Patent Publication Number: US-11032479-B2

Title: Bird&#39;s-eye view video generation device, bird&#39;s-eye view video generation method, and non-transitory storage medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 16/424,704 filed on May 29, 2019, which is a Continuation of PCT International Application No. PCT/JP2017/039368 filed in Japan on Oct. 31, 2017, which claims priority to Japanese Patent Application No. 2017-036658 filed in Japan on Feb. 28, 2017, all of which are hereby incorporated by reference. 
    
    
     FIELD 
     The present application relates to a bird&#39;s-eye view video generation device, a bird&#39;s-eye view video generation system, a bird&#39;s-eye view video generation method, and a non-transitory storage medium. 
     BACKGROUND 
     A technology of capturing a plurality of videos of surroundings of a vehicle with a plurality of cameras that are arranged around the vehicle and displaying, on a monitor, a bird&#39;s-eye view video obtained by performing viewpoint conversion processing on the captured videos and synthesizing the captured videos is known. A bird&#39;s-eye view video is obtained by synthesizing the videos and thus, a part of an object in the captured videos may be not displayed or may be not displayed temporarily at a synthesis boundary at which the videos are synthesized, when the object steps over the synthesis boundary. 
     A technology of creating a bird&#39;s-eye view image in which an obstacle and a synthesis boundary between images of a plurality of cameras do not overlap each other based on information from an obstacle move direction estimator is known (for example, see International Publication Pamphlet No. WO 2011/036892). 
     SUMMARY 
     When a vehicle moves, a position of an obstacle shifts relatively. Accordingly, in the above described technology, the synthesis boundary in the bird&#39;s-eye view video changes dynamically. The dynamic change of the synthesis boundary in the bird&#39;s-eye view video has a risk of becoming complicated. Thus, there is room for improvement in displaying a detected obstacle in a bird&#39;s-eye view video. 
     A bird&#39;s-eye view video generation device, a bird&#39;s-eye view video generation system, a bird&#39;s-eye view video generation method, and a non-transitory storage medium are disclosed. 
     According to one aspect, there is provided a bird&#39;s-eye view video generation device comprising: a video data acquisition unit configured to acquire video data from a plurality of cameras configured to capture videos of surroundings of a vehicle; a bird&#39;s-eye view video generator configured to generate a bird&#39;s-eye view video from a virtual viewpoint above the vehicle by performing viewpoint conversion processing on the video data acquired by the video data acquisition unit to synthesize the viewpoint-converted videos; an obstacle information acquisition unit configured to acquire information from at least one detector configured to detect at least one obstacle around the vehicle and to specify a position of the detected obstacle on the bird&#39;s-eye view video; and a display controller configured to display the bird&#39;s-eye view video in a display, wherein, when the position of the obstacle that is specified by the obstacle information acquisition unit overlaps a synthesis boundary between the videos in the bird&#39;s-eye view video, the bird&#39;s-eye view video generator is further configured to generate a bird&#39;s-eye view video obtained by changing the position of the virtual viewpoint of the bird&#39;s-eye view video to a position from which the obstacle does not overlap the synthesis boundary in the bird&#39;s-eye view video. 
     According to one aspect, there is provided a bird&#39;s-eye view video generation method comprising: acquiring video data from a plurality of cameras that capture videos of surroundings of a vehicle; generating a bird&#39;s-eye view video from a virtual viewpoint above the vehicle by performing viewpoint conversion processing on the acquired video data to synthesize the viewpoint-converted videos; acquiring information from at least one detector configured to detect at least one obstacle around the vehicle and to specify a position of the detected obstacle on the bird&#39;s-eye view video; and displaying the bird&#39;s-eye view video in a display, wherein, on generating the bird&#39;s-eye view video, when the specified position of the obstacle overlaps a synthesis boundary between the videos in the bird&#39;s-eye view video, generating the bird&#39;s-eye view video obtained by changing the position of the virtual viewpoint of the bird&#39;s-eye view video to a position from which the obstacle does not overlap the synthesis boundary in the bird&#39;s-eye view video. 
     According to one aspect, there is provided a non-transitory storage medium that stores a program for causing a computer that operates as a bird&#39;s-eye view video generation device to perform a process comprising: acquiring video data from a plurality of cameras that capture videos of surroundings of a vehicle; generating a bird&#39;s-eye view video from a virtual viewpoint above the vehicle by performing viewpoint conversion processing on the acquired video data to synthesize the viewpoint-converted videos; acquiring information from at least one detector configured to detect at least one obstacle around the vehicle and to specify a position of the detected obstacle on the bird&#39;s-eye view video; and displaying the bird&#39;s-eye view video in a display, wherein, on generating the bird&#39;s-eye view video, when the specified position of the obstacle overlaps a synthesis boundary between the videos in the bird&#39;s-eye view video, generating the bird&#39;s-eye view video obtained by changing the position of the virtual viewpoint of the bird&#39;s-eye view video to a position from which the obstacle does not overlap the synthesis boundary in the bird&#39;s-eye view video. 
     The above and other objects, features, advantages and technical and industrial significance of this application will be better understood by reading the following detailed description of presently preferred embodiments of the application, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an exemplary configuration of a bird&#39;s-eye view video generation system according to a first embodiment. 
         FIG. 2  is a schematic diagram to explain an example of a position of a virtual viewpoint in the bird&#39;s-eye view video generation system according to the first embodiment. 
         FIG. 3  is a diagram illustrating an example of a bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the first embodiment. 
         FIG. 4  is a schematic diagram to explain another example of the position of the virtual viewpoint in the bird&#39;s-eye view video generation system according to the first embodiment. 
         FIG. 5  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the first embodiment. 
         FIG. 6  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the first embodiment. 
         FIG. 7  is a flowchart illustrating a flow of processes in the bird&#39;s-eye view video generation system according to the first embodiment. 
         FIG. 8  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the first embodiment. 
         FIG. 9  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the first embodiment. 
         FIG. 10  is a diagram illustrating an example of a bird&#39;s-eye view video that is generated by a bird&#39;s-eye view video generation system according to a second embodiment. 
         FIG. 11  is a diagram illustrating an example of a bird&#39;s-eye view video that is generated by a bird&#39;s-eye view video generation system according to a third embodiment. 
         FIG. 12  is a flowchart illustrating a flow of processes in a bird&#39;s-eye view video generation device of a bird&#39;s-eye view video generation system according to a fourth embodiment. 
         FIG. 13  is a diagram illustrating an example of a bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the fourth embodiment. 
         FIG. 14  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the fourth embodiment. 
         FIG. 15  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMNODIMENTS 
     With reference to the accompanying drawings, embodiments of a bird&#39;s-eye view video generation device  40 , a bird&#39;s-eye view video generation system  1 , a bird&#39;s-eye view video generation method, and a program will be described in detail below. Note that the following embodiments do not limit the present application. 
     In the following descriptions, a longitudinal direction refers to a direction that is parallel to a direction in which a vehicle goes straight, a side of a wind shield against a driver seat refers to a “front” in the longitudinal direction, and a side of the driver seat against the wind shield refers to a “rear” in the longitudinal direction. The longitudinal direction is referred to as an X-axis direction. A lateral direction refers to a direction that is orthogonal to the longitudinal direction. A left side for the windshield refers to a “left” and a right side for the windshield refers to a “right”. The lateral direction is referred to as a Y-axis direction. A vertical direction refers to a direction that is orthogonal to the longitudinal direction and the lateral direction. The vertical direction is referred to as a Z-axis direction. Accordingly, the longitudinal direction, the lateral direction and the vertical direction are orthogonal with one another three-dimensionally. The front and the rear, the left and the right, and the top and the bottom in the following descriptions refer to a front and a rear, a left and a right, and a top and a bottom of the vehicle with the bird&#39;s-eye view video generation system  1  mounted thereon. 
     First Embodiment 
       FIG. 1  is a block diagram illustrating an exemplary configuration of a bird&#39;s-eye view video generation system according to a first embodiment. The bird&#39;s-eye view video generation system  1  is mounted on a vehicle V. The bird&#39;s-eye view video generation system  1  may be a device mounted on the vehicle V or a device that is portable and usable in the vehicle V. 
     Using  FIG. 1 , the bird&#39;s-eye view video generation system  1  will be described. The bird&#39;s-eye view video generation system  1  includes a front camera  11 , a rear camera  12 , a left-side camera  13 , a right-side camera  14 , a sensor group (detector)  20 , a display panel (display)  30 , and the bird&#39;s-eye view video generation device  40 . 
     Using  FIG. 2 , the front camera  11 , the rear camera  12 , the left-side camera  13 , and the right-side camera  14  will be described.  FIG. 2  is a schematic diagram to explain an example of a position of a virtual viewpoint in the bird&#39;s-eye view video generation system according to the first embodiment. The front camera  11  is arranged on a front of the vehicle V and captures a video of surroundings around the front of the vehicle V. The front camera  11  captures a video of, for example, an imaging area A 1  of approximately 180°. The front camera  11  outputs the captured video to a video data acquisition unit  42  of the bird&#39;s-eye view video generation device  40 . 
     The rear camera  12  is arranged on a rear of the vehicle V and captures a video of surroundings around the rear of the vehicle V. The rear camera  12  captures a video of, for example, an imaging area A 2  of approximately 180°. The rear camera  12  outputs the captured video to the video data acquisition unit  42  of the bird&#39;s-eye view video generation device  40 . 
     The left-side camera  13  is arranged on a left side of the vehicle V and captures a video of surroundings around the left side of the vehicle V. The left-side camera  13  captures a video of, for example, an imaging area A 3  of approximately 180°. The left-side camera  13  outputs the captured video to the video data acquisition unit  42  of the bird&#39;s-eye view video generation device  40 . 
     The right-side camera  14  is arranged on a right side of the vehicle V and captures a video of surroundings around the right side of the vehicle V. The right-side camera  14  captures a video of, for example, an imaging area A 4  of approximately 180°. The right-side camera  14  outputs the captured video to the video data acquisition unit  42  of the bird&#39;s-eye view video generation device  40 . 
     The front camera  11 , the rear camera  12 , the left-side camera  13 , and the right-side camera  14  capture videos in all directions of the vehicle V. 
       FIG. 1  will be referred back here. The sensor group  20  detects an obstacles Q around the vehicle V. The sensor group  20  is capable of detecting the obstacles Q within an area containing an area in which a bird&#39;s-eye view video is displayed. In the present embodiment, the sensor group  20  includes a front sensor, a rear sensor, a left-side sensor, and a right-side sensor. The sensor group  20  is capable of performing sensing within a distance of few tens of meters to few hundreds of meters depending on a sensing system. However, when the sensor group  20  is used for the present purpose, the sensor group  20  detects the obstacle Q within a distance of up to approximately five meters from the vehicle V. For the sensor group  20 , various systems, such as a combination of sensors of multiple systems including an infrared sensor, an ultrasonic sensor, a millimeterwave sensor, and a sensor using image recognition, may be used. 
     The front sensor is arranged on the front of the vehicle V and detects the obstacle Q that is present in an area around the front of the vehicle V. The front sensor detects an object that has a risk of contact with the vehicle V when the vehicle V is going forward and that is higher than the ground. The front sensor, for example, detects the obstacle Q within a distance of approximately five meters from the vehicle V. The detection area of the front sensor overlaps the imaging area A 1  of the front camera  11 . The detection area of the front sensor may overlap a part of detection area of the left-side sensor and a part of detection area of the right-side sensor. The front sensor is formed of a combination of multiple sensors. Accordingly, the front sensor detects the obstacles Q in segmented directions. The front sensor outputs obstacle information on the detected obstacle Q to an obstacle information acquisition unit  43  of the bird&#39;s-eye view video generation device  40 . 
     The rear sensor is arranged on the rear of the vehicle V and detects the obstacle Q that is present in an area around the rear of the vehicle V. The rear sensor detects an object that has a risk of contact with the vehicle V when the vehicle V is reversing and that is higher than the ground. The rear sensor, for example, detects the obstacle Q within a distance of up to about five meters from the vehicle V. The detection area of the rear sensor overlaps the imaging area A 2  of the rear camera  12 . The detection area of the rear sensor may overlap a part of the detection area of the left-side sensor and a part of the detection area of the right-side sensor. The rear sensor is formed of a combination of multiple sensors. Accordingly, the rear sensor detects the obstacle Q in segmented directions. The rear sensor outputs obstacle information on the detected obstacle Q to the obstacle information acquisition unit  43  of the bird&#39;s-eye view video generation device  40 . 
     The left-side sensor is arranged on the left side of the vehicle V and detects the obstacle Q that is present in an area around the left side of the vehicle V. The left-side sensor detects an object that has a risk of contact with the vehicle V when the vehicle V is going forward or reversing while being steered and that is higher than the ground. The left-side sensor, for example, detects the obstacle Q within a distance of up to approximately five meters from the vehicle V. The detection area of the left-side sensor overlaps the imaging area A 3  of the left-side camera  13 . The detection area of the left-side sensor may overlap a part of the detection area of the front sensor and a part of the detection area of the rear sensor. The left-side sensor is formed of a combination of multiple sensors. Accordingly, the left-side sensor detects the obstacle Q in segmented directions. The left-side sensor outputs obstacle information on the detected obstacle Q to the obstacle information acquisition unit  43  of the bird&#39;s-eye view video generation device  40 . 
     The right-side sensor is arranged on the right side of the vehicle V and detects the obstacle Q that is present in an area around the right side of the vehicle V. The right-side sensor detects an object that has a risk of contact with the vehicle V when the vehicle V is going forward or reversing while being steered and that is higher than the ground. The right-side sensor, for example, detects the obstacle Q within a distance of up to approximately five meters from the vehicle V. The detection area of the right-side sensor overlaps the imaging area A 4  of the right-side camera  14 . The detection area of the right-side sensor may overlap a part of the detection area of the front sensor and a part of the detection area of the rear sensor. The right-side sensor is formed of a combination of multiple sensors. Accordingly, the right-side sensor detects the obstacle Q in segmented directions. The right-side sensor outputs obstacle information on the detected obstacle Q to the obstacle information acquisition unit  43  of the bird&#39;s-eye view video generation device  40 . 
     The display panel  30  is, for example, a display including a liquid crystal display (LCD) or an organic electro-luminescence (EL) display. The display panel  30  displays a bird&#39;s-eye view video  100  (refer to  FIG. 3 ) and a bird&#39;s-eye view video  100 A (refer to  FIG. 6 ) based on video signals that are output from the bird&#39;s-eye view video generation device  40  of the bird&#39;s-eye view video generation system  1 . The display panel  30  may be one dedicated to the bird&#39;s-eye view video generation system  1  or may be shared with other systems including a navigation system. The display panel  30  is arranged in a position easily viewable by a driver. 
     When a shape of the display panel  30  is of a landscape rectangle, the display panel  30  may be divided into a plurality of display areas. For example, the display panel  30  has a display area for the bird&#39;s-eye view video  100  and a display area that is arranged beside the display area for the bird&#39;s-eye view video  100  and in which a navigation screen and an audio screen are displayed. The display area for the bird&#39;s-eye view video  100  may have a shape of a portrait rectangle. 
     The bird&#39;s-eye view video generation device  40  includes a controller  41  and a storage  49 . 
     The controller  41  is, for example, an arithmetic processing unit that is formed of a central processing unit (CPU), or the like. The controller  41  loads programs that are stored in the storage  49  and executes commands contained in the programs. The controller  41  includes the video data acquisition unit  42 , the obstacle information acquisition unit  43 , a vehicle information acquisition unit  44 , a bird&#39;s-eye view video generator  45 , and a display controller  48 . 
     The video data acquisition unit  42  acquires surroundings video data obtained by capturing videos of the surroundings of the vehicle V. More specifically, the video data acquisition unit  42  acquires sets of surroundings video data that are output by the front camera  11 , the rear camera  12 , the left-side camera  13  and the right-side camera  14 . The video data acquisition unit  42  outputs the acquired surroundings video data to the bird&#39;s-eye view video generator  45 . 
     The obstacle information acquisition unit  43  acquires obstacle information on the obstacle Q that is detected around the vehicle V and specifies a position of the obstacle Q on the bird&#39;s-eye view video. More specifically, the obstacle information acquisition unit  43  acquires the obstacle information that is output by the sensor group  20 . In the present embodiment, the obstacle information acquisition unit  43  acquires the obstacle information containing a distance to the detected obstacle Q. The obstacle information acquisition unit  43  specifies the position of the obstacle Q on the bird&#39;s-eye view video by the distance between the sensor that detects the obstacle Q and the obstacle Q, which is contained in the acquired obstacle information. The obstacle information acquisition unit  43  outputs the acquired obstacle information and the specified position of the obstacle Q to the bird&#39;s-eye view video generator  45 . 
     The vehicle information acquisition unit  44  acquires vehicle information, such as gear operation information on the vehicle V, serving as a trigger of display of the bird&#39;s-eye view video  100 , from a CAN (Controller Area Network) and various sensors that sense a state of the vehicle V. In the present embodiment, the vehicle information includes information representing a direction to which the vehicle V travels. The vehicle information acquisition unit  44  outputs the acquired vehicle information to the bird&#39;s-eye view video generator  45 . 
     The bird&#39;s-eye view video generator  45  generates the bird&#39;s-eye view video  100  from a virtual viewpoint P above the vehicle V by performing viewpoint conversion processing on the sets of surroundings video data and synthesizing the sets of surroundings video data. 
     Using  FIG. 2 , the virtual viewpoint P will be described. The virtual viewpoint P is positioned above the center of the vehicle V. The virtual viewpoint P is a viewpoint that looks down the vehicle V from a position right above the vehicle V. The center of the vehicle V is a center of the vehicle V in the lateral direction of the vehicle V and a center of the vehicle V in the longitudinal direction. The position right above the vehicle V is a position on a vertical line with respect to a reference plane of the vehicle V. The reference plane is a plane that is, when the vehicle V is positioned on a horizontal and flat road surface, parallel to the road surface. For the position of the virtual viewpoint P, (x,y,z) is set. 
     Using  FIG. 3 , the generated bird&#39;s-eye view video  100  will be described.  FIG. 3  is a diagram illustrating an example of a bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the first embodiment. The bird&#39;s-eye view video  100  contains a front video  101 , a rear video  102 , a left-side video  103 , and a right-side video  104 . The display area of the front video  101  and the display area of the rear video  102  are equal to each other. The display area of the left-side video  103  and the display area of the right-side video  104  are equal to each other. At the center of the bird&#39;s-eye view video  100 , a vehicle icon  200  representing the vehicle V is displayed. The vehicle icon  200  represents a mode in which the vehicle V is looked down from right above. 
     In  FIG. 3 , oblique dotted lines representing a synthesis boundary B 1  between the front video  101  and the left-side video  103 , a synthesis boundary B 2  between the front video  101  and the right-side video  104 , a synthesis boundary B 3  between the rear video  102  and the left-side video  103 , and a synthesis boundary B 4  between the rear video  102  and the right-side video  104  are illustrated for explanation. However, the dotted lines may be or may not be displayed on the bird&#39;s-eye view video  100  that is practically displayed on the display panel  30 . The same applies to other drawings. In the following descriptions, the synthesis boundary B 1 , the synthesis boundary B 2 , the synthesis boundary B 3 , and the synthesis boundary B 4  will be described as a synthesis boundary B when they need not be particularly distinguished from one another. 
     The synthesis boundary B 1  extends forward and to the left from the front left end of the vehicle icon  200 . The synthesis boundary B 1  extends from the front left end of the vehicle icon  200  to a long side  100   a . The synthesis boundary B 2  extends forward and to the right from the front right end of the vehicle icon  200 . The synthesis boundary B 2  extends from the front right end of the vehicle icon  200  to a long side  100   b . The synthesis boundary B 3  extends backward to the left from the rear left end of the vehicle icon  200 . The synthesis boundary B 3  extends from the rear left end of the vehicle icon  200  to the long side  100   a . The synthesis boundary B 4  extends backward to the right from the rear right end of the vehicle icon  200 . The synthesis boundary B 4  extends from the rear right end of the vehicle icon  200  to the long side  100   b.    
     When the position of the obstacle Q that is specified by the obstacle information acquisition unit  43  overlaps the synthesis boundary B that is the boundary between a plurality of videos in the bird&#39;s-eye view video  100 , the bird&#39;s-eye view video generator  45  changes the position of the virtual viewpoint P of the bird&#39;s-eye view video  100 , thereby generating the bird&#39;s-eye view video  100 A corresponding to a virtual viewpoint PA. In other words, if the position of the obstacle Q overlaps the synthesis boundary B when the obstacle Q is represented in the bird&#39;s-eye view video  100 , the bird&#39;s-eye view video generator  45  generates the bird&#39;s-eye view video  100 A corresponding to the virtual viewpoint PA. Furthermore, also if the position of the obstacle Q is located near the synthesis boundary B when the obstacle Q is represented in the bird&#39;s-eye view video  100 , the bird&#39;s-eye view video generator  45  may generate the bird&#39;s-eye view video  100 A corresponding to the virtual viewpoint PA. 
     A position overlapping the synthesis boundary B is a position that overlaps an area in which, when the videos are synthesized, the video-captured object is not displayed or distorted due to image processing and thus the video-captured object is not displayed in a correct mode. The position overlapping the synthesis boundary B is, for example, a position that overlaps an area spread in a beltlike shape centering the synthesis boundary B. 
     A position near the synthesis boundary B is a position in the travel direction with respect to the position overlapping the synthesis boundary B. A position near the synthesis boundary B is a position that is expected to be a position overlapping the synthesis boundary B when the vehicle V travels. 
     In the present embodiment, when the position of the obstacle Q that is specified by the obstacle information acquisition unit  43  overlaps the synthesis boundary B in the travel direction in the bird&#39;s-eye view video  100  (“travel-direction synthesis boundary B” below), the bird&#39;s-eye view video generator  45  generates the bird&#39;s-eye view video  100 A obtained by changing the position of the virtual viewpoint P to the virtual viewpoint PA that corresponds to the direction in which the vehicle V travels. More specifically, when the position of the obstacle Q overlaps the travel-direction synthesis boundary B, the bird&#39;s-eye view video generator  45  generates the bird&#39;s-eye view video  100 A obtained by changing the position of the virtual viewpoint P to the virtual viewpoint PA on the side of the direction in which the vehicle V travels. The position of the virtual viewpoint is represented by (xA,yA,zA). 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 3  or the synthesis boundary B 4  while the vehicle V is reversing, the bird&#39;s-eye view video generator  45  generates the bird&#39;s-eye view video  100 A obtained by changing the position of the virtual viewpoint P to the virtual viewpoint PA behind the vehicle V. 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 1  or the synthesis boundary B 2  while the vehicle V is going forward, the bird&#39;s-eye view video generator  45  generates the bird&#39;s-eye view video  100 A obtained by changing the position of the virtual viewpoint P to the virtual viewpoint PA in front of the vehicle V. 
     The bird&#39;s-eye view video generator  45  includes a viewpoint conversion processor  451 , a cut-out processor  452 , and a synthesis processor  453 . 
     The viewpoint conversion processor  451  performs viewpoint conversion processing on the surroundings video data that is acquired by the video data acquisition unit  42  such that the vehicle V is looked down from the virtual viewpoint P above the vehicle V. More specifically, the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing based on the surroundings video data obtained by capturing the videos with the front camera  11 , the rear camera  12 , the left-side camera  13 , and the right-side camera  14 . The method of the viewpoint conversion processing may be any known method and is not limited. The viewpoint conversion processor  451  outputs the surroundings video data on which the viewpoint conversion processing has been performed to the cut-out processor  452 . 
     When the position of the obstacle Q that is specified by the obstacle information acquisition unit  43  overlaps the synthesis boundary B of the bird&#39;s-eye view video  100 , the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing using the virtual viewpoint PA to which the position of the virtual viewpoint P of the bird&#39;s-eye view video  100  is changed. The viewpoint conversion processor  451  outputs the surroundings video data on which the viewpoint conversion processing has been performed to the cut-out processor  452 . 
     In the present embodiment, the viewpoint conversion processor  451  changes the position of the virtual viewpoint P such that a display area, after changing the position of the virtual viewpoint, of the viewpoint-converted video of the plurality of cameras in which the obstacle is contained becomes wider than that of the viewpoint-converted video before changing the position of the virtual viewpoint. 
     In the present embodiment, when the position of the obstacle Q that is specified by the obstacle information acquisition unit  43  overlaps the travel-direction synthesis boundary B, the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing by changing the position of the virtual viewpoint P to the position corresponding to the direction in which the vehicle V travels. More specifically, when the position of the obstacle Q overlaps the travel-direction synthesis boundary B, the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing by changing the position of the virtual viewpoint P to the side of the direction in which the vehicle V travels. 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 3  or the synthesis boundary B 4  while the vehicle V is reversing, the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing by changing the position of the virtual viewpoint P to the virtual viewpoint PA behind the vehicle V. 
     Using  FIG. 4 , the virtual viewpoint PA will be described.  FIG. 4  is a schematic diagram to explain another example of the position of the virtual viewpoint in the bird&#39;s-eye view video generation system according to the first embodiment. In the present embodiment, the virtual viewpoint PA is positioned behind and above the vehicle V. The virtual viewpoint PA is a viewpoint that looks down the vehicle V obliquely from behind and above the vehicle V. 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 1  or the synthesis boundary B 2  while the vehicle is going forward, the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing by changing the position of the virtual viewpoint P to the virtual viewpoint PA in front of the vehicle V. 
     The cut-out processor  452  performs cut-out processing of cutting videos of predetermined areas out of the surroundings video data on which the viewpoint conversion processing has been performed. The cut-out processor  452  cuts a forward cut area out of the surroundings video data from the front camera  11  on which the viewpoint conversion processing has been performed. The cut-out processor  452  cuts a backward cut area from the surroundings video data out of the rear camera  12  on which the viewpoint conversion processing has been performed. The cut-out processor  452  cuts a left-side cut area out of the surroundings video data from the left-side camera  13  on which the viewpoint conversion processing has been performed. The cut-out processor  452  cuts a right-side cut area out of the surroundings video data from the right-side camera  14  on which the viewpoint conversion processing has been performed. The cut-out processor  452  outputs the video image data of the videos obtained by performing the cutting processing to the synthesis processor  453 . 
     The forward cut area is an area in front of the front end of the vehicle V and is an area surrounded by the synthesis boundary B 1  and the synthesis boundary B 2 . The backward cut area is an area behind the rear end of the vehicle V and is an area surrounded by the synthesis boundary B 3  and the synthesis boundary B 4 . The left-side cut area is an area on the left of the left side of the vehicle V and is an area surrounded by the synthesis boundary B 1  and the synthesis boundary B 3 . The right-side cut area is an area on the right of the right side of the vehicle V and is an area surrounded by the synthesis boundary B 2  and the synthesis boundary B 4 . 
     The position of the synthesis boundaries B of the bird&#39;s-eye view video are defined uniquely according to the position of the virtual viewpoint. For this reason, the forward cut area, the backward cut area, the left-side cut area, and the right-side cut area are determined based on the positions of the synthesis boundaries B corresponding to the position of the virtual viewpoint of the video on which the cut-out processing has been performed. The positions of the synthesis boundaries B of the bird&#39;s-eye view video corresponding to the position of each virtual viewpoint are stored in the storage  49  in advance. In the present embodiment, the positions of the synthesis boundaries B of the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P and the positions of synthesis boundaries BA of the bird&#39;s-eye view video  100 A corresponding to the virtual viewpoint PA are stored. 
     The synthesis processor  453  generates the bird&#39;s-eye view video  100  and the bird&#39;s-eye view video  100 A by synthesizing the videos that are cut out by the cut-out processor  452 . The synthesis processor  453  outputs the generated bird&#39;s-eye view video  100  and the bird&#39;s-eye view video  100 A to the display controller  48 . 
     Using  FIG. 5 , the generated bird&#39;s-eye view video  100  will be described.  FIG. 5  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the first embodiment. The obstacle icon Q representing the obstacle Q is displayed on the rear video  102 . 
     Using  FIG. 6 , the generated bird&#39;s-eye view video  100  will be described.  FIG. 6  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the first embodiment. A vehicle icon  210  represents a mode where the vehicle V is looked down from behind. It is preferable that the vehicle icon  210  is of a display mode where no blind spot is caused by the vehicle icon  210 . For example, the vehicle icon  210  may be semi-transparent. For example, the vehicle icon  210  may be a frame representing an outer shape. The display area of a front video  101 A is narrower than the display area of the front video  101 . The display area of a rear video  102 A is wider forward at the ends on both sides than the display area of the rear video  102 . The display area of the rear video  102 A is wider than the display area of the front video  101 A. The display area of a left-side video  103 A and the display area of a right-side video  104 A are wider forward than the display area of the left-side video  103  and the display area of the right-side video  104 . 
     The synthesis boundary B 1 A extends forward from the front left end of the vehicle icon  210 . The synthesis boundary B 1 A extends from the front left end of the vehicle icon  210  to a short side  100 Ac. The synthesis boundary B 2 A extends forward from the front right end of the vehicle icon  210 . The synthesis boundary B 2 A extends from the front right end of the vehicle icon  210  to the short side  100 Ac. The synthesis boundary B 3 A horizontally extends leftward from the rear left end of the vehicle icon  210 . The synthesis boundary B 3 A extends from the rear left end of the vehicle icon  210  to a long side  100 Aa. The synthesis boundary B 4 A horizontally extends rightward from the rear right end of the vehicle icon  210 . The synthesis boundary B 4 A extends from the rear right end of the vehicle icon  210  to a long side  100 Ab. 
     Near the synthesis boundary B 3 A and the synthesis boundary B 4 A, the surroundings video data from the rear camera  12  has less distortion than that of the surroundings video data from the left-side camera  13  and the right-side camera  14 . For this reason, the synthesis boundary B 3 A and the synthesis boundary B 4 A are set such that the display area of the surroundings video data from the rear camera  12  increases. 
     Near the synthesis boundary B 1 A and the synthesis boundary B 2 A, the surroundings video data from the left-side camera  13  and the right-side camera  14  has less distortion than that of the surroundings video data from the front camera  11 . For this reason, the synthesis boundary B 1 A and the synthesis boundary B 2 A are set such that the display area of the surroundings video data from the left-side camera  13  and the right-side camera  14  increases. 
       FIG. 1  will be referred back. The display controller  48  causes the display panel  30  to display the bird&#39;s-eye view video  100  and the bird&#39;s-eye view video  100 A. 
     The storage  49  stores data necessary for various types of processing performed by the bird&#39;s-eye view video generation device  40  and results of the various types of processing. The storage  49  is, for example, a semiconductor memory device, such as a random access memory (RAM), a read only memory (ROM) or a flash memory, or a storage device, such as a hard disk device or an optical disk. 
     Using  FIG. 7 , a flow of processes performed by the bird&#39;s-eye view video generation device  40  of the bird&#39;s-eye view video generation system  1  will be described.  FIG. 7  is a flowchart illustrating the flow of the processes performed by the bird&#39;s-eye view video generation system according to the first embodiment. 
     When the bird&#39;s-eye view video generation system  1  is started, the controller  41  causes the video data acquisition unit  42  to acquire surroundings video data. The controller  41  causes the obstacle information acquisition unit  43  to acquire obstacle information. 
     The controller  41  determines whether to start displaying a bird&#39;s-eye view video (step S 11 ). In the present embodiment, the controller  41  determines whether to start displaying a bird&#39;s-eye view video based on presence or absence of a reverse trigger. The reverse trigger refers to, for example, a situation where the shift position is changed to the “reverse” position. Alternatively, the reverse trigger refers to a situation where the travel direction of the vehicle is backward. When the reverse trigger is absent, the controller  41  determines not to start displaying a bird&#39;s-eye view video (NO at step S 11 ) and executes the process at step S 11  again. When the reverse trigger is present, the controller  41  determines to start displaying a bird&#39;s-eye view video (YES at step S 11 ) and proceeds to step S 12 . The trigger to start displaying a bird&#39;s-eye view video is not limited to the reverse trigger, and any trigger, such as a user operation, an obstacle detection result or a stop of the vehicle, may be used. 
     The controller  41  determines whether the obstacle Q is detected (step S 12 ). More specifically, the controller  41  determines whether obstacle information on the obstacle Q that meets a predetermined condition is acquired. When it is determined that the obstacle information acquisition unit  43  acquires the obstacle information (YES at step S 12 ), the controller  41  proceeds to step S 13 . When it is determined that the obstacle information acquisition unit  43  does not acquire obstacle information (NO at step S 12 ), the controller  41  proceeds to step S 16 . 
     The predetermined condition is a condition for detecting the obstacle Q. In the embodiment, the predetermined condition is that the obstacle Q is positioned in the direction in which the vehicle V travels. When the obstacle Q is positioned in the direction in which the vehicle V travels, it is determined that the predetermined condition is met and the obstacle Q is detected. For example, when the obstacle Q is positioned behind the rear end of the vehicle V while the vehicle V is reversing, it is determined that the predetermined condition is met and the obstacle Q is detected. More specifically, when the sensor that detects the obstacle Q behind the vehicle V among the sensor group  20  while the vehicle V is reversing, the controller  41  determines that the predetermined condition is met and detects the obstacle Q. 
     The controller  41  acquires information on the position of the obstacle Q with respect to the vehicle V (step S 13 ). More specifically, the controller  41  acquires a position of the obstacle Q on the bird&#39;s-eye view video based on the obstacle information that is acquired by the obstacle information acquisition unit  43 . The controller  41  then proceeds to step S 14 . 
     The controller  41  determines whether the obstacle Q is positioned on the synthesis boundary B of the bird&#39;s-eye view video (step S 14 ). More specifically, based on the positional information on the obstacle Q that is acquired at step S 13 , the controller  41  determines whether the obstacle Q is on the travel-direction synthesis boundary B. When it is determined that the obstacle Q is in a position overlapping the synthesis boundary B of the bird&#39;s-eye view video  100  (YES at step S 14 ), the controller  41  proceeds to step S 15 . When it is determined that the obstacle Q is not in a position overlapping the synthesis boundary B of the bird&#39;s-eye view video  100  (NO at step S 14 ), the controller  41  proceeds to step S 16 . 
     The controller  41  changes the position of the virtual viewpoint (step S 15 ). More specifically, the controller  41  causes the bird&#39;s-eye view video generator  45  to change the position of the virtual viewpoint P of the bird&#39;s-eye view video  100  and thus generate the bird&#39;s-eye view video  100 A corresponding to the virtual viewpoint PA and causes the display panel  30  to display the bird&#39;s-eye view video  100 A. The controller  41  then proceeds to step S 17 . 
     In the embodiment, the controller  41  causes the bird&#39;s-eye view video generator  45  to generate the bird&#39;s-eye view video  100 A obtained by changing the position of the virtual viewpoint P to the virtual viewpoint PA on the side of the direction in which the vehicle V travels according to the direction in which the vehicle V travels. 
     The controller  41  generates and displays the bird&#39;s-eye view video  100  (step S 16 ). More specifically, the controller  41  causes the bird&#39;s-eye view video generator  45  to generate the bird&#39;s-eye view video  100  from the surroundings video data, which is acquired by the video data acquisition unit  42 , by performing the viewpoint conversion processing such that the vehicle V is looked down from above and causes the display panel  30  to display the bird&#39;s-eye view video  100 . The controller  41  proceeds to step S 17 . 
     The controller  41  determines whether to end displaying the bird&#39;s-eye view video (step S 17 ). More specifically, the controller  41  determines whether to end displaying the bird&#39;s-eye view video based on presence or absence of the reverse end trigger. The reverse end trigger refers to, for example, the situation where the shift position is changed from the “reverse” position to another position. When the reverse end trigger is present, the controller  41  determines to end displaying the bird&#39;s-eye view video (YES at step S 17 ) and ends the process. When the reverse end trigger is absent, the controller  41  determines not to end displaying the bird&#39;s-eye view video (NO at step S 17 ) and returns to step S 12  to continue the process. 
     Using  FIG. 5 ,  FIG. 6 ,  FIG. 8  and  FIG. 9 , the case where the obstacle Q is detected behind when the vehicle goes backward will be described.  FIG. 8  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the first embodiment.  FIG. 9  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the first embodiment. The obstacle Q is positioned behind the rear end of the vehicle V on the left. 
     First, when the shift position is changed to the “reverse” position, at step S 11 , it is determined to start displaying a bird&#39;s-eye view video. 
     At step S 12 , the obstacle Q that is positioned behind the vehicle V is detected. At step S 13 , information representing that the position of the obstacle Q is behind the rear end of the vehicle V on the left is acquired. At step S 14 , it is determined that the obstacle Q is not on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 16 , the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P like that represented in  FIG. 5  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     At step S 12 , the obstacle Q is detected and, at step S 13 , the position of the obstacle Q that gets close to the vehicle V is acquired. At step S 14 , it is determined that the obstacle Q is positioned on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 15 , the bird&#39;s-eye view video  100 A corresponding to the virtual viewpoint PA like that represented in  FIG. 6  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     In the bird&#39;s-eye view video  100 A illustrated in  FIG. 6 , the obstacle Q is displayed behind the synthesis boundary B 3 A. 
     At step S 13 , information representing that the position of the obstacle Q is on the left and is close to the rear end of the vehicle V is acquired. At step S 14 , it is determined that the obstacle Q is not positioned on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 16 , the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P like that illustrated in  FIG. 8  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     In the bird&#39;s-eye view video  100  illustrated in  FIG. 8 , the position of the synthesis boundary B is the same position as that of the synthesis boundary B of the bird&#39;s-eye view video  100  illustrated in  FIG. 5 . The obstacle Q is displayed in front of the synthesis boundary B 3 . 
     At step S 13 , information representing that the position of the obstacle Q is in front of the rear end of the vehicle V on the left is acquired. At step S 14 , it is determined that the obstacle Q is not positioned on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 16 , the bird&#39;s-eye view video  100  of the virtual viewpoint P like that illustrated in  FIG. 9  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     In the bird&#39;s-eye view video  100  illustrated in  FIG. 9 , the position of the synthesis boundary B is the same position as that of the synthesis boundary B of the bird&#39;s-eye view video  100 . The obstacle Q is displayed further in front of the synthesis boundary B 3 . 
     When the vehicle V further reverses, the obstacle Q is in a position where the obstacle Q crosses over the synthesis boundary B 1  of the bird&#39;s-eye view video  100 . However, the synthesis boundary B 1  is not in the travel direction and thus the process of changing the position of the virtual viewpoint is not executed. 
     Such processes are repeated until displaying the bird&#39;s-eye view video is ended. 
     As described above, when the position of the obstacle Q overlaps the travel-direction synthesis boundary B, the bird&#39;s-eye view video generation system  1  generates the bird&#39;s-eye view video  100 A obtained by changing the position of the virtual viewpoint P to the position on the side of the travel direction. 
     As described above, in the present embodiment, when the position of the obstacle Q overlaps the travel-direction synthesis boundary B, the bird&#39;s-eye view video  100 A corresponding to the virtual viewpoint PA obtained by changing the position of the virtual viewpoint to the side of the direction in which the vehicle V travels according to the direction in which the vehicle V travels is generated. Accordingly, in the present embodiment, when the obstacle Q overlaps the travel-direction synthesis boundary B, it is possible to display the bird&#39;s-eye view video in which the obstacle Q does not overlap the synthesis boundary B by changing the position of the virtual viewpoint. Accordingly, it is possible to inhibit the obstacle Q from deforming or inhibit the obstacle Q from being not displayed due to the obstacle Q being positioned on the synthesis boundary B. Accordingly, in the present embodiment, it is possible to display the obstacle Q appropriately in the bird&#39;s-eye view video. In the present embodiment, it is possible to improve visibility of the obstacle Q in the bird&#39;s-eye view video. In the present embodiment, it is possible to appropriately recognize the obstacle Q around the vehicle. 
     In the embodiment, the bird&#39;s-eye view video is generated by changing the position of the virtual viewpoint such that the display area which displays the direction in which the obstacle Q is detected in the bird&#39;s-eye view video increases. For example, when the obstacle Q is detected behind, the display area of the rear video  102 A of the bird&#39;s-eye view video  100 A corresponding to the direction in which the obstacle Q is detected is increased to be wider than the display area of the rear video  102  of the bird&#39;s-eye view video  100 . Accordingly, in the present embodiment, it is possible to display the bird&#39;s-eye view video  100 A in which the obstacle Q and its surroundings do not overlap the synthesis boundary B in a wider area. As described above, in the present embodiment, it is possible to appropriately display the obstacle Q and its surroundings in the bird&#39;s-eye view video. In the present embodiment, it is possible to appropriately check the obstacle Q and its surroundings around the vehicle. 
     In the embodiment, by changing the position of the virtual viewpoint according to the direction in which the vehicle V travels, it is possible to display a bird&#39;s-eye view video in which the obstacle Q is recognized more easily. Specifically, in the present embodiment, the bird&#39;s-eye view video  100 A obtained by changing the position of the virtual viewpoint P to the position on the side of the direction in which the vehicle V travels is generated. Accordingly, in the present embodiment, it is possible to display the bird&#39;s-eye view video  100 A representing that the vehicle V approaches to the obstacle Q as a reference. In other words, in the present embodiment, it is possible to display the bird&#39;s-eye view video  100 A from a viewpoint like one to guide the vehicle V from the side of the direction in which the vehicle V travels. Accordingly, in the present embodiment, it is possible to make a display in which closeness of the vehicle V to the obstacle Q is recognized more easily. As described above, in the present embodiment, it is possible to appropriately display the obstacle Q in the bird&#39;s-eye view video. 
     In the present embodiment, when the position of the obstacle Q overlaps the travel-direction synthesis boundary B, the bird&#39;s-eye view video  100 A corresponding to the virtual viewpoint PA is generated and displayed. In the present embodiment, when the position of the obstacle Q deviates from the position overlapping the travel-direction synthesis boundary B, the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P is generated and displayed. As described above, in the present embodiment, only while the position of the obstacle Q overlaps the travel-direction synthesis boundary B, the bird&#39;s-eye view video  100 A corresponding to the virtual viewpoint PA is generated and displayed. Accordingly, in the present embodiment, the position of the virtual viewpoint is not changed frequently and thus it is possible to inhibit display of the bird&#39;s-eye view video from being complicated. 
     In the present embodiment, when the position of the virtual viewpoint is changed, the vehicle icon changes. Accordingly, the driver is able to easily recognize that the position of the virtual viewpoint is changed. 
     Second Embodiment 
     With reference to  FIG. 10 , the bird&#39;s-eye view video generation system  1  according to the present embodiment will be described.  FIG. 10  is a diagram illustrating an exemplary bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to a second embodiment. The basic configuration of the bird&#39;s-eye view video generation system  1  is the same as that of the bird&#39;s-eye view video generation system  1 . In the following descriptions, the same components as those of the bird&#39;s-eye view video generation system  1  are denoted with the same reference numbers or their corresponding reference numbers and detailed descriptions of the components will be omitted. The bird&#39;s-eye view video generation system  1  of the present embodiment is different from the bird&#39;s-eye view video generation system  1  of the first embodiment in the process in the bird&#39;s-eye view video generator  45 . 
     When the position of the obstacle Q that is specified by the obstacle information acquisition unit  43  overlaps the travel-direction synthesis boundary B, the bird&#39;s-eye view video generator  45  generates a bird&#39;s-eye view video  100 B obtained by changing the position of the virtual viewpoint P to a virtual viewpoint PB on a side opposite to the direction in which the vehicle V travels. The position of a virtual viewpoint PB is represented by (xB,yB,zB). 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 3  or the synthesis boundary B 4  while the vehicle V is reversing, the bird&#39;s-eye view video generator  45  generates the bird&#39;s-eye view video  100 B obtained by changing the position of the virtual viewpoint P to the viewpoint PB in front of the vehicle V. 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 1  or the synthesis boundary B 2  while the vehicle V is going forward, the bird&#39;s-eye view video generator  45  generates the bird&#39;s-eye view video  100 B obtained by changing the position the virtual viewpoint P to the viewpoint PB behind the vehicle V. 
     When the position of the obstacle Q overlaps the travel-direction synthesis boundary B, the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing by changing the position of the viewpoint P to the side opposite to the direction in which the vehicle V travels. 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 3  or the synthesis boundary B 4  while the vehicle V is reversing, the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing by changing the position of the virtual viewpoint P to the virtual viewpoint PB in front of the vehicle V. 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 1  or the synthesis boundary B 2  while the vehicle V is going forward, the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing by changing the position of the virtual viewpoint P to the virtual viewpoint PB behind the vehicle V. 
     A flow of the processes performed by the bird&#39;s-eye view video generation device  40  of the bird&#39;s-eye view video generation system  1  will be described. The bird&#39;s-eye view video generation device  40  performs the processes according to the flowchart illustrated in  FIG. 7 . The present embodiment is different from the first embodiment in the process of step S 15  and, as for the process of steps S 11  to S 14 , step S 16  and step S 17 , the same process as that of the first embodiment is performed. 
     The controller  41  changes the position of the virtual viewpoint (step S 15 ). More specifically, the controller  41  causes the bird&#39;s-eye view video generator  45  to change the position of the virtual viewpoint P of the bird&#39;s-eye view video  100  to the side opposite to the direction in which the vehicle V travels and thus generate the bird&#39;s-eye view video  100 B corresponding to the virtual viewpoint PB and causes the display panel  30  to display the bird&#39;s-eye view video  100 B. The controller  41  proceeds to step S 17 . 
     Using  FIG. 10 , the case where, as in the first embodiment, the obstacle Q is detected behind when the vehicle goes backward will be described. 
     First, when the shift position is changed to the “reverse” position, at step S 11 , it is determined to start displaying a bird&#39;s-eye view video. 
     At step S 12 , the obstacle Q that is positioned behind the vehicle V is detected. At step S 13 , information representing that the position of the obstacle Q is behind the rear end of the vehicle V on the left is acquired. At step S 14 , it is determined that the obstacle Q is not on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 16 , the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P like that represented in  FIG. 5  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     At step S 12 , the obstacle Q is detected and, at step S 13 , the position of the obstacle Q that gets close to the vehicle V is acquired. At step S 14 , it is determined that the obstacle Q is positioned on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 15 , the bird&#39;s-eye view video  100 B corresponding to the virtual viewpoint PB like that represented in  FIG. 10  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     Using  FIG. 10 , the generated bird&#39;s-eye view video  100 B will be described. A vehicle icon  220  represents a mode where the vehicle V is looked down from front. The obstacle Q is displayed in front of the synthesis boundary B 3 B. 
     The display area of a front video  101 B is wider backward at the ends on both sides than the display area of the front video  101 . The display area of the front video  101 B is wider than the display area of a rear video  102 B. The display area of a left-side video  103 B and the display area of a right-side video  104 B are wider backward than the display area of the left-side video  103  and the display area of the right-side video  104 . 
     A synthesis boundary B 1 B extends horizontally leftward from the front left end of the vehicle icon  220 . The synthesis boundary B 1 B extends from the front left end of the vehicle icon  220  to a long side  100 Ba. A synthesis boundary B 2 B extends horizontally rightward from the front right end of the vehicle icon  220 . The synthesis boundary B 2 B extends from the front right end of the vehicle icon  220  to a long side  100 Bb. A synthesis boundary B 3 B extends backward from the rear left end of the vehicle icon  220 . The synthesis boundary B 3 B extends from the rear left end of the vehicle icon  220  to a short side  100 Bd. A synthesis boundary B 4 B extends backward from the rear right end of the vehicle icon  220 . The synthesis boundary B 4 B extends from the rear right end of the vehicle icon  220  to the short side  100 Bd. 
     Near the synthesis boundary B 3 B and the synthesis boundary B 4 B, the surroundings video data from the left-side camera  13  and the right-side camera  14  has less distortion than that of the surroundings video data from the rear camera  12 . For this reason, the synthesis boundary B 3 B and the synthesis boundary B 4 B are set such that the display area of the surroundings video data from the left-side camera  13  and the right-side camera  14  increases. 
     Near the synthesis boundary B 1 B and the synthesis boundary B 2 B, the surroundings video data from the front camera  11  has less distortion than that of the surroundings video data from the left-side camera  13  and the right-side camera  14 . For this reason, the synthesis boundary B 1 B and the synthesis boundary B 2 B are set such that the display area of the surroundings video data from the front camera  11  increases. 
     At step S 13 , information representing that the position of the obstacle Q is on the left and is close to the rear end of the vehicle V is acquired. At step S 14 , it is determined that the obstacle Q is not positioned on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 16 , the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P like that represented in  FIG. 8  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     At step S 13 , information representing that the position of the obstacle Q is in front of the rear end of the vehicle V on the left is acquired. At step S 14 , it is determined that the obstacle Q is not positioned on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 16 , the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P like that represented in  FIG. 9  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     Such processes are repeated until displaying the bird&#39;s-eye view video is ended. 
     As described above, in the present embodiment, when the position of the obstacle Q overlaps the travel-direction synthesis boundary B, the bird&#39;s-eye view video  100 B corresponding to the virtual viewpoint PB, which is the bird&#39;s-eye view video obtained by changing the position of the virtual viewpoint to the side opposite to the direction in which the vehicle V travels is generated. Accordingly, in the present embodiment, when the obstacle Q overlaps the travel-direction synthesis boundary B, it is possible to display the bird&#39;s-eye view video in which the obstacle Q does not overlap the synthesis boundary B by changing the virtual viewpoint. Accordingly, it is possible to inhibit the obstacle Q from deforming or inhibit the obstacle Q from being not displayed due to the obstacle Q being positioned on the synthesis boundary B. Accordingly, in the present embodiment, it is possible to display the obstacle Q appropriately in the bird&#39;s-eye view video. In the present embodiment, it is possible to improve visibility of the obstacle Q in the bird&#39;s-eye view video. In the present embodiment, it is possible to appropriately check the obstacle Q around the vehicle. 
     In the present embodiment, the bird&#39;s-eye view video  100 B obtained by changing the position of the virtual viewpoint P to the side opposite to the direction in which the vehicle V travels is generated. Accordingly, in the present embodiment, it is possible to display the bird&#39;s-eye view video  100 B from a viewpoint like one to guide the vehicle V from the side opposite to the direction in which the vehicle V travels. Accordingly, in the present embodiment, it is possible to make a display in which closeness of the vehicle V to the obstacle Q is recognized more easily. As described above, in the present embodiment, it is possible to appropriately display the obstacle Q in the bird&#39;s-eye view video. 
     Third Embodiment 
     With reference to  FIG. 11 , the bird&#39;s-eye view video generation system  1  according to the present embodiment will be described.  FIG. 11  is a diagram illustrating an exemplary bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to a third embodiment. The bird&#39;s-eye view video generation system  1  of the present embodiment is different from the bird&#39;s-eye view video generation system  1  of the first embodiment in the process in the bird&#39;s-eye view video generator  45 . 
     When the position of the obstacle Q that is specified by the obstacle information acquisition unit  43  overlaps the travel-direction synthesis boundary B, the bird&#39;s-eye view video generator  45  generates a bird&#39;s-eye view video  100 C obtained by changing the position of the virtual viewpoint P to a position in a direction intersecting with the direction in which the vehicle V travels, for example, to a side. 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 3  or the synthesis boundary B 4  while the vehicle V is reversing, the bird&#39;s-eye view video generator  45  generates the bird&#39;s-eye view video  100 C obtained by changing the position of the virtual viewpoint P to a viewpoint PC on the left side or the right side of the vehicle V. It is preferable that the virtual viewpoint PC be on the side on which the obstacle Q is detected. The position of the virtual viewpoint PC is represented by (xC,yC,zC). 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 1  or the synthesis boundary B 2  while the vehicle V is going forward, the bird&#39;s-eye view video generator  45  generates the bird&#39;s-eye view video  100 C obtained by changing the position of the viewpoint virtual viewpoint P to a virtual viewpoint PC on the left or on the right of the vehicle V. 
     When the position of the obstacle Q overlaps the travel-direction synthesis boundary B, the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing by changing the position of the viewpoint P to a position in the direction intersecting with the direction in which the vehicle V travels. 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 3  or the synthesis boundary B 4  while the vehicle V is reversing, the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing by changing the position of the virtual viewpoint P to the virtual viewpoint PC on the left or on the right of the vehicle V. 
     For example, when the position of the obstacle Q overlaps the synthesis boundary B 1  or the synthesis boundary B 2  while the vehicle V is going forward, the viewpoint conversion processor  451  generates a video obtained by performing the viewpoint conversion processing by changing the position of the virtual viewpoint P to the virtual viewpoint PC on the left or on the right of the vehicle V. 
     A flow of the processes performed by the bird&#39;s-eye view video generation device  40  of the bird&#39;s-eye view video generation system  1  will be described. The bird&#39;s-eye view video generation device  40  performs the processes according to the flowchart illustrated in  FIG. 7 . The present embodiment is different from the first embodiment in the process of step S 15  and, as for the process of steps S 11  to S 14 , step S 16  and step S 17 , the same process as that of the first embodiment is performed. 
     The controller  41  changes the position of the virtual viewpoint (step S 15 ). More specifically, the controller  41  causes the bird&#39;s-eye view video generator  45  to change the position of the virtual viewpoint P of the bird&#39;s-eye view video  100  to a position in the direction intersecting with the direction in which the vehicle V travels and thus generate the bird&#39;s-eye view video  100 C corresponding to the virtual viewpoint PC and causes the display panel  30  to display the bird&#39;s-eye view video  100 C. The controller  41  proceeds to step S 17 . 
     Using  FIG. 11 , the case where, as in the first embodiment, the obstacle Q is detected behind when the vehicle goes backward will be described. 
     First, when the shift position is changed to the “reverse” position, at step S 11 , it is determined to start displaying a bird&#39;s-eye view video. 
     At step S 12 , the obstacle Q that is positioned behind the vehicle V is detected. At step S 13 , information representing that the position of the obstacle Q is behind the rear end of the vehicle V on the left is acquired. At step S 14 , it is determined that the obstacle Q is not on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 16 , the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P like that represented in  FIG. 5  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     At step S 12 , the obstacle Q is detected and, at step S 13 , the position of the obstacle Q that gets close to the vehicle V is acquired. At step S 14 , it is determined that the obstacle Q is positioned on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 15 , the bird&#39;s-eye view video  100 C corresponding to the virtual viewpoint PC like that represented in  FIG. 11  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     Using  FIG. 11 , the generated bird&#39;s-eye view video  100 C will be described. A vehicle icon  230  represents a mode where the vehicle V is looked down from the left. The obstacle Q is displayed in front of a synthesis boundary B 3 C. 
     The display area of a front video  101 C and the display area of a rear video  102 C are narrower than the display area of the front video  101  and the display area of the rear video  102 . The display area of a left-side video  103 C is wider than the display area of the left-side video  103  in the longitudinal direction. The display area of the left-side video  103 C is wider than the display area of a right-side video  104 C. The display area of the right-side video  104 C is equal to the display area of the right-side video  104 . 
     A synthesis boundary B 1 C extends forward from the front left end of a vehicle icon  230 . A synthesis boundary B 1 C extends from the front left end of the vehicle icon  230  to a short side  100 Cc. A synthesis boundary B 2 C extends rightward from the front right end of the vehicle icon  230 . The synthesis boundary B 2 C extends from the front right end of the vehicle icon  230  to a long side  100 Cb. A synthesis boundary B 3 C extends backward from the rear left end of the vehicle icon  230 . The synthesis boundary B 3 C extends from the rear left end of the vehicle icon  230  to a short side  100 Cd. A synthesis boundary B 4 C extends rightward from the rear right end of the vehicle icon  230 . The synthesis boundary B 4 C extends from the rear right end of the vehicle icon  230  to the long side  100 Cb. 
     Near the synthesis boundary B 3 C, the surroundings video data from the left-side camera  13  has less distortion than that of the surroundings video data from the rear camera  12 . For this reason, the synthesis boundary B 3 C is set such that the display area of the surroundings video data from the left-side camera  13  increases. 
     Near the synthesis boundary B 1 C, the surroundings video data from the left-side camera  13  has less distortion than that of the surroundings video data from the front camera  11 . For this reason, the synthesis boundary B 1 C is set such that the display area of the surroundings video data from the left-side camera  13  increases. 
     At step S 13 , information representing that the position of the obstacle Q is on the left and is close to the rear end of the vehicle V is acquired. At step S 14 , it is determined that the obstacle Q is not on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 16 , the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P like that represented in  FIG. 8  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     At step S 13 , information representing that the position of the obstacle Q is in front of the rear end of the vehicle V on the left is acquired. At step S 14 , it is determined that the obstacle Q is not positioned on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 C. At step S 16 , the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P like that represented in  FIG. 9  is generated and displayed on the display panel  30 . At step S 17 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 12 . 
     Such processes are repeated until displaying the bird&#39;s-eye view video ends. 
     As described above, in the present embodiment, when the position of the obstacle Q overlaps the travel-direction synthesis boundary B, the bird&#39;s-eye view video  100 C corresponding to the virtual viewpoint PC, which is the bird&#39;s-eye view video obtained by changing the position of the virtual viewpoint to the point in the direction intersecting with the direction in which the vehicle V travels, is generated. Accordingly, in the present embodiment, when the obstacle Q overlaps the travel-direction synthesis boundary B, it is possible to display the bird&#39;s-eye view video in which the obstacle Q does not overlap the synthesis boundary B by changing the virtual viewpoint. Accordingly, it is possible to inhibit the obstacle Q from deforming or inhibit the obstacle Q from being not displayed due to the obstacle Q being positioned on the synthesis boundary B. Accordingly, in the present embodiment, it is possible to display the obstacle Q appropriately in the bird&#39;s-eye view video. In the present embodiment, it is possible to improve visibility of the obstacle Q in the bird&#39;s-eye view video. In the embodiment, it is possible to appropriately check the obstacle Q around the vehicle. 
     In the present embodiment, the bird&#39;s-eye view video  100 C obtained by changing the position of the virtual viewpoint P to the position in the direction intersecting with the direction in which the vehicle V travels is generated. Accordingly, in the present embodiment, it is possible to display the bird&#39;s-eye view video  100 C corresponding to the virtual viewpoint PC like one to guide the vehicle V from the side of the vehicle. Accordingly, in the present embodiment, it is possible to make a display in which closeness of the vehicle V to the obstacle Q is recognized more easily. As described above, in the embodiment embodiment, the driver is able to appropriately check the obstacle Q around the vehicle. 
     Fourth Embodiment 
     With reference to  FIGS. 12 to 15 , the bird&#39;s-eye view video generation system  1  according to the present embodiment will be described.  FIG. 12  is a flowchart of a flow of processes in a bird&#39;s-eye view video generation device of a bird&#39;s-eye view video generation system according to a fourth embodiment.  FIG. 13  is a diagram illustrating an example of a bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the fourth embodiment.  FIG. 14  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the fourth embodiment.  FIG. 15  is a diagram illustrating another example of the bird&#39;s-eye view video that is generated by the bird&#39;s-eye view video generation system according to the fourth embodiment. The bird&#39;s-eye view video generation system  1  of the present embodiment is different from the bird&#39;s-eye view video generation system  1  of the second embodiment in the process in the bird&#39;s-eye view video generator  45 . In the present embodiment, the case where multiple obstacles of the obstacles Q 1  and an obstacle Q 2  are detected is described. 
     A flow of the process that is performed by the bird&#39;s-eye view video generation device  40  of the bird&#39;s-eye view video generation system  1  will be described. As for the process of steps S 21 , S 26 , and S 27 , the same process as that of steps S 11 , S 16 , and S 17  of the first embodiment is performed. 
     The controller  41  determines whether the obstacles Q are detected (step S 22 ). More specifically, the controller  41  determines whether obstacle information on the obstacle Q that meets the predetermined condition is acquired. In the present embodiment, multiple obstacles Q meet the predetermined condition. When it is determined that the obstacle Q is detected (YES at step S 22 ), the controller  41  proceeds to step S 23 . When it is determined that the obstacle Q is not detected (NO at step S 22 ), the controller  41  proceeds to step S 26 . 
     The controller  41  acquires information on the positions of the obstacles Q (step S 23 ). More specifically, the controller  41  acquires positons of all the obstacles Q on the bird&#39;s-eye view video based on the obstacle information that is acquired by the obstacle information acquisition unit  43 . The controller  41  then proceeds to step S 24 . 
     The controller  41  determines whether there is the obstacle Q that is positioned on the synthesis boundary B of the bird&#39;s-eye view video (step S 24 ). More specifically, as for the information on the position of the obstacle Q that is acquired at step S 23 , the controller  41  determines whether there is the obstacle Q in a position overlapping the travel-direction synthesis boundary B on the bird&#39;s-eye view video  100 . The controller  41  determines whether there is the obstacle Q in a position that is expected to overlap the travel-direction synthesis boundary B in addition to the obstacle Q in the position overlapping the travel-direction synthesis boundary B. The obstacle Q in a position that is expected to overlap the travel-direction synthesis boundary B refers to the obstacle Q in a position that is expected to overlap the synthesis boundary B when the vehicle V moves in the travel direction. This reduces the number of times of changing the position of the virtual viewpoint. 
     When it is determined that there is the obstacle Q in a position overlapping the synthesis boundary B of the bird&#39;s-eye view video  100  (YES at step S 24 ), the controller  41  proceeds to step S 25 . When it is determined that there is no obstacle Q in a position overlapping the synthesis boundary B of the bird&#39;s-eye view video  100  (NO at step S 24 ), the controller  41  proceeds to step S 26 . 
     The controller  41  changes the position of the virtual viewpoint (step S 25 ). More specifically, the controller  41  causes the bird&#39;s-eye view video generator  45  to change the position of the virtual viewpoint P of the bird&#39;s-eye view video  100  to the virtual viewpoint PA and thus generate the bird&#39;s-eye view video  100 A corresponding to the virtual viewpoint PA, and causes the display panel  30  to display the bird&#39;s-eye view video  100 A. The controller  41  then proceeds to step S 27 . 
     Using  FIGS. 13 to 15 , the case where two obstacles of the obstacle Q 1  and the obstacle Q 2  are detected behind when the vehicle V goes backward will be described. The multiple obstacles Q 1  and Q 2  are positioned behind the rear end of the vehicle V on the left. 
     First, when the shift position is changed to the “reverse” position at step S 21 , it is determined to start displaying a bird&#39;s-eye view video. 
     At step S 22 , the two obstacles Q 1  and Q 2  that are positioned behind the vehicle V are detected. At step S 23 , information representing that the position of the obstacle Q 1  is on the synthesis boundary B 3  in the bird&#39;s-eye view video is acquired. At step S 24 , it is determined that the obstacle Q 1  is positioned on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 . At step S 25 , the bird&#39;s-eye view video  100 A corresponding to the virtual viewpoint PA like that represented in  FIG. 13  is generated and displayed on the display panel  30 . At step S 27 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 22 . 
     In the bird&#39;s-eye view video  100 A illustrated in  FIG. 13 , the position of the synthesis boundary B is the same position as that of the synthesis boundary B of the bird&#39;s-eye view video  100 A illustrated in  FIG. 6 . The obstacle Q 1  and the obstacle Q 2  are positioned behind the synthesis boundary B 3 A. 
     At step S 22 , the obstacle Q 1  and the obstacle Q 2  are detected and, at step S 23 , information representing that the position of the obstacle Q 1  is not a position on the synthesis boundary B 3  of the bird&#39;s-eye view video is acquired. The position of the obstacle Q 2  is not a position on the synthesis boundary B 3  of the bird&#39;s-eye view video. However, it is expected that, when the vehicle V moves in the travel direction, the obstacle Q 2  is in a position on the synthesis boundary B 3 . Accordingly, at step S 24 , it is determined that the obstacle Q 2  is expected to be positioned on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 A. At step S 25 , the bird&#39;s-eye view video  100 A corresponding to the virtual viewpoint PA like that illustrated in  FIG. 14  is generated and displayed on the display panel  30 . At step S 27 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 22 . 
     In the bird&#39;s-eye view video  100 A illustrated in  FIG. 14 , the position of the synthesis boundary B is the same position as that of the synthesis boundary BA of the bird&#39;s-eye view video  100 A illustrated in  FIG. 13 . The obstacle Q 1  is positioned in front of the synthesis boundary B 3 A. The obstacle Q 2  is positioned behind the synthesis boundary B 3 A. 
     At step S 23 , information representing that the positions of the two obstacles Q 1  and Q 2  are in front of the rear end of the vehicle V on the left is acquired. At step S 24 , it is determined that the two obstacles of the obstacle Q 1  and the obstacle Q 2  are not positioned on the synthesis boundary B 3  of the bird&#39;s-eye view video  100 A. At step S 26 , the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P like that illustrated in  FIG. 15  is generated and displayed on the display panel  30 . At step S 27 , it is determined not to end displaying the bird&#39;s-eye view video and the process returns to step S 22 . 
     In the bird&#39;s-eye view video  100  illustrated in  FIG. 15 , the position of the synthesis boundary B is the same position as that of the synthesis boundary B of the bird&#39;s-eye view video  100 A illustrated in  FIG. 6 . The obstacle Q 1  and the obstacle Q 2  are positioned in front of the synthesis boundary B 3 . 
     Such processes are repeated until displaying the bird&#39;s-eye view video ends. 
     As described above, when the multiple obstacles Q are detected, the bird&#39;s-eye view video generation system  1  generates the bird&#39;s-eye view video  100 A obtained by changing the virtual viewpoint while there is the obstacle Q that is positioned in the direction in which the vehicle V travels and that is expected to be positioned on the synthesis boundary B according to traveling of the vehicle V. 
     As described above, in the present embodiment, when the multiple obstacles Q are detected, the bird&#39;s-eye view video  100 A obtained by changing the virtual viewpoint while there is the obstacle Q that is positioned in the direction in which the vehicle V travels and that is expected to be positioned on the synthesis boundary B when the vehicle V travels. Accordingly, in the present embodiment, it is possible to inhibit of the bird&#39;s-eye view video from being changed frequently. In this manner, in the present embodiment, it is possible to appropriately check the obstacle Q around the vehicle. 
     The bird&#39;s-eye view video generation system  1  according to the present application has been described. However, the present application may be carried out in various different modes in addition to the above-described embodiments. 
     The components of the bird&#39;s-eye view video generation system  1  illustrated in the drawings are functional ideas and need not necessarily be configured physically as illustrated in the drawings. In other words, the specific mode of each device is not limited to that illustrated in the drawings, and all or part of the devices may be distributed or integrated functionally or physically according to any unit and according to processing load on each device or situation in which the device is used. 
     The configuration of the bird&#39;s-eye view video generation system  1  is implemented by a program that is loaded as software into a memory. In the embodiment, the configuration has been described as functional blocks implemented by association among the sets of hardware or software. In other words, the functional blocks may be implemented with only hardware or only software or in various forms using combinations of hardware and software. 
     The above-described components include those easily assumable by those skilled in the art and those substantially the same as the above-described components. Furthermore, the above-described components may be combined as appropriate. Furthermore, it is possible to make various types of omission, replacement or change among the components within the scope of the present application. 
     The predetermined condition has been explained as a condition that the obstacle Q is positioned in the direction in which the vehicle V travels. However, the predetermined condition is not limited thereto. The predetermined condition may be a risk of interference with the vehicle V. The risk of interference with the vehicle V is, for example, being positioned in the direction in which the vehicle V travels and having a height from the ground with a risk of contact with the vehicle V. 
     The predetermined condition is, for example, that the obstacle is positioned in the direction in which the vehicle V travels and having an area smaller than an area of a beltlike shape extending with a predetermined width centering the synthesis boundary B. This is because the obstacle having an area larger than the area of a beltlike shape extending with a predetermined width centering the synthesis boundary B partly deviates from the area on which image processing is performed even when the virtual viewpoint is not changed and thus the video-captured object never not be displayed entirely. 
     Alternatively, the predetermined condition is, for example, that the obstacle is positioned in the direction in which the vehicle V travels and having the smallest distance to the vehicle V. This makes it possible to display a bird&#39;s-eye view video in which the obstacle Q that is, for example, the closest and thus has to be checked more preferentially among the multiple detected obstacles Q is checked easily. 
     At step S 11 , for example, the controller  41  may determine whether to start displaying a bird&#39;s-eye view video based on whether an operation to start displaying a bird&#39;s-eye view video on an operation unit is detected. 
     As for the bird&#39;s-eye view video obtained by changing the position of the virtual viewpoint, a bird&#39;s-eye view video in which the center of the vehicle icon is shifted from the center of the bird&#39;s-eye view video may be generated such that the display area in the direction in which the obstacle Q is detected increases. 
     In the second embodiment, after the bird&#39;s-eye view video  100 B corresponding to the virtual viewpoint PB is generated and displayed, even when the vehicle V further goes backward, the obstacle Q is not positioned on the synthesis boundary. Therefore the bird&#39;s-eye view video  100 B corresponding to the virtual viewpoint PB may be maintained without being returned to the bird&#39;s-eye view video  100  corresponding to the virtual viewpoint P. 
     According to the present application, an obstacle is displayed appropriately in a bird&#39;s-eye view video. 
     Although the application has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.