Patent Publication Number: US-2021191423-A1

Title: Self-Location Estimation Method and Self-Location Estimation Device

Description:
TECHNICAL FIELD 
     The present invention relates to a self-location estimation method and a self-location estimation device. 
     BACKGROUND 
     In JP 2006-317286 A, a technology for determining whether the current location of a vehicle is on an ordinary road or an expressway, based on whether, in an image of the vicinity of the vehicle captured by a camera, an ordinary road identifying image for identifying that the vehicle is traveling on an ordinary road or an expressway identifying image for identifying that the vehicle is traveling on an expressway is included is described. 
     SUMMARY 
     Although the technology described in JP 2006-317286 A is capable of discriminating between roads the road types of which are different from each other, the technology is incapable of discriminating between different roads the road types of which are the same. 
     Thus, when different roads the road types of which are the same respectively exist at different heights and the two-dimensional locations of the roads are close to each other, it sometimes becomes impossible to determine on which one of the roads the vehicle is present. 
     An object of the present invention is to enable determination of on which one of roads existing at different heights a vehicle is present. 
     According to one aspect of the present invention, there is provided a self-location estimation method including: detecting a traffic sign in a vicinity of a vehicle; determining a current location of the vehicle; acquiring height information of the detected traffic sign from map data in which two-dimensional coordinate information and height information of a traffic sign existing in a vicinity of a road are recorded, based on a relative location of the detected traffic sign with respect to the vehicle and the current location; and estimating a height at which the vehicle is present according to the height information acquired from the map data. 
     According to the aspect of the present invention, it is possible to determine on which one of roads existing at different heights a vehicle is present. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration diagram of an example of a driving assistance device of an embodiment; 
         FIG. 2  is an explanatory diagram of an example of a self-location estimation method of the embodiment; 
         FIG. 3  is a block diagram illustrative of an example of a functional configuration of an electronic control unit (ECU) illustrated in  FIG. 1 ; 
         FIG. 4  is an explanatory diagram of an example of a calculation method of two-dimensional coordinates of a traffic sign; 
         FIG. 5  is a flowchart of an example of a driving assistance method of the embodiment; 
       and 
         FIG. 6  is a flowchart of an example of a self-location estimation method illustrated in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention will now be described with reference to the drawings. 
     (Configuration) 
       FIG. 1  is now referred to. A driving assistance device  1  performs automatic-driving control for making a vehicle (hereinafter, referred to as “vehicle”) on which the driving assistance device  1  is mounted automatic-drive without involvement of a driver and driving assistance control for assisting a driver in driving the vehicle, based on a travel environment in the surroundings of the vehicle. 
     The driving assistance control may include not only travel control, such as automatic-steering, automatic-braking, constant speed traveling control, and lane keeping control, but also outputting a message prompting the driver to perform a steering operation or a deceleration operation. 
     The driving assistance device  1  includes external sensors  3 , internal sensors  4 , a positioning device  5 , a map database  6 , a navigation system  7 , an electronic control unit (ECU)  8 , a human machine interface (HMI)  9 , and actuators  10 . Note that a map database is denoted as “map DB” in attached drawings. 
     The external sensors  3  are sensors that detect a surrounding environment around the vehicle, such as an object in the surroundings of the vehicle. The external sensors  3  may include a camera  11  and a ranging device  12 . The camera  11  and the ranging device  12  detect a surrounding environment around the vehicle, such as objects existing in the surroundings of the vehicle (for example, another vehicle, a pedestrian, white lines such as a lane boundary line and a lane marking, and ground objects that are installed on a road or in the vicinity of the road, such as a traffic light, a stop line, a traffic sign, a building, a utility pole, a curb, and a crosswalk), relative locations of such objects with respect to the vehicle, relative distances between the vehicle and the objects, and the like. 
     The camera  11  may be, for example, a stereo camera. The camera  11  may be composed of monocular cameras, and, by capturing images of an identical object from a plurality of perspectives using the monocular cameras, a distance to the object may be calculated. The distance to the object may be calculated based on a ground contact position of the object detected from captured images captured by the monocular cameras. 
     The ranging device  12  may be, for example, a laser range-finder (LRF) or a radar. 
     The camera  11  and the ranging device  12  output surrounding environment information, which is information on the detected surrounding environment, to the ECU  8  and the navigation system  7 . 
     The internal sensors  4  are sensors that detect a travel state of the vehicle. The internal sensors  4  may include, for example, a wheel speed sensor  13  and a gyro-sensor  14 . 
     The wheel speed sensor  13  detects a wheel speed of the vehicle. The gyro-sensor  14  detects a pitch angular velocity, a roll angular velocity, and a yaw angular velocity of the vehicle. The wheel speed sensor  13  and the gyro-sensor  14  output travel state information, which is information on the detected travel state, to the ECU  8  and the navigation system  7 . 
     The positioning device  5  receives radio waves from a plurality of navigation satellites and thereby acquires a current location of the vehicle and outputs the acquired current location of the vehicle to the ECU  8  and the navigation system  7 . The positioning device  5  may have, for example, a global positioning system (GPS) receiver or another global navigation satellite system (GNSS) receiver other than a GPS receiver. 
     The map database  6  stores road map data. The road map data include shapes (lane shapes) and two-dimensional coordinates (for example, latitude and longitude) of white lines, such as lane boundary lines and lane markings, heights of roads and white lines, two-dimensional coordinate information (for example, latitude and longitude) and height information of ground objects that are installed on roads and in the vicinities of the roads, such as traffic lights, stop lines, traffic signs, buildings, utility poles, curbs, and crosswalks. 
     The road map data may also include information on road types, gradients of roads, the numbers of lanes, legal velocities (velocity limits), road widths, presence or absence of junctions, and the like. In the road types, for example, an ordinary road and an expressway may be included. 
     The map database  6  is referred to by the ECU  8  and the navigation system  7 . 
     The navigation system  7  performs route guidance to a destination that is set on a map by the driver of the vehicle for a passenger on the vehicle. The navigation system  7  estimates a current location of the vehicle, using various types of information input from the external sensors  3 , the internal sensors  4 , and the positioning device  5 , generates a route to the destination, and performs route guidance for a passenger. The navigation system  7  outputs the route information to the ECU  8 . 
     The ECU  8  estimates a current location of the vehicle and sets a target travel trajectory on which the vehicle is required to travel, based on the estimated current location, the road map data in the map database  6 , the route information output from the navigation system  7 , the surrounding environment, and the travel state of the vehicle. The ECU  8  performs automatic-driving control and driving assistance control of the vehicle, based on the set target travel trajectory, and drives the actuators  10  and thereby controls travel of the vehicle. 
     The external sensors  3 , the internal sensors  4 , the positioning device  5 , the map database  6 , and the ECU  8  constitute a self-location estimation device  2  according to the embodiment. 
     The ECU  8  includes a processor  15  and peripheral components, such as a storage device  16 . The processor  15  may be, for example, a central processing unit (CPU) or a micro-processing unit (MPU). 
     The storage device  16  may include a semiconductor storage device, a magnetic storage device, and an optical storage device. The storage device  16  may include registers, a cache memory, and a memory, such as a read only memory (ROM) and a random access memory (RAM), that are used as a main storage device. 
     Note that the ECU  8  may be achieved by a functional logic circuit that is implemented in a general-purpose semiconductor integrated circuit. For example, the ECU  8  may include a programmable logic device (PLD), such as a field-programmable gate array (FPGA), and the like. 
     The HMI  9  is an interface for inputting and outputting information between a passenger on the vehicle and the navigation system  7  and ECU  8 . 
     The HMI  9  may accept, for example, an input operation of inputting a destination to the navigation system  7  that is performed by the passenger. The HMI  9  may, for example, output driving guidance given by the navigation system  7  or road guidance information based on the road map data of the surroundings of the vehicle. 
     The actuators  10  operate the steering wheel, accelerator opening, and a braking device of the vehicle according to a control signal output from the ECU  8  and thereby generate vehicle behavior of the vehicle. 
     The actuators  10  include a steering actuator  17 , an accelerator opening actuator  18 , and a brake control actuator  19 . 
     The steering actuator  17  controls steering direction and the amount of steering of the vehicle. The accelerator opening actuator  18  controls the accelerator opening of the vehicle. The brake control actuator  19  controls braking action of the braking device of the vehicle. 
     Next, outline of self-location estimation processing performed by the ECU  8  will be described.  FIG. 2  is now referred to. The reference numeral  20  indicates a vehicle on which the driving assistance device  1  is mounted. The reference numerals  21  and  22  indicate roads existing at different heights h 1  and h 2 , respectively, the reference numerals  21   a  and  21   b  indicate lane boundary lines (white lines) on the road  21 , and the reference numerals  22   a  and  22   b  indicate lane boundary lines (white lines) on the road  22 . A case where the vehicle  20  is present on the road  21  is now assumed. 
     When the two-dimensional locations of the roads  21  and  22  that exist at different heights are close to each other, it becomes impossible to determine on which road the vehicle  20  is present only from the two-dimensional coordinate information. 
     Although it is conceivable that, in order to estimate a self-location including height, map matching is performed in a three-dimensional space (for example, a space represented by latitude, longitude, and height), the three-dimensional map matching requires a high computational cost. Therefore, it is preferable to be able to estimate a self-location including height without performing three-dimensional map matching. As an estimation technology of a self-location, dead reckoning based on wheel speed and angular velocity has been known. 
     However, in the self-location estimation using the dead reckoning, error caused by measurement error accumulates. Therefore, it is necessary to acquire an observed value of height from some information source and correct an estimated value calculated using the dead reckoning with the observed value. 
     Thus, the driving assistance device  1  acquires height information of a traffic sign  23  in the vicinity of the vehicle  20  that is installed on the road  21  from the map database and estimates a height at which the vehicle  20  is present, based on the height information of the traffic sign  23 . 
     Specifically, a relative location of the traffic sign  23  with respect to the vehicle  20  is detected using the external sensors  3 . The ECU  8  determines a current location of the vehicle  20 . For example, the ECU  8  estimates the current location of the vehicle  20 , using the dead reckoning, based on the wheel speed detected by the wheel speed sensor  13  and the pitch angular velocity, the roll angular velocity, and the yaw angular velocity detected by the gyro-sensor  14 . For example, the ECU  8  may measure the current location of the vehicle  20 , using the positioning device  5 . 
     The ECU  8  acquires height information of the traffic sign  23  from the map database  6  in which two-dimensional coordinate information (for example, longitude and latitude) and height information of traffic signs  23  and  24  existing in the vicinities of the roads are recorded, based on the two-dimensional coordinates of the current location of the vehicle  20  and the relative location of the traffic sign  23 . 
     The ECU  8  estimates a height at which the vehicle  20  is present, based on the height information acquired from the map database  6 . For example, the ECU  8  estimates a height indicated by the height information acquired from the map database  6  as the height at which the vehicle  20  is present. 
     Correcting an estimated value of the height calculated using the dead reckoning with the height estimated in this manner enables error caused by measurement error to be prevented from accumulating. 
     In addition, since the height can be estimated without performing three-dimensional map matching, it is possible to keep the computational cost low. 
     Further, since the height is estimated based on the coordinate information of the traffic sign  23  recorded in the map database  6 , it is possible to correctly estimate the height at which the vehicle  20  is present even when separate roads of the same road type respectively exist at different heights and the two-dimensional locations of the roads are close to each other. 
     Note that, as illustrated in  FIG. 2 , the traffic sign  24  is installed on the road  22 , which exists at a height different from the height of the road  21  on which the vehicle  20  is present, as well. However, since the traffic sign  24  is shielded from the vehicle  20  on the road  21  by the road structure, the external sensors  3  cannot detect the traffic sign  24 . Therefore, erroneously estimating the height at which the vehicle  20  is present based on the height information of the traffic sign  24 , which is installed on the road  22  that is different from the road  21 , never occurs. Thus, the height information of a traffic sign does not necessarily have to be a numerical value representing a height, and it may be configured to acquire information indicating on which one of roads that are close to each other the traffic sign is installed. For example, when the traffic sign  23  is detected, it is possible to acquire information indicating that the installation location of the traffic sign  23  is on the road  21  and determine that the vehicle  20  is traveling on one existing at a higher height of the roads that are close to each other. On the other hand, when the traffic sign  24  is detected, it is possible to acquire information indicating that the installation location of the traffic sign  24  is on the road  22  and determine that the vehicle  20  is traveling on the other existing at a lower height of the roads that are close to each other. 
     Next, a functional configuration of the ECU  8  will be described with reference to  FIG. 3 . The ECU  8  includes a self-location estimation unit  30 , a target trajectory setting unit  31 , and a travel control unit  32 . Functions of the self-location estimation unit  30 , the target trajectory setting unit  31 , and the travel control unit  32  may be achieved by, for example, the processor  15  of the ECU  8  executing computer programs stored in the storage device  16 . 
     The self-location estimation unit  30  estimates a self-location of the vehicle, based on various information input from the external sensors  3 , the internal sensors  4 , and the positioning device  5  and information acquired with reference to the map database  6 . 
     The self-location estimation unit  30  includes a dead reckoning unit  40 , a map matching unit  41 , a traffic sign detection unit  42 , a coordinate calculation unit  43 , and a height information acquisition unit  44 . 
     The dead reckoning unit  40  calculates a predicted location of the vehicle at a present time point, using the dead reckoning based on the wheel speed, the pitch angular velocity, the roll angular velocity, and the yaw angular velocity detected by the internal sensors  4 . The predicted location of the vehicle includes two-dimensional coordinates, a height, and an azimuth of the forward direction of the vehicle. 
     The dead reckoning unit  40  outputs the calculated predicted location to the map matching unit  41 . 
     In this processing, the dead reckoning unit  40  calculates two-dimensional coordinates in a two-dimensional coordinate system used in the map database  6 . Hereinafter, the two-dimensional coordinate system used in the map database  6  is referred to as “map coordinate system”. 
     Although, in the following description, an example in which the two-dimensional coordinate system used in the map database  6  is a geographical coordinate system in which the coordinates are represented by latitude and longitude will be described, the two-dimensional coordinate system is not limited to the geographical coordinate system and another coordinate system, such as a plane rectangular coordinate system and a polar coordinate system, may be used. 
     The map matching unit  41  calculates, based on the relative locations of ground objects in the surroundings of the vehicle and relative locations of white lines, which are detected by the external sensors  3 , and the predicted location of the vehicle, which is calculated by the dead reckoning unit  40 , two-dimensional coordinates in the map coordinate system of the ground objects and the white lines. 
     The map matching unit  41  matches the two-dimensional coordinates of the ground objects and the white lines with the map database  6 , using two-dimensional map matching and calculates a mapping correction value of the vehicle location with respect to each of latitude, longitude, and azimuth. 
     The map matching unit  41  corrects the predicted location of the vehicle, which is calculated by the dead reckoning unit  40 , with the calculated mapping correction values and thereby acquires an estimated value of the current location of the vehicle. 
     The map matching unit  41  outputs the estimated value of the current location of the vehicle to the coordinate calculation unit  43  and the target trajectory setting unit  31 . 
     The traffic sign detection unit  42  detects a relative location of a traffic sign, which is detected by the external sensors  3 , in the vicinity of the vehicle with respect to the vehicle. The X-coordinate and the Y-coordinate of the relative location of a traffic sign are denoted as “TS_X [m]” and “TS_Y [m]”, respectively. 
     The traffic sign detection unit  42  outputs the relative location of the traffic sign to the coordinate calculation unit  43 . 
     The coordinate calculation unit  43  calculates estimated values of the two-dimensional coordinates of the traffic sign in the map coordinate system. 
     As illustrated in  FIG. 4 , latitude and longitude of the traffic sign are denoted as “TS_B [rad]” and “TS_L [rad]”, respectively. 
     The latitude and the longitude of the estimated value of the current location of the vehicle and the azimuth of the forward direction of the vehicle, which are acquired by the map matching unit  41 , are denoted as “V_B [rad]”, “V_L [rad]”, and “θ [rad]”, respectively. 
     The coordinate calculation unit  43  calculates estimated values of the two-dimensional coordinates (TS_B [rad], TS_L [rad]) of the traffic sign by approximation in accordance with the formulae (1) and (2) below. 
       TS_ B=V _ B +(TS_ X  sin θ+TS_ Y  cos θ)/ M   (1)
 
       TS_ L=V _ L +(TS_ X  cos θ−TS_ Y  sin θ)/( N  cos  V _ B )  (2)
 
     In the above formulae, M denotes radius of curvature of the meridian [m] and N denotes radius of curvature of the prime vertical [m] at a latitude V_B. 
     The coordinate calculation unit  43  outputs the estimated values of the two-dimensional coordinates (TS_B [rad], TS_L [rad]) of the traffic sign to the height information acquisition unit  44 . 
     The height information acquisition unit  44  matches the two-dimensional coordinates (TS_B [rad], TS_L [rad]) of the traffic sign calculated by the coordinate calculation unit  43  with the two-dimensional coordinate information of traffic signs recorded in the map database  6 . 
     When a traffic sign that has two-dimensional coordinate information that matches the two-dimensional coordinates (TS_B [rad], TS_L [rad]), which are calculated by the coordinate calculation unit  43 , exists in the map database  6 , the height information acquisition unit  44  acquires the coordinate information (latitude TS_M_B [rad], longitude TS_M_L [rad], and height TS_M_H [m]) of the matching traffic sign from the map database  6 . 
     In the above processing, cases where the two-dimensional coordinates (TS_B [rad], TS_L [rad]) and the two-dimensional coordinates (TS_M_B [rad], TS_M_L [rad]) match each other include not only a case where the two two-dimensional coordinates completely coincide with each other but also a case where a difference between the two two-dimensional coordinates is less than a predetermined value. 
     The height information (TS_M_H [m]) of a traffic sign may be height information of the ground (that is, the base) at the installation point of the traffic sign or height information of the sign plate of the traffic sign. 
     Note that a traffic sign the height information of which is to be acquired may be, for example, an information sign, a danger warning sign, a regulatory sign, or a direction sign. 
     The height information acquisition unit  44  estimates that the height at which the vehicle is present is a height that the height information of the traffic sign acquired from the map database  6  indicates. The height information acquisition unit  44  may update the estimated value of the height at which the vehicle is present, using a Kalman filter, based on height information of the traffic sign that is acquired multiple times at different time points. 
     The height information acquisition unit  44  outputs the estimated height at which the vehicle is present to the dead reckoning unit  40  and the target trajectory setting unit  31 . 
     The dead reckoning unit  40  corrects the predicted value of the height at which the vehicle is present that is calculated using the dead reckoning, according to the height estimated by the height information acquisition unit  44 . For example, the dead reckoning unit  40  corrects (overwrites) the predicted value of the height at which the vehicle is present, which is calculated using the dead reckoning, with the height estimated by the height information acquisition unit  44  and calculates a subsequent predicted location of the vehicle, based on the corrected height. 
     The dead reckoning unit  40  may correct the predicted value of the height at which the vehicle is present, which is calculated using the dead reckoning, according to the height estimated by the height information acquisition unit  44  every time the vehicle travels a predetermined distance. This configuration enables error of the dead reckoning that accumulates according to travel distance to be efficiently corrected. 
     The target trajectory setting unit  31  sets a target travel trajectory on which the vehicle is required to travel, based on the current location of the vehicle estimated by the map matching unit  41 , the road map data in the map database  6 , the route information output from the navigation system  7 , the surrounding environment detected by the external sensors  3 , and the travel state of the vehicle detected by the internal sensors  4 . 
     On this occasion, the target trajectory setting unit  31  determines a road on which the vehicle is present based on the two-dimensional coordinates of the current location of the vehicle estimated by the map matching unit  41  and the height at which the vehicle is present estimated by the height information acquisition unit  44 . For example, when a plurality of roads the heights of which are different from each other exist at the two-dimensional coordinates of the current location of the vehicle, the target trajectory setting unit  31  determines on which one of the plurality of roads the vehicle is present, based on the height at which the vehicle is present that is estimated by the height information acquisition unit  44 . 
     The target trajectory setting unit  31  sets a target travel trajectory in which the vehicle travels on the road on which the vehicle is present in accordance with the route generated by the navigation system  7 . 
     The target trajectory setting unit  31  outputs the set target travel trajectory to the travel control unit  32 . 
     The travel control unit  32  performs the automatic-driving control and the driving assistance control of the vehicle by driving the actuators  10  in such a way that the vehicle travels on the travel trajectory generated by the target trajectory setting unit  31  and thereby operating a steering mechanism, an acceleration mechanism, and a brake mechanism of the vehicle. 
     (Operation) 
     Next, an example of a driving assistance method of the embodiment will be described with reference to  FIG. 5 . 
     In step S 1 , the self-location estimation unit  30  in  FIG. 3  performs the self-location estimation processing of estimating a current location of the vehicle. 
       FIG. 6  is a flowchart of an example of the self-location estimation processing S 1 . 
     In step S 10 , the dead reckoning unit  40  calculates a predicted location (latitude, longitude, height, and azimuth) of the vehicle at a present time point, using the dead reckoning based on the wheel speed, the pitch angular velocity, the roll angular velocity, and the yaw angular velocity detected by the internal sensors  4 . 
     In step S 11 , the map matching unit  41  calculates, based on the relative locations of the ground objects in the surroundings of the vehicle and the relative locations of the white lines, which are detected by the external sensors  3 , the predicted location of the vehicle, which was calculated by the dead reckoning unit  40 , and the map database  6 , an estimated value of the current location of the vehicle, using the two-dimensional map matching. 
     In step S 12 , the traffic sign detection unit  42  detects a relative location (TS_X [m], TS_Y [m]) of the traffic sign, which is detected by the external sensors  3 , in the surroundings of the vehicle with respect to the vehicle. 
     In step S 13 , the coordinate calculation unit  43  calculates estimated values (TS_B [rad], TS_L [rad]) of the two-dimensional coordinates of the traffic sign in the map coordinate system. 
     In step S 14 , the height information acquisition unit  44  matches the two-dimensional coordinates (TS_B [rad], TS_L [rad]) of the traffic sign calculated in step S 13  with the two-dimensional coordinate information of traffic signs recorded in the map database  6 . The height information acquisition unit  44  determines whether or not a traffic sign that has two-dimensional coordinate information matching the two-dimensional coordinates (TS_B [rad], TS_L [rad]) exists in the map database  6 . 
     When no traffic sign the two-dimensional coordinates of which match the two-dimensional coordinates (TS_B [rad], TS_L [rad]) exists in the map database  6  (step S 14 : N), the self-location estimation processing S 1  is terminated without correcting the height calculated using the dead reckoning. 
     When a traffic sign the two-dimensional coordinates of which match the two-dimensional coordinates (TS_B [rad TS_L [rad]) exists in the map database  6  (step S 14 : Y), the process proceeds to step S 15 . 
     In step S 15 , the height information acquisition unit  44  acquires the coordinate information (latitude TS_M_B [rad], longitude TS_M_L [rad], and height TS_M_H [m]) of the traffic sign the two-dimensional coordinates of which match the two-dimensional coordinates (TS_B [rad], TS_L [rad]) from the map database  6 . The height information acquisition unit  44  estimates that the height at which the vehicle is present is the height (TS_M_H [m]) of the traffic sign. 
     In step S 16 , the dead reckoning unit  40  corrects the predicted value of the height at which the vehicle is present, which was calculated using the dead reckoning, to the height estimated by the height information acquisition unit  44 . Subsequently, the self-location estimation processing S 1  is terminated. 
       FIG. 5  is now referred to. In step S 2 , the target trajectory setting unit  31  determines a road on which the vehicle is present based on the two-dimensional coordinates of the current location of the vehicle, which was estimated by the map matching unit  41 , and the height at which the vehicle is present, which was estimated by the height information acquisition unit  44 . 
     When a plurality of roads the heights of which are different from each other exist at the two-dimensional coordinates of the current location of the vehicle, the target trajectory setting unit  31  determines on which one of the plurality of roads the vehicle is present, based on the height at which the vehicle is present, which was estimated by the height information acquisition unit  44 . Note that the height information of the vehicle is only required to be information that enables on which one of a plurality of roads the heights of which are different from each other the vehicle is present at the two-dimensional coordinates of the current location of the vehicle to be determined. For example, the height information of the vehicle may be information that indicates on which one of a plurality of different roads a traffic sign, among traffic signs respectively installed on the plurality of roads, that the traffic sign detected by the vehicle matches is installed. 
     In step S 3 , the target trajectory setting unit  31  sets a target travel trajectory in which the vehicle travels on the road on which the vehicle is currently present, based on the current location of the vehicle, which was estimated by the map matching unit  41 , the road map data in the map database  6 , the route information output from the navigation system  7 , the surrounding environment detected by the external sensors  3 , and the travel state of the vehicle detected by the internal sensors  4 . 
     On this occasion, the target trajectory setting unit  31  sets a target travel trajectory in which the vehicle travels on the road on which the vehicle is present, which was determined in step S 2 , in accordance with the route generated by the navigation system  7 . 
     In step S 4 , the travel control unit  32  performs travel control, such as the automatic-driving control and the driving assistance control, of the vehicle by driving the actuators  10  in such a way that the vehicle travels on the travel trajectory that was generated by the target trajectory setting unit  3 . 
     Advantageous Effects of Embodiment 
     (1) The traffic sign detection unit  42  detects a traffic sign in the vicinity of the vehicle. The dead reckoning unit  40  and the map matching unit  41  determine a current location of the vehicle. The coordinate calculation unit  43  and the height information acquisition unit  44  acquire the height information of the detected traffic sign from the map database  6 , based on the relative location of the detected traffic sign with respect to the vehicle and the current location and estimate a height at which the vehicle is present according to the height information. 
     Since this processing enables the height at which the vehicle is present to be estimated, it becomes possible to determine on which one of roads existing at different heights the vehicle is present. 
     In particular, since the height is estimated based on the coordinate information of the traffic sign  23  recorded in the map database  6 , it is possible to correctly estimate the height at which the vehicle  20  is present even when roads of the same road type respectively exist at different heights and the two-dimensional locations of the roads are close to each other. 
     (2) The dead reckoning unit  40  and the map matching unit  41  determine two-dimensional coordinates of the current location in the map coordinate system. The coordinate calculation unit  43  calculates two-dimensional coordinates of the detected traffic sign in the map coordinate system, based on the two-dimensional coordinates of the relative location of the detected traffic sign and the current location. The height information acquisition unit  44  acquires the height information of a traffic sign that has two-dimensional coordinate information corresponding to the two-dimensional coordinates of the detected traffic sign from the map database  6  as the height information of the detected traffic sign. 
     This processing enables the height information of the traffic sign detected in the vicinity of the vehicle to be appropriately acquired from the map database  6 , in which two-dimensional coordinate information and height information of traffic signs existing in the vicinities of roads are recorded. 
     (3) The map matching unit  41  calculates two-dimensional coordinates of the current location in the map coordinate system, using two-dimensional map matching. 
     That is, the map matching unit  41  calculates two-dimensional coordinates of the current location, using two-dimensional map matching and estimates a height at which the vehicle is present, based on the coordinate information of the traffic sign  23  recorded in the map database  6 . Since, because of this configuration, a self-location including height can be estimated without performing three-dimensional map matching, it is possible to keep the computational cost low. 
     (4) The dead reckoning unit  40  corrects the estimated value of the height at which the vehicle is present, which is calculated using dead reckoning, according to the height information acquired from the map database  6 . 
     This configuration enables error in the height caused by measurement error to be prevented from accumulating. 
     (5) The dead reckoning unit  40  corrects the estimated value according to the height information acquired from the map database every time the vehicle travels a predetermined distance. 
     This configuration enables error of the dead reckoning, which accumulates as travel distance increases, to be efficiently corrected. 
     (6) A traffic sign that the traffic sign detection unit  42  detects may be an information sign. Such information signs are often installed at sites where roads cross each other vertically, such as a junction. Therefore, it is possible to appropriately determine on which one of roads the vehicle is traveling at a site where the roads cross each other vertically. 
     All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Driving assistance device 
               2  Self-location estimation device 
               3  External sensor 
               4  Internal sensor 
               5  Positioning device 
               6  Map database 
               7  Navigation system 
               10  Actuator 
               11  Camera 
               12  Ranging device 
               13  Wheel speed sensor 
               14  Gyro-sensor 
               15  Processor 
               16  Storage device 
               17  Steering actuator 
               18  Accelerator opening actuator 
               19  Brake control actuator 
               20  Vehicle 
               21 ,  22  Road 
               21   a ,  21   b ,  22   a ,  22   b  Lane boundary line (white line) 
               23 ,  24  Traffic sign 
               30  Self-location estimation unit 
               31  Target trajectory setting unit 
               32  Travel control unit 
               40  Dead reckoning unit 
               41  Map matching unit 
               42  Traffic sign detection unit 
               43  Coordinate calculation unit 
               44  Height information acquisition unit