (S 8634 ).  FIG. 136  illustrates an example in the case where button  8663  for sensor  1  is pressed, and the point cloud of sensor  1  is presented.  FIG. 137  illustrates an example in the case where both button  8663  for sensor  1  and button  8664  for sensor  2  are pressed, and the point clouds of sensor  1  and sensor  2  are presented. 
     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.