Patent Publication Number: US-2023150579-A1

Title: Parking assistance device, parking assistance method, and non-transitory computer readable medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 17/675,514, filed Feb. 18, 2022, which is a continuation of U.S. patent application Ser. No. 16/867,119, filed May 5, 2020 and now U.S. Pat. No. 11,285,997, which is a continuation of U.S. patent application Ser. No. 16/566,352, filed Sep. 10, 2019 and now U.S. Pat. No. 10,683,035, which is a continuation-in-part of U.S. patent application Ser. No. 15/779,263, filed May 25, 2018 and now U.S. Pat. No. 10,450,004, which is a National Phase application of International Pat. Appl. No. PCT/JP2016/005064, filed Dec. 6, 2016, and claims the benefit of Japanese Pat. Appl. No. 2015-239092, filed Dec. 8, 2015. The entire disclosure of each of the above-identified documents, including the specification, drawings, and claims, is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a parking assistance device, a parking assistance method, and a non-transitory computer readable medium storing a parking assistance program, for assisting a driving operation for parking a vehicle. 
     2. Description of the Related Art 
     Recently, a parking assistance device that assists a driving operation for parking a vehicle has been developed and put in practical use (for example, PLT 1). A parking assistance device, described in PLT 1, calculates a recommended backward movement start position from which an own vehicle can reach a target parking position while maintaining a steering angle, and displays, on a display unit, a backward movement start frame in addition to an own vehicle figure representing a position of the own vehicle and a parking target frame showing the target parking position, to thereby assist a driving operation for parking. 
     According to the parking assistance device described in Japanese Patent No. 4900232 (hereinafter referred as PLT 1), an own vehicle figure, a parking target frame, and a backward movement start frame are displayed as parking guidance. Therefore, a driver can easily recognize a target parking position and a recommended backward movement start position. By performing a driving operation according to the parking guidance, the driver can move the own vehicle to the target parking position and park the own vehicle. 
     SUMMARY 
     An object of the present disclosure is to provide a parking assistance device, a parking assistance method, and a non-transitory computer readable medium storing a parking assistance program that enable parking to be completed by a driving operation according to parking guidance, and enable driving efficiency for parking to be improved. 
     A parking assistance device according to the present disclosure includes an imager that captures an image of a surrounding of a vehicle, and a display that displays a guidance image far guiding the vehicle from a parking start position to a target parking position and displays a moving area in which the vehicle can move during a parking operation. An area and dimension of the moving area displayed on the display changes based on a change in a steering angle of the vehicle. 
     A parking assistance method according to the present disclosure includes receiving a captured image of a surrounding of a vehicle. The parking assistance method further includes displaying a guidance image for guiding the vehicle from a parking start position to a target parking position and a moving area in which the vehicle can move during a parking operation. The parking assistance method further includes changing an area and dimension of the displayed moving area based on a change in a steering angle of the vehicle. 
     A non-transitory computer readable medium according to the present disclosure recording a parking assistance program for causing a computer of a parking assistance device to perform processes of receiving a captured image of a surrounding of a vehicle; displaying a guidance image for guiding the vehicle from a parking start position to a target parking position and a moving area in which the vehicle can move during a parking operation; and changing an area and dimension of the displayed moving area based on a change in a steering angle of the vehicle. 
     According to the present disclosure, a parking route is set in consideration of presence or absence of an obstacle on the parking route. Therefore, a driver can complete parking by a driving operation according to the parking guidance. Accordingly driving efficiency for parking is improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram illustrating a configuration of a parking assistance device according to an exemplary embodiment. 
         FIG.  2    illustrates a disposition state of on-vehicle cameras. 
         FIG.  3    illustrates an example of a display screen of a display unit. 
         FIG.  4 A  illustrates a steering icon. 
         FIG.  4 B  illustrates a steering icon. 
         FIG.  5    is a flowchart illustrating an example of a parking assistance process. 
         FIG.  6    is a flowchart illustrating an example of a parking route setting process. 
         FIG.  7    is a flowchart illustrating an example of a parking guiding process. 
         FIG.  8    is a flowchart illustrating an example of a steering operation assistance process. 
         FIG.  9 A  illustrates an example of a parking operation. 
         FIG.  9 B  illustrates an example of a parking operation. 
         FIG.  10    illustrates an imaging area. 
         FIG.  11    illustrates an example of a moving area. 
         FIG.  12    illustrates another example of a moving area. 
         FIG.  13    illustrates an exemplary display for guiding parking. 
         FIG.  14    illustrates another exemplary display for guiding parking. 
         FIG.  15    illustrates an example of an obstacle area. 
         FIG.  16    illustrates another example of an obstacle area. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Prior to the description of an exemplary embodiment of the present disclosure, a problem in a conventional device is briefly described. In a driving assistance device described in PLT 1, parking guidance is merely performed according to a parking route calculated at a parking start position, and presence or absence of an obstacle on the parking route is not considered. Therefore, when there is an obstacle on the parking route, a driving operation may not be performed according to the parking guidance. In that case, a parking route is reset when the driving operation cannot be performed. Accordingly, the operating efficiency for parking may be lowered. In the worst case, a parking route cannot be generated and the system may be interrupted. 
     Hereinafter, an exemplary embodiment of the present disclosure will be described in detail with reference to the drawings. 
       FIG.  1    is a diagram illustrating a configuration of parking assistance device  1  according to the present exemplary embodiment. Parking assistance device  1  assists a driving operation for parking own vehicle V (see  FIG.  2   ) at a target parking position. As illustrated in  FIG.  1   , parking assistance device  1  includes controller  11 , imager  12 , display unit  13 , sound output unit  14 , operating unit  15 , steering angle sensor  16 , and the like. 
     Controller  11  includes central processing unit (CPU)  111  as an arithmetic/control device, and random-access memory (RAM)  112  and read-only memory (ROM)  113  as main memories. CPU  111  reads from ROM  113  a program in accordance with a processing content, deploys the program in RAM  112 , and controls respective blocks in cooperation with the deployed program. 
     ROM  113  stores, besides a basic program called a basic input output system (BIOS), a parking assistance program for assisting a driving operation for parking a vehicle. Specific functions of controller  11  will be described below. 
     Imager  12  is at least one on-vehicle camera mounted on own vehicle V. As illustrated in  FIG.  2   , imager  12  includes front camera  121 , rear camera  122 , right-side camera  123 , and left-side camera  124 , for example. Each of on-vehicle cameras  121  to  124  is a wide angle camera having a field angle of about 180°, for example. On-board cameras  121  to  124  are disposed so as to image the whole circumference of own vehicle V. 
     For example, front camera  121  is provided on a front grille of own vehicle V, and captures an image of a front area in an obliquely downward direction toward the ground. Rear camera  122  is provided on a roof spoiler of own vehicle V, and captures an image of a rear area in an obliquely downward direction toward the ground. Each of right-side camera  123  and left-side camera  124  is provided on a side mirror of own vehicle F, and captures an image of a side area in an obliquely downward direction toward the ground. 
     Display unit  13  is a display of a navigation system disposed on an instrument panel, for example. Display unit  13  displays an image for guiding own vehicle V to a target parking position. Sound output unit  14  is a speaker, for example, and outputs sound at the time of guiding own vehicle V to the target parking position. 
     Operating unit  15  includes a main switch for enabling a parking assistance function, a parking position setting button for setting a target parking position, a route determination button for determining a parking route, and a parking mode selection button for setting necessity of steering wheel actuation operation. 
     Steering angle sensor  16  detects a current steering angle of steering wheel SW. 
     Controller  11  functions as image management unit  11 A, parking guidance creating unit  11 B, expected moving locus creating unit  11 C, display controller  11 D, moving area determining unit  11 E, and stop position determining unit  11 F. 
     Image management unit  11 A acquires an image captured by imager  12 , and stores it temporarily. Further, image management unit  11 A creates a whole circumferential view image by combining a plurality of images captured by imager  12 . 
     Parking guidance creating unit  11 B creates parking guidance information showing an ideal parking route, based on basic information including a current position (parking start position) of own vehicle V, a set target parking position, and a surrounding environment (presence or absence of an obstacle). The parking guidance information includes a steering position, a parking guide line, a target steering angle, and the like. 
     The steering position means a position at which a turn is made at the time of parking own vehicle V, including a backward movement start position or a steering wheel actuation operation position. The target steering angle means a steering angle for guiding own vehicle V to a moving target position including the steering position or the target parking position. This means that when the steering angle is set to the target steering angle, own vehicle V can be guided to the moving target position without any steering operation thereafter. 
     It should be noted that while parking guidance creating unit  11 B creates parking guidance information when operating unit  15  performs an operation to set the target parking position, definitive parking guidance information is determined based on the steering angle when parking is started. The parking guidance information may also be finely adjusted when moving to the steering position is completed. 
     Expected moving locus creating unit  11 C creates an expected moving locus based on the current position and the current steering angle of own vehicle V. The expected moving locus is a locus of the own vehicle when it moves in a state of keeping the current steering angle. 
     Display controller  11 D controls a display mode of an image on display unit  13 . Display controller  11 D displays, on display unit  13 , a guidance image for guiding own vehicle V to the target parking position, for example. 
       FIG.  3    illustrates an example of a display screen of display unit  13 . As illustrated in  FIG.  3   , display unit  13  includes whole circumferential view display area  131 , front/rear view display area  132 , icon display area  133 , and message display area  134 . 
     Whole circumferential view display area  131  displays a whole circumferential view as if the vehicle is seen downward from the above. Such a view is created by combining images captured by imager  12 . In whole circumferential view display area  131 , stop icons indicating stop positions including a target parking position and a steering position are displayed in a superimposed manner on the captured images. Here, a stop icon includes letters “stop” and an image of a stop line. 
     Front/rear view display area  132  displays an image captured by front camera  121  or rear camera  122 . The display image in front/rear view display area  132  is switched based on a traveling direction (gear position) of own vehicle V. In front/rear view display area  132 , a parking guide line and an expected moving locus are displayed in a superimposed manner on the captured image. 
     In icon display area  133 , icons I 1 , I 2  representing information related to parking assistance are displayed. Icon I 1  is an icon for instructing an angle of a steering wheel (hereinafter referred to as a “target steering angle”) to be operated (hereinafter referred to as “steering icon I 1 ”). Icon I 2  is an icon showing an area displayed in front/rear view display area  132  (front side in  FIG.  3   ). 
     In message display area  134 , information related to parking assistance is displayed as a message. In message display area  134 , a warning message for parking, a message instructing a driving operation that should be performed by a driver, a message informing completion of moving to a moving target position, and the like are displayed, for example. These messages are displayed in message display area  134 , and are also output as sound from sound output unit  14 . 
       FIGS.  4 A and  4 B  illustrate steering icon I 1 .  FIG.  4 A  illustrates a case where current steering angle θ is 23 degrees, and target steering angle ϕ is 100 degrees.  FIG.  4 B  illustrates a case where current steering angle θ is 90 degrees, and target steering angle ϕ is 100 degrees. 
     As illustrated in  FIGS.  4 A,  4 B , steering icon I 1  includes first icon I 11  showing current steering angle θ, second icon I 12  showing a given angle range around target steering angle ϕ, and third icon I 13  showing current steering angle θ and target steering angle ϕ in numerical values. 
     In the present exemplary embodiment, steering angles θ, ϕ are indicated as a positive angle in a clockwise direction and a negative angle in a counterclockwise direction, with a state of steering wheel SW in straight traveling being used as a reference (0°). 
     First icon I 11  includes an image of a steering wheel and an index line indicating steering angle θ, for example. Second icon I 12  is an arcuate band image along an outer circumference of the steering wheel of first icon I 11 , for example, and may include an index line indicating target steering angle ϕ. 
     First icon I 11  and third icon I 13  (numerical values representing current steering angle θ) vary as steering wheel SW is operated. Second icon I 12  is set based on the current position and the moving target position of own vehicle V With second icon I 12 , a driver can intuitively recognize how much he/she should operate steering wheel SW. 
     Further, with third icon I 13 , as current steering angle θ and target steering angle ϕ are represented as numerical values, it is possible to prevent an operating direction of the steering wheel from being recognized erroneously. Even in a case where the target steering angle ϕ is 360 degrees or larger, recognition can be made reliably. 
     The given angle range around target steering angle ϕ is ±20°, for example. When steering angle θ is within a range of ±20°, the steering angle of a tire can be considered to be almost the same. Accordingly; own vehicle V can be guided to the moving target position. It is only necessary that the given angle range is a range in which a steering angle of a tire corresponding to steering angle θ can be deemed to be similar. The given angle range may be set appropriately depending on a vehicle on which parking assistance device  1  is mounted. 
     It is preferable that a display mode of second icon I 12  be changed according to current steering angle θ. For example, a display color is controlled to be changed such that the color is “red” when current steering angle θ is largely deviated from target steering angle ϕ, the color is “yellow” when it comes close to target steering angle ϕ, and the color is “green” when it enters the given angle range. Thereby the driver can easily recognize how much he/she should further operate steering wheel SW. 
     In conjunction with a change in the display mode of second icon I 12 , a display mode of third icon I 13  may be changed. The display mode to be changed is not limited to the display color. The display mode can be changed from lighting display to flicking display (or from flicking display to lighting display), for example. 
       FIG.  5    is a flowchart illustrating an example of a driving assistance process performed by controller  11 . This process is realized when CPU  111  calls out a parking assistance program stored in ROM  113  and executes it, along with an operation by a driver in operating unit  15 , for example. 
     Here, specific description will be given on a parking operation of a case where after own vehicle V is moved from a parking start position to a backward movement start position as illustrated in  FIG.  9 A , own vehicle V is moved to a target parking position and parked in perpendicular parking, as illustrated in  FIG.  9 B . 
     In step S 1  of  FIG.  5   , controller  11  performs a parking route setting process. Specifically, the parking route setting process is performed according to the flowchart of  FIG.  6   . 
     That is, in step S 101  of  FIG.  6   , controller  11  determines whether or not the target parking position is set by the driver. As illustrated in  FIG.  9 A , for example, the driver can set the target parking position by operating the parking position setting button of operating unit  15 , in a state where the own vehicle is stopped at a side of the target parking position (parking start position). When the target parking position is set by the driver (“YES” in step S 101 ), a process of step S 102  starts. 
     In step S 102 , controller  11  acquires an image captured by imager  12  (a process as image management unit  11 A). Imager  12  images an imaging area illustrated in  FIG.  10   , for example. Even after step S 102 , controller  11  sequentially acquires images captured by imager  12 . 
     In step S 103 , controller  11  acquires a current steering angle based on a detection result of steering angle sensor  16 . 
     In step S 104 , controller  11  creates parking guidance information for guiding own vehicle V from the parking start position to the target parking position (a process as parking guidance creating unit  11 B). Specifically controller  11  creates a whole circumferential view image and calculates an ideal parking route (hereinafter referred to as “a first parking route”), based on basic information including a current position (parking start position) of own vehicle V, the set target parking position, and a surrounding environment (presence or absence of an obstacle), for example. 
     Controller  11  also calculates a parking route to be used for actual parking guidance (hereinafter referred to as a “second parking route”), based on the basic information and the current steering angle. 
     Here, whether or not steering wheel actuation operation is required is also determined by controller  11 . In the case of the parking operation illustrated in  FIGS.  9 A,  9 B , a parking route in which a steering position (backward movement; start; position) is set as a moving target position, and a parking route in which the target parking position is set as a moving target position, are calculated. 
     In step S 105 , controller  11  specifies a moving area when own vehicle V moves according to the second parking route (a process as moving area determining unit  11 E). The moving area is an area in which own vehicle V can move according to the second parking route, and is calculated in consideration of a whole length and a vehicle width of own vehicle V. 
     In step S 106 , controller  11  displays moving area AR together with the current position of own vehicle V, in whole circumferential view display area  131  (see  FIGS.  11 ,  12   ). At that time, it is preferable to change the display mode (display color, for example) of moving area AR, depending on a number of steering wheel actuation operation included in the parking guidance information. Thereby, the driver can recognize easiness of the parking operation, based on the display mode of moving area AR. It should be noted that while moving area AR is illustrated as a simple figure in  FIGS.  11  and  12   , it is actually a much more complicated figure. Further while  FIGS.  11 ,  12    illustrate moving area AR, it is also possible to display a figure of obstacle area BR having an obstacle, on the contrary as illustrated in  FIGS.  15 ,  16   . 
     In message display area  134 , a message prompting to confirm that there is no obstacle such as a parked vehicle in moving area AR. This message is also output from sound output unit  14 . The driver confirms whether there is no obstacle in moving area AR. In a case where there is an obstacle in moving area AR, parking operation cannot be completed with the second parking route calculated based on current steering angle θ. Therefore, the driver performs a steering operation to avoid the obstacle in moving area AR. In a case where obstacle area BR is displayed, the driver performs a steering operation such that there is no obstacle other than obstacle area BR. 
     At that time, in icon display area  133 , it is possible to display steering icon I 1  showing a steering angle for moving own vehicle V to the backward movement start position on the first parking route. Alternatively a steering operation assistance process, described below, may be performed. A steering operation is performed promptly such that current steering angle θ becomes target steering angle ϕ shown by steering icon I 1 , while presence or absence of an obstacle in moving area AR is checked. 
     In step S 107 , controller  11  determines whether or not a steering operation is performed. When the steering operation is performed (“YES” in step S 107 ), the process of step S 103  starts. When the steering operation is not performed (“NO” in step S 107 ), a process of step S 108  starts. 
     When the steering operation is performed, a second parking route is calculated anew based on steering angle θ after the operation, and moving area AR is updated. For example, when the steering operation is performed toward a positive side from the state illustrated in  FIG.  11    and the steering angle is increased, moving area AR is updated such that the front side of own vehicle V is reduced and the right side thereof is expanded, as illustrated in  FIG.  12   . In a case of displaying obstacle area BR, the front side of own vehicle V is expanded and the right side thereof is reduced. 
     In step S 108 , controller  11  determines whether or not the driver performs an operation to determine a parking route (operation of a parking route determination button, for example). When the operation to determine the parking route is performed (“YES” in step S 108 ), a process of step S 109  starts. When the operation to determine the parking route is not performed (“NO” in step S 108 ), the process of step S 107  starts. The driver recognizes moving area AR that varies according to a steering operation, and confirms that there is no obstacle interrupting the parking operation on the second parking route. Then, the driver fixes the parking route. In a case of displaying obstacle area BR, the driver recognizes obstacle area BR that varies according to a steering operation, and confirms that there is no obstacle interrupting the parking operation in an area other than obstacle area BR, on the second parking route. Then, the driver fixes the parking route. 
     In step S 109 , controller  11  sets the second parking route when the determination operation is performed by the driver, to be a parking route for which parking guidance is provided. Parking guidance is provided according to the set second parking route. When the parking route setting process ends, a process of step S 2  of  FIG.  5    starts. 
     In this way a definitive parking route is set after confirming that there is no obstacle interrupting the parking operation on the parking route when a steering operation for moving to the backward movement start position is performed. Accordingly, the parking operation according to the parking guidance is never interrupted by an obstacle. 
     In step S 2  of  FIG.  5   , controller  11  performs a parking guiding process. Specifically the parking guiding process is performed according to the flowchart of  FIG.  7   . Own vehicle V is guided up to the backward movement start positions by the parking guiding process from the parking start position, and is guided up to the target parking position by the parking guiding process from the backward movement start position. 
     That is, in step S 201  of  FIG.  7   , controller  11  specifies a parking position based on the set parking route (a process as stop position determining unit  11 F). The stop position is equivalent to the moving target position, and includes the backward movement start position, the steering wheel actuation operation position, or the target parking position. In the parking guiding process, display/non-display of a stop icon at the specified stop position is controlled according to an approaching state of own vehicle V relative to the stop position. 
     In step S 202 , controller  11  displays first parking guidance without any stop icon. That is, after the parking operation is started from the parking start position toward the backward movement start position (stop position), or after the parking operation is started from the backward movement start position toward the target parking position, the stop icon is not displayed for a given period (see  FIG.  13   ). 
     In message display area  134 , a message prompting a forward movement with the steering wheel being fixed is displayed. This message is also output from sound output unit  14 . According to this instruction, a forward moving operation or a backward moving operation is started promptly. When the forward movement or the backward movement is started, own vehicle V smoothly moves toward the moving target position. Displays in whole circumferential view display area  131  and front/rear view display area  132  are changed as own vehicle V moves. 
     In step S 203 , controller  11  determines whether or not own vehicle V has approached the stop position. For example, when an approaching distance of own vehicle V to the stop position is about 1.0 m, it is determined that own vehicle V has approached the stop position. When own vehicle V has approached the stop position (“YES” in step S 203 ), a process of step S 204  starts. When own vehicle V has not approached the stop position (“NO” in step S 203 ), the process moves to step S 202 . 
     In step S 204 , controller  11  displays second parking guidance with a stop icon. This means that when own vehicle V approaches the backward movement start position (stop position) to some extent, stop icon I 3  appears for the first time (see  FIG.  14   ). 
     After stop icon I 3  is displayed, a display color or transparency may be changed such that the visibility thereof is gradually improved according to an approaching state of own vehicle V toward the stop position. Specifically it is possible to change the icon from a less visible mode (pale color display high transparency) to an easily visible mode (deep color, low transparency) as the approaching distance becomes closer. It is also possible to inform the approaching state of the own vehicle toward the stop position by an informing unit other than display unit  13 . As the informing unit, sound output unit  14  is applicable, for example. Further, a vibrator (not illustrated) that vibrates a seat or the steering wheel is also applicable. 
     In message display area  134 , a message prompting to stop at the position of stop icon I 3  is displayed. This message is also output from sound output unit  14 . Thereby the driver watches the stop position in the parking guidance, and stops traveling at a point when own vehicle V reaches the parking position. 
     As described above, stop icon I 3  is not displayed from the beginning of the parking operation, but is displayed only when own vehicle V approaches the stop position. Thereby the driver does not watch only the parking guidance in an attempt to make the own vehicle follow the stop icon from the beginning of the parking operation. Accordingly; the driver can sufficiently watch surrounding obstacles not displayed, whereby the safety is improved. 
     In step S 205 , controller  11  determines whether or not own vehicle V has reached the stop position. As illustrated in  FIGS.  9 A and  9 B , when own vehicle V moves forward from the parking start position to the backward movement start position, the backward movement start position is the stop position. Meanwhile, when own vehicle V moves backward from the backward movement start position to the target parking position, the target parking position is the stop position. Whether or not own vehicle V has reached the stop position can be determined based on an imaging result by imager  12 , for example. When own vehicle V has reached the stop position (“YES” in step S 205 ), a process of step S 206  starts. When own vehicle V has not reached the stop position (“NO” in step S 205 ), the process moves to step S 204 . 
     In step S 206 , controller  11  displays a message prompting a stop in message display area  134 , and also outputs it from sound output unit  14 . Thereby, the driver performs a stop operation, and own vehicle V stops at the stop position. When the parking guiding process ends, a process of step S 3  in  FIG.  5    starts. 
     in step S 3  of  FIG.  5   , controller  11  determines whether or not own vehicle V has reached the target parking position. Whether or not own vehicle V has reached the target parking position can be determined based on an imaging result by imager  12 , for example. When own vehicle V finally has reached the target parking position (“YES” in step S 3 ), a fact that the vehicle has reached the target parking position is informed, and the parking assistance process ends. At that time, it may instruct to return the steering wheel to a reference state and move straight backward to complete the parking operation. 
     On the other hand, when own vehicle V has not reached the target parking position (“NO” in step S 3 ), that is, when own vehicle V is in a state of reaching the steering position (backward movement start position or steering wheel actuation operation position), the process of step S 4  starts, and a steering operation assistance process is performed. In that case, a fact that own vehicle V has reached the steering position is informed, and an instruction is given to switch the gear from forward movement to backward movement, or from backward movement to forward movement. Specifically the steering operation assistance process is performed according to the flowchart of  FIG.  8   . 
     In S 401  of  FIG.  8   , controller  11  switches an image in front/rear view display area  132  along with a gear change operation by the driver, and updates an icon image in icon display area  133 . 
     At that time, in message display area  134 , a message instructing a steering operation for allowing steering angle θ to fall within a range shown by second icon I 12  is displayed. With steering icon I 1 , the driver can easily recognize how much he/she should operate steering wheel SW. Thereby the instructed steering operation is performed promptly. 
     In step S 402 , controller  11  determines whether or not the steering operation is performed by the driver. When the steering operation is performed by the driver (“YES” in step S 402 ), a process of step S 403  starts. 
     In step S 403 , controller  11  updates steering icon I 1  along with the steering operation by the driver. Specifically, along with the steering operation by the driver, first icon I 11  (an image of the steering wheel and an index line of steering angle θ) is turned, and a numerical value representing current steering angle θ of third icon I 13  is changed. 
     In step S 404 , controller  11  determines whether or not steering angle θ falls within a given angle range. When steering angle θ falls within the given angle range (“YES” in step S 404 ), a process of step S 405  starts. When steering angle θ does not fall within the given angle range (“NO” in step S 404 ), the process of step S 402  starts. 
     In step S 405 , controller  11  changes the display mode (display color, for example) of second icon I 12  and third icon I 13 . Thereby; the driver can easily recognize that current steering angle θ is in an appropriate state. 
     In step S 406 , controller  11  displays, in message display area  134 , a message informing that steering angle θ is in the appropriate state and informing a start of parking guidance. When the steering operation assistance process ends, the process of step S 2  of  FIG.  5    starts. By the parking guiding process after the steering operation assistance process, own vehicle V is finally guided to the target parking position. 
     As described above, as target steering angle ϕ is displayed with an icon showing a range of a required operation amount of the steering wheel, the driver can intuitively recognize how much he/she should operate the steering wheel. Accordingly the driver can complete the required steering operation in a short time without, being excessively conscious of target steering angle ϕ. Thereby the driving efficiency for parking is improved. 
     As described above, parking assistance device  1  according to the present exemplary embodiment includes imager  12  that captures an image of a surrounding of own vehicle V, display unit  13  that displays a guidance image for guiding own vehicle V from a parking start position to a target parking position, parking guidance creating unit  11 B that creates parking guidance information showing a parking route, based on basic information including an imaging result by imager  12 , the parking start position, and the target parking position, moving area determining unit  11  E that determines moving area AR in which own vehicle V can move, based on the parking guidance information, and display controller  11 D that displays, on display unit  13 , an image showing moving area AR together with the guidance image based on guidance information. 
     According to parking assistance device  1 , a parking route is set in consideration of presence or absence of an obstacle on the parking route. Therefore, a driver can complete parking by a driving operation according to the parking guidance. Accordingly driving efficiency for parking is improved. 
     Although the disclosure made by the present inventor has been specifically described above based on the exemplary embodiment, the present disclosure is not limited to the above exemplary embodiment, and can be modified without departing from the gist of the present disclosure. 
     For example, it is possible to allow a driver to select a parking mode involving steering wheel actuation operation or a parking mode not involving steering wheel actuation operation. In that case, parking assistance device  1  calculates an ideal parking route according to the selected parking mode. It is also possible that after a target parking position is set at a parking start position, the own vehicle moves without parking guidance up to a backward movement start position, and then parking guidance starts from the backward movement start position. 
     The present disclosure is applicable not only to a case of performing perpendicular parking but also to a case of performing parallel parking in which a large number of steering wheel actuation operation is expected. 
     Furthermore, moving area AR may be displayed by lines that indicate the outside edges or periphery of moving area AR. For example, moving area AR may be displayed by frame-shaped straight lines that surround moving area AR. Alternatively moving area AR may be displayed by a pair of straight lines that sandwich moving area AR along a width direction of own vehicle V or along a traveling direction of own vehicle V. Furthermore, the lines that indicate the outside edges or periphery of moving area AR are not limited to straight lines, and may be curved lines. In the case where moving area AR is displayed by the lines, inner area of moving area AR may be displayed with a color different from that of the outside edges or periphery of moving area AR. Such a color-coding allows moving area AR to be emphatically displayed. 
     Meanwhile, controller  11  may communicate with an external terminal and display moving area AR together with the current position of own vehicle V on a display of the external terminal. Such configuration can be used when a user performs parking assistance by operating the external terminal from outside of own vehicle V, for example, such as “remote parking”. According to the configuration, the user can check moving area AR even when the user exists outside of own vehicle V. Therefore, the user can confirm whether or not there is no obstacle in moving area AR, and moving area AR is safe for own vehicle V. 
     Moreover, moving area AR may include the second parking route and a possibly moving area. The second parking route is defined as a route of own vehicle from the parking start position to the target parking position and an area having a predetermined width along the route. The width is, for example, the vehicle width of own vehicle or slightly large of the vehicle width of own vehicle. The possibly moving area is defined as an area in which own vehicle may probably travel off of the second parking route. Own vehicle travels within the second parking route; however, does not necessarily travel within the possibly moving area. According to the configuration, the user can confirm whether or not there is no obstacle in the possibly moving area and the possibly moving area is safe for own vehicle V when own vehicle V becomes off of the second parking route. Examples of the case of traveling off of the second parking route include a case where it occurs due to a time lag between the braking timing requested to the user by the parking assistance device and the actual braking operation timing by the user. Note that moving area determining unit  11 E only has to specify, as moving area AR, an area including the area defined as the second parking route and a predetermined area. The predetermined area may be determined in consideration of the whole length, the vehicle width, and the like of own vehicle V. 
     Furthermore, the guidance image only has to an image for guiding own vehicle V from the parking start position to the target parking position. For example, the guidance image may be a whole circumferential view image, a front view image, or a rear view image. Alternatively, the guidance image may be a combination image of two or more of a whole circumferential view image, a front view image, and a rear view image. Further alternatively the guidance image may be a synthetic image in which stop icons, a moving area, a parking target frame, and a backward movement start frame are overlapped on one of a whole circumferential view image, a front view image, and a rear view image. 
     In the present exemplary embodiment, the parking assistance process described above is realized through execution of a parking assistance program by controller  11 . However, it can be realized by using a hardware circuit. The parking assistance program can be provided to controller  11  by being stored on a computer-readable storage medium such as a magnetic disk, an optical disk, a flash memory, or the like. The parking assistance program can also be provided by being downloaded via a communication line such as the Internet. 
     It should be construed that the exemplary embodiment disclosed herein is illustrative in all aspects, and is not restrictive. The scope of the present disclosure is represented by the scope of the claims and not by the above description, and it is intended that all modifications within the sense and scope equivalent to the claims are involved in the scope of the present disclosure. 
     The parking assistance device, the parking assistance method, and the parking assistance program according to the present disclosure are preferable in a case of parking a vehicle at a target parking position.