Patent Publication Number: US-2023135641-A1

Title: Superimposed image display device

Description:
INCORPORATION BY REFERENCE 
     This application claims the benefit of priority from Japanese Patent Application No. 2021-177446 filed on Oct. 29, 2021, of which the specification, drawings and abstract are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE DISCLOSURE 
     The present disclosure relates to superimposed image display devices that assist in driving a vehicle. 
     Description of the Related Art 
     Conventionally, various units are used as an information providing unit for providing various kinds of information that assist in driving a vehicle, such as route guidance and warnings against obstacles, to a vehicle occupant. Examples of such an information providing unit include display on a liquid crystal display installed in a vehicle and voice that is output from a speaker. Devices that provide information by displaying an image superimposed on the surrounding environment of a vehicle occupant (landscape or actual view) have been recently used as one of such an information providing unit. For example, there is a method in which an image is displayed superimposed on a captured image of the surroundings of a vehicle displayed on a liquid crystal display, in addition to a head-up display or a windshield display. 
     For example, Japanese Unexamined Patent Application Publication No. 2014-48146 (JP 2014-48146 A) discloses a technique of providing guidance particularly on a recommended lane, namely a lane in which a vehicle should travel, by displaying an image superimposed on the surrounding environment of a vehicle occupant. In the technique disclosed in JP 2014-48146 A, an captured image of the landscape in front of a vehicle is displayed on a display unit, and when the remaining distance to an intersection is greater than a reference value and the vehicle is not traveling in a recommended lane, namely a lane recommended for the vehicle to pass through the intersection, an image of an arrow is displayed superimposed on the recommended lane included in the landscape in front of the vehicle in order to notify a vehicle occupant of the position of the recommended lane. 
     SUMMARY OF THE DISCLOSURE 
     However, in order to provide guidance on the recommended lane by superimposing an image on the road surface of the recommended lane as disclosed in JP 2014-48146 A ( FIG.  5   ), it is necessary that the position of the recommended lane as viewed from the vehicle (i.e., on which side of and how far from the lane in which the vehicle is currently traveling the recommended lane is located) have been identified. In order to identify the position of the recommended lane as viewed from the vehicle, it is necessary to accurately identify the lane in which the vehicle is currently traveling (hereinafter also referred to as the “lane of travel”). 
     In the technique disclosed in JP 2014-48146 A ( FIG.  5   ), image recognition is used as a unit for identifying the lane of travel. Specifically, lane lines are detected by performing image recognition on an image of the area in front of the vehicle captured by a camera, and the lane of travel is identified based on the detection results. However, the identification result of the traveling line may not be confident when, for example, the weather is bad or when the painted lane lines are faded. In JP 2014-48146 A ( FIG.  5   ), even when the identification result of the lane of travel is not confident, guidance is provided by superimposing an image on the road surface of the recommended lane. Accordingly, wrong guidance may be provided, which may cause a disadvantage to the vehicle occupant. 
     The aspects of the disclosure were made to solve the above conventional problem, and it is an aspect of the present disclosure to provide a superimposed image display device that, when providing guidance on a recommended lane using a guide object displayed superimposed on the landscape around a vehicle, displays the guide object in a display mode according to the confidence of the identification result of a lane of travel, and thus reduces or eliminates the possibility that a disadvantage may be caused to a vehicle occupant even when the confidence is low. 
     In order to achieve these aspects, the superimposed image display device according to a first aspect of the present disclosure is a superimposed image display device that is mounted on a vehicle and that superimposes a guide object providing guidance on information to an occupant of the vehicle on a landscape around the vehicle to allow the occupant to see the guide object. The superimposed image display device includes: a recommended lane acquisition unit that acquires a recommended lane in which the vehicle is recommended to travel on a road on which the vehicle is currently traveling; a lane-of-travel identification unit that identifies a lane of travel, the lane of travel being a lane in which the vehicle is currently traveling on the road on which the vehicle is currently traveling; a confidence acquisition unit that acquires a confidence indicating how confident an identification result of the lane of travel by the lane-of-travel identification unit is; and an object display unit that displays the guide object providing guidance on the recommended lane in such a manner that the guide object is superimposed on a road surface, based on the lane of travel and the recommended lane. The object display unit displays the guide object in a display mode according to the confidence. 
     As used herein, the “landscape” includes not only a landscape (actual view) that is actually seen from a vehicle, but also a captured image of the landscape, and a reproduced image of the landscape. 
     The “guidance on the recommended lane” may be guidance that makes the vehicle aware of the position and direction of the recommended lane with no purpose of guiding the vehicle to the recommended lane, or may be guidance that guides the vehicle to the recommended lane. 
     According to the superimposed image display device of the first aspect of the present disclosure having the above configuration, when providing guidance on the recommended lane using the guide object displayed superimposed on the landscape around the vehicle, the superimposed image display device displays the guide object in a display mode according to the confidence of the identification result of the lane of travel. This allows accurate guidance to be provided when the confidence is high, and reduces or eliminates the possibility that a disadvantage may be caused to the vehicle occupant even when the confidence is low. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG.  1    is a block diagram of a navigation device according to a first embodiment; 
         FIG.  2    is a flow chart of a driving assistance processing program according to the first embodiment; 
         FIG.  3    shows examples of a first guide object displayed on a liquid crystal display; 
         FIG.  4    shows an example of a second guide object displayed on the liquid crystal display; 
         FIG.  5    is a flowchart of a sub-process program of a first guide object display position determination process; 
         FIG.  6    illustrates a method for detecting a vehicle&#39;s lane of travel; 
         FIG.  7    illustrates a method for detecting a vehicle&#39;s lane of travel; 
         FIG.  8    illustrates a method for detecting a vehicle&#39;s lane of travel; 
         FIG.  9    shows an example of a recommended lane when passing through a guide branch point on an expressway; 
         FIG.  10    shows an example of a recommended lane when passing through a guide branch point on a local road; 
         FIG.  11    shows an example of the first guide object; 
         FIG.  12    shows an example of the first guide object; 
         FIG.  13    shows an example of the first guide object; 
         FIG.  14    shows an example of the first guide object displayed on the liquid crystal display; 
         FIG.  15    shows an example of the first guide object displayed on the liquid crystal display; 
         FIG.  16    is a flowchart of a sub-process program of a second guide object display position determination process; 
         FIG.  17    shows an arrangement example of the second guide objects; 
         FIG.  18    shows how the second guide object displayed on the liquid crystal display changes as a vehicle travels; 
         FIG.  19    is a schematic configuration diagram of a superimposed image display device according to a second embodiment; and 
         FIG.  20    shows a display example of a guide object in the superimposed image display device according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, first and second embodiments in which a superimposed image display device according to the present disclosure is embodied as a navigation device will be described in detail with reference to the drawings. 
     First Embodiment 
     First, a schematic configuration of a navigation device  1  according to the first embodiment will be described with reference to  FIG.  1   .  FIG.  1    is a block diagram of the navigation device  1  according to the first embodiment. 
     As shown in  FIG.  1   , the navigation device  1  according to the first embodiment includes: a current position detection unit  11  that detects the current position of a vehicle equipped with the navigation device  1 ; a data recording unit  12  having various kinds of data recorded thereon; a navigation electronic control unit (ECU)  13  that performs various arithmetic operations based on input information; an operation unit  14  that receives operations from a user; a liquid crystal display  15  that displays a captured image of an actual view of the area located in front of the user in the direction of travel; a speaker  16  that outputs voice guidance for route guidance; a digital versatile disc (DVD) drive  17  that reads a DVD as a storage medium; and a communication module  18  that communicates with an information center such as a probe center or Vehicle Information and Communication System (VICS, registered trademark) Center. A front camera  19  and various sensors that are mounted on the vehicle equipped with the navigation device  1  are connected to the navigation device  1  via an in-vehicle network such as Controller Area Network (CAN). 
     Each component of the navigation device  1  will be described below. 
     The current position detection unit  11  includes a Global Positioning System (GPS)  21 , a vehicle speed sensor  22 , a steering sensor  23 , and a gyro sensor  24 , and can detect the current vehicle position, vehicle orientation, vehicle speed, current time, etc. In particular, the vehicle speed sensor  22  is a sensor that detects the travel distance and speed of the vehicle. The vehicle speed sensor  22  generates pulses as drive wheels of the vehicle rotate, and outputs the pulse signal to the navigation ECU  13 . The navigation ECU  13  calculates the rotational speed of the drive wheels and the travel distance by counting the generated pulses. The navigation device  1  need not necessarily include all of the above four types of sensors. The navigation device  1  may include only one or more of the four types of sensors. 
     The data recording unit  12  includes: a hard disk (not shown) as an external storage device and recording medium; and a recording head (not shown) that is a driver for reading a map information database (DB)  31 , predetermined program, etc. recorded on the hard disk and writing predetermined data to the hard disk. The data recording unit  12  may include a flash memory, a memory card, or an optical disc such as compact disc (CD) or DVD, instead of the hard disk. The map information DB  31  may be stored in an external server, and the navigation device  1  may acquire the map information DB  31  from the external server through communication. 
     The map information DB  31  is a storage unit having stored therein, for example, link data  32  regarding roads (links), node data  33  regarding node points, branch point data  34  regarding branch points, point data regarding points such as facilities, map display data for displaying a map, search data for searching for a route, and search data for searching for a point. 
     The following data is recorded as the link data  32 : data on each link forming a road, data on a corner, data on a road, data on road attributes, and data on the road type. The data on each link forming a road includes data indicating width, slope, cant, bank, road surface condition, number of lanes of the road, direction of travel of each lane, whether there is any oncoming lane (whether it is a two-way traffic section), location where the number of lanes decreases, location where the road narrows, railroad crossing, etc. The data on a corner includes data indicating radius of curvature, intersection, T-intersection, entrance and exit of the corner, etc. The data on road attributes include data indicating a downhill road, an uphill road, etc. The data on the road type include data indicating an expressway and a local road (national road, prefectural road, narrow street, etc.). 
     The following data is recorded as the node data  33 : coordinates (position) of each branch point (including an intersection, a T-intersection, etc.) on an actual road or each node point set on each road at every predetermined distance according the radius of curvature etc., node attributes indicating whether the node is a node corresponding to an intersection etc., a connection link number list that is a list of link numbers of links that connect to the node, an adjacent node number list that is a list of node numbers of nodes that are adjacent to the node via links, height (altitude) of each node point, etc. 
     The following data is recorded as the branch point data  34 : name of an intersection of the branch point, relevant node information identifying the node forming the branch point, connection link information identifying the link connected to the branch point, name of the direction corresponding to the link connected to the branch point, information identifying the shape of the branch point, etc. Structures that can serve as landmarks when providing guidance on a right or left turn at the branch point are also stored. 
     The navigation ECU  13  is an electronic control unit that controls the entire navigation device  1 . The navigation ECU  13  includes: a central processing unit (CPU)  41  as an arithmetic device and a control device; and an internal storage device such as a random access memory (RAM)  42  that is used as a working memory when the CPU  41  performs various arithmetic operations and that stores route data etc. when route search is performed, a read-only memory (ROM)  43  having stored therein, for example, a driving assistance processing program ( FIG.  2   ) that will described later in addition to a control program, and a flash memory  44  that stores a program read from the ROM  43 . The navigation ECU  13  includes various units as processing algorithms. For example, a recommended lane acquisition unit acquires a recommended lane in which the vehicle is recommended to travel on a road on which the vehicle is currently traveling. A lane-of-travel identification unit identifies a lane of travel that is a lane in which the vehicle is currently traveling on the road on which the vehicle is currently traveling. A confidence acquisition unit acquires the confidence indicating how confident the identification result of the lane of travel by the lane-of-travel identification unit is. An object display unit displays a guide object that provides guidance on the recommended lane based on the lane of travel and the recommended lane. 
     The operation unit  14  is operated when entering a departure point as a travel start point and a destination as a travel end point, and includes a plurality of operation switches (not shown) such as various keys and buttons. The navigation ECU  13  performs control to execute various corresponding operations based on switch signals output in response to depression etc. of the switches. The operation unit  14  may include a touch panel mounted on the front of the liquid crystal display  15 . The operation unit  14  may include a microphone and a voice recognition device. 
     The liquid crystal display  15  displays a map image including roads, traffic information, operation guidance, an operation menu, guidance on the keys, a guide route from the departure point to the destination, guide information on the guide route, news, a weather forecast, time, emails, a television program, etc. Particularly in the first embodiment, when the vehicle approaches a guide branch point, an image captured by the front camera  19 , that is, a current landscape (image of a current actual view) around the vehicle (particularly in front of the vehicle), is displayed on the liquid crystal display  15 , and as necessary, the guide object is displayed superimposed on the landscape on the liquid crystal display  15 . 
     The guide object displayed superimposed on the landscape includes information on the vehicle and various kinds of information that are used to assist a vehicle occupant in driving. Examples of the guide object include: warnings or alerts against objects against which the vehicle occupant is to be warned or alerted (other vehicles, pedestrians, and guide signs); a guide route set in the navigation device  1  and guidance information based on the guide route (arrows indicating right and left turn directions, an icon marking the guide branch point, distance to the guide branch point, position of the recommended lane and direction toward the recommended lane to which the vehicle travels, guidance encouraging to change lanes to the recommended lanes, etc.); warnings or alerts to be displayed on the road surface (frequent collision areas, speed limits, etc.); lane lines of the lane in which the vehicle travels; current vehicle speed; shift position; remaining energy; advertising images; facility information; guide signs; map image; traffic information; news; weather forecast; time; and screen of a connected smartphone. In the first embodiment described below, the guide object is guide information that provides guidance on a guide branch point located ahead in the direction of travel of the vehicle. More specifically, the guide object is an arrow indicating the exit direction at the guide branch point along the guide route, a guide image indicating the position and direction of a recommended lane in which the vehicle is recommended to travel on the road on which the vehicle is currently traveling in order to pass through the guide branch point along the guide route, a guide image encouraging to move to the recommended lane, etc. 
     The speaker  16  outputs voice guidance that guides the vehicle to travel along the guide route based on instructions from the navigation ECU  13  and guidance on traffic information. 
     The DVD drive  17  is a drive that can read data recorded on a recording medium such as DVD and CD. For example, music or video is played or the map information DB  31  is updated based on the read data. The navigation device  1  may include a card slot for reading and writing a memory card, instead of the DVD drive  17 . 
     The communication module  18  is a communication device that receives traffic information transmitted from a traffic information center such as VICS center or probe center. The traffic information includes various kinds of information such as traffic congestion information, traffic regulation information, and traffic accident information. The communication module  18  is, for example, a mobile phone or a Data Communication Module (DCM). 
     The front camera  19  is an imaging device with a camera using a solid-state imaging device such as charge-coupled device (CCD). For example, the front camera  19  is mounted on the back of a rearview mirror or on a front bumper with its optical axis extending forward in the direction of travel of the vehicle. As described above, an image captured by the front camera  19  is displayed on the liquid crystal display  15  as a landscape (image of an actual view) around the vehicle (particularly in front of the vehicle). As will be described later, the image captured by the front camera  19  is also used when identifying the lane in which the vehicle is currently traveling. 
     Next, the driving assistance processing program that is executed by the navigation ECU  13  in the navigation device  1  having the above configuration will be described with reference to  FIG.  2   .  FIG.  2    is a flowchart of the driving assistance processing program according to the first embodiment. The driving assistance processing program is a program that is executed after an accessory (ACC) power supply of the vehicle is turned on, and that assists in driving the vehicle by making visible the guide object displayed superimposed on the landscape around the vehicle on the liquid crystal display  15 . Programs shown in the flowcharts of  FIGS.  2 ,  5 , and  16    that will be described below are stored in the RAM  42  and ROM  43  of the navigation device  1  and are executed by the CPU  41 . 
     An example in which travel guidance on a guide route set in the navigation device  1  is provided as driving assistance for the vehicle using the guide object will be described below. The guide object to be displayed is guide information that provides guidance on a guide branch point located ahead in the direction of travel of the vehicle. A process that is performed when an arrow indicating the exit direction at the guide branch point, a guide image indicating the position and direction of a recommended lane, and a guide image encouraging to move to the recommended lane are displayed as the guide object will be described as an example. However, the navigation device  1  can also provide guidance and information other than the driving assistance by using the guide object. The guide object to be displayed can be information other than the arrow and the guide image. For example, the following can be displayed as the guide object: warnings against objects against which the vehicle occupant is to be warned or alerted (other vehicles, pedestrians, and guide signs); warnings to be displayed on the road surface (frequent collision areas, speed limits, etc.); distance to the next guide branch point; current vehicle speed; shift position; remaining energy; advertising images; facility information; guide signs; map image; traffic information; news; weather forecast; time; and screen of a connected smartphone. 
     In the driving assistance processing program, in step (hereinafter abbreviated as “S”)  1  (“S 1 ”), the CPU  41  first identifies the current position of the vehicle based on the detection result of the current position detection unit  11  and map information. When identifying the current position of the vehicle, the CPU  41  also performs a map matching process in which the current position of the vehicle is matched with the map information. The CPU  41  then reads the guide route set in the navigation device  1 , and calculates the distance from the identified current position of the vehicle to the next guide branch point on the guide route. The guide branch point is a branch point (intersection) on which the navigation device  1  provides guidance, such as instructing to turn right or left, when the navigation device  1  provides travel guidance according to the guide route set in the navigation device  1 . A branch point (difficult intersection) that does not require a right turn or left turn but has an unusual shape is also the guide branch point. 
     Next, in S 2 , the CPU  41  determines whether the distance to the next guide branch point calculated in S 1  is less than a predetermined guidance start distance. The guidance start distance is determined by the type of the road on which the vehicle travels. For example, the guidance start distance for expressways is 1 km, and the guidance start distance for local roads is 300 m that is shorter than the guidance start distance for expressways. However, the guidance start distance may be a variable value instead of a fixed value. For example, when there is another branch point within 300 m before the guide branch point on a local road, the guidance start distance may be the distance from the guide branch point to the another branch point. 
     When the CPU  41  determines that the distance to the next guide branch point calculated in S 1  is less than the guidance start distance (S 2 : YES), the routine proceeds to S 3 . When the CPU  41  determines that the distance to the next guide branch point calculated in S 1  is not less than the guidance start distance (S 2 : NO), the routine returns to S 1 . 
     In S 3 , the CPU  41  determines whether the distance to the next guide branch point is less than a predetermined exit direction guidance start distance. The exit direction guidance start distance is a distance shorter than the guidance start distance that is a criterion for determination in S 2 , and is determined by the type of the road on which the vehicle travels. For example, the exit direction guidance start distance for expressways is 300 m, and the exit direction guidance start distance for local roads is 50 m that is shorter than the exit direction guidance start distance for expressways. 
     When the CPU  41  determines that the distance to the next guide branch point is less than the exit direction guidance start distance (S 3 : YES), the routine proceeds to S 6 . When the CPU  41  determines that the distance to the next guide branch point is not less than the exit direction guidance start distance (S 3 : NO), the routine proceeds to S 4 . 
     Thereafter, in S 4 , the CPU  41  performs a first guide object display position determination process ( FIG.  5   ) that will be described later. The first guide object display position determination process is a process in which a guide image indicating the position and direction of the recommended lane or a guide image encouraging to move to the recommended lane is used as a guide object (hereinafter referred to as the “first guide object”) to be displayed, and the display size and shape of the first guide object on the liquid crystal display  15  and the display position (range) of the first guide object on the liquid crystal display  15  are specifically determined. The display size and shape of the first guide object and the display position of the first guide object determined in S 4  are, for example, the conditions for superimposing the guide object on the recommended lane in the landscape, the vehicle&#39;s lane of travel, or the lane between the recommended lane and the vehicle&#39;s lane of travel so that the vehicle occupant can see the guide object. 
     Subsequently, in S 5 , the CPU  41  generates an image of the first guide object with the display size and shape determined in S 4 , transmits a control signal to the liquid crystal display  15 , and draws the generated image of the first guide object at the display position (in the display range) determined in S 4  on the liquid crystal display  15 . An image captured by the front camera  19  in advance before the distance from the vehicle to the guide branch point became less than the guidance start distance, that is, the current landscape (image of the current actual view) around the vehicle (particularly in front of the vehicle), has been displayed on the liquid crystal display  15 . The vehicle occupant can thus see the first guide object superimposed on the landscape. 
       FIG.  3    shows examples of a travel guidance screen  51  displayed on the liquid crystal display  15  in S 5 . As shown in  FIG.  3   , a current landscape  52  in front of the vehicle captured by the front camera  19  is displayed on the liquid crystal display  15 . An image  53  of the first guide object is displayed superimposed on the landscape  52  in front of the vehicle. 
     In the first embodiment, a plurality of types of guide objects is present as guide objects to be used for guidance, and one or more types of guide objects selected according to the content of guidance and the current situation are displayed. There are cases where two or more types of guide objects are selected to be displayed at the same time. The examples shown in  FIG.  3    are examples of the travel guidance screen  51  displayed when the distance from the current position of the vehicle to the guide branch point becomes less than the guidance start distance and equal to or greater than the exit direction guidance start distance (e.g., 1 km to 300 m to the guide branch point). These examples show a first display mode, a second display mode, and a third display mode. In the first display mode, a guide image providing guidance by distinguishing a recommended lane  54  in which the vehicle is recommended to travel on the road on which the vehicle is currently traveling in order for the vehicle to pass through the guide branch point along the guide route is displayed as the image  53  of the first guide object. In the second display mode, a guide image that provides guidance by distinguishing the recommended lane  54  from the other lanes and that encourages to move to the recommended lane  54  is displayed as the image  53  of the first guide object. In the third display mode, a guide image that provides guidance on the direction toward the recommended lane  54  (that is also the exit direction at the guide branch point) is displayed as the image  53  of the first guide object. 
     As shown in  FIG.  3   , the image  53  of the first guide object is basically displayed superimposed on the recommended lane  54  in the landscape  52 , or on the region from a lane  55  in which the vehicle is currently traveling (hereinafter also referred to as the “vehicle&#39;s lane of travel”) to the recommended lane  54 . Whether the first guide object is displayed in the first display mode, the second display mode, or the third display mode is determined based on the confidence of the identification result of the lane in which the vehicle is currently traveling, as described below. Specifically, when the confidence of the identification result of the lane in which the vehicle is currently traveling is high (when the identification result of the lane is confident), the first guide object is displayed in the first or second display mode having high guiding capability to guide the vehicle to the recommended lane. On the other hand, when the confidence of the identification result of the lane in which the vehicle is currently traveling is low (when the identification result of the lane is not confident), the first guide object is displayed in the third display mode having low guiding capability to guide the vehicle to the recommended lane. When the confidence is high, whether the guide object is displayed in the first display mode or the second display mode may be switched based on the distance from the vehicle to the guidance branch point or may be switched based on the positional relationship between the vehicle&#39;s lane of travel and the recommended lane, or the guide object may be displayed in only a predetermined one of the display modes. 
     The distance to the guide branch point may be displayed on the image  53  of the first guide object. Thereafter, the routine returns to S 3 , and the image  53  of the first guide object continues to be displayed until the distance to the next guide branch point becomes less than the exit direction guidance start distance. The first guide object will be described in more detail later. 
     In S 6 , the CPU  41  performs a second guide object display position determination process ( FIG.  16   ) that will be described later. The second guide object display position determination process is a process in which an arrow indicating the exit direction at the guide branch point is used as a guide object (hereinafter referred to as the “second guide object”) to be displayed, and the display size and shape of the second guide object on the liquid crystal display  15  and the display position (range) of the second guide object on the liquid crystal display  15  are specifically determined. The display size and shape of the second guide object and the display position of the second guide object determined in S 6  are, for example, the conditions for superimposing the guide object above the road at a predetermined distance from the vehicle or above the road at the guide branch point in the landscape so that the vehicle occupant can see the guide object. 
     Subsequently, in S 7 , the CPU  41  generates an image of the second guide object with the display size and shape determined in S 6 , transmits a control signal to the liquid crystal display  15 , and draws the generated image of the second guide object at the display position (in the display range) determined in S 6  on the liquid crystal display  15 . An image captured by the front camera  19  in advance before the distance from the vehicle to the guide branch point became less than the guidance start distance, that is, the current landscape (image of the current actual view) around the vehicle (particularly in front of the vehicle), has been displayed on the liquid crystal display  15 . The vehicle occupant can thus see the second guide object superimposed on the landscape. 
       FIG.  4    shows an example of the travel guidance screen  51  displayed on the liquid crystal display  15  in S 7 . As shown in  FIG.  4   , the current landscape  52  in front of the vehicle captured by the front camera  19  is displayed on the liquid crystal display  15 . An image  57  of the second guide object is displayed superimposed on the landscape  52  in front of the vehicle. 
     In the first embodiment, a plurality of types of guide objects is present as guide objects to be used for guidance, and one or more types of guide objects selected according to the content of guidance and the current situation are displayed. There are cases where two or more types of guide objects are selected to be displayed at the same time. The example shown in  FIG.  4    is an example of the travel guidance screen  51  displayed when the distance from the current position of the vehicle to the guide branch point becomes less than the exit direction guidance start distance (e.g., 300 m to the guide branch point). In this example, a plurality of arrows indicating the exit direction at the guide branch point is displayed as the image  57  of the second guide object at the position above the road on which the vehicle is currently traveling along the future course of the vehicle. 
     The image  57  of the second guide object includes images of a plurality of arrow-shaped objects. The images of the arrow-shaped objects are displayed above the road on which the vehicle is currently traveling in such a way that the images of the arrow-shaped objects are located at predetermined intervals along the future course of the vehicle. The direction of each arrow indicates the exit direction of the vehicle at the guide object point. As will be described later, when the vehicle is away from the guide branch point, the image  57  of the second guide object is displayed in a mode in which the image  57  is located at a fixed relative position with respect to the vehicle (hereinafter referred to as the “first mode”). When the vehicle approaches the guide branch point to a certain extent, the image  57  of the second guide object is displayed in a mode in which the image  57  is located at a fixed relative position with respect to the guide branch point located in the landscape  52  (hereinafter referred to as the “second mode”). Particularly in the second mode, a part of the image  57  of the second guide object is fixedly displayed superimposed on the guide branch point. Accordingly, when the vehicle occupant sees the travel guidance screen  51 , he or she can be accurately aware of the course of the vehicle, the position of the guide branch point where the vehicle is supposed to turn right or left, and the exit direction at the guide branch point. The image  57  of the second guide object continues to be displayed until the vehicle passes through the guide branch point. The second guide object will be described in more detail later. 
     Thereafter, in S 8 , the CPU  41  determines whether the vehicle has passed through the guide branch point. For example, the CPU  41  determines whether the vehicle has passed through the guide branch point, based on the current position of the vehicle detected by the current position detection unit  11  and the map information. 
     When the CPU  41  determines that the vehicle has passed through the guide branch point (S 8 : YES), the CPU  41  transmits a control signal to the liquid crystal display  15  to stop display of the guide object being displayed on the liquid crystal display  15  (S 9 ). When stopping display of the guide object, it is desirable to increase the transmittance of the displayed image of the guide object stepwise according to the distance to the guide branch point so that the transmittance eventually becomes equal to 100% when the vehicle reaches the guide branch point. The image captured by the front camera  19 , that is, the current landscape (image of the actual view) around the vehicle (particularly in front of the vehicle), continues to be displayed for a certain period of time even after display of the guide object is stopped. The display of the captured image is then switched to the display of the map image. 
     When the CPU  41  determines that the vehicle has not passed through the guide branch point (S 8 : NO), the routine returns to S 6 , and the guide object continues to be displayed. 
     Next, a sub-process of the first guide object display position determination process that is performed in S 4  will be described with reference to  FIG.  5   .  FIG.  5    is a flowchart of a sub-process program of the first guide object display position determination process. 
     First, in S 11 , the CPU  41  generates a three-dimensional space corresponding to the area around the current position of the vehicle (particularly in front of the vehicle in the direction of travel of the vehicle). Not only roads but also building, road signs, etc. may be modeled in the three-dimensional space, or only roads may be modeled in the three-dimensional space. Alternatively, the three-dimensional space may be a mere empty three-dimensional space in which roads are not modeled and there is only the ground. Alternatively, the three-dimensional space may be stored in advance in the map information DB  31  as three-dimensional map information, and the three-dimensional map information on the relevant area around the vehicle position may be read from the map information DB  31  in S 11 . The CPU  41  may generate a three-dimensional space based on the image captured by the front camera  19 . For example, the CPU  41  can generate a three-dimensional space by performing point cloud matching on the image captured by the front camera  19  and thus detecting a road and structures located around the road. 
     In S 11 , the CPU  41  also identifies the current position and orientation of the vehicle in the generated three-dimensional space based on the parameters detected by the current position detection unit  11 . In particular, the position of the front camera  19  mounted on the vehicle is identified as the current position of the vehicle, and the optical axis direction of the front camera  19  is identified as the orientation of the vehicle. The position of the front camera  19  is the position of the vehicle occupant, and the optical axis direction of the front camera  19  is the gaze direction of the vehicle occupant. In S 11 , the CPU  41  also identifies the position of the guide branch point located in front of the vehicle in the direction of travel of the vehicle in the generated three-dimensional space. 
     Next, in S 12 , the CPU  41  perceives (detects) features located around the vehicle by performing image processing on the image captured by the front camera  19 . Specifically, in the present embodiment, lane lines drawn on the road surface (including not only the road surface of the lane in which the vehicle travels but also the road surface of the lane(s) other than the lane in which the vehicle travels) and road edges (specifically, the edges of a roadway, and when there is a sidewalk, the boundary between the roadway and the sidewalk) are to be perceived (detected). As for the lane lines, it is desirable to detect the colors and types (solid line, dashed line, etc.) of the lane lines as well. As for the road edges, structures installed along the road edges, such as blocks, guardrails, and medians, are basically detected as the road edges. For roads with no such structures along the road edges, the edges of asphalt paving or the outermost lane lines may be detected as the road edges. 
     The lane line detection process in S 12  will be briefly described below. First, the CPU  41  performs brightness correction on the road surface and the lane lines based on the brightness difference in order to detect the lane lines in the image captured by the front camera  19 . Next, the CPU  41  performs processes such as a binarization process for separating the lane lines from the image, a geometric process for correcting distortion, and a smoothing process for removing noise from the image, and thus detects the boundary lines between the road surface and the lane lines. The presence and types of the lane lines are identified by the detected boundary lines. The color of each lane line can also be detected by extracting an image portion of the range where the lane lines have been detected, and performing color recognition (red, green, and blue (RGB) value detection) on the extracted image portion. 
     Next, the road edge detection process in S 12  will be briefly described. First, in order to detect the road edges in the image captured by the front camera  19 , the CPU  41  performs brightness correction on the road surface and the structures installed along the road edges (such as blocks, guardrails, and medians) based on the brightness difference. Next, the CPU  41  performs processes such as a binarization process for separating the structures from the image, a geometric process for correcting distortion, and a smoothing process for removing noise from the image, and thus detects the boundary lines between the road surface and the structures. The presence of the road edges is identified by the detected boundary lines. A pattern matching process using feature points and templates may be performed to detect the lane lines and the road edges. Since these image recognition processes are already known in the art, detailed description thereof will be omitted. Other vehicles etc. located on the road may also be detected in addition to the lane lines and the road edges. 
     Then, in S 13 , the CPU  41  identifies the “vehicle&#39;s lane of travel” that is the lane in which the vehicle is currently driving, based on the detection results of the feature perception process performed in S 12 . Specifically, the CPU  41  identifies the vehicle&#39;s lane of travel by the following process. In S 13 , the position of the “vehicle&#39;s lane of travel” in the three-dimensional space generated in S 11  is also identified. 
     Examples of the method for identifying the vehicle&#39;s lane of travel include a method using the types and number of lane lines and a method using the distances from the road edges and the lane widths. 
     [Identification of Vehicle&#39;s Lane of Travel (Pattern  1 )] 
     The method using the types and number of lane lines will be described. For example, it is herein assumed that the vehicle travels on an expressway with three lanes in each direction as shown in  FIGS.  6  to  8   . In this example, the CPU  41  first acquires the perception results of the road edge and lane lines located on the left side of the vehicle. As for the perception results of the lane lines, the CPU  41  also acquires the colors and types of the lane lines. For example, when a road edge  61  is detected, an edge line  62  that is a solid white line located next to the road edge  61  is detected, and one lane boundary line  63  that is a dashed or solid white line is detected between the edge line  62  and the vehicle, it can be identified that the vehicle is traveling in the second lane from the left as shown in  FIG.  6   . Similarly, when two lane boundary lines  63 ,  66  are detected between the edge line  62  and the vehicle, it can be identified that the vehicle is traveling in the third lane from the left as shown in  FIG.  7   . When no lane boundary line  63 ,  66  is detected between the edge line  62  and the vehicle, it can be identified that the vehicle is traveling in the leftmost lane as shown in  FIG.  8   . 
     The CPU  41  also acquires the perception results of the road edge and lane lines located on the right side of the vehicle in a manner similar to that described above. As for the perception results of the lane lines, the CPU  41  also acquires the colors and types of the lane lines. For example, when a road edge  64  is detected, an edge line  65  that is a solid white line located next to the road edge  64  is detected, and one lane boundary line  66  that is a dashed or solid white line is detected between the edge line  65  and the vehicle, it can be identified that the vehicle is traveling in the second lane from the right as shown in  FIG.  6   . Similarly, when two lane boundary lines  63 ,  66  are detected between the edge line  65  and the vehicle, it can be identified that the vehicle is traveling in the third lane from the right as shown in  FIG.  8   . When no lane boundary line  63 ,  66  is detected between the edge line  65  and the vehicle, it can be identified that the vehicle is traveling in the rightmost lane as shown in  FIG.  7   . 
     The CPU  41  identifies the vehicle&#39;s lane of travel by ultimately combining the following two positions of the vehicle&#39;s lane of travel identified as described above: the position of the vehicle&#39;s lane of travel identified with respect to the left edge of the road (number of lanes from the left edge of the road to the lane in which the vehicle is currently traveling), and the position of the vehicle&#39;s lane of travel identified with respect to the right edge of the road (number of lanes from the right edge of the road to the lane in which the vehicle is currently traveling). For example, in the example shown in  FIG.  6   , the vehicle&#39;s lane of travel is identified as the second lane from the left and the second lane from the right. In the example shown in  FIG.  7   , the vehicle&#39;s lane of travel is identified as the third lane from the left and the first lane from the right. In the example shown in  FIG.  8   , the vehicle&#39;s lane of travel is identified as the first lane from the left and the third lane from the right. 
     It is desirable to identify the vehicle&#39;s lane of travel by considering the map information in addition to the perception results of the road edges and lane lines. The link data  32  included in the map information stores, for each road, the number of lanes and whether there is any oncoming lane (whether the road is a two-way traffic section). With the image recognition by the front camera  19 , when a solid or dashed white line is detected near the center of a local road, it is difficult to determine whether this section line is a center line or a lane boundary line. However, this determination can be easily made by using the map information. As a result, even in a section in which there is an oncoming lane(s), the vehicle&#39;s lane of travel can be accurately identified by considering the presence of the oncoming lane(s). For example, when the vehicle is traveling on a road with two lanes in each direction without a median, namely a road with a total of four lanes without a median, and it is identified that the vehicle is traveling in the third lane from the right, it can be determined from the map information that the first and second lanes from the right are oncoming lanes. Therefore, it can be identified that the vehicle is traveling on the right lane of the road with two lanes in each direction. 
     [Identification of Vehicle&#39;s Lane of Travel (Pattern  2 )] 
     Next, the method using the distances from the road edges and the lane widths will be described. For example, as in the case of the method using the types and number of lane lines, it is herein assumed that the vehicle travels on an expressway with three lanes in each direction as shown in  FIGS.  6  to  8   . In this example, the CPU  41  first detects the lane lines on both sides of the vehicle (in the example shown in  FIG.  6   , the lane boundary lines  63 ,  66 ; in the example shown in  FIG.  7   , the lane boundary line  66  and the edge line  65 ; and in the example shown in  FIG.  8   , the edge line  62  and the lane boundary line  63 ), and identifies the width of the lane in which the vehicle is traveling based on the distance between the detected lane lines. The CPU  41  then calculates the distance from the road edge  61  or edge line  62  located on the left side of the vehicle to the vehicle in the lateral direction of the road, and calculates how many lanes the calculated distance is equivalent to. When the calculated distance from the road edge  61  or edge line  62  to the vehicle is equivalent to one lane, it can be identified that the vehicle is traveling in the second lane from the left as shown in  FIG.  6   . Similarly, when the calculated distance from the road edge  61  or edge line  62  to the vehicle is equivalent to two lanes, it can be identified that the vehicle is traveling in the third lane from the left as shown in  FIG.  7   . When the calculated distance from the road edge  61  or edge line  62  to the vehicle is less than one lane, it can be identified that the vehicle is traveling in the leftmost lane as shown in  FIG.  8   . 
     The CPU  41  also similarly calculates the distance from the road edge  64  or edge line  65  located on the right side of the vehicle to the vehicle. When the calculated distance from the road edge  64  or edge line  65  to the vehicle is equivalent to one lane, it can be identified that the vehicle is traveling in the second lane from the right as shown in  FIG.  6   . Similarly, when the calculated distance from the road edge  64  or edge line  65  to the vehicle is equivalent to two lanes, it can be identified that the vehicle is traveling in the third lane from the right as shown in  FIG.  8   . When the calculated distance from the road edge  64  or edge line  65  to the vehicle is less than one lane, it can be identified that the vehicle is traveling in the right lane as shown in  FIG.  7   . 
     The CPU  41  identifies the vehicle&#39;s lane of travel by ultimately combining the following two positions of the vehicle&#39;s lane of travel identified as described above: the position of the vehicle&#39;s lane of travel identified with respect to the left edge of the road (number of lanes from the left edge of the road to the lane in which the vehicle is currently traveling), and the position of the vehicle&#39;s lane of travel identified with respect to the right edge of the road (number of lanes from the right edge of the road to the lane in which the vehicle is currently traveling). For example, in the example shown in  FIG.  6   , the vehicle&#39;s lane of travel is identified as the second lane from the left and the second lane from the right. In the example shown in  FIG.  7   , the vehicle&#39;s lane of travel is identified as the third lane from the left and the first lane from the right. In the example shown in  FIG.  8   , the vehicle&#39;s lane of travel is identified as the first lane from the left and the third lane from the right. 
     It is desirable to identify the vehicle&#39;s lane of travel by considering the map information in addition to the perception results of the road edges and lane widths. The link data  32  included in the map information stores, for each road, the number of lanes and whether there is any oncoming lane (whether the road is a two-way traffic section). As a result, even in a section in which there is an oncoming lane(s), the vehicle&#39;s lane of travel can be accurately identified by considering the presence of the oncoming lane(s). For example, when the vehicle is traveling on a road with two lanes in each direction without a median, namely a road with a total of four lanes without a median, and it is identified that the vehicle is traveling in the third lane from the right, it can be determined from the map information that the first and second lanes from the right are oncoming lanes. Therefore, it can be identified that the vehicle is traveling on the right lane of the road with two lanes in each direction. 
     In addition to the lane lines and road edges, the detection results of other vehicles traveling on the road may be used to identify the vehicle&#39;s lane of travel. For example, even when lane lines cannot be clearly detected, a lane(s) can be estimated to be present based on the positions of other vehicles. 
     Subsequently, in S 14 , the CPU  41  calculates the confidence indicating how confident the identification result of the vehicle&#39;s lane of travel obtained in S 13  is. In particular, in the present embodiment, the CPU  41  calculates the following three confidences: (a) right-side confidence, (b) left-side confidence, and (c) overall confidence. The right-side confidence is the confidence when the position of the vehicle&#39;s lane of travel is identified with respect to the right edge of the road based on the detection results of the lane lines and road edge located on the right side of the vehicle in the direction of travel of the vehicle. The left-side confidence is the confidence when the position of the vehicle&#39;s lane of travel is identified with respect to the left edge of the road based on the detection results of the lane lines and road edge located on the left side of the vehicle in the direction of travel of the vehicle. The overall confidence is the overall confidence (total confidence) of the right-side confidence and the left-side confidence. 
     A method for calculating the right-side confidence, the left-side confidence, and the overall confidence will be described below using examples. 
     [Right-Side Confidence] 
     First, the confidence for each lane line estimated to be present on the right side of the vehicle&#39;s lane of travel identified in S 13  (hereinafter referred to as the “lane line confidence C”) is calculated by the following expression (1). For example, when the vehicle&#39;s lane of travel is identified as the middle lane of an expressway with three lanes in each direction as shown in  FIG.  6   , the lane boundary line  66  and the edge line  65  are supposed to be present on the right side of the vehicle&#39;s lane of travel. The lane line confidence C is calculated for each of these two lane lines. When the vehicle&#39;s lane of travel is identified as the rightmost lane of an expressway with three lanes in each direction as shown in  FIG.  7   , the edge line  65  is supposed to be present on the right side of the vehicle&#39;s lane of travel. The lane line confidence C is calculated for this single lane line. When the vehicle&#39;s lane of travel is identified as the leftmost lane of an expressway with three lanes in each direction as shown in  FIG.  8   , the lane boundary lines  63 ,  66  and the edge line  65  are supposed to be present on the right side of the vehicle&#39;s lane of travel. The lane line confidence C is calculated for each of these three lane lines. 
         C =(10× V 1+ V 2+ V 3+ V 4)/13   (1)
 
     V 1  represents whether the lane line for which the lane line confidence C is to be calculated was able to be detected in the image recognition process in S 12  (whether the presence of the lane line was able to be perceived). V 1  is set to “1” when the lane line was able to be detected, and is set to “0” when the lane line was not able to be detected. 
     V 2  represents whether the color of the lane line for which the lane line confidence C is to be calculated was able to be detected in the image recognition process in S 12 . V 2  is set to “1” when the color of the lane line was able to be detected, and is set to “0” when the color of the lane line was not able to be detected. Even when the color of the lane line was able to be detected, V 2  may be set to “0” when the detected color does not match the color estimated using map information etc. 
     V 3  represents whether the type (e.g., solid line or dashed line) of the lane line for which the lane line confidence C is to be calculated was able to be detected in the image recognition process in S 12 . V 3  is set to “1” when the type of the lane line was able to be detected, and is set to “0” when the type of the lane line was not able to be detected. Even when the type of the lane line was able to be detected, V 3  may be set to “0” when the detected type does not match the type estimated using map information etc. 
     V 4  represents whether the tilt of the lane line for which the lane line confidence C is to be calculated particularly with respect to the direction of travel of the road as detected in the image recognition process in S 12  is less than a threshold (e.g., 10 degrees). V 4  is set to “1” when the detected tilt is less than the threshold, and is set to “0” when the detected tilt is equal to or greater than the threshold. 
     Thereafter, the right-side confidence CR is calculated by adding all of the lane line confidences C calculated for each of the lane lines estimated to be present on the right side of the vehicle&#39;s lane of travel. The right-side confidence CR is calculated based more on the lane line confidence C of the lane line far away from the vehicle than on the lane line confidence C of the lane line near the vehicle. For example, when the vehicle&#39;s lane of travel is identified as the middle lane of an expressway with three lanes in each direction as shown in  FIG.  6   , the right-side confidence CR is calculated by the following expression (2), where C 1  represents the lane line confidence C calculated for the lane boundary line  66  that is closest to the vehicle&#39;s lane of travel, and C 2  represents the lane line confidence C calculated for the edge line  65  that is second closest to the vehicle&#39;s lane of travel. 
         CR =( C   1 +2× C   2 )/3   (2)
 
     When the vehicle&#39;s lane of travel is identified as the rightmost lane of an expressway with three lanes in each direction as shown in  FIG.  7   , the right-side confidence CR is calculated by the following expression (3), where C 1  represents the lane line confidence C calculated for the edge line  65  that is the only lane line located on the right side of the vehicle&#39;s lane of travel. 
       CR=C 1    (3)
 
     When the vehicle&#39;s lane of travel is identified as the leftmost lane of an expressway with three lanes in each direction as shown in  FIG.  8   , the right-side confidence CR is calculated by the following expression (4), where C 1  represents the lane line confidence C calculated for the lane boundary line  63  that is closest to the vehicle&#39;s lane of travel, C 2  represents the lane line confidence C calculated for the lane boundary line  66  that is second closest to the vehicle&#39;s lane of travel, and C 3  represents the lane line confidence C calculated for the edge line  65  that is third closest to the vehicle&#39;s lane of travel. 
         CR =( C   1 +2× C   2 +4× C   3 )/7   (4)
 
     The coefficients by which each lane line confidence C is multiplied in the above expressions (2) to (4) can be changed as appropriate. It is desirable to set the coefficients so that the lane line confidence C calculated for the lane line farther away from the vehicle&#39;s lane of travel is multiplied by a greater coefficient. 
     The right-side confidences CR thus calculated by the above expressions (2) to (4) have a value of 0 or more and 1 or less. The closer to 1 the calculated right-side confidence CR is, the higher the confidence of the position of the vehicle&#39;s lane of travel identified with respect to the right edge of the road is. 
     [Left-Side Confidence] 
     Next, the lane line confidence C for each lane line estimated to be present on the left side of the vehicle&#39;s lane of travel identified in S 13  is calculated by the above expression (1). For example, when the vehicle&#39;s lane of travel is identified as the middle lane of an expressway with three lanes in each direction as shown in  FIG.  6   , the edge line  62  and the lane boundary line  63  are supposed to be present on the left side of the vehicle&#39;s lane of travel. The lane line confidence C is calculated for each of these two lane lines. When the vehicle&#39;s lane of travel is identified as the rightmost lane of an expressway with three lanes in each direction as shown in  FIG.  7   , the edge line  62  and the lane boundary lines  63 ,  66  are supposed to be present on the left side of the vehicle&#39;s lane of travel. The lane line confidence C is calculated for each of these three lane lines. When the vehicle&#39;s lane of travel is identified as the leftmost lane of an expressway with three lanes in each direction as shown in  FIG.  8   , the edge line  62  is supposed to be present on the left side of the vehicle&#39;s lane of travel. The lane line confidence C is calculated for this single lane line. Since the method for calculating the lane line confidence C is similar to that described above for the right-side confidence, description thereof will be omitted. 
     Thereafter, the left-side confidence CL is calculated by adding all of the lane line confidences C calculated for each of the lane lines estimated to be present on the left side of the vehicle&#39;s lane of travel. The left-side confidence CL is calculated based more on the lane line confidence C of the lane line far away from the vehicle than on the lane line confidence C of the lane line near the vehicle. For example, when the vehicle&#39;s lane of travel is identified as the middle lane of an expressway with three lanes in each direction as shown in  FIG.  6   , the left-side confidence CL is calculated by the following expression (5), where C 1  represents the lane line confidence C calculated for the lane boundary line  63  that is closest to the vehicle&#39;s lane of travel, and C 2  represents the lane line confidence C calculated for the edge line  62  that is second closest to the vehicle&#39;s lane of travel. 
         CL =( C   1 +2× C   2 )/3   (5)
 
     When the vehicle&#39;s lane of travel is identified as the rightmost lane of an expressway with three lanes in each direction as shown in  FIG.  7   , the left-side confidence CL is calculated by the following expression (6), where C 1  represents the lane line confidence C calculated for the lane boundary line  66  that is closest to the vehicle&#39;s lane of travel, C 2  represents the lane line confidence C calculated for the lane boundary line  63  that is second closest to the vehicle&#39;s lane of travel, and C 3  represents the lane line confidence C calculated for the edge line  62  that is third closest to the vehicle&#39;s lane of travel. 
         CL =( C   1 +2× C   2 +4× C   3 )/7   (6)
 
     When the vehicle&#39;s lane of travel is identified as the leftmost lane of an expressway with three lanes in each direction as shown in  FIG.  8   , the left-side confidence CL is calculated by the following expression (7), where C 1  represents the lane line confidence C calculated for the edge line  62  that is the only lane line located on the left side of the vehicle&#39;s lane of travel. 
       CL=C 1    (7)
 
     The coefficients by which each lane line confidence C is multiplied in the above expressions (5) to (7) can be changed as appropriate. It is desirable to set the coefficients so that the lane line confidence C calculated for the lane line farther away from the vehicle&#39;s lane of travel is multiplied by a greater coefficient. 
     The left-side confidences CL thus calculated by the above expressions (5) to (7) have a value of 0 or more and 1 or less. The closer to 1 the calculated left-side confidence CL is, the higher the confidence of the position of the vehicle&#39;s lane of travel identified with respect to the left edge of the road is. 
     [Overall Confidence] 
     Finally, the overall confidence CT is calculated by adding the right-side confidence CR and left-side confidence CL calculated as described above. The overall confidence CT may be calculated by merely adding the right-side confidence CR and the left-side confidence CL, or may be calculated by giving a weight to either the right-side confidence CR or the left-side confidence CL. For example, the overall confidence CT is calculated by the following expression (8). 
         CT =( CR+CL )/2   (8)
 
     The overall confidence CT thus calculated by the above expression (8) has a value of 0 or more and 1 or less. The closer to 1 the calculated overall confidence CT is, the higher the total confidence of the position of the vehicle&#39;s lane of travel identified with respect to the right and left edges of the road is. 
     Next, in S 15 , the CPU  41  identifies the “recommended lane” that is a lane in which the vehicle is recommended to travel on the road on which the vehicle is currently traveling. Specifically, the CPU  41  identifies the recommended lane by the following process. In S 15 , the position of the “recommended lane” in the three-dimensional space generated in S 11  is also identified. 
     [Identification of Recommended Lane] 
     The CPU  41  identifies, as the recommended lane, the lane in which the vehicle needs to travel in order to pass through the guide branch point ahead of the vehicle in the exit direction (guide direction) along the guide route, based on the map information and the guide route. More specifically, the CPU  41  acquires the lane that allows the vehicle to pass through the guide branch point in the exit direction of the vehicle as the recommended lane. The link data  32  included in the map information stores the direction of travel of each lane, and the branch point data  34  included in the map information stores the shapes of branch points. The CPU  41  identifies the recommended lane using these pieces of information. For example, as shown in  FIG.  9   , when the exit direction (guide direction) at a guide branch point  70  ahead of the vehicle traveling on an expressway is a slightly leftward direction toward an exit road, the recommended lane is the leftmost one of the three lanes of the road on which the vehicle is traveling. As shown in  FIG.  10   , when the exit direction (guide direction) at a guide branch point  70  ahead of the vehicle traveling on a local road is the right direction, the recommended lane is the rightmost one of the four lanes of the road on which the vehicle is traveling, namely the right-turn lane. The number of recommended lanes is not limited to one, and may be two or more. 
     Subsequently, in S 16 , the CPU  41  determines whether the overall confidence CT calculated in S 14  is equal to or higher than a first threshold. The first threshold is, for example, 0.8, although it can be set as appropriate. 
     When the CPU  41  determines that the overall confidence CT calculated in S 14  is equal to or higher than the first threshold (S 16 : YES), the CPU  41  considers the vehicle&#39;s lane of travel identified in S 13  to be sufficiently confident, and the routine proceeds to S 17 . On the other hand, when the CPU  41  determines that the overall confidence CT calculated in S 14  is less than the first threshold (S 16 : NO), the routine proceeds to S 20 . 
     In S 17 , the CPU  41  generates a first guide object  71  to be displayed. When the confidence of the identification result of the lane in which the vehicle is currently traveling is high (when the identification result of the lane is confident), the first guide object is displayed in the first or second display mode having high guiding capability to guide the vehicle to the recommended lane. As shown in  FIG.  3   , in the first display mode, a guide image that provides guidance by distinguishing the recommended lane from the other lanes is displayed as the first guide object. In the second display mode, a guide image that provides guidance by distinguishing the recommended lane from the other lanes and that encourages to move to the recommended lane is displayed as the first guide object. When the confidence is high, the display may be switched between the first display mode and the second display mode based on the distance from the vehicle to the guide branch point or may be switched based on the positional relationship between the vehicle&#39;s lane of travel and the recommended lane, or the display may be given only in a predetermined one of the display modes. An example in which the first guide object is displayed in the first display mode will be particularly described below. 
     As shown in  FIG.  11   , the first guide object  71  has a rectangular shape, the lateral length of the first guide object  71  is set to the width of the recommended lane, and the longitudinal length of the first guide object  71  is set to, for example, 90 m. The distance to the guide branch point may be drawn inside the first guide object  71 . It is herein assumed that the first guide object  71  is a two-dimensional polygon and basically has no thickness. However, the first guide object  71  may be a three-dimensional polygon with a thickness. The shape of the first guide object  71  generated in S 17  can be changed as appropriate. The first guide object  71  may have a shape other than a rectangle as long as the recommended lane can be distinguished from the other lanes. 
     In S 17 , the CPU  41  places the generated first guide object  71  in the three-dimensional space generated in S 11 . As shown in  FIG.  11   , the first guide object  71  is placed on the road surface of the recommended lane in the three-dimensional space, and is placed in the range form the current position of the vehicle to 90 m ahead.  FIG.  11    shows an example in which the recommended lane is different from the vehicle&#39;s lane of travel. When the recommended lane is the same as the vehicle&#39;s lane of travel, the first guide object is placed in the vehicle&#39;s lane of travel. The first guide object is placed at the same height as the road surface. The routine then proceeds to S 18 . 
     In S 18 , the CPU  41  stores, as the size and shape of the guide object to be displayed on the liquid crystal display  15 , the size and shape of the first guide object  71  that is visible in the three-dimensional space where the first guide object  71  is placed in S 17  when seen in the direction of travel of the vehicle from the height of the front camera  19  at the current position of the vehicle. The size and shape of the guide object that are stored in S 18  are the size and shape of the first guide object  71  that is visible when the first guide object  71  placed in the three-dimensional space is seen from the current point of view of the vehicle (more precisely, the front camera  19 ). 
     Thereafter, in S 19 , the CPU  41  estimates the position of the recommended lane in the landscape  52  displayed on the liquid crystal display  15 , based on the current position of the vehicle and the position of the guide branch point in the three-dimensional space generated in S 11  and the positions of the recommended lane and vehicle&#39;s lane of travel identified in S 13  and S 15 . The CPU  41  then determines the range from the current position of the vehicle to 90 m ahead on the road surface of the estimated recommended lane to be the position where the first guide object  71  is to be displayed on the liquid crystal display  15 . When the recommended lane is the same as the vehicle&#39;s lane of travel, the position where the first guide object  71  is to be displayed is on the road surface of the vehicle&#39;s lane of travel. 
     Subsequently, the routine proceeds to S 5 . In S 5 , the CPU  41  generates an image of the first guide object  71  with the size and shape determined in S 18 , transmits a control signal to the liquid crystal display  15 , and draws the generated image of the first guide object  71  at the position (in the range) determined in S 19  on the liquid crystal display  15 . [0069] In S 20  that is performed when the CPU  41  determines that the overall confidence CT is less than the first threshold, the CPU  41  determines whether the confidence corresponding to the exit direction of the vehicle at the guide branch point out of the right-side confidence CR and left-side confidence CL calculated in S 14  is equal to or higher than a second threshold. The second threshold is, for example, 0.8, although it can be set as appropriate. For example, the confidence corresponding to the exit direction of the vehicle is the right-side confidence CR when the vehicle exits to the right at the guide branch point, and is the left-side confidence CL when the vehicle exits to the left at the guide branch point. As shown in  FIGS.  9  and  10   , the recommended lane is basically present in the exit direction at the guide branch point. Therefore, for example, in the case where the exit direction at the guide branch point is the right direction, at least the positional relationship between the vehicle&#39;s lane of travel and the recommended lane is confident when the right-side confidence CR, namely the confidence of the position of the vehicle&#39;s lane of travel identified with respect to the right edge of the road, is high. That is, the position of the recommended lane in the landscape can be accurately estimated when superimposing the guide object on the actual view. On the other hand, in the case where the exit direction at the guide branch point is the left direction, at least the positional relationship between the vehicle&#39;s lane of travel and the recommended lane is confident when the left-side confidence CL, namely the confidence of the position of the vehicle&#39;s lane of travel identified with respect to the left edge of the road, is high. That is, the position of the recommended lane in the landscape can be accurately estimated when superimposing the guide object on the actual view. 
     When the CPU  41  determines that the confidence corresponding to the exit direction of the vehicle at the guide branch point out of the right-side confidence CR and left-side confidence CL calculated in S 14  is equal to or higher than the second threshold (S 20 : YES), the CPU  41  considers at least the positional relationship between the vehicle&#39;s lane of travel identified in S 13  and the recommended lane to be confident, and the routine proceeds to S 17 . In S 17 , as described above, the first guide object is displayed in the first or second display mode having high guiding capability to guide the vehicle to the recommended lane. 
     On the other hand, when the CPU  41  determines that the confidence corresponding to the exit direction of the vehicle at the guide branch point out of the right-side confidence CR and left-side confidence CL calculated in S 14  is less than the second threshold (S 20 : NO), the CPU  41  considers the vehicle&#39;s lane of travel identified in S 13  to be not confident, and the routine proceeds to S 21 . 
     In S 21 , the CPU  41  generates first guide objects  72  to  74  to be displayed. When the confidence of the identification result of the lane in which the vehicle is currently traveling is low (when the identification result of the lane is not confident), the first guide objects are displayed in the third display mode having low guiding capability to guide the vehicle to the recommended lane. As shown in  FIG.  3   , in the third display mode, a guide image providing guidance on the direction toward the recommended lane (that is also the exit direction at the guide branch point) is displayed as the first guide object. The direction toward the recommended lane is not the direction relative to the current position of the vehicle, but the direction in which the recommended lane is located on the road. Therefore, for example, when the leftmost lane is the recommended lane as shown in  FIG.  9   , a guide image showing the left direction is displayed as the first guide object even if the vehicle is traveling in the recommended lane. 
     The first guide objects  72  to  74  are arrows indicating the direction toward the recommended lane (that is also the exit direction at the guide branch point). Particularly, the CPU  41  generates three arrows having an isosceles triangular shape, as shown in  FIGS.  12  and  13   . When the recommended lane is located to the right (that is, the exit direction at the guide branch point is the right direction), the first guide objects  72  to  74  are arrows indicating the right direction. When the recommended lane is located to the left (that is, the exit direction at the guide branch point is to the left), the first guide objects  72  to  74  are arrows indicating the left direction. It is herein assumed that the first guide objects  72  to  74  are two-dimensional polygons and basically have no thickness. However, the first guide objects  72  to  74  may be three-dimensional polygons with a thickness. The shape of the first guide objects  72  to  74  generated in S 21  can be changed as appropriate. The first guide objects  72  to  74  may have a shape other than an arrow as long as their shape can indicate the direction toward the recommended lane. The number of arrows need not necessarily be three, and may be only one. 
     In S 21 , the CPU  41  places the generated first guide objects  72  to  74  in the three-dimensional space generated in S 11 . The first guide objects  72  to  74  are placed at the following positions in the three-dimensional space. As shown in  FIG.  12   , the first guide objects  72  to  74  that are three arrows are placed at predetermined intervals at the position a predetermined distance ahead (e.g., 10 m ahead) of the current position of the vehicle above the road on which the vehicle is currently traveling in the three-dimensional space. Particularly, the three first guide objects  72  to  74  are placed in such a manner that the distance from the current position of the vehicle to the first guide object  72  located closest to the vehicle out of the first guide objects  72  to  74  is equal to the fixed predetermined distance (e.g., 10 m). The first guide objects  72  to  74  have an isosceles triangular shape and are placed parallel to a direction crossing the direction of travel of the vehicle (that is, such that the front sides of the first guide objects  72  to  74  face the vehicle). Each of the first guide objects  72  to  74  indicates the direction toward the recommended lane by the direction of the apex with respect to the base. When the recommended lane is located on the left side of the road, the first guide objects  72  to  74  are in the shape of an isosceles triangle with its apex pointing to the left, as shown in  FIG.  12   . The intervals of the three first guide objects  72  to  74  are, for example, 10 m. However, the intervals can be changed as appropriate. The three first guide objects  72  to  74  are not arranged parallel to the course of the vehicle (that is, the direction of travel of the road), but are arranged gradually away from the course of the vehicle such that the closer to the guide branch point  70  the arrow is to be seen, the more in the direction toward the recommended lane (the more to the left in  FIG.  12   ) the arrow is placed with respect to the course of the vehicle. The first guide objects  72  to  74  are also placed on the condition that two or more of the first guide objects  72  to  74  do not overlap each other by a predetermined percentage (e.g., 20%) or more when seen from the vehicle. The first guide objects  72  to  74  may be arranged parallel to the direction of travel. Regarding the vertical positions of the first guide objects  72  to  74 , as shown in  FIG.  13   , the first guide objects  72  to  74  are placed such that their lower ends are at a predetermined distance (e.g., 1 m) away from the road surface. 
     In S 22 , the CPU  41  stores, as the size and shape of the guide objects to be displayed on the liquid crystal display  15 , the size and shape of the first guide objects  72  to  74  that are visible in the three-dimensional space where the first guide objects  72  to  74  are placed in S 21  when seen in the direction of travel of the vehicle from the height of the front camera  19  at the current position of the vehicle. The size and shape of the guide objects that are stored in S 22  are the size and shape of the first guide objects  72  to  74  that are visible when the first guide objects  72  to  74  placed in the three-dimensional space are seen from the current point of view of the vehicle (more precisely, the front camera  19 ). 
     Thereafter, in S 23 , the CPU  41  estimates the future course of the vehicle in the landscape  52  displayed on the liquid crystal display  15 , based on the current position of the vehicle and the position of the guide branch point in the three-dimensional space generated in S 11 . The CPU  41  then determines the range along the estimated course to be the position where the first guide objects  72  to  74  are to be displayed on the liquid crystal display  15 . 
     Subsequently, the routine proceeds to S 5 . In S 5 , the CPU  41  generates an image of the first guide objects  72  to  74  with the size and shape determined in S 22 , transmits a control signal to the liquid crystal display  15 , and draws the generated image of the first guide objects  72  to  74  at the position (in the range) determined in S 23  on the liquid crystal display  15 . 
     As a result of the above process, when the distance from the vehicle to the guide branch point is less than the guidance start distance and is equal to or greater than the exit direction guidance start distance, the travel guidance screen  51  that is displayed on the liquid crystal display  15  as the vehicle travels varies depending on the confidence of the identification result of the lane in which the vehicle is currently traveling, as shown in  FIG.  14  or  15   . 
     For example, when the confidence of the identification result of the lane in which the vehicle is currently traveling is high (when the identification result of the lane is confident), such a travel guidance screen  51  as shown in  FIG.  14    is displayed on the liquid crystal display  15 . 
     Specifically, the “image  53  of the first guide object that distinguishes the recommended lane from the other lanes” is displayed. As shown in  FIG.  14   , the “image  53  of the first guide object that distinguishes the recommended lane from the other lanes” is the image  53  of the first guide object displayed superimposed on the road surface of the recommended lane  54  (S 17  to S 19 ). This allows the vehicle occupant to become clearly aware of the presence and position of the recommended lane  54 . By clearly identifying which lane is the recommended lane  54  in the landscape  52 , guidance with high guiding capability to guide the vehicle to the recommended lane can be provided. 
     On the other hand, when the confidence of the identification result of the lane in which the vehicle is currently traveling is low (when the identification result of the lane is not confident), such a travel guidance screen  51  as shown in  FIG.  15    is displayed on the liquid crystal display  15 . 
     Specifically, the “image  53  of the first guide object indicating the direction toward the recommended lane” is displayed. As shown in  FIG.  15   , the “image  53  of the first guide object indicating the direction toward the recommended lane” is the image  53  of the first guide object that is displayed superimposed above the road surface ahead in the direction of travel of the vehicle rather than being displayed superimposed on the road surface of the recommended lane  54  (S 21  to S 23 ). Rather than clearly indicating the position of the recommended lane  54  to the occupant, only the direction in which the recommended lane is present is indicated. This provides guidance with low guiding capability to guide the vehicle to the recommended lane. The possibility that wrong guidance is provided can be reduced or prevented even in a situation where the position of the recommended lane in the landscape  52  cannot be accurately identified. 
     As described above, whether the travel guidance screen  51  of  FIG.  14    or the travel guidance screen  51  of  FIG.  15    is displayed when the distance from the vehicle to the guide branch point is less than the guidance start distance and is equal to or greater than the exit direction guidance start distance depends on the current confidence of the identification result of the vehicle&#39;s lane of travel. Accordingly, for example, the display is switched to the travel guidance screen  51  of  FIG.  15    when the vehicle enters a section with faint lane lines while the travel guidance screen  51  of  FIG.  14    is being displayed on the liquid crystal display  15 , and the confidence of the identification result of the vehicle&#39;s lane of travel decreases. Similarly, the display is switched to the travel guidance screen  51  of  FIG.  14    when the confidence of the identification result of the vehicle&#39;s lane of travel increases while the travel guidance screen  51  of  FIG.  15    is being displayed on the liquid crystal display  15 . However, the display need not necessarily be switched even when the confidence of the identification result of the vehicle&#39;s lane of travel changes during traveling. 
     When the distance from the vehicle to the guide branch point subsequently becomes less than the exit direction guidance start distance (300 m for an expressway), the image  57  of the second guide object, namely arrows indicating the exit direction at the guide branch point, will be newly displayed instead of the image  53  of the first object (see  FIG.  18   ), as will be described later. 
     Next, a sub-process of the second guide object display position determination process that is performed in S 6  will be described with reference to  FIG.  16   .  FIG.  16    is a flowchart of a sub-process program of the second guide object display position determination process. 
     First, in S 31 , the CPU  41  acquires the distance from the current position of the vehicle to the coordinates X of the next guide point along the guide route. For example, as shown in  FIG.  17   , the vertex of a gore area located at the branch on an expressway is the coordinates X of the guide branch point. 
     Next, in S 32 , the CPU  41  determines whether the distance to the coordinates X of the guide branch point acquired in S 31  is less than a predetermined threshold. The timing at which the distance to the coordinates X of the guide branch point becomes equal to the threshold is the timing at which at least a part of the image of the guide object displayed on the liquid crystal display  15  at a fixed relative position with respect to the vehicle as in S 33  described later (in the first mode) is superimposed on the coordinates X of the guide branch point, that is, the timing at which at least part of the guide object is seen superimposed on the guide branch point by the vehicle occupant. This will be described in detail later. 
     When the CPU  41  determines that the distance to the coordinates X of the guide branch point acquired in S 31  is less than the threshold (S 32 : YES), the routine proceeds to S 34 . On the other hand, when the CPU  41  determines that the distance to the coordinates X of the guide branch point acquired in S 31  is equal to or greater than the threshold (S 32 : NO), the routine proceeds to S 33 . 
     In S 33 , the CPU  41  sets the “position where the second guide object is to be superimposed on the landscape” to the position where the second guide object displayed at a fixed position relative to the vehicle is seen superimposed by the vehicle occupant (i.e., to the position for display in the first mode). Specifically, the CPU  41  sets the position where the second guide object is to be superimposed (placed) to the position a predetermined distance ahead (e.g., 10 m ahead) of the current position of the vehicle. 
     In S 34 , the CPU  41  sets the “position where the second guide object is to be superimposed on the landscape” to the position where the second guide object displayed at a fixed position relative to the guide branch point is seen superimposed by the vehicle occupant (i.e., to the position for display in the second mode). Specifically, the CPU  41  sets the position where the second guide object is to be superimposed on the landscape to the position where at least a part of the guide object is seen superimposed on the guide branch point (including the area around the guide branch point) by the vehicle occupant. 
     Thereafter, in S 35 , the CPU  41  generates a three-dimensional space corresponding to the area around the current position of the vehicle (particularly in front of the vehicle in the direction of travel of the vehicle). The CPU  41  also identifies the current position and orientation of the vehicle and the position of the guide branch point in the generated three-dimensional space. Since S 35  is similar to S 11 , detailed description thereof will be omitted. 
     Subsequently, in S 36 , the CPU  41  generates second guide objects  81  to  83  to be displayed on the liquid crystal display  15 . The shape of the second guide objects  81  to  83  is the same as that of the first guide objects  72  to  74  displayed in the third display mode described above. That is, the second guide objects  81  to  83  are arrows indicating the exit direction at the guide branch point located ahead in the direction of travel of the vehicle. The CPU  41  generates three arrows having an isosceles triangular shape as shown in  FIGS.  12  and  13   . When the guide route is a route with a right turn at the guide branch point located ahead in the direction of travel, the CPU  41  generates arrows indicating the right direction. When the guide route is a route with a left turn at the guide branch point located ahead in the direction of travel, the CPU  41  generates arrows indicating the left direction. It is herein assumed that the second guide objects  81  to  83  are two-dimensional polygons and basically have no thickness. However, the second guide objects  81  to  83  may be three-dimensional polygons with a thickness. The shape of the second guide objects  81  to  83  generated in S 36  can be changed as appropriate. The second guide objects  81  to  83  may have a shape other than an arrow as long as their shape can indicate the exit direction at the guide branch point. The number of arrows need not necessarily be three, and may be only one. 
     In S 36 , the CPU  41  places the generated second guide objects  81  to  83  in the three-dimensional space generated in S 35 . The positions where the second guide objects  81  to  83  are to be placed in the three-dimensional space are determined based on the “position where the second guide object is to be superimposed in the landscape” set in S 33  or S 34 . 
     For example, when the “position where the second guide object is to be superimposed on the landscape” is set to the position a predetermined distance ahead (e.g., 10 m ahead) of the current position of the vehicle in S 33 , the second guide objects  81  to  83  are placed at the same positions as the first guide objects  72  to  74  displayed in the third display mode ( FIG.  12   ). That is, the second guide objects  81  to  83  that are three arrows are placed at predetermined intervals at the position the predetermined distance ahead of the current position of the vehicle above the road on which the vehicle is currently traveling in the three-dimensional space. The three second guide objects  81  to  83  are placed at positions along the future course of the vehicle. Since S 36  is similar to that in S 21 , detailed description thereof will be omitted. 
     When the “position where the second guide object is to be superimposed in the landscape” is set to the position where at least a part of the second guide object is seen superimposed on the guide branch point in S 34 , the second guide objects  81  to  83  that three arrows are placed at predetermined intervals at the position of the guide branch point above the road on which the vehicle is currently traveling in the three-dimensional space as shown in  FIG.  17   . The three second guide objects  81  to  83  are placed at positions along the future course of the vehicle.  FIG.  17    shows an arrangement example of the second guide objects when a set guide route is a route exiting in the left direction at the guide branch point  70  on an expressway. Specifically, as shown in  FIG.  17   , the three second guide objects  81  to  83  are arranged at regular intervals along the course of the vehicle. Particularly, the three second guide objects  81  to  83  are placed in such a manner that the left end (right end when the arrows indicate the right direction) of the second guide object  83  located farthest away from the vehicle in the direction of travel out of the three second guide objects  81  to  83  matches (matches in the horizontal direction) the coordinates X of the guide branch point. The coordinates X of the guide branch point are identified from the map information in the navigation device  1 . However, the coordinates X of the guide branch point may be identified by performing image recognition on the image captured by the front camera  19 . In that case, the coordinates X of the guide branch point are set to the vertex of the gore area located at the branch. The intervals of the three second guide objects  81  to  83  are, for example, 10 m. However, the intervals can be changed as appropriate. The three second guide objects  81  to  83  are not arranged parallel to the course of the vehicle, but are arranged gradually away from the course of the vehicle such that the closer to the guide branch point  70  the arrow is to be seen, the more in the direction of travel at the guide branch point  70  (the more to the left in  FIG.  17   ) the arrow is placed with respect to the course of the vehicle. The second guide objects  81  to  83  are also placed on the condition that two or more of the second guide objects  81  to  83  do not overlap each other by a predetermined percentage (e.g., 20%) or more when seen from the vehicle. The second guide objects  81  to  83  may be arranged parallel to the direction of travel. Regarding the vertical positions of the second guide objects  81  to  83 , the second guide objects  81  to  83  are placed such that their lower ends are at a predetermined distance (e.g., 1 m) away from the road surface as shown in  FIG.  13   . 
     Thereafter, in S 37 , the CPU  41  stores, as the size and shape of the guide objects to be displayed on the liquid crystal display  15 , the size and shape of the second guide objects  81  to  83  that are visible in the three-dimensional space where the second guide objects  81  to  83  are placed in S 36  when seen in the direction of travel of the vehicle from the height of the front camera  19  at the current position of the vehicle. The size and shape of the guide objects that are stored in S 37  are the size and shape of the second guide objects  81  to  83  that are visible when the second guide objects  81  to  83  placed in the three-dimensional space are seen from the current point of view of the vehicle (more precisely, the front camera  19 ). 
     Thereafter, in S 38 , the CPU  41  estimates the future course of the vehicle in the landscape  52  displayed on the liquid crystal display  15 , based on the current position of the vehicle and the position of the guide branch point in the three-dimensional space generated in S 35 . The CPU  41  then determines the range along the estimated course to be the position where the second guide objects  81  to  83  are to be displayed on the liquid crystal display  15 . 
     Subsequently, the routine proceeds to S 7 . In S 7 , the CPU  41  generates an image of the second guide objects  81  to  83  with the size and shape determined in S 37 , transmits a control signal to the liquid crystal display  15 , and draws the generated image of the second guide objects  81  to  83  at the position (in the range) determined in S 38  on the liquid crystal display  15 . 
     As a result, such a travel guidance screen  51  as shown in  FIG.  18    is displayed on the liquid crystal display  15  as the vehicle travels. First, as soon as the distance from the vehicle to the guide branch point becomes less than the exit direction guidance start distance (e.g., 300 m), display of the image  53  of the first guide object shown in  FIGS.  14  and  15    is stopped, and instead, the image  57  of the second guide object is displayed superimposed on the landscape  52  ahead in the direction of travel of the vehicle as captured by the front camera  19  in the first mode. The position where the image  57  of the second guide object is first superimposed is a position relatively fixed with respect to the current position of the vehicle and is, for example,  10  m ahead of the vehicle. In the first mode, the image  57  of the second guide object displayed superimposed at a fixed relative position with respect to the vehicle is seen by the vehicle occupant. The image  57  of the second guide object is displayed superimposed at a relatively fixed position with respect to the current position of the vehicle for a while after that. Since the relative position with respect to the vehicle is fixed, the display size of the image  57  of the second guide object image is also fixed. 
     Thereafter, as the vehicle approaches the guide branch point and the image  57  of the second guide object displayed superimposed at the relatively fixed position with respect to the current position of the vehicle is superimposed (reaches) the guide branch point (that is, when the CPU  41  determines YES for the first time in S 32 ), the display is switched from the first mode to the second mode. The image  57  of the second guide object is thus displayed superimposed at a fixed relative position with respect to the guide branch point in the landscape  52 . That is, the image  57  of the second guide object is fixedly displayed at a position superimposed on the guide branch point. The switching from the first mode to the second mode is not performed in order to change the guide object to be displayed. The guide object to be displayed is the same before and after the switching. That is, only the display mode (mode that is seen by the vehicle occupant) is switched from the first mode to the second mode, and the object to be displayed does not change. In the second mode, the image  57  of the second guide object displayed superimposed at a fixed relative position with respect to the guide branch point is seen by the vehicle occupant. Thereafter, as the vehicle approaches the guide branch point, the image  57  of the second guide object gradually becomes larger. The transmittance of the image  57  of the second guide object also gradually increases, so that the image  57  of the second guide object disappears from the liquid crystal display  15  when the vehicle passes through the guide branch point (S 9 ). 
     As described in detail above, with the navigation device  1  and the computer program that is executed by the navigation device  1  according to the first embodiment, the recommended lane in which the vehicle is currently traveling is acquired (S 15 ), the lane in which the vehicle is currently traveling on the road on which the vehicle is currently traveling is identified (S 13 ), the confidence indicating how confident the identification result of the specified lane of travel is acquired (S 14 ), and the guide object providing guidance on the recommended lane is displayed in a display mode according to the confidence (S 5 ). This allows accurate guidance to be provided when the confidence of the lane of travel is high, and reduces or eliminates the possibility that a disadvantage may be caused to the vehicle occupant even when the confidence of the lane of travel is low. 
     As the confidence increases, the guide object is displayed in the display mode having higher guiding capability to guide the vehicle to the recommended lane. Therefore, guidance capable of accurately guiding the vehicle to the recommended lane is provided when the confidence of the lane of travel is high. Moreover, the possibility that a disadvantage may be caused to the vehicle occupant can be reduced or eliminated even when the confidence of the lane of travel is low. 
     When the confidence is lower than the threshold, an image indicating the direction toward the recommended lane is displayed as a guide object. When the confidence is higher than the threshold, an image distinguishing the recommended lane from the other lanes is displayed as a guide object. Therefore, when the confidence of the lane of travel is high, the guide object allows the vehicle occupant to become accurately aware of the recommended lane. When the confidence is low, the recommended lane is intentionally not distinguished from the other lanes to reduce or eliminate the possibility of giving wrong guidance. 
     An image superimposed on the road surface of the recommended lane is displayed as the image distinguishing the recommended lane from the other lanes. Therefore, when the confidence of the lane of travel is high, the vehicle occupant can be accurately aware of the recommended lane by the position where the image is superimposed. 
     The lane lines around the vehicle and the edges of the road on which the vehicle is current traveling are detected based on the captured image of the area around the vehicle, the number of lanes between each road edge and the lane in which the vehicle is currently traveling is estimated based on the detection results of the lane lines and road edges, and the lane of travel is identified based on the estimation results (S 12 , S 13 ). Therefore, the lane of travel can be accurately identified based on the detection results of the lane lines and road edges. 
     The confidence includes: the right-side confidence that is the confidence when the position of the lane of travel with respect to the right edge of the road is identified based on the detection results of the lane lines and road edge located on the right side of the vehicle in the direction of travel; and the left-side confidence that is the confidence when the position of the lane of travel with respect to the left edge of the road is identified based on the detection results of the lane lines and road edge located on the left side of the vehicle in the direction of travel. The guide object is displayed in the display mode according to the overall confidence calculated based on the right-side confidence and the left-side confidence. Therefore, the total confidence indicating whether the identification result of the lane of travel is confident regardless of whether the lane of travel is on the right side or left side of the road can be calculated based on the confidences of the lane of travel with respect to the right and left road edges. As a result, appropriate guidance can be provided according to the total confidence. 
     When the guide branch point is present within a predetermined guidance start distance ahead in the direction of travel of the vehicle, the lane corresponding to the exit direction of the vehicle at the guide branch point is acquired as a recommended lane (S 15 ). The confidence includes: the right-side confidence that is the confidence when the position of the lane of travel with respect to the right edge of the road is identified based on the detection results of the lane lines and road edge located on the right side of the vehicle in the direction of travel; and the left-side confidence that is the confidence when the position of the lane of travel with respect to the left edge of the road is identified based on the detection results of the lane lines and road edge located on the left side of the vehicle in the direction of travel. The guide object is displayed in the display mode according to the confidence corresponding to the exit direction of the vehicle at the guide branch point. Therefore, even when the identification result of the position of the lane of travel is not confident enough, accurate guidance can be provided when at least the positional relationship between the lane of travel and the recommended lane is confident. 
     The right-side confidence is calculated based on at least one of the detection results obtained by detecting the lane lines on the right side of the vehicle in the direction of travel by image recognition of the captured image of the area around the vehicle, namely based on at least one of the following: whether any lane lines have been detected, the color of the detected lane lines, the type of the detected lane lines, and the tilt of the detected lane lines with respect to the direction of travel of the road. The left-side confidence is calculated based on at least one of the detection results obtained by detecting the lane lines on the left side of the vehicle in the direction of travel by image recognition of the captured image of the area around the vehicle, namely based on at least one of the following: whether any lane lines have been detected, the color of the detected lane lines, the type of the detected lane lines, and the tilt of the detected lane lines with respect to the direction of travel of the road. Therefore, the confidence based on the right and left road edges can be accurately calculated. 
     The right-side confidence and the left-side confidence are calculated based more on the detection results of the lane lines far away from the vehicle than on the detection results of the lane lines near the vehicle. Therefore, the confidence is calculated based on determination as to whether an object that is difficult to perceive has been able to be perceived rather than an object that is easy to perceive. The confidence can thus be more accurately calculated. 
     Second Embodiment 
     Next, a superimposed image display device according to a second embodiment will be described with reference to  FIGS.  19  and  20   . In the following description, the same signs as those of the configurations of the superimposed image display device according to the first embodiment shown in  FIGS.  1  to  18    represent the portions that are the same as or correspond to the configurations of the superimposed image display device according to the first embodiment. 
     The schematic configuration of the superimposed image display device according to the second embodiment is substantially the same as that of the superimposed image display device according to the first embodiment. Various control processes are substantially the same as those of the superimposed image display device according to the first embodiment. 
     The superimposed image display device according to the first embodiment is different from the superimposed image display device according to the second embodiment in the following point. The superimposed image display device according to the first embodiment displays a guide object superimposed on the landscape around the vehicle by displaying an image captured by the front camera  19  on the liquid crystal display  15  of the navigation device  1  and further displaying the guide object on the liquid crystal display  15 . However, the superimposed image display device according to the second embodiment uses a head-up display system as a unit for displaying an image superimposed on the landscape around the vehicle. 
     Hereinafter, a schematic configuration of the superimposed image display device according to the second embodiment will be described with reference to  FIG.  19   .  FIG.  19    shows a schematic configuration of a superimposed image display device  101  according to the second embodiment. 
     As shown in  FIG.  19   , the superimposed image display device  101  basically includes a navigation device  103  mounted on a vehicle  102 , and a front display  104  mounted on the vehicle  102  and connected to the navigation device  103 . The front display  104  functions as a head-up display together with a windshield  105  of the vehicle  102 , and serves as an information providing unit that provides various kinds of information to an occupant  106  of the vehicle  102 . 
     The front display  104  is a liquid crystal display installed inside a dashboard  107  of the vehicle  102  and having a function to display an image on an image display surface on the front side of the liquid crystal display. For example, a cold cathode fluorescent lamp (CCFL) or a white light-emitting diode (LED) is used as a backlight. The front display  104  may be a combination of an organic electroluminescent (EL) display or a liquid crystal projector, instead of the liquid crystal display. 
     The front display  104  functions as a head-up display together with the windshield  105  of the vehicle  102 . The front display  104  is configured to reflect an image output from the front display  104  on the windshield  105  in front of the driver&#39;s seat so that the occupant  106  of the vehicle  102  can see the image. A guide object is displayed on the front display  104 , as necessary. In the second embodiment that will be described below, as in the first embodiment, the guide object is an arrow indicating the exit direction at the guide branch point along the guide route, a guide image indicating the position and direction of the recommended lane in which the vehicle is recommended to travel on the road on which the vehicle is currently traveling in order for the vehicle to pass through the guide branch point along the guide route, and a guide image encouraging the vehicle occupant to move to the recommended lane. 
     When the occupant  106  sees the image displayed on the front display  104  using reflection on the windshield  105 , the occupant  106  sees the image displayed on the front display  104  as a virtual image  110  at a distant position ahead of the windshield  105  rather than at the position of the windshield  105 . The virtual image  110  is displayed superimposed on the surrounding environment (landscape, actual view) ahead of the vehicle. For example, the virtual image  110  can be displayed superimposed on any desired object located ahead of the vehicle (road surface, building, an object against which the vehicle occupant is to be warned or alerted). 
     The position where the virtual image  110  is generated, more specifically, the distance L from the occupant  106  to the virtual image  110  (hereinafter referred to as the “imaging distance L”), is determined by the position of the front display  104 . For example, the imaging distance L is determined by the distance along the optical path from the position where the image is displayed on the front display  104  to the windshield  105  (optical path length). For example, the optical path length is set so that the imaging distance L is 1.5 m. 
     A front camera  111  is installed above the front bumper of the vehicle, on the back of the rearview mirror, etc. The front camera  111  is an imaging device with a camera using a solid-state imaging device such as CCD. The front camera  111  is installed with its optical axis extending forward in the direction of travel of the vehicle. For example, the situation of the environment ahead of the vehicle (i.e., the environment on which the virtual image  110  is superimposed) that is seen by the occupant  106  through the windshield  105  is detected by performing image processing on the image captured by the front camera  111 . A sensor such as a millimeter-wave radar may be used instead of the front camera  111 . 
     An in-vehicle camera  112  is installed on the upper surface of an instrument panel of the vehicle. The in-vehicle camera  112  is an imaging device with a camera using a solid-state imaging device such as CCD. The in-vehicle camera  112  is installed with its optical axis extending toward the driver&#39;s seat. The detection range (imaging range of the in-vehicle camera  112 ) is set to the range in which the occupant&#39;s face is typically expected to be located in the vehicle, and the in-vehicle camera  112  captures an image of the face of the occupant  106  sitting in the driver&#39;s seat. The positions of the eyes of the occupant  106  (the line-of-sight start position) and the gaze direction of the occupant  106  are detected by performing image processing on the image captured by the in-vehicle camera  112 . 
     As shown in  FIG.  20   , the superimposed image display device according to the second embodiment displays an image  120  of a guide object on the front display  104  in S 5  and S 7  of the driving assistance processing program described above ( FIG.  2   ). As the vehicle occupant sees the image  120  of the guide object displayed on the front display  104  as shown in  FIG.  20   , the vehicle occupant sees a virtual image  121  of the image  120  of the guide object superimposed on the landscape through the windshield  105 . 
     Accordingly, as in the superimposed image display device according to the first embodiment, the vehicle occupant can be accurately aware of the position and orientation of the recommended lane and the exit direction at the guide branch point. In the superimposed image display device according to the second embodiment, the size and shape of the guide object to be displayed on the front display  104  and the position (range) where the guide object is to be displayed on the front display  104  are determined in the guide object display position determination process in S 4  and S 6 . It is desirable that the current position and orientation of the vehicle that are identified in the three-dimensional space in S 11  and S 35  be the position of the occupant of the vehicle and the gaze direction of the occupant detected using the in-vehicle camera  112 . 
     It is to be understood that the present disclosure is not limited to the above embodiments and various improvements and modifications can be made without departing from the spirit and scope of the present disclosure. 
     For example, in the first embodiment, the liquid crystal display  15  displaying an image of an actual view is used as a unit for displaying an image superimposed on the landscape around the vehicle. In the second embodiment, the head-up display system is used as a unit for displaying an image superimposed on the landscape around the vehicle. However, a windshield display (WSD) that displays an image on the windshield may be used. In the WSD, the windshield may be used as a screen to display an image from a projector, or the windshield may be a transmissive liquid crystal display. An image displayed on the windshield by the WSD is an image superimposed on the landscape around the vehicle. 
     In the first and second embodiments, when the confidence of the identification result of the vehicle&#39;s lane of travel is higher than the threshold, an image of a guide object distinguishing the recommended lane from the other lanes is displayed as guidance having high guiding capability to guide the vehicle to the recommended lane (S 17  to S 19 ). When the confidence is lower than the threshold, an image of a guide object indicating the direction toward the recommended lane is displayed as guidance having low guiding capability to guide the vehicle to the recommended lane (S 21  to S 23 ). However, how the manner in which guidance is provided is changed based on the confidence can be changed as appropriate. For example, the guide object may be displayed with a transmittance or color according to the confidence. Specifically, the higher the confidence is, the more visible to the user the transmittance or color of the guide object is made when displayed. For example, when the identification result of the vehicle&#39;s lane of travel is higher than the threshold, the guide object is displayed in a more visible color such as yellow or red, or is displayed with a low transmittance (e.g., 10%). On the other hand, when the confidence of the identification result of the vehicle&#39;s lane of travel is lower than the threshold, the guide object is displayed in a less visible color such as green or white or is displayed with a high transmittance (e.g., 80%). 
     In the first and second embodiments, the right-side confidence CR, the left-side confidence CL, and the overall confidence CT are calculated as the confidences for the identification result of the vehicle&#39;s lane of travel. However, not all of the right-side confidence CR, the left-side confidence CL, and the overall confidence CT need be calculated, and only one or two of them may be calculated. The right-side confidence and the left-side confidence are calculated based on whether the lane lines that are supposed to be present are correctly perceived (Expressions (1) to (7)). However, the right-side confidence and the left-side confidence may be calculated using the perception results of the road edges rather than the perception results of the lane lines. In Expressions (1) to (7) for calculation of the right-side confidence CR and the left-side confidence CL, each confidence is calculated using all of the following: whether any lane lines have been detected, the color of the detected lane lines, the type of the detected lane lines, and the tilt of the detected lane lines with respect to the direction of travel of the road. However, each confidence need not be calculated using all of them, and may be calculated using only a part of them. 
     In the first and second embodiments, the guide objects are the first guide objects  71  to  74  that provide guidance on the recommended lane of the vehicle and the second guide objects  81  to  83  that are arrows indicating the exit direction of the vehicle at the guide branch point located ahead in the direction of travel. However, only the first guide objects  71  to  74  may be used. The first guide objects  71  to  74  need not necessarily have a rectangular or triangular shape superimposed on the lane, and may have other shapes as long as they can indicate the position and orientation of the recommended lane. 
     In the first and second embodiments, the guide object is used to provide guidance on the guide branch point. However, the point whose guidance is to be provided by the guide object is not limited to the guide branch point. For example, guidance on the position and direction of the recommended lane may be provided using the guide object when the vehicle passes through a point where the number of lanes decreases or a merging section. 
     In the first embodiment, an image of an actual view captured by the front camera  19  and a guide object are displayed on the liquid crystal display  15  of the navigation device  1 . However, the display that displays an image of an actual view and a guide object may be a display other than the liquid crystal display  15  as long as the display is placed inside the vehicle. 
     In the second embodiment, a virtual image is generated ahead of the windshield  105  of the vehicle  102  by the front display  104 . However, a virtual image may be generated ahead of a window other than the windshield  105 . An image from the front display  104  may be reflected on a visor (combiner) installed around the windshield  105 , rather than on the windshield  105 , or may be a wearable display such as an eyeglass or a display device. 
     In the first and second embodiments, the navigation ECU  13  of the navigation device  1  performs the processes of the driving assistance processing program ( FIG.  2   ). However, the unit that performs the processes of the driving assistance processing program may be changed as appropriate. For example, a control unit of the liquid crystal display  15 , a vehicle control ECU, or other on-vehicle equipment may perform the processes of the driving assistance processing program.