Patent Publication Number: US-9418461-B2

Title: Character string placement device

Description:
FIELD OF THE INVENTION 
     The present invention relates to a character string placement device that places a character string on a graphic such as a map. 
     BACKGROUND OF THE INVENTION 
     A conventional map display device has a function of placing a character string, such as a road name, from a point where the placement of the character string is started (referred to as a character string placement start point from here on) along a road line (referred to as a road node series from here on) (for example, refer to  FIG. 21 ). In this case, when the character string placement start point is not appropriate, an overlap between the character string and another character string as shown in  FIG. 22( a ) , a reduction in the readability due to a change in the display angle of a character as shown in  FIG. 22( b ) , and a reduction in the readability due to a high degree of closeness between the character string and another character string as shown in  FIG. 22( c )  take place. 
     As a method of solving such an overlap between character strings as shown in  FIG. 22( a ) , and such a reduction in the readability as shown in  FIG. 22( b ) , for example, a method of changing a character string placement start point to a position having high readability is described in nonpatent reference 1. Concretely, the method is the one of changing a character string placement start point by minimizing an evaluation function f shown by the following equation (1) and consisting of both a function overlap(i) showing an overlap between character strings as shown in  FIG. 23( a )  and a function flatness(i) showing a variation in the angle of a road node series along which a character string is placed as shown in  FIG. 23( b ) . α1 and α2 in the equation (1) are parameters for adjusting the values of overlap(i) and flatness(i) respectively, and String_num shows the number of character strings. 
     
       
         
           
             
               
                 
                   f 
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                         ∑ 
                         i 
                         String_num 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           α 
                           1 
                         
                         ⁢ 
                         
                           overlap 
                           ⁡ 
                           
                             ( 
                             i 
                             ) 
                           
                         
                       
                     
                     + 
                     
                       
                         α 
                         2 
                       
                       ⁢ 
                       flatness 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         ( 
                         i 
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
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     RELATED ART DOCUMENT 
     Nonpatent Reference 
     
         
         Nonpatent reference 1: Shawn Edmondson, “A General Cartographic Labeling Algorithm”, The International Journal for Geographic Information and Geovisualization, Volume 33, Number 4/Winter 1996 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     A problem with the method disclosed in the above-mentioned nonpatent reference 1 is, however, that because the method is provided to simply solve an overlap between character strings as shown in  FIG. 22( a )  and a reduction in the readability due to a variation in the angle of a road along which a character string is placed as shown in  FIG. 22( b ) , a reduction in the readability due to a high degree of closeness between character strings as shown in  FIG. 22( c )  cannot be avoided. 
     The present invention is made in order to solve the above-mentioned problem, and it is therefore an object of the present invention to provide a character string placement device that changes a character string placement start point to an optimal position by taking into consideration not only an overlap between character strings and a variation in the display angle of a character, but also the degree of closeness between character strings. 
     Means for Solving the Problem 
     In accordance with the present invention, there is provided a character string placement device including: an evaluation function calculator that calculates a plurality of evaluation function values, each of which shows an evaluation of placement of a character string placed at each of a plurality of candidate points on a node series; and a minimum evaluation function value storer that determines at which of the plurality of candidate points to place the character string on a basis of comparison between the plurality of evaluation function values calculated by the evaluation function calculator, wherein the evaluation function calculator includes: a character gap function calculator that calculates a character gap function value for evaluating a distance between the character string placed at each of the plurality of candidate points and another character string placed at another node series, which us different from the node series on winch the plurality of candidate points are placed; an angle function calculator that calculates an angle function value showing an evaluation of an angle of the node series along which the character string is placed at each of the plurality of candidate points; and an evaluation function value calculator that calculates the evaluation function value of the character string placed at each of the plurality of candidate points on a basis of the character gap function value and the angle function value. 
     Advantages of the Invention 
     The character string placement device in accordance with the present invention can prevent a reduction of the readability due to an overlap between character strings and a change of the display angle of a character, and can also prevent the degree of closeness between character strings from becoming high, thereby being able to improve the visibility of each character string. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a block diagram showing the structure of a character string placement device in accordance with Embodiment 1; 
         FIG. 2  is a flow chart showing the operation of the character string placement device in accordance with Embodiment 1; 
         FIG. 3  is a block diagram showing the structure of a candidate point generator of the character string placement device in accordance with Embodiment 1; 
         FIG. 4  is a block diagram showing the structure of a character string placer of the character string placement device in accordance with Embodiment 1; 
         FIG. 5  is a block diagram showing the structure of an evaluation function calculator of the character string placement device in accordance with Embodiment 1; 
         FIG. 6  is a diagram showing a relationship between two sets of road node series along each of which a character string is to be placed; 
         FIG. 7  is a flow chart showing the operation of the candidate point generator of the character string placement device in accordance with Embodiment 1; 
         FIG. 8  is a diagram showing the results of generation of candidate points obtained by the character string placement device in accordance with Embodiment 1; 
         FIG. 9  is a flow chart showing the operation of the character string placer of the character string placement device in accordance with Embodiment 1; 
         FIG. 10  is a diagram showing the result of placement by the character string placement device in accordance with Embodiment 1; 
         FIG. 11  is a diagram showing the result of placement by the character string placement device in accordance with Embodiment 1; 
         FIG. 12  is a diagram showing the result of placement by the character string placement device in accordance with Embodiment 1; 
         FIG. 13  is a diagram showing the result of placement by the character string placement device in accordance with Embodiment 1; 
         FIG. 14  is a flow chart showing the operation of the evaluation function calculator of the character string placement device in accordance with Embodiment 1; 
         FIG. 15  is an explanatory drawing showing an example of calculation of a link angle by the character string placement device in accordance with Embodiment 1; 
         FIG. 16  is a diagram showing an example of placement by the character string placement device in accordance with Embodiment 1; 
         FIG. 17  is a diagram showing an example of placement by the character string placement device in accordance with Embodiment 1; 
         FIG. 18  is a diagram showing the results of generation of candidate points by the character string placement device in accordance with Embodiment 1; 
         FIG. 19  is a diagram showing an example of placement by the character string placement device in accordance with Embodiment 1; 
         FIG. 20  is a diagram showing an example of placement by the character string placement device in accordance with Embodiment 1; 
         FIG. 21  is an explanatory drawing showing conventional placement of a character string; 
         FIG. 22  is an explanatory drawing showing conventional placement of character strings; and 
         FIG. 23  is an explanatory drawing showing an improvement in the readability of conventional placement of character strings. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     Hereafter, in order to explain this invention in greater detail, the preferred embodiments of the present invention will be described with reference to the accompanying drawings. Embodiment 1. 
       FIG. 1  is a block diagram showing the structure of a character string placement device in accordance with Embodiment 1 of the present invention. The character string placement device  100  is comprised of a character string data storage  1 , a character string data acquirer (data acquirer)  2 , a candidate point generator  3 , a character string placer  4 , an evaluation function calculator  5 , a minimum evaluation function value storer  6 , a minimum evaluation function value data storage  7 , a character string placement data storage  8 , and a character string placement start point data storage  9 . 
     The character string data storage  1  is a storage area for storing a set of data about a plurality of character strings, and stores the number of character strings, the number of characters included in each of the character strings, the width and the height of each of the characters, and a road node series along which each of the character strings is to be placed. The character string data acquirer  2  acquires character string data stored in the character string data storage  1 . The candidate point generator  3  generates two or more placement candidates (referred to as candidate points from here on) for the character string on a road node along which the character string is to be placed. The character string placer  4  places the character string along the road node series from each of the candidate points. 
     The evaluation function calculator  5  evaluates the readability of a character string which is placed. The minimum evaluation function value storer  6  stores, in each storage area, an evaluation function value, character string placement, and a character string placement start point at a time when an evaluation function has a minimum. The minimum evaluation function value data storage unit  7  is a storage area for storing the minimum evaluation function value. The character string placement data storage unit  8  is a storage area for storing the character string placement at the time that the evaluation function has the minimum evaluation function value. The character string placement start point data storage unit  9  is a storage area for storing the character string placement start point at the time that the evaluation function value is a minimum. 
     Next, the operation of the character string placement device will be explained.  FIG. 2  is a flow chart showing the operation of the character string placement device in accordance with Embodiment 1 of the present invention. The character string data acquirer  2  refers to character string data storage  1  to acquire the character string data about a character string to be placed (step ST 1 ). The candidate point generator  3  generates candidate points from each of which the character string acquired in step ST 1  is to be placed on the road node series along which the character string is to be placed (step ST 2 ). The character string placer  4  places the character string from each of the candidate points generated in step ST 2  along the road node series (step ST 3 ). The character string placer  4  further refers to the result of the placement in step ST 3 , and determines whether or not the character string can be placed along the road node series (step ST 4 ). For example, when the character string is placed while extending off the road node series, the character string placer determines that the character string cannot be placed. When the character string placer determines that the character string cannot be placed along the road node series (when NO in step ST 4 ), the character string placement device ends the processing. 
     In contrast, when the character string placer determines that the character string can be placed along the road node series (when YES in step ST 4 ), the evaluation function calculator  5  calculates the evaluation function value of the character string which is placed (step ST 5 ). The minimum evaluation function value storer  6  determines whether or not the evaluation function value calculated in step ST 5  is less than a minimum evaluation function value mini_cost already stored in the minimum evaluation function value data storage unit  7  (step ST 6 ). When the evaluation function value is equal to or greater than the minimum evaluation function value mini_cost (when NO in step ST 6 ), the character string placement device ends the processing. In contrast, when the evaluation function value is less than the minimum evaluation function value mini_cost (when YES in step ST 6 ), the minimum evaluation function value storer  6  stores the evaluation function value calculated in step ST 5  in the minimum evaluation function value data storage  7  (step ST 7 ) and stores data about the character string placement and data about the character string placement start point in the character string placement data storage  8  and in the character string placement start point data storage  9  respectively (step ST 8 ), and the character string placement device ends the processing. 
     Next, a more detailed structure and a more detailed operation of the character string placement device  100  will be explained.  FIGS. 3 to 5  are block diagrams showing each structural component of the character string placement device  100  in details.  FIG. 3  is a block diagram showing the structure of the candidate point generator  3 ,  FIG. 4  is a block diagram showing the structure of the character string placer  4 , and  FIG. 5  is a block diagram showing the structure of the evaluation function calculator  5 . First, as shown in  FIG. 3 , the candidate point generator  3  is comprised of a first link length calculator  31  that calculates the length of each link connecting between two nodes in the road node series, a link full length updater  32  that adds the length of each link calculated by the first link length calculator  31  to determine the full length of the road node series, a candidate point gap calculator  33  that calculates the gap between candidate points from the full length of the links road node series, a generator  34  that generates candidate points on the road node series, a second link length calculator  35  that, when the length of a set link does not satisfy a predetermined condition, changes the nodes and calculates the length of another link, a distance updater  36  that updates the link length on the basis of the length of the other link calculated by the second link length calculator  35 , and an information storage unit  37  that stores information about candidate points including the candidate point gap (cand_gap), a candidate point number (cand_idx), and the length (dist) of a link connecting from the leading node of the road node series to a predetermined node. 
     Next, as shown in  FIG. 4 , the character string placer  4  is comprised of an initial character position determinator  41  that sets the position of the first character of a character string, a link angle calculator  42  that calculates an angle of a link, a character placement position calculator  43  that calculates the placement position of the character, a character-outside-link determinator  44  that determines whether or not the character is placed outside the link, a character placer  45  that sets the placement of the character, an overlap determinator  46  that determines whether the character overlaps another character which is placed previously, a first parameter updater (parameter updater)  47  that updates a parameter necessary for the placement of the character when the character exists on a link and does not overlap any other character, and a second parameter updater  48  that updates a parameter necessary for the placement of the character when the character is placed outside the link. 
     Next, as shown in  FIG. 5 , the evaluation function calculator  5  is comprised of a character gap function calculator  51  that calculates a function value showing the influence of the character gap between character strings on the readability of a character string, a road angle function calculator  52  that calculates a function value showing the influence of an angle of a road on the readability of the character string, and an evaluation function value calculator  53  that calculates an evaluation function value. Further, the character gap function calculator  51  is comprised of an initial character string determinator  54  that determines whether or not the character string is the first one, a first Gaussian function value calculator  55  that calculates a value of a Gaussian function, and a character gap function updater  56  that updates a function value showing the influence of the character gap between character strings on the readability of a character string. In addition, the road angle function calculator  52  is comprised of a second Gaussian function value calculator  57  that calculates a value of a Gaussian function, and a road angle function updater  58  that updates a function value showing the influence of an angle of a road on the readability of a character string. 
     Next, the detailed operations of the candidate point generator  3 , the character string placer  4 , and the evaluation function calculator  5  will be explained. The following explanation of the operations will be made assuming that the character string data about character strings each of which is to be placed along a road node series are the data about a character string “String11” and a character string “String2,” and the widths of the characters are all 5, and the heights of the characters are all 10. Further, a relationship between the road node series along which the character string “String11” is to be placed and the road node series along which the character string “String2” is to be placed is shown in  FIG. 6 . The road node series P(0) to P(2) along which the character string “String11” is to be placed consists of a node P(0)=(10, 20), a node P(1)=(10, 50), and a node P(2)=(100, 50). Similarly, the road node series P(3) to P(5) along which the character string “String2” is to be placed consists of a node P(3)=(50, 70), a node P(4)=(50, 10), and a node P(5)=(110, 10). In addition, STEP_SIZE is set to 1 and CANDIDATE_NUM (the number of candidate points) is set to 3, Σ is expressed by the following equation (2), H is expressed by the following equation (3), RC is set to 1, and SC is set to 1. 
     
       
         
           
             
               
                 
                   Σ 
                   = 
                   
                     ( 
                     
                       
                         
                           1 
                         
                         
                           0 
                         
                       
                       
                         
                           0 
                         
                         
                           1 
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   H 
                   = 
                   
                     ( 
                     
                       
                         
                           1 
                         
                         
                           0 
                         
                       
                       
                         
                           0 
                         
                         
                           1 
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     First, in step ST 1  of the flow chart shown in  FIG. 2 , the character string data acquirer  2  acquires the first character string “String11,” the second character string “String2,” the road node series P(0) to P(2) and the road node series P(3) to P(5) along which the character strings are to be placed respectively, and the width and the height of each of the characters which form each of the character strings from the character string data storage  1 . Next, the character string placement device optimizes the placement of the first character string “String11.” As a method of optimizing the placement, the candidate point generator  3  generates candidate points whose number is equal to preset CANDIDATE_NUM on the road node series P(0) to P(2) along which the character string “String11” is to be placed, i.e., three candidate points at equal intervals. 
     A concrete method of generating candidate points will be explained with reference to a flow chart shown in  FIG. 7 .  FIG. 7  is a flow chart showing the operation of the candidate point generator of the character string placement device in accordance with Embodiment 1. The first link length calculator  31  of the candidate point generator  3  refers to each node information stored in the information storage unit  37 , and calculates the length of the link connecting between the n-th node P(n) and the (n+1)-th node P(n+1) (step ST 11 ). After the first link length calculator  31  calculates the length of the link, the link full length updater  32  adds the length to a link full length which the first link length calculator has calculated the last time and updates the link full length (total_dist) (step ST 12 ). 
     The first link length calculator  31  determines whether the first link length calculator has completed the calculation the lengths of all the links which form the road node series (step ST 13 ). When the first link length calculator has not completed the calculation of the lengths of the links associated with all the nodes (when NO in step ST 13 ), the character string placement device returns to the process of step ST 11  and repeats the above-mentioned processes. In contrast, when the first link length calculator has completed the calculation of the lengths of the links associated with all the nodes (when YES in step ST 13 ), the candidate point gap calculator  33  acquires the number of candidate points (CANDIDATE_NUM) with reference to the information storage  37 , and calculates the gap between candidate points according to the following equation (4) and stores the candidate point gap (cand_gap) calculated thereby in the information storage  37  (step ST 14 ).
 
cand_gap=total_dist/CANDIDATE_NUM  (4)
 
     Next, the generator  34  refers to the information storage  37  acquires the information about the candidate point gap (cand_gap), the candidate point number (cand_idx), and the link length (dist) of the link connecting between the leading node of the road node series and the predetermined node, and determines whether the candidate point satisfies a condition shown by the following equation (5) (step ST 15 ).
 
dist&gt;cand_idxxcand_gap  (5)
 
An initial value of the candidate point number (cand_idx) is 0, and an initial link length (dist) is the length of the link connecting between the leading node of the road node series and the node placed next to the leading node. It is assumed that these initial conditions are stored in advance in the information storage  37 .
 
     When the condition shown in the above-mentioned equation (5) is satisfied (when YES in step ST 15 ), the generator  34  generates a candidate point Q which is located along the road node series at a distance of the candidate point number (cand_idx) x the candidate point gap (cand_gap) from the leading node of the road node series (step ST 16 ). After that, the generator  34  determines whether the generator has generated all candidate points Q whose number is CANDIDATE_NUM (step ST 17 ). When the generator has generated all the candidate points (when YES in step ST 17 ), the character string placement device ends the processing. In contrast, when the generator has not generated all the candidate points (when NO in step ST 17 ), the character string placement device increments the candidate point number by one and stores the candidate point number in the information storage  37  (cand_idx+1 in step ST 18 ), and returns to the process of step ST 15 . 
     In contrast, when the condition shown in the above-mentioned equation (5) is not satisfied (when NO in step ST 15 ), the generator increments the node number in the determining process of step ST 15  by one (step ST 19 ), and calculates the length of the link connecting between the node of the incremented node number and the node placed next to the node of the incremented node number (step ST 20 ). The distance updater  36  adds the length of the link which is newly calculated in step ST 20  to the link length (dist) which is used for the determining process of step ST 15 , and updates the link length (dist) (step ST 21 ). The pieces of information updated insteps ST 19  to ST 21  are stored in the information storage  37 . After that, the flow chart returns to the process of step ST 15 . 
     Next, an explanation will be made by using the concrete example shown in  FIG. 6  along with the flow chart shown in  FIG. 7 . In step ST 11 , the first link length calculator  31  calculates the length: 30 of the link connecting between the 0-th node P(0) and the first node P(1). In step ST 12 , the link full length updater  32  adds the length: 30 of the link to the link full length: 0 which is calculated the last time, and updates the link full length. The first link length calculator similarly calculates the length: 90 of the link connecting between the first node P(1) and the second node P(2), and updates the link full length to 120. When it is determined, in step ST 13 , that the lengths of all the links which form the road node series P(0) to P(2) are calculated, the candidate point gap calculator  33 , in step ST 14 , acquires the number of candidate points (CANDIDATE_NUM)=3 with reference to the information storage  37 , and calculates the candidate point gap (cand_gap): 120/3=40. 
     In step ST 15 , the generator  34  refers to the information storage unit  37  and acquires the candidate point gap (cand_gap): 40, the candidate point number (cand_idx): 0 (initial value), and the link length (dist): 30 (the initial link (P(0), P(1))), and determines whether the candidate point Q(0) satisfies the condition shown by the above-mentioned equation (5). In the example of  FIG. 6 , since 30&gt;0×40, the generator determines that the candidate point satisfies the condition shown by the equation (5). 
     In step ST 16 , the generator  34  generates the candidate point Q(0) at a distance of 0×40=0 from the start node P(0). More specifically, the 0-th candidate point Q(0) is located at the same point as P(0). The position of the candidate point Q(0) is (10, 20), the index of the start node of the link (P(0), P(1)) on which the candidate point Q(0) is placed is 0, and the distance from the start node P(0) of the link on which the candidate point is placed to the candidate point is zero. In step ST 17 , the generator  34  determines that it has not generated all candidate points, and, in step  18 , increments the candidate point number by one and shifts to generation of a candidate point Q(1), and returns to the process of step ST 15 . 
     Next, a generating process of generating the candidate point Q(1) will be explained. In step ST 15 , the generator  34  refers to the information storage unit  37  and acquires the candidate point gap (cand_gap): 40, the candidate point number (cand_idx): 1, and the link length (dist): 30 (the initial link (P(0), P(1))), and determines whether the candidate point Q(1) satisfies the condition shown by the above-mentioned equation (5). In the example of  FIG. 6 , since 30&lt;1×40, the generator determines that the candidate point does not satisfy the condition shown by the equation (5). Then, in steps ST 19  and  20 , the generator adds 1 to the node number of the node P(0) and shifts to the node P(1), and calculates the length: 90 of the link connecting between the node P(1) and the node P(2). In step ST 21 , the distance updater  36  updates the link length (dist) to a value of 120 which the distance updater obtains by adding the link length: 90 calculated thereby to the link length (dist): 30 which is used for the determining process in above-mentioned step ST 15 . After storing the updated information in the information storage  37 , the character string placement device returns to the process of step ST 15 . 
     In step ST 15 , the generator  34  refers to the information storage unit  37  and acquires the candidate point gap (cand_gap): 40, the candidate point number (cand_idx): 1, and the link length (dist): 120 (the link (P(0), P(2))), and determines whether the candidate point Q(1) satisfies the condition shown by the above-mentioned equation (5). In the example of  FIG. 6 , since 120&gt;1×40, the generator determines that the candidate point satisfies the condition shown by the equation (5). In step ST 16 , the generator  34  generates the candidate point Q(1) at a distance of 1×40=40 from the start node P(0). After that, in step ST 17 , the generator  34  determines that it has not generated all candidate points, and, in step  18 , increments the candidate point number by one and shifts to generation of a candidate point Q(2), and returns to the process of step ST 15 . The character string placement device repeatedly performs the above-mentioned processes until the character string placement generates the candidate point Q(2). 
     The results of generating the candidate points for the road node series P(0) to P(2) shown in  FIG. 6  are shown in  FIG. 8 . Further, a positional relationship among the three candidate points Q(0), Q(1), and Q(2) shown in  FIG. 8  is as shown below. 
     Candidate point Q(0) Position: (10, 20), Index of start node: 0, Distance from start node: 0 
     Candidate point Q(1) Position: (20, 50), Index of start node: 1, Distance from start node: 10 
     Candidate point Q(2) Position: (60, 50), Index of start node: 1, Distance from start node: 50 
     Next, an operation of the character string placer  4  placing a character string at a candidate point Q generated by the candidate point generator  3  will be explained.  FIG. 9  is a flow chart showing the operation of the character string placer of the character string placement device in accordance with Embodiment 1. Hereafter, the index of the start node of the link R(Q) on which the candidate point Q is placed is expressed as road_idx, and the distance from the leading node of the road node series along which the candidate point Q is placed to the candidate point Q is expressed as dist. 
     The initial character position determinator  41  carries out an initial setting of road_idx and dist at the time of starting its process (step ST 31 ). Next, the link angle calculator  42  calculates an angle θ of the link connecting between the road_idx(n)-th node and the road_idx(n+1)-th node (step ST 32 ). The angle θ of the link is defined as the angle of the link (road_idx(n), road_idx(n+1)), i.e., the angle of the vector (road_idx(n), road_idx(n+1)), where an X axis direction is defined as 0 degrees and a Y axis direction is defined as 90 degrees. The character placement position calculator  43  calculates a position at a distance of dist from the road_idx(n)-th node in a direction of θ as a character placement position (step ST 33 ). 
     The character-outside-link determinator  44  determines whether the character placement position exists on the link (road_idx(n), road_idx(n+1)) (step ST 34 ). When the character placement position exists on the link (road_idx(n), road_idx(n+1)) (when YES in step ST 34 ), the character placer  45  determines the placement position of the character (step ST 35 ). As a concrete process, the character placer sets the coordinates of the character string placement position which the character placement position calculator  43  calculates in step ST 33  as left bottom coordinates of the character first. In addition, the character placer calculates left top coordinates, right bottom coordinates, and right top coordinates of the character according to the following equation (6). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             LT 
                             ⁡ 
                             
                               ( 
                               char_idx 
                               ) 
                             
                           
                           = 
                           
                             
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                               ⁡ 
                               
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                                 char_idx 
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                                   char_idx 
                                   ) 
                                 
                               
                               ⁢ 
                               
                                 
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                                             ( 
                                             
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                                           sin 
                                           ⁡ 
                                           
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                                               + 
                                               
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                                 T 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           
                             RD 
                             ⁡ 
                             
                               ( 
                               char_idx 
                               ) 
                             
                           
                           = 
                           
                             
                               LD 
                               ⁡ 
                               
                                 ( 
                                 char_idx 
                                 ) 
                               
                             
                             + 
                             
                               
                                 W 
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                                   ( 
                                   char_idx 
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                               ⁢ 
                               
                                 
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                                           ⁢ 
                                           
                                               
                                           
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                                           θ 
                                         
                                       
                                     
                                   
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                                 T 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           
                             RT 
                             ⁡ 
                             
                               ( 
                               char_idx 
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                           = 
                           
                             
                               RD 
                               ⁡ 
                               
                                 ( 
                                 char_idx 
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                             + 
                             
                               
                                 H 
                                 ⁡ 
                                 
                                   ( 
                                   char_idx 
                                   ) 
                                 
                               
                               ⁢ 
                               
                                 
                                   ( 
                                   
                                     
                                       
                                         
                                           cos 
                                           ⁡ 
                                           
                                             ( 
                                             
                                               θ 
                                               + 
                                               
                                                 90 
                                                 ∘ 
                                               
                                             
                                             ) 
                                           
                                         
                                       
                                     
                                     
                                       
                                         
                                           sin 
                                           ⁡ 
                                           
                                             ( 
                                             
                                               θ 
                                               + 
                                               
                                                 90 
                                                 ∘ 
                                               
                                             
                                             ) 
                                           
                                         
                                       
                                     
                                   
                                   ) 
                                 
                                 T 
                               
                             
                           
                         
                       
                     
                   
                   } 
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     In the equation (6), char_idx is an index showing the placement order of each character which forms the character string. In addition, H(char_idx) shows the height of the char_idx-th character, W(char_idx) shows the width of the char_idx-th character, LD(char_idx) shows the left bottom coordinates of the char_idx-th character, LT(char_idx) shows the left top coordinates of the char_idx-th character, RD(char_idx) shows the right bottom coordinates of the char_idx-th character, and RT(char_idx) shows the right top coordinates of the char_idx-th character. 
     The overlap determinator  46  determines whether the placement position determined in step ST 35  overlaps a character which is placed through a previous process (step ST 36 ). When the placement position does not overlap any character (when NO in step ST 36 ), the first parameter updater  47  adds the width of the char_idx-th character to dist and also increments char_idx by “1” (step ST 37 ). After that, the first parameter updater  47  determines whether the character placer has determined the placement positions of all the characters which form the character string (step ST 38 ). After the character placer has determined the placement positions of all the characters (when YES in step ST 38 ), the character string ends the processing. In contrast, when the character placer has not determined the placement positions of all the characters yet (when NO in step ST 38 ), the first parameter updater  47  commands the character placement position calculator  43  to calculate a placement position again on the basis of the parameter updated in step ST 37  (step ST 39 ). After that, the character string placement device returns to the process of step ST 33  and repeats the above-mentioned processes. 
     In contrast, when the placement position overlaps a character (when YES in step ST 36 ), the overlap determinator  46  adds STEP_SIZE to dist (step ST 40 ), and commands the character placement position calculator  43  to calculate a placement position again on the basis of the parameter added in step ST 40  (step ST 41 ) After that, the character string placement device returns to the process of step ST 33  and repeats the above-mentioned processes. 
     In addition, when the character placement position does not exist on the link (when NO in step ST 34 ), the second parameter updater  48  updates the parameter (step ST 42 ). Concretely, the second parameter updater  48  updates dist to a value which the second parameter updater obtains by subtracting the length of the link (road_idx (n), road_idx (n+1)) from dist, and, after incrementing road_idx by one, also commands the character placement position calculator  43  to calculate a placement position again on the basis of the updated parameter (step ST 43 ). After that, the character string placement device returns to the process of step ST 32  and repeats the above-mentioned processes. 
     Next, an explanation will be made by using the concrete example shown in  FIGS. 6 and 8  along with the flow chart shown in  FIG. 9 . First, in step ST 31 , the initial character position determinator  41  carries out an initial setting of road_idx and dist to set the index: 0 showing the start node of the candidate point Q(0) to road_idx and also set the distance: 0 from the leading node P(0) of the road node series P(0) to P(2) to the candidate point Q to dist. In step ST 32 , the link angle calculator  42  calculates the angle θ of the link (P(0), P(1)) as 90 degrees. In step ST 33 , the character placement position calculator  43  calculates, as the character string placement position, the position LD(0)=(10, 20) at a distance of dist=0 from the road_idx=0-th node in a direction of θ=90 degrees. 
     The character-outside-link determinator  44  determines that LD(0) exists on the link (P(0), P(1)) in the determining process of step ST 34 . In step ST 35 , the character placer  45  determines the placement position of the 0-th character “S” of the character string “String11.” The character-outside-link determinator sets LD(0) as the left bottom coordinates of the character “S” first, and then sets LT(0)=(0, 20) as the left top coordinates of the character “S.” After that, the character-outside-link determinator sets RD(0)=(10, 25) as the right bottom coordinates of the character “S.” Finally, the character-outside-link determinator sets RT(0)=(0, 25) as the right top coordinates of the character “S.” The placement of a circumscribed rectangle of the character “S” is shown in FIG.  10 . In step ST 36 , the overlap determinator  46  determines whether or not there is an overlap between the character “S” which is placed in step ST 35  and the character which is placed the last time. In this example, since no character which is placed the last time exists, the overlap determinator determines that there is no overlap. 
     In step ST 37 , the first parameter updater  47  adds the 0-th width “5” to dist and sets dist to dist=0+5=5, and adds “1” to char_idx and sets char_idx to char_idx=0+1=1. Because the first parameter updater  47 , in step ST 38 , determines that the character placer has not determined the placement positions of all the characters which form the character string, the first parameter updater, in step ST 39 , commands the character placement position calculator  43  to calculate a placement position again on the basis of the updated parameter, and returns to the process of step ST 33 . 
     The character placement position calculator  43  which has received the command in step ST 39  calculates the character placement position of the second character “t.” The calculation is carried out on the basis of dist=5 and char_idx=1, which are updated in step ST 37 . In step ST 33 , the character placement position calculator  43  calculates the position LD(1)=(10, 25) as the character string placement position. The character string placement device carries out the processes of steps ST 34  to ST 36 . As a result, it is determined that LD(1) exists on the link (P(0), P(1)), and the left bottom coordinates, the left top coordinates, the right bottom coordinates, and the right top coordinates of the second character “t” are LD (1)=(10, 25), LT(1)=(0, 25), RD(1)=(10, 30), and RT(1)=(0, 30) respectively. The placement of a circumscribed rectangle of the second character “t” is shown in  FIG. 11 . Because it is determined, in step ST 36 , that the character which is placed as the first character overlaps the character which is placed as the second character, the overlap determinator  46 , in step ST 40 , adds STEP_SIZE=1 to dist, and, in step ST 41 , commands the character placement position calculator  43  to calculate the character placement position of the second character “t” again on the basis of the incremented parameter. 
     The character string placement device repeats the processes of steps ST 33  to ST 36  again, and calculates the character placement position of the second character “t.” The calculation is carried out on the basis of dist=6, which is incremented in step ST 40 , and char_idx=1. The results of repeating the above-mentioned processes and placing the second character LD(1) through the sixth character LD(5) are shown in  FIG. 12 . Only the left bottom coordinates of each of the characters are shown in  FIG. 12 . 
     After placing the sixth character, the character placement position calculator  43  calculates the placement position of the seventh character “1” of the character string “String11.” At this time, because dist=35, cand_idx=6, and road_idx=0, the position at a distance of dist from the road_idx-th node in a direction of θ is LD(6)=(10, 55). In step ST 34 , the character-outside-link determinator  44  determines that the placement position (10, 55) is outside the link (P(0), P(1)), and the second parameter updater  48 , in step ST 42 , updates the parameter. Concretely, because the length of the link connecting between the 0-th node and the first node is “30”, dist is updated to dist=35−30=5 and road_idx is set to road_idx=0+1=1. After that, the second parameter updater, in step ST 43 , issues a command for calculating the placement position again on the basis of the parameter updated by the second parameter updater  48 , and returns to the process of step ST 32 . 
     In step ST 32 , the link angle calculator  42  calculates the angle θ of the link (P(1), P(2)) as 0 degrees on the basis of the updated parameter. After that, the character string placement device carries out the same processes as those mentioned above to place the seventh character and the eighth character, and, when it is determined in the determining process of step ST 38  that the placement positions of all the characters have been determined, ends the processing. The results of placing all the characters are shown in  FIG. 13 . Also in  FIG. 13 , only the left bottom coordinates of each of the characters are shown. 
     Next, a method of calculating an evaluation function value showing the influence of a character string which is placed on the readability will be explained.  FIG. 14  is a flow chart showing the operation of the evaluation function calculator of the character string placement device in accordance with Embodiment 1. First, the character gap function calculator  51  calculates a value P(S string   _   idx |{S string   _   idx-1 }) of a character gap function which is a function showing the character gap between each character string (each of 0-th to (string_idx−1)-th character strings) whose placement is already determined and the string_idx(n)-th character string. Concretely, the initial character string determinator  54  of the character gap function calculator  51  determines whether either string_idx=0 or string_idx≧1 is established (step ST 51 ). When it is determined, in step ST 51 , that string_idx=0 is established, the initial character string determinator sets “1” to the character gap function value P(S string   _   idx |{S string   _   idx-1 }) (step ST 52 ), and then advances to the process by the road angle function calculator  52 . 
     In contrast, when it is determined, in step T 51 , that string_idx≧1 is established, the character gap function updater  56  calculates the character gap function value P(S string   _   idx |{S string   _   idx-1 }) according to the following equation (7) (step ST 53 ), and advances to the process by the road angle function calculator  52 . 
                     P   ⁡     (       S   string_idx     ❘     {     S     string_idx   -   1       }       )       =       ∑       char_idx   =   0     ⁢               C   string_idx       ⁢           ⁢       ∑       string_idx   ⁢           ⁢   2     =   0       string_idx   -   1       ⁢           ⁢       ∑       char_idx   ⁢   2     =   0       C     string_idx   ⁢   2         ⁢           ⁢       N   ′     ⁡     (       x   char_idx     ❘     x     char_idx   ⁢   2         )                     (   7   )               
In the above-mentioned equation (7), C string   _   idx  and C string   _   idx2  shows the number of characters of the string_idx-th character string and the number of characters of the string_idx2-th character string respectively. Further, x char   _   idx  and x char   _   idx2  in the equation (7) show the center coordinates of the char_idx-th character and the center coordinates of the char_idx2-th character respectively.
 
     N′(x char   _   idx |x char   _   idx2 ) in the above-mentioned equation (7) is calculated by the first Gaussian function output unit  55  according to the following equation (8). 
                       N   ′     ⁡     (       x   char_idx     ❘     x     char_idx   ⁢   2         )       =     SC   ×     exp   (     -           (       x   char_idx     -     x     char_idx   ⁢   2         )     T     ⁢       H     -   1       ⁡     (       x   char_idx     -     x     char_idx   ⁢   2         )         2       )               (   8   )               
x char   _   idx  and x char   _   idx2  in the above-mentioned equation (8) show the center coordinates of the char_idx-th character and the center coordinates of the char_idx2-th character respectively, SC shows a constant, and H −1  shows a covariance matrix.
 
     The road angle function updater  58  calculates a road angle function value P(R string   _   idx |S string   _   idx ) according to the following equation (9) (step ST 54 ). 
                     P   ⁡     (       R   string_idx     ❘     S   string_idx       )       =       ∑     char_idx   =   0       C   string_idx       ⁢           ⁢       ∑     road_idx   =   1         No   string_idx     -   1       ⁢           ⁢     N   ⁡     (       x   char_idx     ❘     μ   road_idx       )                   (   9   )               
No string   _   idx  in the above-mentioned equation (9) shows the number of nodes in the road node series along which the string_idx-th character string is to be placed, and μ road   _   idx  shows the coordinates of the road_idx-th node in the road node series.
 
     N(x char   _   idx |μ road   _   idx ) in the above-mentioned equation (9) is calculated by the second Gaussian function value calculator  57  according to the following equation (10). 
     
       
         
           
             
               
                 
                   
                     N 
                     ⁡ 
                     
                       ( 
                       
                         
                           x 
                           char_idx 
                         
                         ❘ 
                         
                           μ 
                           road_idx 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       Angle 
                       ⁡ 
                       
                         ( 
                         road_idx 
                         ) 
                       
                     
                     × 
                     
                       exp 
                       ( 
                       
                         - 
                         
                           
                             
                               
                                 ( 
                                 
                                   
                                     x 
                                     char_idx 
                                   
                                   - 
                                   
                                     μ 
                                     road_idx 
                                   
                                 
                                 ) 
                               
                               T 
                             
                             ⁢ 
                             
                               
                                 ∑ 
                                 
                                   - 
                                   1 
                                 
                               
                               ⁢ 
                               
                                 ( 
                                 
                                   
                                     x 
                                     char_idx 
                                   
                                   - 
                                   
                                     μ 
                                     road_idx 
                                   
                                 
                                 ) 
                               
                             
                           
                           2 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     In the above-mentioned equation (10), x char   _   idx  and μ road   _   idx  are vectors show position coordinates, x char   _   idx  shows the center of the char_idx-th character, and μ road   _   idx  shows the road_idx-th road node. Further, T shows a transposition, and Σ −1  shows the inverse matrix of Σ. Angle(road_idx) in the above-mentioned equation (10) shows an angle variation which the link connecting between the (road_idx−1)-th node and the road_idx-th node forms with the link connecting between the (road_idx+1)-th node and the road_idx-th node. An example of the calculation of Angle(road_idx) is shown in  FIG. 15 . R(road_idx) in  FIG. 15  shows the road_idx-th road node. As shown in  FIG. 15 , an angle variation which two links form with each other is defined as a variation in the angles of the links. 
     The evaluation function value calculator  53  calculates the evaluation function value F by using the character gap function value P(S string   _   idx |{S string   _   idx-1 }) calculated in step ST 52  or ST 53  and the road angle function value P(R string   _   idx |S string   _   idx ) calculated in step ST 54  according to the following equation (11) (step ST 55 ).
 
 F =log  P ( R   string   _   idx   |S   string   _   idx )+log  P ( S   string   _   idx   |{S   string   _   idx-1 })  (11)
 
The calculated evaluation function value F is outputted to the minimum evaluation function value storer  6  (step ST 56 ), and the character string placement device ends the processing.
 
     Next, an explanation will be made by using the concrete example shown in  FIG. 13  along with the flow chart shown in  FIG. 14 . In step ST 51 , the initial character string determinator  54  determines whether either string_idx=0 or string_idx≧1 is established. First, since the determination is the first one, string_idx=0 is established at this time, and the initial character string determinator sets, in step ST 52 , sets “1” to the character gap function value P(S string   _   idx |{S string   _   idx-1 }). 
     Next, the road angle function updater  58 , in step ST 54 , calculates the value of P(R string   _   idx |S string   _   idx ) as 2.36036×10 −85  according to the above-mentioned equation (9). After that, the road angle function updater  58  updates char_idx and road_idx to repeat the process of step ST 54 , and finally acquires the value of P(R string   _   idx |S string   _   idx )=0.000777442. 
     In step ST 55 , the evaluation function value calculator  53  calculates the evaluation function value on the basis of the character gap function value P(S string   _   idx |{S string   _   idx-1})= 1 which is calculated in step ST 52 , and the road angle function value P(R string   _   idx |S string   _   idx )=0.000777442 which is finally acquired in step ST 54  according to the above-mentioned equation (11), and acquires the evaluation function value F=log 0.000777442+log 1=−3.109331764. In step ST 56 , the evaluation function value calculator outputs the evaluation function value F calculated thereby to the minimum evaluation function value storer  6 . The minimum evaluation function value storer  6  determines that the calculated evaluation function value F is less than min_cost and then sets F=−3.109331764 to the value of min_cost and stores this value in the minimum evaluation function value data storage  7 , and also sets Q(0) to the character string start point of the 0-th character string and stores this character string start point in the character string placement start point data storage  9 . The minimum evaluation function value storer further stores the character string placement shown in  FIG. 13  in the character string placement data storage  8 , and the character string placement device ends the processing. 
     After that, the character string placement device repeats the above-mentioned processes, and the character string placer  4  places the 0-th character string from the first candidate point Q(1). An example of the placement in this case is shown in  FIG. 16 . The evaluation function value calculator  53  calculates the evaluation function value F for the example of the placement shown in  FIG. 16 . In this example, the evaluation function value F is −19.48284883 and is outputted to the minimum evaluation function value storer  6 . Because the evaluation function value F is less than mini_cost, the minimum evaluation function value storer  6  updates the value of mini_cost to −19.48284883 and sets Q(1) to the character string start point, and stores the character string placement shown in  FIG. 16  in the character string data storage  7 , and the character string placement device ends the processing. 
     The character string placement device further repeats the same processes, and places the character string from the second candidate point Q(2). In this case, up to the seventh character is placed as shown in  FIG. 17 . After that, the character placement position calculator  43  of the character string placer  4  calculates the placement position of the eighth character. At this time, dist=101 and road_idx=1. Therefore, the character placement position calculator calculates a position LD(7) at a distance of dist from the road_idx-th node P(1) along the link connecting between the road_idx-th node and the (road_idx+1)-th node. LD(7)=(101, 50) is obtained as the result of the calculation. 
     After that, the character-outside-link determinator  44  determines whether or not LD(7) is located outside the link. Because LD(7) is located outside the link, the second parameter updater  48  updates dist. In this case, dist is updated to dist=1. After that, because no link along which the eighth character is to be placed exists, the character string placement device ends the processing. More specifically, because it is impossible to place the character string “String11” from the candidate point Q(2), the calculation using the evaluation function is not carried out. The character string placement start point of the 0-th character string is determined in this way. In this case, the character string placement start point of the 0-th character string which is the character string “String11” is set to Q(1). Further, the character string placement (refer to  FIG. 16 ) to place the character string from Q(1) along the road node series is used for optimization of the character string placement start points of the first and subsequent character strings. 
     After determining the character string placement point of the 0-th character string “String11,” the character string placement device then carries out the same processes also on “String2” which is the first character string. First, the candidate point generator  3  generates candidate points on the road link along which the first character string is to be placed. In this case, as shown in  FIG. 18 , three candidate points Q(3), Q(4), and Q (5) are generated. Next, the character string placer  4  places the first character string from the candidate point Q(3) (refer to  FIG. 19 ). After that, the evaluation function calculator  5  calculates the evaluation function value F. 
     Concretely, the initial character string determinator  54 , in step ST 51 , determines that string_idx=1 is established, and the character gap function updater  56 , in step ST 53 , calculates the value of the character gap function value P(S string   _   idx |{S string   _   idx-1 }) as 5.1×10 −264  according to the above-mentioned equation (7). After that, the character string placement device repeats the process by the character gap function updater  56  to update the character gap function value P(S string   _   idx |{S string   _   idx-1 }), and finally acquires the value of P(S string   _   idx |{S string   _   idx-1 })=0.040705. 
     Next, the road angle function updater  58 , in step ST 54 , calculates the value of P(R string   _   idx |S string   _   idx ) as 1.96618×10 −53 . In step ST 55 , the evaluation function value calculator  53  calculates the evaluation function value F on the basis of the character gap function value P(S string   _   idx |{S string   _   idx-1 })=0.040705 and the road angle function value P(R string   _   idx |S string   _   idx )=1.96618×10 −53  according to the above-mentioned equation (11). In this case, the evaluation function value F is F=log 1.96618×10 −53 +log 0.040705=−52.7063767−1.3936=−54.0999767. In step ST 56 , the evaluation function value calculator outputs the evaluation function value F calculated thereby to the minimum evaluation function value storer  6 . 
     After that, the minimum evaluation function value storer  6  determines that the calculated evaluation function value F is less than min_cost, and sets min_cost to min_cost=−54.0999767 and stores this value in the minimum evaluation function value data storage  7 . The minimum evaluation function value storer also sets the character string placement start point of the first character string to Q(3) and stores this character string placement start point in the character string placement start point data storage  9 , and further stores the character string placement shown in  FIG. 19  in the character string placement data storage  8 . 
     After that, the character string placer  4  similarly places the first character string “String2” from the candidate point Q(4) (refer to  FIG. 20 ). The character gap function calculator  51  calculates the character gap function value P(S string   _   idx |{S string   _   idx-1 })=2.7947×10 −166 . After that, the road angle function calculator  52  calculates the road angle function value P(R string   _   idx |S string   _   idx )=0.002850205. The evaluation function value calculator  53  calculates the evaluation function value F by using these values according to the above-mentioned equation (11). In this case, the evaluation function value F is F=log 2.7947×10 −166 +log 0.002850205=−165.55367−2.244093909=−167.7977639. The minimum evaluation function value storer  6  determines that the calculated evaluation function value F is less than min_cost, and sets min_cost to min_cost=−167.7977639 and also sets the character string placement start point of the first character string to Q(4). 
     Similarly, the character string placer  4  places the character string from Q(5). In this case, because in the placement of the character string from Q(5), the length of the road link is not sufficient and hence the character string cannot be placed properly, the character string placer determines that the character string placement has failed, and the character string placement device ends the processing. Through the above-mentioned processes, the character string placement start point of the first character string which is the character string “String2” is determined as Q(4). 
     As mentioned above, because the character string placement device in accordance with this Embodiment 1 is constructed in such a way that the character gap function calculator  51  that calculates a function value showing the influence of the character gap between character strings on the readability of each of the character strings is disposed in the evaluation function calculator  5 , the character string placement device can set the character string placement start point of each of the character strings to an optimal position in such a way that the gap between character strings becomes large, in addition to taking into consideration an overlap between character strings and a variation in the angle of a road along which each of the character string is to be placed. As a result, the gap between character strings can be made to become wide, the degree of closeness between character strings can be prevented from becoming high, and the visibility of each of the character strings can be improved. 
     Further, because the character string placement device in accordance with this Embodiment 1 is constructed in such a way as to include the first Gaussian function value calculator  55  that calculates a Gaussian function value when calculating the character gap function value, a Gaussian distribution can be placed at the middle point between a road node and a character which is already placed, and the character string placement start point can be changed to an optimal position in such a way that the gap between character strings becomes wide. 
     While the invention has been described in its preferred embodiment, it is to be understood that various changes can be made in an arbitrary component in accordance with the embodiment, and an arbitrary component in accordance with the embodiment can be omitted within the scope of the invention. 
     INDUSTRIAL APPLICABILITY 
     The character string placement device in accordance with the present invention can be used for an improvement in the visibility of a display device or the like, and can also be utilized for application to a navigation device which provides an improved user visibility, and so on. 
     EXPLANATIONS OF REFERENCE NUMERALS 
       1  character string data storage,  2  character string data acquirer,  3  candidate point generator,  4  character string placer,  5  evaluation function calculator,  6  minimum evaluation function value storer,  7  minimum evaluation function value data storage,  8  character string placement data storage,  9  character string placement start point data storage,  31  first link length calculator,  32  link full length updater,  33  candidate point gap calculator,  34  generator,  35  second link length calculator,  36  distance updater,  37  information storage,  41  initial character position determinator,  42  link angle calculator,  43  character placement position calculator,  44  character-outside-link determinator,  45  character placer,  46  overlap determinator,  47  first parameter updater,  48  second parameter updater,  51  character gap function calculator,  52  road angle function calculator,  53  evaluation function value calculator,  54  initial character string determinator,  55  first Gaussian function value calculator,  56  character gap function updater,  57  second Gaussian function value calculator,  58  road angle function updater,  100  character string placement device.