JP2016188792A - Position measuring method and position measuring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform satellite positioning of a land mobile body such as a railroad train having a limited track with high positional accuracy by eliminating influence of multipath.SOLUTION: A position measuring device 100: calculates a position of a satellite signal receiver 10 from data d1 on respective satellites input therefrom; obtains a sectional number of a track to which a mobile body belongs on the basis of the position of the satellite signal receiver 10 and track geometry data; calculates the positions of a plurality of satellites st1 to st4 viewed from the mobile body on the basis of the position of the satellite signal receiver 10 and the data d1 on respective satellites; identifies the satellite with a radio wave thereof shielded by an obstacle before being received by the mobile body on the basis of the sectional number of the track to which the mobile body belongs, the positions of the plurality of satellites st1 to st4 and shield data; and recalculates the position of the satellite signal receiver 10 on the basis of the data d1 on the satellites except the same with the radio wave thereof shielded by the obstacle.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a position measuring method and a position measuring system, and in particular, by using a multi-GNSS system in which a plurality of satellite positioning systems coexist, a position on a land mobile body having a limited travel path such as a railway train is specified. In this case, the present invention relates to a position measurement method and a position measurement system suitable for eliminating the influence of multipath and realizing high-precision positioning.

  A satellite positioning system (Global Navigation Satellite System: GNSS) that uses satellites on the earth to determine the position of a receiver and that is used in car navigation systems or on mobile phones. It is widely used. Among such satellite positioning systems, the most famous and widely used is the GPS (Global Positioning System) operated by the United States. On the other hand, satellite positioning systems are being constructed in various countries, and in Japan, quasi-zenith satellite systems are being constructed for practical use, and are expected as systems that complement GPS. As described above, it is a basic recognition of the parties concerned that the satellite positioning system will shift to multi-GNSS, which is an environment in which a plurality of satellite systems coexist in the future.

  By the way, in the measurement by the satellite positioning system, an error due to multipath becomes a big problem. Multipath is a phenomenon in which radio waves transmitted from a satellite are reflected and diffracted on a building, the surface of the earth, etc., and are received from a plurality of transmission paths. For example, Patent Literature 1 discloses a GPS specifying device that determines an error factor due to multipath based on a change amount of a pseudo distance included in received data, and performs a removal process and a correction process. Further, in Patent Document 2, in order to remove the influence of multipath, for the captured candidate satellite, the difference between the change amount of the pseudorange and the relative movement amount between the candidate satellite and the vehicle based on the Doppler shift frequency, A vehicle position measurement system that selects a satellite to be used for positioning is disclosed.

JP 2010-32306 A JP 2014-153084 A

  Conventionally, as a multipath determination method, a method of determining whether a multipath component is included by comparing the received signal strengths from satellites of a reference station and a mobile station has been used. In this method, there is a restriction that the use of the same GPS signal processing unit and the GPS antenna and a communication device for comparing the signal strength are necessary to perform the signal strength comparison.

  Further, in the method of detecting a multipath component included in a mobile station due to a change in pseudorange included in a received signal from a satellite or a decrease in signal strength, as in Patent Document 1, a multipath component is included. In such a case, a decrease in position accuracy is detected because there may be a phenomenon in which the signal strength decreases, or there may be a multipath component that does not decrease the signal strength. Can not. Therefore, there is a problem that position information with poor accuracy is obtained and reliability is lowered.

  In particular, in the location determination by positioning such as railways, even if the GPS positioning performance deteriorates due to multipath, it is necessary for safety to use the location information without excluding the possibility that the train is at the positioning location. For this reason, there is a problem in that it is necessary to use data whose position accuracy is lowered.

  The present invention has been made to solve the above problems, and its purpose is to eliminate the influence of multipaths when satellite positioning is performed on land mobile objects such as railway trains with limited travel routes. An object of the present invention is to provide a position measuring method and system capable of performing satellite positioning with high position accuracy.

The position measuring method or system according to the present invention preferably measures the position of a moving body that operates on a predetermined orbit by receiving and analyzing radio waves from a plurality of artificial satellites. A satellite signal receiver mounted on the body and a position measurement device, representing the shape of the orbit, storing track number data for each segmented track section, and each track segment being artificially viewed from the moving body It holds shielding azimuth / elevation angle data representing the position of the shield of radio waves received from the satellite.
The satellite signal receiver outputs the data for each artificial satellite to the position measuring device based on the radio wave received from the artificial satellite, and the position measuring device calculates the position of the satellite signal receiver from the data for each artificial satellite. . Next, the position measuring device obtains the number of the existing line section to which the moving body belongs based on the calculated position of the satellite signal receiver and the orbital shape data, and the position measuring device further calculates the position of the calculated satellite signal receiver. And the positions of a plurality of artificial satellites as viewed from the moving object are calculated from the position of each satellite and the data for each artificial satellite.
Then, the position measuring device detects an artificial satellite in which radio waves received by the mobile body are shielded by a shielding object based on the determined number of the existing section to which the mobile body belongs, the positions of the plurality of artificial satellites, and the shielding data. Further, the position measuring device calculates the position of the satellite signal receiver based on the data for each artificial satellite of the artificial satellite excluding the artificial satellite in which the radio wave received by the moving body is shielded by the shielding object.

  According to the present invention, when performing satellite positioning on a land mobile body such as a railroad train whose traveling route is limited, a position measuring method capable of performing satellite positioning with high positional accuracy by eliminating the influence of multipath and That system can be provided.

It is a functional lineblock diagram of a position measuring system concerning one embodiment. It is a hardware block diagram of a satellite signal receiver. It is a hardware block diagram of a position measuring device. It is a figure which shows an example of track | line shape data. It is a figure which shows an example of satellite position data. It is a figure which shows an example of shielding azimuth / elevation angle data. It is a flowchart explaining the process which performs a position measurement. It is a figure which shows a mode that a standing line area is calculated | required from the result of a receiver position. It is a schematic diagram which imagines the satellite position which satellite data express. It is a schematic diagram which images the shielding object which shielding azimuth / elevation angle data expresses. It is a schematic diagram which images the satellite which receives an influence by shielding. It is a figure showing the mode of a train and track condition.

  Hereinafter, an embodiment according to the present invention will be described with reference to FIGS.

  The position measurement system according to an embodiment of the present invention is premised on a satellite positioning system that receives radio waves emitted from a plurality of artificial satellites by a satellite signal receiver and obtains its own position. In general, satellite positioning, when receiving a signal from an artificial satellite positioning, grasps the distance to the satellite (determined from the time of propagation of radio waves in the propagation path), and coordinates (X, Y, Z) of its own position and This is a technique for identifying a clock error (t: the time error is taken into account because the receiver clock has a large error and needs to be corrected). In order to calculate these four variables, at least four artificial satellites are required. In general, the greater the number of satellites that can be received by the satellite signal receiver, the more desirable to eliminate measurement errors. However, the present invention specifically eliminates information on satellites that are affected by multipath. Therefore, it should be noted that operation in a multi-GNSS environment (for example, a hybrid environment of GPS and a quasi-zenith satellite system) where many satellites that can be measured are obtained is desirable.

  First, a position measurement system according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a functional configuration diagram of a position measurement system according to an embodiment. FIG. 2 is a hardware configuration diagram of the satellite signal receiver. FIG. 3 is a hardware configuration diagram of the position measurement apparatus.

  As shown in FIG. 1, the position measurement system according to the present embodiment includes a satellite signal receiver 10 and a position measurement device 100, and the satellite signal receiver 10 operates on a predetermined track such as a railway train. It is assumed that it will be mounted and measured in the means of transportation.

  A satellite signal receiver (hereinafter also simply referred to as “receiver”) 10 receives satellite radio waves emitted from artificial satellites (hereinafter also simply referred to as “satellite”) st1, st2, st3, st4,. It is a device that outputs in a format (raw data). Radio waves from artificial satellites generally use the GHz band as a frequency band, and information includes a satellite identification code and a navigation message (satellite orbit information).

  The position measuring device 100 is a device that outputs a positioning result d4 based on satellite-specific data (raw data) d1 output from the satellite signal receiver 10. Although the positioning result d4 is not shown in detail, it is input to the train operation system 500, and becomes the original data of the warning of the crossing position and signal position and related control.

  The receiver position calculation unit 182 obtains the position of the receiver (more precisely, the position of the antenna of the satellite signal receiver 10) based on the satellite-specific data d1, specifically, the three-dimensional coordinates in a specified coordinate system. Part. In the present embodiment, the receiver position calculation unit 182 outputs coordinates represented by (latitude, longitude, height).

  The satellite position data generation unit 184 is a part that obtains the position of the satellite as seen from the receiver based on the satellite-specific data d1 and the receiver position calculated by the receiver position calculation unit 182. The satellite position is expressed as seen from the receiver (elevation angle, azimuth angle).

  The section mapping unit 186 determines which section of the train on which the receiver is mounted from the receiver position calculated by the receiver position calculation unit 182 and the line shape data (track shape data) d3 (described later) It is a part for determining whether it belongs to.

  The satellite extraction unit 188 calculates the receiver position at the time of recalculation in order to eliminate the influence of multipath based on the existing section number obtained by the section mapping unit 186 and the shielding azimuth / elevation angle data d2 (described later). This is the part that asks for unused satellites.

Next, the hardware configuration of the satellite signal receiver 10 will be described with reference to FIG.
As shown in FIG. 2, the satellite signal receiver 10 includes an antenna 201, a high frequency amplifier 202, a frequency converter 203, an intermediate frequency amplifier 204, an A / D converter 205, a local transmitter 206, and a code correlation unit 207. The calculation unit 208 is configured.

  In the satellite signal receiver 10, the satellite 201 receives satellite radio waves emitted from the artificial satellites st1, st2, st3, st4,. The received signal is amplified by the high frequency amplification unit 202, mixed with the signal from the local transmitter 205 by the frequency converter (mixer) 203, and converted into an intermediate frequency signal. The intermediate frequency signal is amplified by the intermediate frequency amplification unit 204 and converted into a digital signal by the A / D converter 205. The code correlation unit 207 demodulates codes (C / A codes) unique to each satellite. The calculation unit 208 performs navigation message demodulation, satellite orbit calculation, position calculation, and the like. In the present embodiment, it has been described that the data for each satellite (raw data) d1 is output to the position measuring device 100 and the position calculation is performed on the position measuring device 100 side. You may make it the structure which utilizes the position calculating function of the receiver 10. FIG.

Next, the hardware configuration of the position measurement apparatus 100 will be described with reference to FIG.
The hardware configuration of the position measuring apparatus 100 is realized by an information processing apparatus such as a general personal computer as shown in FIG.

  The position measuring device 100 includes a CPU (Central Processing Unit) 102, a main storage device 104, a network I / F 106, a display I / F 108, an input / output I / F 110, an auxiliary storage I / F 112, and a serial I / F 114 connected by a bus. It has become a form. The CPU 102 controls each unit of the position measurement device 100 and loads and executes a necessary program in the main storage device 104. The main storage device 104 is usually composed of a volatile memory such as a RAM, and stores a program executed by the CPU 102 and data to be referred to. The network I / F 106 is an interface for connecting to the network 60. The position specifying device 100 transmits a positioning result to a server of a train operation system, a control device (both not shown), etc. via the network 60.

The display I / F 108 is an interface for connecting a display device 120 such as an LCD (Liquid Crystal Display). The input / output I / F 110 is an interface for connecting an input / output device. In the example of FIG. 3, a keyboard 130 and a mouse 132 of a pointing device are connected. The auxiliary storage I / F 112 is an interface for connecting an auxiliary storage device such as an HDD (Hard Disk Drive) 150 and an SSD (Solid State Drive).
The serial I / F 114 is, for example, a USB (Universal Serial Bus) interface. The satellite signal receiver 10 is connected to the serial I / F 114, and receives the satellite-specific data d1.

  The HDD 150 has a large storage capacity, and stores a program for executing this embodiment. A position measurement program 160 is installed in the position measurement apparatus 100. The position measurement program 160 includes a receiver position calculation module 162, a satellite for realizing the receiver position calculation unit 182, the satellite position data generation unit 184, the section mapping unit 186, and the satellite extraction unit 188 described in FIG. The software configuration includes a position data generation module 164, a section mapping module 166, a satellite extraction module 168, and a receiver interface module 170 for connecting to the satellite signal receiver 10. As data, the shielding azimuth / elevation angle data d2 and line shape data d3 shown in FIG. 1 are stored.

Next, a data structure used in the position measurement system according to the embodiment will be described with reference to FIGS. FIG. 4 is a diagram illustrating an example of line shape data. FIG. 5 is a diagram illustrating an example of satellite position data. FIG. 6 is a diagram illustrating an example of shielding azimuth / elevation angle data.
In the present embodiment, the line is captured as a pseudo line segment, and the line shape data d1 promises to represent one of the vertices of the line segment. The line shape data d1 includes fields of latitude, longitude, kilometer, and existing line section.

  Latitude and longitude represent the latitude and longitude of the current section, respectively, and the kilometer is the length of the track. The standing line section represents a number representing the section. For example, in the first record, the latitude = (north latitude) 38 degrees 02 minutes 50.550 seconds, the longitude = (east longitude) 140 degrees 08 minutes 55.532 seconds to 100.000 m is the current section 1, No3 The record of latitude = (northern latitude) 38 degrees 02 minutes 51.860 seconds and longitude = (east longitude) 140 degrees 08 minutes 55.874 seconds to 135.711 m is a track section 2. In the case of a double line, the line shape data d1 is held for each uplink (FIG. 4 (a)) and for each downlink (FIG. 4 (b)). The standing line section is created in consideration of, for example, a shield in the vicinity of the track or between stations.

The satellite position data d5 is data representing which section the elevation angle / azimuth angle of each satellite viewed from the receiver belongs to. The satellite position data d5 is represented by a 6 × 12 matrix, for example, as shown in FIG. Here, a _i (i = 0,..., 11) represents a range in which the azimuth is 30 [degree] × i or more and less than 30 × (i + 1) [degree], respectively, and b _j (j = 0,..., 5) represents a range in which the elevation angle is 15 [degrees] × j or more and less than 15 × (j + 1) [degrees]. Here, the elevation angle is based on the horizon, and the azimuth is based on the north-facing line. The numbers in the matrix are numbers for identifying satellites. 0 indicates that there are no satellites, and a plurality of satellites means that a plurality of satellites are present. For example, there is a satellite with satellite number 2 in an elevation angle of 0 ° to less than 15 ° and an azimuth angle of 270 ° to less than 300 ° (b ₀ , a ₉ ), an elevation angle of 30 ° to less than 45 °, and an azimuth angle of It is shown that there are satellites with satellite numbers 4 and 8 at 210 degrees or more and less than 240 degrees (b ₀ , a ₇ ). The satellite position data d5 is updated every moment in real time.

Shielding azimuth / elevation angle data d4 is used to represent the current state of shielding for positioning by means of shielding around the track, such as buildings, tunnels, Takagi, and other high-rise buildings, for each section of the track. Similar to the satellite position data d5, this data is represented by a 6 × 12 matrix that classifies the elevation angle and azimuth angle of each satellite viewed from the receiver. Here, a _i (i = 0,..., 11) represents a range in which the azimuth is 30 [degree] × i or more and less than 30 × (i + 1) [degree], respectively, and b _j (j = 0,..., 5) is the same as the satellite position data d5 in that the elevation angle represents a range of 15 [degrees] × j or more and less than 15 × (j + 1) [degrees]. The element 0 of each matrix can be used for positioning without being affected by the satellite at the position, and the element 1 of each matrix is conversely the satellite at the position by the shield. This means that it is not preferable to use for positioning. For example, in the standing section 1, the elevation angle = 0 to 15 degrees ((b ₀ , a ₀ ) to (b ₀ , a ₁₁ )), the elevation angle = 15 degrees to less than 30 degrees, and the azimuth angle from 0 degrees to less than 240 degrees ((B ₁ , a ₀ ) to (b ₀ , a ₉ )), elevation angle = 30 degrees or more and less than 45 degrees, azimuth angle 30 degrees or more and less than 90 degrees ((b ₂ , a ₁ ), (b ₂ , a ₂ )) In the image of the presence of a shield such as a building or a high tree, and in the existing section 2, it is imagined that there is a tunnel, and that all satellites cannot be used for positioning. Show.

  Next, processing in which the position measurement system according to the embodiment performs position measurement will be described with reference to FIGS. FIG. 7 is a flowchart illustrating a process for performing position measurement. FIG. 8 is a diagram illustrating a state in which a standing section is obtained from the result of the receiver position. FIG. 9 is a schematic diagram for imagining the satellite position expressed by the satellite data. FIG. 10 is a schematic diagram for imagining the shielding object represented by the shielding azimuth / elevation angle data. FIG. 11 is a schematic diagram of an image of a satellite that is affected by shielding. FIG. 12 is a diagram illustrating a train and track situation.

  The processing of the position measuring apparatus 100 is performed by the CPU 100 illustrated in FIG. 3 executing each module of the position measuring program 160.

  First, the position measurement apparatus 100 reads satellite data (raw data) d1 from the satellite signal receiver 10. Then, the position of the receiver (antenna position) is obtained by a basic algorithm for satellite positioning (S01). The position of the receiver may be obtained by the position measuring device 100 of the receiver, or an interface to be obtained by the satellite signal receiver 10 side is prepared so that the position measuring device 100 issues a command and receives the answer. May be.

  Next, the number of the line segment is obtained from the position of the receiver (S02). Specifically, referring to the line shape data shown in FIG. 4 from the determined receiver position (latitude and longitude), as shown in FIG. 8, the line from the receiver position (latitude and longitude) A perpendicular line is dropped and the nearest existing section becomes the corresponding existing section. In the example of FIG. 8, the standing line section 1 is the corresponding standing section.

  Next, the elevation angle and azimuth angle of the satellite viewed from the position of the receiver (that is, the train) are obtained from the position of the receiver obtained in S01, the number of the line segment obtained in S02, and the data of each satellite d1, The satellite position data d5 shown in FIG. 5 is generated (S03). In the satellite position data d5 shown in FIG. 5, the image of the satellite position represented by the satellite data is as shown in FIG.

Next, the satellite to be removed from the positioning is specified based on the shielding azimuth / elevation angle data d2 shown in FIG. 6 and the satellite position data d5 obtained in S03 (S04). That is, the satellite belonging to the element having the value of 1 in the shielding azimuth / elevation angle data d2 is a satellite to be removed. Specifically, in the image diagram of FIG. 11, the satellite of the location indicated by ×, the satellite of satellite number = 2 in (b ₀ , a ₉ ) in the in-zone section 3 (FIG. 11C), (b _The satellite with satellite number = 9 in ₀ , a ₁₀ ) and the satellite with satellite number = 7 in (b ₃ , a ₅ ) are identified as satellites to be removed from positioning. Here, it should be noted that the image diagram of FIG. 11 is obtained by superimposing the image diagram of the satellite position shown in FIG. 9 and the image diagram representing the shielding object of FIG.

  Then, the satellite-specific data d1 of the satellite belonging to the element of 1 value is extracted from the satellite that has not been removed and the shielding azimuth / elevation angle data d2, and the receiver position is recalculated (S05).

Specifically, in the image diagram of FIG. 11, the satellite of the location indicated by ●, the in-line section 3 (FIG. 11C) is the satellite of satellite number = 12 in (b ₃ , a ₁ ), ( The satellite with satellite number = 19 in b ₄ , a ₃ ), the satellite with satellite number = 4,8 in (b ₂ , a ₇ ), and the satellite with satellite number = 193 in (b ₃ , a ₉ ) It is a satellite used for calculation. As described above, when the data of the shielded satellite is removed from the position calculation as viewed from the receiver position (train position), the influence of multipath is eliminated and the positioning accuracy can be improved.

  And the positioning result calculated | required by S05 is output to the train operation system 500 (S06), and becomes the original data of the warning of a crossing position or a signal position and related control.

  FIG. 12 shows the model of the standing line section and the relationship between the vicinity of the track and the shielding object. The standing section 1 starts from the station A700 on the down line and extends to the front of the tunnel 600. The tunnel 600 has a margin for measurement. In the standing line section 1, there are shielding objects of the building 602 and the Takagi 601 in the vicinity of the track. The standing section 2 extends from before the tunnel 600 to after the tunnel 600. Since there is a tunnel, positioning is impossible as shown in FIG. 6B. The standing line section 3 extends from the rear of the tunnel 600 to the station B 701. Like the standing line section 1, there are a building 602 and a Takagi 601 as shielding objects. There is a little more.

  As described above, according to the present embodiment, a satellite that does not include a multipath is used to finally eliminate the positioning performance degradation of the satellite positioning due to the multipath and the occurrence of the shielding due to the shielding object by the position calculation process. It becomes possible to maintain high-precision position accuracy only by the signal.

  In particular, in the future, multi-GNSS systems will become widespread, and the number of artificial satellites that can be used for measurement will increase. It is expected that a sufficient number of satellites can be secured. Therefore, the significance of the present invention becomes significant.

DESCRIPTION OF SYMBOLS 10 ... Satellite radio wave receiver, 60 ... Network, 100 ... Position measuring device, 102 ... Central processing unit (CPU), 104 ... Main memory, 106 ... Network I / F, 108 ... Display I / F, 110 ... Input / output I / F, 112 ... Auxiliary storage I / F, 114 ... Serial I / F,
160 ... Position measurement program, 162 ... Receiver position calculation module, 164 ... Satellite position data generation module, 166 ... Section mapping module, 168 ... Satellite extraction module,
182 ... Receiver position calculation unit, 184 ... Satellite position data generation unit, 186 ... Section mapping unit, 188 ... Satellite extraction unit,
DESCRIPTION OF SYMBOLS 201 ... Antenna, 202 ... High frequency amplification part, 203 ... Intermediate frequency amplification part, 204 ... AD converter, 205 ... Local transmitter, 206 ... Code correlation part, 207 ... Operation part,
d1 ... satellite data (raw data), d2 ... shielding azimuth / elevation angle data, d3 ... line shape data, d4 ... positioning results.

Claims (4)

A position measurement method for a position measurement system that measures the position of a moving object that travels on an orbit determined by receiving and analyzing radio waves from a plurality of satellites,
The position measurement system includes a satellite signal receiver mounted on the mobile body and a position measurement device, and represents the shape of the orbit, and orbit shape data for storing a number for each segmented track section; For each standing section, shielding data representing the position of the shielding object of the radio wave received from the artificial satellite as seen from the mobile body, and
The satellite signal receiver outputs data for each artificial satellite to the position measuring device based on radio waves received from the artificial satellite;
The position measuring device calculates the position of the satellite signal receiver from the data for each artificial satellite; and
The position measuring device, based on the calculated position of the satellite signal receiver and the orbit shape data, to determine the number of the existing line section to which the mobile body belongs;
The position measuring device calculates the position of the plurality of artificial satellites viewed from the mobile body from the calculated position of the satellite signal receiver and data for each artificial satellite;
The position measuring device shields radio waves received by the moving body with a shielding object based on the determined number of the existing section to which the moving body belongs, the positions of the plurality of artificial satellites, and the shielding data. Seeking an artificial satellite;
The position measuring device calculates the position of the satellite signal receiver based on the data for each artificial satellite of the artificial satellite excluding the artificial satellite in which the radio wave received by the mobile body is shielded by a shielding object; A position measuring method characterized by comprising:   The position measurement method according to claim 1, wherein the positions of the plurality of artificial satellites viewed from the moving body are represented by an azimuth angle and an elevation angle from the moving body. A position measurement system that measures the position of a moving object that travels on a predetermined orbit by receiving and analyzing radio waves from a plurality of artificial satellites,
A satellite signal receiver mounted on the mobile body, and a position measuring device,
Orbital shape data that represents the shape of the orbit and stores a number for each segmented line section, and shielding data that represents the position of a shield for radio waves received from an artificial satellite as viewed from the mobile body for each line segment. And hold
The satellite signal receiver outputs the data for each artificial satellite to the position measuring device based on the radio wave received from the artificial satellite,
The position measuring device calculates the position of the satellite signal receiver from the data for each artificial satellite,
The position measuring device obtains the number of the existing section to which the moving body belongs, based on the calculated position of the satellite signal receiver and the orbit shape data,
The position measuring device calculates the positions of the plurality of artificial satellites viewed from the mobile body from the calculated position of the satellite signal receiver and data for each artificial satellite,
The position measuring device shields radio waves received by the moving body with a shielding object based on the determined number of the existing section to which the moving body belongs, the positions of the plurality of artificial satellites, and the shielding data. Seeking an artificial satellite,
The position measuring device calculates the position of the satellite signal receiver based on data for each artificial satellite of an artificial satellite excluding an artificial satellite in which radio waves received by the mobile body are shielded by a shield. Position measurement system.   The position measurement system according to claim 3, wherein positions of the plurality of artificial satellites viewed from the moving body are represented by azimuth and elevation angles from the moving body.

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