JP2011095141A - On-vehicle navigation device and method for navigation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an on-vehicle navigation device and a method for navigation which enable accurate determination about on which road a vehicle runs, on an elevated road or a road under the elevated extending parallel with the elevated road, on the basis of necessary minimum information. <P>SOLUTION: On the occasion when the vehicle runs on either the elevated road or the road under the elevated extending parallel with the elevated, an artificial satellite wherefrom a satellite radio wave can be received is discriminated and also the position information on that satellite is acquired, based on almanac data received by a satellite radio wave receiving means 14. When a reception level of the satellite radio wave from the artificial satellite located on one side of the running direction of the vehicle, in relation to the running direction of the vehicle detected by a running direction detecting means 17, is a prescribed level or below, the vehicle is determined as running on the road under the elevated, and when the reception level is higher than the prescribed, it is determined as running on the elevated road. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an in-vehicle navigation device and a navigation method, and more particularly, to an in-vehicle navigation device and a navigation method for determining and guiding whether a vehicle is traveling on an elevated road or an underpass road that runs parallel to the elevated road.

  There is known an in-vehicle navigation device that uses a Global Navigation Satellite Systems (GNSS) typified by GPS (Global Positioning System) to detect a current position of a vehicle and guide a driving route to a driver. Yes.

  In this case, an error of about 10 m is generated in the detected current position of the vehicle due to a displacement of the artificial satellite, a delay of radio waves due to the ionosphere or the troposphere, an error of the atomic clock, and the like. If the current position is displayed as it is on the map of the display without correcting this error, the current position of the vehicle is displayed at an inappropriate position such as a place without a road, which may give the user a sense of incongruity. is there. In order to avoid such a problem, a map matching technique has been developed that estimates a travel path with reference to a road shape, a travel history of a vehicle, and the like, and displays the current position of the vehicle on the estimated travel path.

  However, for example, when a general road is running side by side under the expressway or on the side of the expressway, as in the Tokyo metropolitan area, the general road is estimated as a travel path even though the expressway is running, or In some cases, the estimation is reversed. Therefore, various techniques for preventing such an erroneous traveling path from being estimated have been proposed.

  For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2001-289653), when a general road and a toll road are running side by side, or when a vehicle is running outside a road such as a parking lot, DSRC communication is performed. There is disclosed a current position calculation device that calculates the current position of a vehicle with high accuracy using information on ETC fee collection by (dedicated narrow area communication).

  Further, in Patent Document 2 (Japanese Patent Laid-Open No. 2005-23379), when a Y-branch road is detected from road map data when traveling on an elevated road and a road that runs parallel to the top and bottom, Car navigation system and own vehicle that determine which side of a Y-branch is traveling on a Y-branch based on a change in reception sensitivity of radio waves received from GPS satellites in the left and right sky regions A position determination method is disclosed. In other words, when the vehicle travels under an elevated road that passes through a Y-branch and runs under the elevated road, the reception sensitivity of radio waves received from one of the left and right GPS satellites is reduced. It is determined that the vehicle is traveling on the opposite underpass road.

JP 2001-289653 A (paragraphs [0039] and [0040]) JP-A-2005-233779 ([Claim 1], [Claim 2])

  However, in the case of Patent Document 1, in order to calculate the current position of the vehicle with high accuracy, it is a condition that information on ETC fee collection can be received. Therefore, the current position cannot be estimated with high accuracy in a place where this information cannot be received.

  Further, in the case of Patent Document 2, since the detection of the Y-shaped branch road is a condition, when the branch road data cannot be acquired, map matching is performed assuming that the previous road is correct. There is a risk of guiding the wrong traveling route.

  Further, in Patent Document 2, for example, when there is a structure other than an elevated road such as a high-rise building on the left side in the traveling direction, the traveling path is determined based on only the change in the reception sensitivity of the received radio waves from the GPS satellites in the left and right sky regions. If it is determined, it may be erroneously determined that the vehicle is traveling on an elevated road.

  An object of the present invention is to solve the above-mentioned problems, and based on the minimum necessary information, it is accurately determined whether an elevated road or an underpass road running parallel to the elevated road is running. It is an object of the present invention to provide an in-vehicle navigation device and a navigation method that can be used.

  In order to solve the above-mentioned problems, the invention according to claim 1 is based on a receiver that receives satellite radio waves from a plurality of artificial satellites, and position information and time information of each artificial satellite obtained from the satellite radio waves. In the vehicle-mounted navigation device comprising: calculating means for calculating the current position of the vehicle equipped with the receiver; and guide means for guiding the traveling path of the vehicle based on the calculated current position and map information. From the position information of each artificial satellite and the current position of the vehicle, satellite determination means for determining an artificial satellite capable of receiving satellite radio waves by the receiver, traveling direction detection means for detecting the traveling direction of the vehicle, A reception level detecting means for detecting a reception level of the satellite radio wave received by the receiver and one side of the traveling direction of the vehicle, and determined to be able to receive the satellite radio wave; A reception level determination means for determining whether or not the reception level of the satellite radio wave from the engineering satellite is below a predetermined level, and whether the vehicle is traveling on an elevated road based on the determination result by the reception level determination means, or And a travel path determination means for determining whether the vehicle is traveling on an underpass road, wherein the guide means guides the travel path of the vehicle based on a determination result by the travel path determination means. .

  According to a second aspect of the present invention, in the in-vehicle navigation device according to the first aspect, the travel direction detecting means is obtained from the current position of the vehicle calculated last time and the current position of the vehicle calculated this time. The traveling direction is detected from the determined azimuth angle.

  According to a third aspect of the present invention, in the in-vehicle navigation device according to the first or second aspect, the travel path determination means is one side in the travel direction of the vehicle by the reception level determination means, When it is determined that the reception level of satellite radio waves from an artificial satellite determined to be capable of receiving satellite radio waves is below a predetermined level, it is determined that the vehicle is traveling on an underpass road.

  According to a fourth aspect of the present invention, in the in-vehicle navigation device according to any one of the first to third aspects, the guidance unit includes a determination result of the travel path determination unit, the calculated current position, and the map. The travel route of the vehicle is guided by map matching based on the information.

  The invention according to claim 5 receives satellite radio waves from a plurality of artificial satellites, calculates the current position of the vehicle based on position information and time information of each artificial satellite obtained from the satellite radio waves, and calculates the calculated In the navigation method for guiding the travel route of the vehicle based on a current position and map information, a step of determining an artificial satellite that can receive the satellite radio wave from the positional information of each artificial satellite and the current position of the vehicle. Detecting a traveling direction of the vehicle, detecting a reception level of satellite radio waves from the artificial satellite determined to be able to receive the satellite radio waves, and one side of the traveling direction of the vehicle. Determining whether or not the reception level of the satellite radio wave from the artificial satellite determined to be capable of receiving the satellite radio wave is equal to or lower than a predetermined level; and determining the reception level. Based on the result, determining whether the vehicle is traveling on an elevated road or traveling on an underpass road, and guiding the traveling path of the vehicle based on the determination result; It is characterized by including.

  In the invention according to claim 1, in this case, when determining the travel path, by limiting the reception state of the satellite radio wave transmitted from the satellite on one side in the travel direction of the vehicle, In this case, even if a structure such as a high-rise building other than the road exists on the left side in the traveling direction, there is no possibility that the structure is erroneously detected as an elevated road. Therefore, based on the minimum necessary information, it is possible to accurately determine which of the elevated road and the underpass road that runs parallel to the elevated road.

  In the invention according to claim 2, in the invention according to claim 1, the travel direction detection means is obtained from the current position of the vehicle calculated last time and the current position of the vehicle calculated this time. An azimuth angle is detected as the traveling direction.

  According to a third aspect of the present invention, in the invention according to the first or second aspect, the travel path determination means is one side of the travel direction of the vehicle by the reception level determination means, and the satellite radio wave is transmitted. When it is determined that the reception level of the satellite radio wave from the artificial satellite determined to be receivable is equal to or lower than the predetermined level, it is determined that the vehicle is traveling on the elevated road.

  Since the satellite radio wave from the artificial satellite on one side in the traveling direction is blocked by the elevated road, it can be determined that the vehicle is traveling on the elevated road.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the guide means includes a determination result of the travel path determination means, the calculated current position, and the map information. Based on the map matching, the travel route of the vehicle is guided.

  When performing map matching, the travel path is accurately determined by the travel path determination means, so that the current position of the vehicle can be guided without error.

  In the invention according to claim 5, in this case, when determining the travel path, by limiting the reception state of the satellite radio wave transmitted from the satellite on one side in the travel direction of the vehicle, However, even if a structure such as a high-rise building other than the road exists on the left side in the traveling direction, there is no possibility that the structure is erroneously detected as an elevated road. Therefore, based on the minimum necessary information, it is possible to accurately determine which of the elevated road and the underpass road that runs parallel to the elevated road.

1 is a configuration block diagram of an in-vehicle navigation device according to an embodiment of the present invention. It is a process flowchart of the vehicle-mounted navigation apparatus which concerns on the Example of this invention. It is explanatory drawing of the positional relationship of the vehicle and artificial satellite which drive | work the underpass road parallel to an elevated road. FIG. 4 is a plan view of FIG. 3. It is explanatory drawing of the azimuth angle of an artificial satellite.

  Hereinafter, specific examples of the present invention will be described in detail with reference to examples and drawings. However, the embodiments described below exemplify an in-vehicle navigation device and a navigation method for embodying the technical idea of the present invention, and the present invention is specified to the in-vehicle navigation device and the navigation method. However, the present invention is equally applicable to the in-vehicle navigation device and the navigation method of other embodiments included in the claims.

  FIG. 1 is a configuration block diagram of an in-vehicle navigation device according to an embodiment of the present invention. In the following description, it is assumed that the vehicle travels in a left-hand traffic area.

  The control means 10 is constituted by a processor including a CPU 11, a ROM 12 and a RAM 13, and controls the operation of each part of the in-vehicle navigation device according to a control program recorded in the ROM 12 and the RAM 13.

  The satellite radio wave receiving means 14 is composed of a receiver that receives satellite radio waves including position information and time information of each artificial satellite from a plurality of artificial satellites orbiting over the earth. The satellite radio wave includes two types of data, almanac data and ephemeris data. The almanac data includes orbit information of all the artificial satellites and correction information of the satellite clock, and the ephemeris data includes detailed position information of each artificial satellite and time information when the satellite radio wave is emitted.

  Based on the almanac data and the ephemeris data received by the satellite radio wave reception means 14, the current position calculation means 15 calculates the current position of the vehicle consisting of latitude information and longitude information. Note that the calculated current position of the vehicle includes errors caused by fluctuations in the transmission speed of satellite radio waves, displacement of artificial satellites, multipath, and the like.

  The satellite discriminating means 16 estimates the position information of each artificial satellite based on the almanac data received by the satellite radio wave receiving means 14 and is calculated by the estimated position information of each artificial satellite and the current position calculating means 15. From the current position of the vehicle, the satellite radio wave reception means 14 determines an artificial satellite that can receive the satellite radio wave. The artificial satellite capable of receiving satellite radio waves is, for example, an artificial satellite having an elevation angle of 20 to 90 ° when viewed from the horizontal direction.

  The traveling direction detection means 17 detects the traveling direction of the vehicle in which north is 0 ° and the counterclockwise direction is +. For example, the current position of the vehicle detected last time and the current position of the vehicle detected this time The azimuth angle obtained from the above can be detected as the traveling direction. Further, a gyro sensor may be mounted on the vehicle, and the traveling direction may be detected directly from the output.

  The reception level detection means 18 detects the reception level of the satellite radio wave transmitted from the artificial satellite determined to be receivable by the satellite determination means 16.

  The reception level determination means 19 includes the vehicle traveling direction detected by the traveling direction detection means 17, the position information of the artificial satellite determined to be receivable by the satellite determination means 16, and the satellite detected by the reception level detection means 18. From the radio wave reception level, it is determined whether the reception level of the satellite radio wave from the artificial satellite arranged on the right side in the traveling direction of the vehicle is equal to or lower than a predetermined level.

  The traveling road determination means 20 determines that the vehicle is not traveling on an underpass road running parallel to at least an elevated road when the reception level of the satellite radio wave is higher than a predetermined level in the determination result by the reception level determination means 19. When the satellite radio wave reception level is equal to or lower than the predetermined level, it is determined that the vehicle is traveling on the underpass road. In addition, the underpass road as used in the present application is a general term for roads that run parallel to the overpass at an extremely short distance, such as a road installed directly under the overpass and a side road installed beside the expressway.

  The input means 21 is composed of various keys, switches, touch panels and the like operated by a driver of the vehicle. For example, when performing route guidance to a destination using an in-vehicle navigation device, This is for inputting destinations, waypoints, and the like.

  The map storage means 22 stores map information for indicating a travel route of the vehicle, a guide route to the destination, a travel distance to the destination, and a travel time. Specifically, map information including road node data having nodes as nodes such as road branch points and road link data having links as paths connecting the nodes is stored. The road node data includes road node numbers, position coordinates, number of connection links, branch point names, etc., and route guidance that provides route guidance such as turning left and right and straight ahead at a guide point that is a predetermined distance away from the branch point. Data and position coordinates of the guide point are stored.

  The road link data includes a road node number as a start point and an end point, a road type, a link length (link cost) as distance information between nodes, a required time, the number of lanes, a road width, and the like. Further, data such as bridges, tunnels, railroad crossings, and toll gates are added to the road link data as link attributes. The road type is information including distinction between elevated roads and underpass roads, distinction between expressways and toll roads, distinction between national roads and prefectural roads.

  Further, the map storage means 22 stores background data including water system data such as coastlines, lakes, and river shapes, administrative boundary data, facility locations including parking lots, facility shapes, and facility data including facility names. Yes.

  When the user inputs a destination using the input unit 21, the route search unit 23 refers to the map information stored in the map storage unit 22 and reaches the destination from the current location or the departure point designated by the driver. It searches for the optimum guide route.

  The search for the guide route searches for links and nodes from the road node corresponding to the current position or starting point to the road node corresponding to the destination by various methods such as Dijkstra method, and the link length (link cost) and required By accumulating time and the like, a route having the shortest total link length (travel distance) or total required time is set as a guide route, and road nodes and links belonging to the route are provided as guide route data.

  The display means 24 is for displaying a map image, a guide route image, a mark indicating the current position of the vehicle, and the like so that the user can visually recognize it, and is configured by a liquid crystal display. In addition, you may make this display means 24 function as the input means 21 provided with the touch sensor. In this case, selection input is performed when the user touches an icon displayed on the display.

  The in-vehicle navigation device of this embodiment is basically configured as described above. Next, the operation will be described.

  First, route guidance by the vehicle-mounted navigation device will be briefly described. The user inputs a destination using the input means 21. The route search means 23 is the map information read from the map storage means 22, the vehicle current position calculated by the current position calculation means 15 based on the satellite radio wave received by the satellite radio wave reception means 14, and the input purpose. The optimum route is searched using the ground. The display means 24 displays the searched guidance route and the current position of the vehicle on the map. The driver starts traveling to the destination according to the displayed guide route.

  Next, according to the flowchart of FIG. 2, the process in the case where the current position of the vehicle is displayed on the display means 24 and the current travel route is guided will be described in detail.

  First, the satellite radio wave receiving means 14 mounted on the vehicle receives satellite radio waves from a plurality of artificial satellites (step S101). This satellite radio wave basically includes almanac data including orbit information of all artificial satellites orbiting over the earth, ephemeris data including detailed position information of each artificial satellite and time information at which the satellite radio waves are emitted. Consists of.

  The current position calculation means 15 calculates the time until the satellite radio wave arrives at the vehicle from the artificial satellite based on the time information when the satellite radio wave included in the ephemeris data is emitted and the time information on the clock of the in-vehicle navigation device. Then, the distance between the artificial satellite and the vehicle is calculated by multiplying the time by the speed of light. Then, the current position (latitude information and longitude information) of the vehicle is calculated from the distance between the three or more artificial satellites and the vehicle by the triangular intersection method (step S102).

  Next, the control means 10 acquires map information including the calculated current position of the vehicle from the map storage means 22 (step S103), and the vehicle is currently traveling based on the road type information included in the map information. It is determined whether the existing road is a road in which an elevated road such as an expressway and an underpass road are running side by side (step S104). If the vehicle is not traveling on a road on which an elevated road and an underpass road run side by side (N in step S104), the traveling path according to the current position is determined, and the processing from step S101 is repeated to obtain satellite radio waves. And the process of calculating the current position of the vehicle is continued.

  When the vehicle is traveling on a road in which an elevated road and an underpass road run side by side (Y in step S104), the elevated roads are aligned between the underpass roads based on the road type information included in the map information. It is determined whether or not the vehicle is running (step S105). When the vehicle is not traveling on the road where the elevated road runs parallel between the underpass roads (in the case of N in step S105), the traveling path according to the current position is determined, and the processing from step S101 is repeated. And the process of calculating the current position of the vehicle is continued.

  On the other hand, as shown in FIGS. 3 and 4, the elevated road 25 and the underpass roads 26a and 26b are running side by side (in the case of Y in step S104), and between the underpass roads 26a and 26b. When the vehicle 27 is traveling on a road on which the elevated road 25 is running side by side (Y in step S105), the vehicle 27 is traveling closer to the elevated road 25, and therefore a plurality of artificial satellites 28a to 28a ~. 28d, the satellite radio wave 29 from the artificial satellite 28d located on the right side with respect to the traveling direction of the vehicle 27 is blocked by the elevated road 25. 3 and 4, for convenience of explanation, it is assumed that the satellite radio wave 29 from one artificial satellite 28d is blocked by the elevated road 25 among the four artificial satellites 28a to 28d. The number of artificial satellites 28 a to 28 c that can receive the satellite radio wave 29 and the number of artificial satellites 28 d that cannot receive the satellite radio wave 29 are not limited to this.

  Therefore, when the vehicle 27 is traveling on the road shown in FIGS. 3 and 4, the satellite discriminating means 16 uses the orbit information of all the artificial satellites included in the almanac data of the satellite radio wave 29 and the watch included in the in-vehicle navigation device. The position information (elevation angle and azimuth angle) of all the artificial satellites at the current position is calculated based on the current time information and the current position calculated by the current position calculation means 15 (step S106). The calculated position information of the artificial satellite is based on orbit information, and is estimated information including information that cannot receive the satellite radio wave 29. Next, the satellite discriminating unit 16 discriminates an artificial satellite from which the satellite radio wave receiving unit 14 can receive the satellite radio wave 29 from the calculated position information of all the artificial satellites and the current position of the vehicle 27 calculated in Step S102 ( Step S107). In this case, the satellite discriminating means 16 sets the artificial satellites 28a to 28d whose elevation angles are 20 ° to 90 ° as viewed from the vehicle 27, with the horizontal direction being 0 ° and the zenith being 90 °. Extracted as an artificial satellite capable of receiving the satellite radio wave 29. When there is no obstacle around the vehicle 27, the satellite radio wave receiving means 14 can receive the satellite radio waves 29 emitted from all the extracted artificial satellites 28a to 28d.

  On the other hand, the traveling direction detection means 17 detects the traveling direction 30 (see FIG. 4) of the vehicle 27 from the current position of the vehicle 27 calculated last time and the current position of the vehicle 27 calculated this time (step S108). . In this case, as shown in FIG. 6, for example, the traveling direction 30 is detected as an azimuth angle in which north (N) is 0 ° and the counterclockwise direction is +. The traveling direction 30 can also be detected directly using a gyro sensor mounted on the vehicle 27.

  The reception level detection means 18 detects the reception level of the satellite radio waves 29 transmitted from the artificial satellites 28a to 28d determined that the satellite radio waves 29 can be received by the satellite discrimination means 16 (step S109).

  The reception level determination unit 19 includes the traveling direction 30 of the vehicle 27 detected by the traveling direction detection unit 17, the azimuth angles of the artificial satellites 28 a to 28 d determined to be receivable by the satellite determination unit 16, and the reception level detection unit 18. From the reception level of the satellite radio wave 29 detected by the step S110, it is determined whether the satellite 27 is an artificial satellite on the right side in the traveling direction 30 and the reception level of the satellite radio wave 29 is equal to or lower than a predetermined level (step S110). . In addition, by limiting the artificial satellites 28a to 28d for determining the reception level of the satellite radio wave 29 to the right side in the traveling direction of the vehicle 27, a structure such as a high-rise building on the left side of the vehicle 27 is erroneously detected as the elevated road 25. The situation can be avoided. Here, for example, as shown in FIG. 5, when the traveling direction 30 is 30 ° counterclockwise with respect to the north, the artificial satellite on the right side of the traveling direction is the artificial satellite relative to the current position. It is an artificial satellite with an azimuth angle between 20 ° and −140 °.

  When the reception level of the satellite radio wave 29 from the artificial satellite 28d determined to be on the right side of the traveling direction 30 of the vehicle 27 is equal to or lower than a predetermined level (Y in step S110), the satellite radio wave 29 from the artificial satellite 28d is Since the road is blocked by the elevated road 25 or the reception level is greatly reduced, the traveling path determination means 20 determines that the vehicle 27 is traveling on the lower left elevated road 26 a of the elevated road 25. According to this determination result, the control means 10 sets a mark indicating the current position of the vehicle 27 on the elevated road 26a by map matching processing (step S111), and displays the image on the display means 24.

  On the other hand, when the reception level of the satellite radio wave 29 from the artificial satellite 28d determined to be on the right side of the traveling direction 30 of the vehicle 27 is higher than a predetermined level (N in step S110), the satellite radio wave from the artificial satellite 28d. Since it is estimated that 29 is not obstructed by the elevated road 25, the traveling path determination means 20 determines that the vehicle 27 is traveling on the elevated road 25. According to this determination result, the control means 10 sets a mark indicating the current position of the vehicle 27 on the elevated road 25 by map matching processing (step S112), and displays the image on the display means 24.

  As described above in detail, according to the vehicle-mounted navigation device and navigation method of the present embodiment, the elevated road 25 and the elevated roads 26a and 26b run side by side in the left-handed area, and When the vehicle 27 is traveling in a place where the elevated road 25 runs parallel between the roads 26a and 26b, the reception level of the satellite radio waves from the artificial satellites 28a to 28d positioned on the right side with respect to the traveling direction 30 of the vehicle 27 is reached. Based on this, it is possible to accurately determine which road the vehicle 27 is traveling on without being affected by a structure such as a structural building.

  In the embodiment described above, since the elevated road is on the right side in the area where the vehicle is on the left side, the satellite radio wave from the artificial satellite capable of receiving the satellite radio wave on the right side in the traveling direction of the vehicle. The reception level is determined. However, in an area where the vehicle is on the right side of the vehicle, it may be configured to determine the reception level of satellite radio waves from an artificial satellite capable of receiving satellite radio waves on the left side of the vehicle traveling direction. . In addition, when the positional relationship between the elevated road and the road under the elevated road is different from the principle of left-hand traffic and right-hand traffic, satellite radio waves on the appropriate side are received from the position relationship and direction of travel of each road. What is necessary is just to comprise so that the reception level of the satellite radio wave from a possible artificial satellite may be discriminate | determined.

10 ... Control means 11 ... CPU
12 ... ROM
13 ... RAM
14 ... Satellite radio wave reception means 15 ... Current position calculation means 16 ... Satellite discrimination means 17 ... Traveling direction detection means 18 ... Reception level detection means 19 ... Reception level determination means 20 ... Traveling route determination means 21 ... input means 22 ... map storage means 23 ... route search means 24 ... display means 25 ... elevated roads 26a, 26b ... elevated road 27 ... Vehicles 28a to 28d ... artificial satellite 29 ... satellite radio wave 30 ... traveling direction

Claims (5)

A receiver for receiving satellite radio waves from a plurality of artificial satellites, and a calculation means for calculating a current position of a vehicle on which the receiver is mounted based on position information and time information of each artificial satellite obtained from the satellite radio waves; In the vehicle-mounted navigation device provided with guidance means for guiding the travel path of the vehicle based on the calculated current position and map information,
Satellite discriminating means for discriminating an artificial satellite capable of receiving satellite radio waves by the receiver from the position information of each artificial satellite and the current position of the vehicle;
Traveling direction detection means for detecting the traveling direction of the vehicle;
Reception level detection means for detecting the reception level of satellite radio waves received by the receiver;
Reception level determination means for determining whether a reception level of satellite radio waves from an artificial satellite determined to be capable of receiving the satellite radio waves on one side of the traveling direction of the vehicle is equal to or lower than a predetermined level; ,
Based on the determination result by the reception level determination means, traveling road determination means for determining whether the vehicle is traveling on an elevated road or traveling on an elevated road;
And the guide means guides the travel path of the vehicle based on the determination result by the travel path determination means.   2. The travel direction detecting means detects the travel direction from an azimuth angle obtained from a current position of the vehicle calculated last time and a current position of the vehicle calculated this time. Car navigation system.   The travel path determination means is on one side of the traveling direction of the vehicle by the reception level determination means, and a reception level of satellite radio waves from an artificial satellite determined to be able to receive the satellite radio waves is a predetermined level or less. 3. The in-vehicle navigation device according to claim 1, wherein when it is determined that the vehicle is traveling, the vehicle is determined to be traveling on an underpass road.   The guide means guides the travel path of the vehicle by map matching based on a determination result of the travel path determination means, the calculated current position, and the map information. The vehicle-mounted navigation device according to any one of the above. Receives satellite radio waves from a plurality of artificial satellites, calculates the current position of the vehicle based on the position information and time information of each artificial satellite obtained from the satellite radio waves, and based on the calculated current position and map information In the navigation method for guiding the travel path of the vehicle,
Determining a satellite capable of receiving the satellite radio wave from the position information of each artificial satellite and the current position of the vehicle;
Detecting the traveling direction of the vehicle;
Detecting a reception level of satellite radio waves from the artificial satellite determined to be capable of receiving the satellite radio waves;
Determining whether a reception level of satellite radio waves from an artificial satellite determined to be capable of receiving the satellite radio waves is one side in a traveling direction of the vehicle is equal to or lower than a predetermined level;
Determining whether the vehicle is traveling on an elevated road or on an elevated road based on the determination result of the reception level;
Guiding the travel path of the vehicle based on the result of the determination;
A navigation method comprising:

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