Patent Publication Number: US-2022230297-A1

Title: Evaluation apparatus, evaluation method, and non-transitory storage medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of U.S. patent application Ser. No. 17/262,964 filed on Jan. 25, 2021, which is a National Stage Entry of international application PCT/JP2018/028557 filed on Jul. 31, 2018, the disclosures of all of which are incorporated in their entirety by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an evaluation apparatus, an obtaining apparatus, a surveillance method, a surveillance apparatus, an evaluation method, a computer program, and an obtaining method. 
     BACKGROUND ART 
     When surveillance is performed with images from a camera, the arrangement of cameras has an influence on the accuracy of the surveillance. That is, in order to surveil the target region as thoroughly as possible, it is necessary to arrange the cameras appropriately. 
     Patent Document 1 discloses a surveillance apparatus that processes an image obtained by a camera to track an object. 
     Patent Document 2 discloses a technique of obtaining a camera arrangement for facilitating image processing for surveillance. 
     Patent Document 3 discloses that an orientation evaluation, an obstruction evaluation, and an image quality evaluation are performed for a plurality of image capturing apparatuses that capture an image of a surveillance target, and the representative image capturing apparatus is determined. 
     Patent Document 4 discloses that the next action of an intruder is predicted based on the trajectory information of the intruder, and the importance is ranked based on a plurality of camera images, or the orientation and the like of a surveillance camera is controlled in accordance with the computed movement direction of the intruder. 
     Patent Document 5 discloses an evaluation apparatus that evaluates the arrangement position of a surveillance camera using a non-diffraction Voronoi diagram. 
     Patent Document 6 discloses a technique of selecting a camera to be used for display in a method of switching a plurality of cameras and displaying an image. 
     RELATED DOCUMENTS 
     Patent Documents 
     
         
         [Patent Document 1] Japanese Patent Application Publication No. H7-49952 
         [Patent Document 2] International Publication No. WO 2014/002398 
         [Patent Document 3] Japanese Patent Application Publication No. 2016-127571 
         [Patent Document 4] Japanese Patent Application Publication No. 2014-36414 
         [Patent Document 5] Japanese Patent Application Publication No. 2011-86995 
         [Patent Document 6] Japanese Patent Application Publication No. 2017-139725 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     However, in the techniques in Patent Documents 1 to 6, it is not possible to realize a surveillance apparatus with decreased frequency of overlooking. For example, Patent Document 1 does not disclose the camera arrangement suitable for surveilling an object. The technique in Patent Document 2 is a technique for intending to obtain an image suitable for image processing, and thus it is difficult to perform the evaluation and the optimization for clearly capturing the entire target region. The techniques in Patent Documents 3 and 6 are techniques of selecting the best image from the obtained images, and it is not possible to evaluate the arrangement of the image capturing apparatus in consideration of other factors than the arrangement of the image capturing apparatus already provided. The technique in Patent Document 4 is a technique of focusing on and tracking a specific object, and it is not possible to reduce the blind spot in the entire target region. In the technique in Patent Document 5, it is difficult to perform the evaluation in consideration of conditions other than the target region and the shape of an obstacle. 
     The present invention has been made in view of the above problems. An object of the present invention is to provide a technique capable of realizing surveillance in which overlooking occurs less frequently. 
     Solution to Problem 
     According to the present invention, an evaluation apparatus evaluates an arrangement of one or more image capturing apparatuses that surveil a target region. The evaluation apparatus includes an acquisition unit that acquires arrangement information and environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, and the environmental information indicating an environment of the target region, an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     According to the present invention, an obtaining apparatus obtains an arrangement of one or more image capturing apparatuses that surveil a target region. The obtaining apparatus includes an acquisition unit that acquires condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region, an arrangement information generation unit that generates a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, an evaluation unit that evaluates each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information, and a selection unit that selects one or more pieces of the arrangement information from among the plurality of pieces of arrangement information, based on an evaluation result of the evaluation unit. The evaluation unit includes an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     According to the present invention, a first surveillance apparatus surveils a target region with one or more image capturing apparatuses. The first surveillance apparatus includes an obtaining unit that obtains an arrangement of the image capturing apparatus, and an arrangement control unit that controls the arrangement of the image capturing apparatus based on the arrangement of the image capturing apparatus obtained by the obtaining unit. The obtaining unit includes an acquisition unit that acquires condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region, an arrangement information generation unit that generates a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, an evaluation unit that evaluates each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information, and a selection unit that selects one or more pieces of the arrangement information from among the plurality of pieces of arrangement information, based on an evaluation result of the evaluation unit. The evaluation unit includes an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     According to the present invention, there is provided an evaluation method of evaluating an arrangement of one or more image capturing apparatuses that surveil a target region. The evaluation method includes an acquisition step of acquiring arrangement information and environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, and the environmental information indicating an environment of the target region, an index computation step of computing, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and a suitability computation step of computing suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     According to the present invention, there is provided a first computer program for realizing an evaluation apparatus that evaluates an arrangement of one or more image capturing apparatuses that surveil a target region. The first computer program causes a computer to function as an acquisition unit that acquires arrangement information and environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, and the environmental information indicating an environment of the target region, an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     According to the present invention, there is provided an obtaining method of obtaining an arrangement of one or more image capturing apparatuses that surveil a target region. The obtaining method includes an acquisition step of acquiring condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region, an arrangement information generation step of generating a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, an evaluation step of evaluating each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information, and a selection step of selecting one or more pieces of the arrangement information from the plurality of pieces of arrangement information, based on an evaluation result in the evaluation step. The evaluation step includes an index computation step of computing, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and a suitability computation step of computing suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     According to the present invention, there is provided a second computer program for realizing an obtaining apparatus that obtains an arrangement of one or more image capturing apparatuses that surveil a target region. The second computer program causes a computer to function as an acquisition unit that acquires condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region, an arrangement information generation unit that generates a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, an evaluation unit that evaluates each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information, and a selection unit that selects one or more pieces of the arrangement information from among the plurality of pieces of arrangement information, based on an evaluation result of the evaluation unit. The evaluation unit includes an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     According to the present invention, there is provided a surveillance method of surveilling a target region with one or more image capturing apparatuses. The surveillance method includes an obtaining step of obtaining an arrangement of the image capturing apparatus, and an arrangement control step of controlling the arrangement of the image capturing apparatus based on the arrangement of the image capturing apparatus obtained in the obtaining step. The obtaining step includes an acquisition step of acquiring condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region, an arrangement information generation step of generating a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, an evaluation step of evaluating each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information, and a selection step of selecting one or more pieces of the arrangement information from among the plurality of pieces of arrangement information, based on an evaluation result in the evaluation step. The evaluation step includes an index computation step of computing, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and a suitability computation step of computing suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     According to the present invention, there is provided a third computer program for realizing a surveillance apparatus that surveils a target region with one or more image capturing apparatuses. The third computer program causes a computer to function as an obtaining unit that obtains an arrangement of the image capturing apparatus, and an arrangement control unit that controls the arrangement of the image capturing apparatus based on the arrangement of the image capturing apparatus obtained by the obtaining unit. The obtaining unit includes an acquisition unit that acquires condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region, an arrangement information generation unit that generates a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, an evaluation unit that evaluates each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information, and a selection unit that selects one or more pieces of the arrangement information from among the plurality of pieces of arrangement information, based on an evaluation result of the evaluation unit. The evaluation unit includes an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     According to the present invention, a second surveillance apparatus surveils a target region with one or more image capturing apparatuses. The second surveillance apparatus includes at least one of an analysis unit that analyzes an image captured by the image capturing apparatus and a display unit that displays the image. The image capturing apparatus is placed based on arrangement information obtained based on distribution of a surveillance index in the target region. The surveillance index is computed based on environmental information indicating an environment of the target region for each of a plurality of positions in the target region, and indicates difficulty or easiness of surveillance of a target object in a case where the target object is located at the position. The arrangement information indicates at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide a technique capable of realizing surveillance in which overlooking occurs less frequently. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-described object, other objects, features, and advantages will be further clarified by the preferred example embodiments described below and the accompanying drawings. 
         FIG. 1  is a block diagram illustrating a configuration of an evaluation apparatus according to a first example embodiment. 
         FIG. 2  is a diagram illustrating an evaluation method according to the first example embodiment. 
         FIG. 3  is a flowchart illustrating the evaluation method according to the first example embodiment. 
         FIGS. 4( a ) and 4( b )  are diagrams illustrating an example in which an index computation unit computes a surveillance index based on brightness of a target object captured by an image capturing apparatus. 
         FIG. 5  is a graph illustrating a relation between the brightness and a surveillance-unsuitability index. 
         FIG. 6  is a diagram illustrating a method of computing suitability by a suitability computation unit. 
         FIG. 7  is a graph illustrating a relation between a statistical value D and the suitability. 
         FIG. 8  is a diagram illustrating a second example of arrangement of the image capturing apparatus. 
         FIGS. 9( a ) to 9( c )  are diagrams illustrating third to fifth examples of the arrangement of the image capturing apparatus, respectively. 
         FIGS. 10( a ) and 10( b )  are diagrams illustrating a sixth example and a seventh example of the arrangement of the image capturing apparatus, respectively. 
         FIGS. 11( a ) and 11( b )  are diagrams illustrating an eighth example and a ninth example of the arrangement of the image capturing apparatus, respectively. 
         FIG. 12  is a diagram illustrating a computer of realizing the evaluation apparatus. 
         FIG. 13  is a block diagram illustrating a configuration of an obtaining apparatus according to a fourth example embodiment. 
         FIG. 14  is a flowchart illustrating an obtaining method according to the fourth example embodiment. 
         FIG. 15  is a flowchart illustrating contents of an evaluation step according to the fourth example embodiment. 
         FIG. 16  is a block diagram illustrating a configuration of a surveillance apparatus according to a fifth example embodiment. 
         FIG. 17  is a block diagram illustrating a configuration of a surveillance apparatus according to a sixth example embodiment. 
         FIG. 18  is a flowchart illustrating a surveillance method according to the sixth example embodiment. 
         FIG. 19  is a block diagram illustrating a configuration of a surveillance apparatus according to a seventh example embodiment. 
         FIG. 20  is a flowchart illustrating contents of processing of updating the arrangement, which is performed by the surveillance apparatus according to the seventh example embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, example embodiments of the present invention will be described with reference to the drawings. In all the drawings, the similar constituents are denoted by the similar reference signs, and description thereof will not be repeated. 
     First Example Embodiment 
       FIG. 1  is a block diagram illustrating a configuration of an evaluation apparatus  10  according to a first example embodiment. In addition,  FIG. 2  is a diagram illustrating an evaluation method according to the first example embodiment. The evaluation apparatus  10  according to the present example embodiment evaluates the arrangement of one or more image capturing apparatuses  50  that surveil a target region  60 . The evaluation apparatus  10  includes an acquisition unit  110 , an index computation unit  120 , and a suitability computation unit  140 . 
     The acquisition unit  110  acquires arrangement information and environmental information. The arrangement information indicates at least any of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 . The environmental information indicates the environment of the target region  60 . The index computation unit  120  computes, for each of a plurality of positions p i  in the target region  60 , a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at each of the plurality of positions p i . The suitability computation unit  140  computes the suitability of the arrangement of the image capturing apparatus  50  indicated by the arrangement information, based on the distribution of the surveillance index in the target region  60 . This will be described in detail below. 
     The target region  60  is a region to be surveilled. The target region  60  may be indoors or outdoors. The target region  60  may be a region surrounded by a wall, a door, or the like. A portion of a region wider than the target region  60  may be freely defined as the target region  60 . 
     The target region  60  is surveilled by one or more image capturing apparatuses  50 . The target region  60  may be surveilled by one image capturing apparatus  50 , but is preferably surveilled by a plurality of image capturing apparatuses  50 . The image capturing apparatus  50  is arranged to enable capturing of an image of at least a portion of the target region  60 . The image captured by the image capturing apparatus  50  may be a still image or may form a moving image. The image capturing apparatus  50  is, for example, a security camera or a video camera. The image capturing apparatus  50  may be an analog camera or a network camera (IP camera). The image capturing apparatus  50  may be a visible light camera, or may be a camera such as an infrared camera that detects light other than the visible light. 
     The evaluation apparatus  10  according to the present example embodiment evaluates the arrangement of the image capturing apparatus  50  in the target region  60 . That is, the evaluation apparatus  10  evaluates an image capturing region of the image capturing apparatus  50 . The image capturing region of the image capturing apparatus  50  is defined by the arrangement of the image capturing apparatus  50 . The arrangement of the image capturing apparatus  50  includes the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 . The evaluation apparatus  10  can evaluate the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 , as the arrangement of the image capturing apparatus  50 . That is, it is possible to compute the suitability for the combination of the position, orientation, and the field angle of the image capturing apparatus  50 . 
     When the target region  60  is surveilled by a plurality of image capturing apparatuses  50 , the evaluation apparatus  10  computes the evaluation result for the combination of the arrangement of the plurality of image capturing apparatuses  50 , that is, computes the suitability for surveillance. 
     On the other hand, some of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50  may be predetermined, and the evaluation apparatus  10  may evaluate the remaining of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 . For example, the position and the field angle of the image capturing apparatus  50  may have already been defined, and the evaluation apparatus  10  may evaluate only the orientation of the image capturing apparatus  50 . That is, the evaluation apparatus  10  may compute the suitability of the orientation of the image capturing apparatus  50  on the premise of the position and the field angle of the image capturing apparatus  50 , which have been predetermined. 
     The acquisition unit  110  acquires the arrangement information and the environmental information from the outside of the evaluation apparatus  10  or in the evaluation apparatus  10 . For example, a user may perform an input operation on the evaluation apparatus  10 , and the acquisition unit  110  may acquire the arrangement information and the environmental information based on the input contents of the user. The acquisition unit  110  may acquire the environmental information from a detection unit such as a sensor or a camera. Further, the arrangement information and the environmental information may be stored in advance in the storage unit  100  provided outside or inside the evaluation apparatus  10 , and the acquisition unit  110  may read and acquire the arrangement information and the environmental information. The storage unit  100  refers to any storage device.  FIG. 1  illustrates an example in which the evaluation apparatus  10  includes the storage unit  100 . 
     As described above, the arrangement information indicates at least any of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 . The position of the image capturing apparatus  50  is represented by, for example, the spatial coordinates of the image capturing apparatus  50 , that is, the planar position coordinates and the height. The coordinate space may be a coordinate system relative to the target region  60 , or may be a real world coordinate system defined with a certain point in the real space as the origin. The orientation of the image capturing apparatus  50  is, that is, the pose of the image capturing apparatus  50 , and is represented by, for example, a vector in the coordinate space. The orientation of the image capturing apparatus  50  may be represented by a combination of an elevation angle or a depression angle with a rotation angle in a horizontal direction. In a case where the image capturing apparatus  50  is attached to a drive apparatus capable of changing the orientation of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50  may be represented by a control parameter of the drive apparatus. The field angle of the image capturing apparatus  50  is represented by, for example, a combination of a horizontal angle and a vertical angle, or by a diagonal angle. Further, the field angle of the image capturing apparatus  50  may be represented by a camera parameter representing, for example, the degree of zoom of the image capturing apparatus  50 . 
     In a case where the target region  60  is surveilled by a plurality of image capturing apparatuses  50 , the arrangement information includes information regarding all the image capturing apparatuses  50 . It should be noted that, the acquisition unit  110  may acquire some pieces of the arrangement information by a method different from a method for acquiring other pieces of the arrangement information. For example, some pieces of the arrangement information may be stored in the storage unit  100  in advance, and the other pieces may be input by the user. 
     The environmental information indicates at least any of the shape of the target region  60 , the size of the target region  60 , the position of an object  660  (for example, illustrated in  FIG. 11 ) placed in the target region  60 , the shape of the object  660 , the size of the object  660 , and the orientation of the object  660 . Preferably, the environmental information includes at least information indicating the shape of the target region  60  and the size of the target region  60  among the above-described items. The environmental information may further include information indicating the type of the target region or the type of at least a portion of the target region. The type of target region or the type of at least the portion of the target region is, for example, indoors, an elongated passage, or outdoors. The information indicating the shape of the target region  60  and the size of the target region  60  is, for example, drawing information. Further, the environmental information may be three-dimensional model data indicating the target region  60  and the object  660 . 
     The object  660  placed in the target region  60  is a so-called obstacle in surveillance. For example, the object  660  is a pillar, a wall, a window, an appliance, a lighting (for example, hanging from a ceiling), an advertisement, a display, a guide plate, or the like. Information indicating the position of the object  660  is represented by spatial coordinates. The coordinate space may be a coordinate system relative to the target region  60 , or may be a real world coordinate system. Information indicating the shape of the object  660 , the size of the object  660 , and the orientation of the object  660  is, for example, drawing information. A plurality of objects  660  may be arranged in the target region  60 . The environmental information may further include information indicating the type of product arranged on the appliance in a case where the target region  60  is the sales floor of a store. Further, in a case where a staircase, a slope, a step, or the like is in the target region  60 , the environmental information may further include information indicating the length, the height, and the incline thereof. 
     In a case where a lighting exists as the object  660 , the environmental information may include information indicating the distribution of the illuminance of the lighting. The environmental information may further include information indicating the irradiation direction of sunlight. 
     The arrangement information is associated with the environmental information. Thus, the arrangement of the image capturing apparatus  50  for the target region  60  is indicated by the arrangement information and the environmental information. It should be noted that, the image capturing apparatus  50  is not necessarily required to be arranged in the target region  60  as long as the image capturing apparatus  50  is capable of capturing an image of at least a portion of the target region  60 . 
     In a case where the user performs an input operation on the evaluation apparatus  10  and the acquisition unit  110  acquires the environmental information based on the input contents of the user, for example, the user may use an input unit such as a touch panel on a screen of a display device to set the target region  60 , and may input conditions for the disposition of the object  660  or the like, a lighting, or sunlight. In a case where the user performs an input operation on the evaluation apparatus  10  and the acquisition unit  110  acquires the arrangement information based on the input contents of the user, for example, the image capturing apparatus  50  may be arranged on the screen showing the target region  60  by using the input unit such as the touch panel, and the orientation and the field angle may be input for the image capturing apparatus  50 . 
     As described above, the index computation unit  120  computes the surveillance index for each of a plurality of positions p i  in the target region  60 . The surveillance index may have a value that increases as it is more difficult to surveil a target object  70 , for example, in a case where the target object  70  is located at the position p i  (for example, illustrated in  FIG. 4( a ) ). Alternatively, the surveillance index may have a value that increases as it is easier to surveil a target object  70  when the target object  70  is located at the position p i . The index computation unit  120  determines the easiness or the difficulty of surveillance based on the arrangement information and the environmental information, and applies the determination result to the surveillance index. The target object  70  is, for example, a person or a vehicle. 
     The surveillance index indicates the difficulty or the easiness of surveilling the target object  70  using an image obtained by the image capturing apparatus  50 . It should be noted that, in a case where the target region  60  is surveilled by a plurality of image capturing apparatuses  50 , the surveillance index at each position p i  is obtained in consideration of the influences of all the image capturing apparatuses  50 . 
     The viewing difficulty or viewing easiness of the target object  70  in an image in a case where a surveillant visually checks the image captured by the image capturing apparatus  50  has been applied to the surveillance index. For example, in a case where the target object  70  in the image is small, the lighting condition is as poor as it is not possible to clearly see the target object, or a portion or the entirety of the target object  70  is not captured in the image, it is difficult to visually recognize the target object  70  and to surveil the target object  70 . 
     The appropriateness for image processing in a case where some processing are performed on an image captured by the image capturing apparatus  50  to perform surveillance is applied to the surveillance index. The processing on the image is, for example, at least any of detection, matching, tracking, and abnormality detection of the target object  70 . For example, in a case where the resolution of the portion corresponding to the target object  70  in the image is low, the depression angle (gazing point angle) from the image capturing apparatus  50  to the target object  70  is large, or the portion or the entirety of the target object  70  is not captured in the image, the appropriateness for the processing is low and it is difficult to perform the surveillance. A method of computing the surveillance index will be described in detail later. 
     It should be noted that, an example in which the index computation unit  120  computes and uses a surveillance-unsuitability index indicating the difficulty of surveilling a target object will be described below. However, the present example embodiment is not limited to this example, the index computation unit  120  may compute and use a surveillance suitability index indicating the easiness of surveilling the target object  70 . The surveillance-unsuitability index for the position p i  at which it is more difficult to surveil the target object  70  has a larger value. 
     The magnitude of the surveillance suitability index is opposite to the magnitude of the surveillance-unsuitability index. The surveillance suitability index and the surveillance-unsuitability index can have values which are equal to or more than 0 and equal to or less than 1, for example. 
     The suitability computation unit  140  acquires the surveillance index from the index computation unit  120 , and computes the suitability of the arrangement of the image capturing apparatus  50  in the target region  60 . As the suitability increases, overlooking of the target object  70  in surveillance of the target region  60  due to the arrangement of the image capturing apparatus  50  occurs less frequently. Specifically, the suitability computation unit  140  evaluates whether the positions p i  at which the surveillance-unsuitability index is high are not distributed together. In a case where a plurality of positions p i  at which the surveillance-unsuitability index is high, that is, a plurality of positions p i  at which surveillance has difficulty are densely provided, the plurality of positions p i  form a surveillance-unsuitable region  620  in which surveillance has difficulty. This is because, when the target object  70  enters the surveillance-unsuitable region, it takes a long time to pass through the region, and the target object  70  is easily lost. The suitability computation unit  140  computes a lower suitability for the arrangement of the image capturing apparatus  50  as the size of the surveillance-unsuitable region  620  formed by the positions p i  at which the surveillance-unsuitability index is high and which are densely provided becomes larger. A method of computing the suitability will be described in detail later. 
     The suitability computed by the suitability computation unit  140  is displayed by a display unit such as a display. The suitability may be stored in the storage unit  100 , or may be input to a device outside the evaluation apparatus  10 . 
     As described above, the evaluation apparatus  10  in the present example embodiment computes the surveillance index for each position p i  in the target region  60 , and obtains the suitability of the arrangement of the image capturing apparatus  50  from the distribution of the surveillance index in the target region  60 . With such a method, it is possible to evaluate the quality of the arrangement of the image capturing apparatus  50  for the entirety of the target region  60 . As a result, it is possible to reduce the blind spot and a place in which it is difficult to recognize the target object  70  from an image, as much as possible, and to obtain the arrangement of the image capturing apparatus  50  in which overlooking of the target object  70  occurs less frequently in the target region  60 . 
     For example, the user of the evaluation apparatus  10  can evaluate a plurality of arrangement candidates with the evaluation apparatus  10  and adopt the arrangement having the best evaluation result obtained. 
       FIG. 3  is a flowchart illustrating an evaluation method according to the first example embodiment. The evaluation method in the present example embodiment is a method of evaluating the arrangement of one or more image capturing apparatuses  50  that surveil the target region  60 . The present evaluation method includes an acquisition step S 110 , an index computation step S 120 , and a suitability computation step S 130 . In the acquisition step S 110 , the arrangement information including at least any of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 , and the environmental information indicating the environment of the target region  60  are acquired. In the index computation step S 120 , for each of a plurality of positions p i  in the target region  60 , the surveillance index indicating difficulty or easiness of surveilling the target object  70  in a case where the target object  70  is located at the position p i  is computed using the arrangement information and the environmental information. In the suitability computation step S 130 , the suitability of the arrangement of the image capturing apparatus  50  indicated by the arrangement information is computed based on the distribution of the surveillance index in the target region  60 . 
     The evaluation method according to the present example embodiment is realized by the evaluation apparatus  10  according to the present example embodiment. 
     &lt;Method of Computing Surveillance Index&gt; 
     The method in which the index computation unit  120  computes the surveillance index in the index computation step S 120  will be described below. For example, the target region  60  is partitioned into a plurality of positions p i . In a case where the target objects  70  are respectively located at a plurality of positions p i  in the target region  60 , the index computation unit  120  computes the surveillance index based on at least any of the size, the brightness, the hiding degree of the target object  70  captured by the image capturing apparatus  50 . 
       FIGS. 4( a ) and 4( b )  are diagrams illustrating an example in which the index computation unit  120  computes the surveillance index based on the brightness of the target object  70  captured by the image capturing apparatus  50 . In the example of  FIGS. 4( a ) and 4( b ) , the environmental information indicates that a plurality of lightings  640  are installed on the ceiling. The environmental information includes information indicating the distribution of the illuminance of each lighting  640 . For example, as illustrated in  FIG. 4( b ) , the distribution of the brightness at each position p i  is obtained. In the example of  FIGS. 4( a ) and 4( b ) , a position A is brighter than a position B. Here, the brightness refers to the luminance of the portion corresponding to the target object  70  in an image when the image of the target object  70  is captured by the image capturing apparatus  50 . For example, information indicating the relation between the illuminance and the luminance is stored in the storage unit  100  in advance, and the index computation unit  120  can read the information and use the information for computing the brightness based on the illuminance. The information indicating the relation between the illuminance and the luminance may be in a form of a mathematical expression, a graph, a table, or the like. 
     The distribution of the luminance may be computed using, for example, information regarding the characteristics of the lighting. The information regarding the characteristics of the lighting includes information indicating the intensity of light of the lighting or the degree of diffusion of the light, for each type of lighting (for example, type, size, model number, and the like of an LED or a fluorescent lamp), and is stored in the storage unit  100  in advance. It is possible to obtain the distribution of the luminance of each lighting based on the information regarding the characteristics of the lighting. In addition, the environmental information includes information indicating the position and the type of the lighting placed in the target region  60 . It is possible to compute the distribution of the total luminance by superimposing the distribution of the luminance of the individual lighting on the assumption that the lighting is placed in accordance with the environmental information. 
       FIG. 5  is a graph illustrating the relation between the brightness and the surveillance-unsuitability index. The storage unit  100  further stores information indicating the relation between the brightness and the surveillance index in advance, and the index computation unit  120  can obtain the surveillance index based on the information and the brightness. The information indicating the relation between the brightness and the surveillance index may be in a form of a mathematical expression, a graph, a table, or the like. It is possible to obtain the information indicating the relation between the brightness and the surveillance index, by examining the relation between the brightness, and the easiness of visually recognizing the target object  70  in the image and the accuracy of image processing, in advance. 
     In a case where the brightness is not sufficient, the visibility of the target object  70  in a case where the image is visually observed is decreased. In addition, adverse effects such as a decrease in the detection rate of the target object  70  by image processing occur. On the other hand, in a case where the target object  70  is too bright, the original color, the original pattern, and the like of the target object  70  will be overexposed in the image. Therefore, it is difficult to surveil the target object  70  in any case, and the surveillance-unsuitability index is higher than in other cases. 
     The index computation unit  120  may further obtain the brightness or the surveillance index in consideration of the sunshine condition. For example, in a case where the target region  60  is outdoors, the index computation unit  120  can estimate the influence of sunlight from the position of the object  660  or the irradiation direction of sunlight, which are included in the environmental information, and apply the estimated influence to the brightness or the surveillance index. For example, in a case where the image capturing apparatus  50  faces in a direction from which the sunlight comes, the target object  70  is darkened by the backlight. Therefore, it is difficult to surveil the target object  70 , and the surveillance-unsuitability index is higher than in a case where the image capturing apparatus  50  does not face in the direction from which the sunlight comes. Even in a case where the image capturing apparatus  50  does not face in the direction from which the sunlight comes and the target object  70  is directly exposed to the sunlight, the target object  70  becomes too bright. Therefore, it is difficult to surveil the target object  70 , and the surveillance-unsuitability index is higher than in a case where the image capturing apparatus  50  does not face in the direction from which the sunlight comes. On the other hand, in a case where the sunlight is blocked by a wall or the like and thus the target object  70  is not directly exposed to the sunlight, the brightness of the target object  70  is maintained at an appropriate value. Therefore, it is easy to surveil the target object  70 , and the surveillance-unsuitability index is low. 
     Even in a case where the target region  60  is indoors, the sunshine condition can be obtained from the position of a window and the irradiation direction of sunlight, which are included in the environmental information. Therefore, similar to the case where the target region is outdoors, it is possible to apply the influence of the sunlight to the brightness or the surveillance index. 
     Next, a method in which the index computation unit  120  computes the surveillance index based on the size of the target object  70  captured by the image capturing apparatus  50  will be described. For example, the index computation unit  120  estimates that, as the distance from the image capturing apparatus  50  to a target position becomes longer, the target object  70  in the image captured by the image capturing apparatus  50  is reduced, and sets the surveillance-unsuitability index at the target position to be high. The target position refers to the position p i  at which computation of the surveillance index is intended. In a case where the target position is too close to the image capturing apparatus  50 , it is estimated that the target object  70  protrudes from the field of view of the image capturing apparatus  50 , so that the degree of hiding of the target object  70  increases and the surveillance-unsuitability index increases as described later. The index computation unit  120  computes the distance between the image capturing apparatus  50  and the target position based on the arrangement information and the environmental information. Then, for example, information indicating the relation between the distance from the image capturing apparatus  50  and the surveillance index is stored in advance in the storage unit  100 , and the index computation unit  120  can read and use the information for computing the surveillance index. The information indicating the relation between the distance and the surveillance index may be in a form of a mathematical expression, a graph, a table, or the like. 
     The size of the target object  70  in the image also changes depending on the zoom ratio of the image capturing apparatus  50 . Thus, the information indicating the relation between the distance and the surveillance index may be prepared for each parameter representing the zoom ratio. In this case, the index computation unit  120  may select and use the information indicating the relation between the distance and the surveillance index, based on the zoom ratio indicated by the arrangement information. 
     The index computation unit  120  may generate an image captured by the image capturing apparatus  50  in a case where the evaluation apparatus  10  is placed at the target position, by simulation. Then, the index computation unit may compute the area (number of pixels) of a portion corresponding to the target object  70  in the image or the area of a rectangle surrounding the target object  70 . In this manner, the index computation unit may obtain the surveillance index. As the area becomes larger, the target object  70  in the image becomes larger. For example, information indicating the relation between the area and the surveillance index is stored in advance in the storage unit  100 , and the index computation unit  120  can read and use the information for computing the surveillance index. The information indicating the relation between the area and the surveillance index may be in a form of a mathematical expression, a graph, a table, or the like. 
     Next, the method in which the index computation unit  120  computes the surveillance index based on the degree of hiding of the target object  70  captured by the image capturing apparatus  50  will be described. Firstly, the index computation unit  120  sets the surveillance-unsuitability index at the position p i  at which the image of the target object  70  is not captured by the image capturing apparatus  50 , to a value higher than the surveillance-unsuitability index at the position p i  at which the image of the target object  70  is captured by the image capturing apparatus  50 . In a case where a plurality of positions p i  at which the image of the target object  70  is not captured by the image capturing apparatus  50  are provided, the index computation unit  120  may set the surveillance-unsuitability index to increase as the position p i  becomes farther from the image capturing region of the image capturing apparatus  50 . When the target object  70  moves from the image capturing region of the image capturing apparatus  50  to the position p i  outside the image capturing region of the image capturing apparatus  50 , the elapsed time until the target object  70  reaches the position p i  after the image of the target object has been captured finally in the image capturing region of the image capturing apparatus  50  becomes longer as the position p i  becomes farther from the image capturing region of the image capturing apparatus  50 . Therefore, the ambiguity of the position of the target object  70  becomes higher as the position p i  becomes farther from the image capturing region. 
     Specifically, the index computation unit  120  uses the arrangement information and the environmental information to perform distance conversion on the image in which the image capturing region (field of view) of the image capturing apparatus  50  is drawn. Then, it is possible to obtain the shortest distance from the boundary between the outside and the inside of the image capturing region to the target position and to obtain the surveillance index of the target position. The index computation unit  120  may obtain the distance or the estimated time until the target object reaches the target position after the target object goes out of the image capturing region of the image capturing apparatus  50  by simulation, and define the surveillance index at the target position in accordance with the distance or the time. 
     On the other hand, the index computation unit  120  reduces the surveillance-unsuitability index as the ratio of a portion of the target object  70 , which is captured by the image capturing apparatus  50 , to the entirety of the target object  70  increases. Specifically, the index computation unit  120  generates an image captured by the image capturing apparatus  50  in a case where the target object  70  is placed at the target position by simulation. Then, the index computation unit obtains the ratio of a portion of the target object  70  that fits in the image. On the other hand, information indicating the relation between the ratio and the surveillance index is stored in advance in the storage unit  100 . The index computation unit  120  computes the surveillance index using the obtained ratio and the information indicating the relation between the ratio and the surveillance index read from the storage unit  100 . The information indicating the relation between the ratio and the surveillance index may be in a form of a mathematical expression, a graph, a table, or the like. 
     The index computation unit  120  may compute the surveillance index based on the gazing point angle at which the image of the target object  70  is captured. The gazing point angle is an angle formed by a straight line connecting the image capturing apparatus  50  and the gazing point in the target object  70  and a horizontal plane. The gazing point is a notable position of the target object  70 , for example, the gravity center of the target object  70  or the midpoint of the axis of the gravity center. For example, it is estimated that, as the gazing point angle becomes larger, overlapping between the target object  70  and the object  660  is decreased. Therefore, the surveillance-unsuitability index may be set to decrease as the gazing point angle becomes larger. In a case where object detection or object recognition is performed on an image, the surveillance-unsuitability index may be set to decrease as the gazing point angle approaches a specific angle at which it is easy to perform processing. Information indicating the relation between the gazing point angle and the surveillance index is stored in advance in the storage unit  100 , and the index computation unit  120  can read and use the information for computing the surveillance index. The information indicating the relation between the gazing point angle and the surveillance index may be in a form of a mathematical expression, a graph, a table, or the like. 
     In a case where the target region  60  is surveilled by a plurality of image capturing apparatuses  50 , the index computation unit  120  may perform, for example, processing as follows for the above-described individual factors (brightness, size, degree of hiding, gazing point angle, and the like) for determining the surveillance index. That is, the index computation unit  120  computes the surveillance index v m  (m=1, 2, . . . , M, and M is a positive integer and indicates the number of image capturing apparatuses  50 ) for all image capturing apparatus  50  at each position p i , as described above. In a case where the surveillance index is the surveillance-unsuitability index indicating the difficulty of surveillance, for example, the smallest surveillance index v m  among the surveillance indices v m  (m=1, 2, . . . , M) is set to a surveillance index V k  as a representative value for a factor k. In a case where the surveillance index is the surveillance suitability index indicating the easiness of surveillance, the index computation unit  120  may set the largest surveillance index v m  among the surveillance indices v m  (m=1, 2, . . . , M) to the surveillance index V k  as the representative value for the factor k. That is, the index computation unit can set the surveillance index v m  indicating that the surveillance is performed the easiest among the surveillance indices v m  (m=1, 2, . . . , M) to the surveillance index V k  as the representative value for the factor k. Alternatively, the result of a simple average of the surveillance index v m  or a weighted average thereof may be used as the surveillance index V k . Here, only the surveillance index v m  for the image capturing apparatus  50  that is capable of capturing the image of the target object  70  placed at the target position is used for the simple average or the weighted average of the surveillance index v m . The method of obtaining the surveillance index V k  from the surveillance index v m  (m=1, 2, . . . M) can be defined for each factor. 
     As described above, there are a plurality of factors for which the surveillance index can be computed. Preferably, the final surveillance index is obtained comprehensively considering the factors. A method of obtaining the surveillance index V to which the plurality of factors are applied will be described below. 
     The surveillance index based on the factor k is set to V k  (k=1, 2, . . . , K, and K is a positive integer and indicates the number of factors). In a case where the target region  60  is surveilled by a plurality of image capturing apparatuses  50 , V k  can be obtained as described above. In addition, in a case where the target region  60  is surveilled by one image capturing apparatus  50 , the surveillance index obtained by the factor k for the image capturing apparatus  50  may be set to V k . Then, a function such as V=F (V 1 , . . . , V K ) can be defined to obtain the surveillance index V to which the plurality of factors are applied. For example, in a case where all V 1 , . . . , and V K  have values which is equal to or more than 0 and equal to or less than 1, V can be obtained by using a function such as Expression (1). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                         
                     1 
                   
                   ] 
                 
               
               
                  
               
             
             
               
                 
                   
                     F 
                     ⁡ 
                     ( 
                     
                       
                         V 
                         1 
                       
                       , 
                       … 
                           
                       , 
                       
                         V 
                         K 
                       
                     
                     ) 
                   
                   = 
                   
                     1 
                     - 
                     
                       
                         ∏ 
                         
                           k 
                           = 
                           1 
                         
                         K 
                       
                       
                         ( 
                         
                           1 
                           - 
                           
                             V 
                             k 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     It should be noted that, even in a case where V k  is not in a range which is equal to or more than 0 and equal to or less than 1, Expression (1) can be similarly applied by normalization within a range of values that can be taken by V k . 
     Furthermore, the surveillance index may change depending on the time slot (time range). For example, in a store, the layout may be changed depending on the time slot to increase the number of cash registers. The lighting and sunlight conditions vary depending on the time. Therefore, the acquisition unit  110  may acquire the environmental information for each time slot, the index computation unit  120  may compute the surveillance index for each time slot, and the suitability computation unit  140  may use each result. At this time, validity information is associated with each of the environmental information, the surveillance index, and the suitability. The validity information indicates a time range in which the environmental information, the surveillance index, and the suitability are valid. The validity information may further include information indicating the ratio per unit time (such as one day or one week). The validity information is acquired by the acquisition unit  110  together with the environmental information, and is output from the index computation unit  120  and the suitability computation unit  140  together with the surveillance index and the suitability, respectively. 
     &lt;Method of Computing Suitability&gt; 
       FIG. 6  is a diagram illustrating the method of computing the suitability by the suitability computation unit  140 .  FIG. 6  illustrates one (region S 1 ) of surveillance-unsuitable regions  620  in  FIG. 2 . In  FIG. 6 , an example of a route  622  in the surveillance-unsuitable region  620  is indicated by an arrow. A method in which the suitability computation unit  140  computes the suitability of the arrangement of the image capturing apparatus  50  in the suitability computation step S 130  will be described below. The suitability computation unit  140  specifies one or more surveillance-unsuitable regions  620  in which it is difficult to surveil the target object  70  by the image capturing apparatus  50 , based on distribution of the surveillance index in the target region  60 . The suitability computation unit  140  obtains the length of the route  622  in a case where the target object  70  passes through the surveillance-unsuitable region  620  for each surveillance-unsuitable region  620 . The suitability computation unit  140  computes the suitability based on the length of the route  622 . The details will be described below. 
     The suitability computation unit  140  acquires the surveillance index for each position p i  in the target region  60  from the index computation unit  120 . The suitability computation unit  140  extracts the position p i  at which the surveillance has difficulty, based on a predetermined reference for the surveillance index. Information indicating the reference is stored in the storage unit  100  in advance, and the suitability computation unit  140  can read and use the information for extraction. The reference for extracting the position p i  at which the surveillance has difficulty is, for example, a threshold value. 
     Specifically, in a case where the surveillance index is the surveillance-unsuitability index, the position p i  at which the surveillance-unsuitability index is equal to or higher than the threshold value is extracted as the position p i  at which the surveillance has difficulty. On the other hand, in a case where the surveillance index is the surveillance suitability index, the position p i  at which the surveillance suitability index is equal to or lower than the threshold value is extracted as the position p i  at which the surveillance has difficulty. 
     Then, the suitability computation unit  140  determines whether or not the extracted positions p i  are adjacent to each other. The suitability computation unit  140  groups a plurality of positions p i  that are adjacent to each other to form a surveillance-unsuitable region  620 . A plurality of surveillance-unsuitable regions  620  may be formed in the target region  60 . Each surveillance-unsuitable region  620  is configured by the plurality of positions p i  that are grouped together. Each surveillance-unsuitable region  620  may be also referred to as a surveillance-unsuitable region S n  (n=1, N, N is a positive integer and indicates the number of surveillance-unsuitable regions  620 ) below. 
     The suitability computation unit  140  obtains, for each surveillance-unsuitable region  620 , the length d n  (n=1, N) of the route  622  in which the target object  70  passes through the formed surveillance-unsuitable region S n . d n  is also referred to as a region-passing route length below. Here, in a case where a plurality of routes for passing through the surveillance-unsuitable region S n  are assumed, the suitability computation unit  140  obtains a representative value of the route length based on the lengths of the plurality of routes, and sets the representative value as d n . The representative value is, for example, the maximum value, the average value, or the median value of the lengths of the plurality of routes. The suitability computation unit  140  may consider the size of the target object  70  when obtaining the length of each route, and may set the length of a range in which the target object  70  is completely hidden, as the length of the route. Considering the frequency of use of the route, the suitability computation unit  140  may set the length of the route estimated to be used the most frequently, as the representative value, or may set a value obtained by a weighted average in accordance with the frequency of use of the route, as the representative value. The frequency of use of the route may be input by the user, for example, based on the environment of the target region  60  and actual measurement data. The suitability computation unit  140  may estimate the frequency of use of the route based on the position of the route in the target region  60 , the relation with the object  660 , and the like. 
     Then, the suitability computation unit  140  performs statistical processing on d n  and computes the suitability A based on the obtained statistical value D. For example, the suitability computation unit sets the maximum value of all the obtained d n  is set as the statistical value D in accordance with Expression (2). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                         
                     2 
                   
                   ] 
                 
               
               
                  
               
             
             
               
                 
                   D 
                   = 
                   
                     
                       
                         max 
                            
                       
                       
                         
                           n 
                           = 
                           1 
                         
                         , 
                         … 
                             
                         , 
                         N 
                       
                     
                     ⁢ 
                     
                       d 
                       n 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     The suitability computation unit  140  may obtain the statistical value D by using Expression (3) instead of Expression (2). That is, the suitability computation unit  140  may set the result of weighting and averaging the obtained plurality of d n  as the statistical value D. Here, the weight w n  may be constant, and the weight w n  may be set to increase as the estimated frequency of use of the route becomes more. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                         
                     3 
                   
                   ] 
                 
               
               
                  
               
             
             
               
                 
                   D 
                   = 
                   
                     
                       
                         ∑ 
                         
                           n 
                           = 
                           1 
                         
                         N 
                       
                         
                       
                         
                           w 
                           n 
                         
                         ⁢ 
                         
                           d 
                           n 
                         
                       
                     
                     
                       
                         ∑ 
                         
                           n 
                           = 
                           1 
                         
                         N 
                       
                       
                         w 
                         n 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
       FIG. 7  is a graph illustrating a relation between the statistical value D and the suitability. The suitability computation unit  140  computes the suitability A from the statistical value D, for example, by using the monotonous non-increasing function f(D) as illustrated in  FIG. 7 . Here, A=f(D). That is, as the statistical value D becomes smaller, the suitability A increases. 
     The suitability computation unit  140  may compute the suitability A by using a plurality of references for extracting the position p i  at which the surveillance has difficulty. Specifically, a plurality of threshold values b j  are set as the reference in advance. The suitability computation unit  140  computes the suitability A j  for each threshold value b j  from the extraction result obtained by using the threshold value b j , by a method similar to the method of computing the suitability A described above. The suitability computation unit performs statistical processing on the obtained plurality of pieces of suitability A j , to compute the final suitability A. The statistical processing for obtaining the suitability A from the plurality of pieces of suitability A j  includes, for example, computation of the average value, the median value, or the minimum value. The suitability computation unit  140  may further obtain the amount of change in the suitability A when changing the reference, and the amount of change may be used in the evaluation together with the suitability. For example, this means that, as the amount of change in the suitability A in response to the change of reference becomes smaller, it is difficult to decrease the suitability even though a strict reference is set. Therefore, the more preferable arrangement is made as the amount of change becomes smaller. 
     A specific example of computing the suitability will be described below with a plurality of arrangements. Examples in which the maximum value of the lengths of a plurality of routes for passing through the surveillance-unsuitable region  620  is set as the region-passing route length will be described below. A method of computing the region-passing route length is not limited to the examples. 
     A first example of the arrangement of the image capturing apparatus  50  will be described in detail with reference to  FIGS. 2 and 6 .  FIG. 2  illustrates a state in which a rectangular room is viewed from the top. In this example, the planar shape of the target region  60  is a rectangle, and the image capturing apparatus  50  is located at each of opposing corners of the rectangle. The target region  60  in this example is surveilled by two image capturing apparatuses  50 . Each image capturing apparatus  50  is directed toward the center of the short side opposite to the short side of the corner at which the image capturing apparatus  50  is located. In  FIG. 2 , the regions S 1  and S 2  are surveillance-unsuitable regions  620  different from each other. The region S 1  is far from an image capturing apparatus  50   a , and is not included in an image capturing region of an image capturing apparatus  50   b . Thus, the region S 1  is the surveillance-unsuitable region  620  in which the surveillance has difficulty. Similarly, the region S 2  is far from the image capturing apparatus  50   b , and is not included in the image capturing region of the image capturing apparatus  50   a . Thus, the region S2 is the surveillance-unsuitable region  620  in which the surveillance has difficulty. In this manner, firstly, the regions S 1  and S 2  are specified. 
     Then, the suitability computation unit  140  obtains the region-passing route length. Assuming that the target object  70  proceeds straight, the route  622  indicated by the arrow in  FIG. 6  is the longest route for the region S 1  In a case where the maximum value of the route length is used as the region-passing route length, the length of the route  622  is set as a region-passing route length d 1 . Similarly, the region-passing route length d 2  can be obtained for the region S 2 . The suitability computation unit  140  can compute the statistical value D using Expression (2) or (3) and further compute the suitability A. 
       FIG. 8  is a diagram illustrating a second example of the arrangement of the image capturing apparatus  50 . In the second example, the environmental information includes information indicating that a rectangular region is included in the target region  60 , and the image capturing apparatus  50  is placed near a point closer to the center than to the end of the long side of the rectangle.  FIG. 8  illustrates a state where the target region  60  being a rectangular region is viewed from the top. Also in this example, the planar shape of the target region  60  is rectangular. The target region  60  in this example is surveilled by two image capturing apparatuses  50 . In this example, the image capturing apparatus  50  is not located at the corner of the rectangle, but located near (for example, within 1 m) a point in the middle of each of the two long sides of the rectangle, which face each other. That is, in this example, two image capturing apparatuses  50  are closer to the center of the long side than the two image capturing apparatuses  50  in the first example. The distance between the two image capturing apparatuses  50  in this example is shorter than the distance between the two image capturing apparatuses  50  in the first example. It should be noted that, “near” refers to a range in which the distance is, for example, within 1 m, below. 
     In the second example, similarly to the first example, the regions S 1  and S 2  are specified, and the region-passing route lengths d 1  and d 2  are obtained. Here, it is understood that the region-passing route length d 1  in the second example is shorter than the region-passing route length d 1  in the first example, and the region-passing route length d 2  in the second example is shorter than the region-passing route length d 2  in the first example. Therefore, the suitability A in the second example is higher than the suitability A in the first example, and the arrangement of the image capturing apparatus  50  in the second example is more preferable than the arrangement of the image capturing apparatus  50  in the first example. 
       FIGS. 9( a ) to 9( c )  are diagrams illustrating third to fifth examples of the arrangement of the image capturing apparatus  50 , respectively. In the third to fifth examples, the target region  60  is, for example, a passage, and the planar shape of the target region  60  is an elongated rectangle. That is, in the third to fifth examples, the environmental information includes information indicating that there is an elongated passage in the target region  60 .  FIGS. 9( a ) to 9( c )  illustrate a state where the elongated rectangle being the target region  60 , specifically, a region of an elongated passage is viewed from the top. Here, the elongated rectangle and the elongated passage refer to, for example, a rectangle and a passage in which the length of the long side is three times or more the length of the short side. In the third and fourth examples, the target region  60  is surveilled by two image capturing apparatuses  50 . In the fifth example, the target region  60  is surveilled by three image capturing apparatuses  50 . 
     In the third example illustrated in  FIG. 9( a ) , the image capturing apparatuses  50  are located near the midpoints of the two short sides, respectively. The two image capturing apparatuses  50  are directed toward the center of the target region  60  to face each other. In this example, as illustrated in  FIG. 9( a ) , a plurality of surveillance-unsuitable regions  620  are specified. The region-passing route length in the center region S 1  among the surveillance-unsuitable regions has the maximum value. When the image capturing apparatuses  50  are provided at both ends of the target region  60  as in this example, it is easy to form a large surveillance-unsuitable region  620  in the center of the target region  60 . As a result, the suitability A easily decreases. 
     In the fourth example illustrated in  FIG. 9( b ) , the two image capturing apparatuses  50  are arranged near the center of the target region  60  so as to face in opposite directions to each other. Thus, the region-passing route length in the regions S 1  and S 2  located at both ends of the target region  60  has the maximum value. For example, in a case where the regions S 1  and S 2  are axial-symmetric or substantially axial-symmetric, the region-passing route length in the regions S 1  and S 2  in the fourth example is shorter than the region-passing route length in the region S 1  in the third example. Therefore, the suitability in the fourth example is higher than the suitability in the third example. 
     In the fourth example, the two image capturing apparatuses  50  are arranged in directions opposite to each other in the vicinity of the center of the elongated passage. An image of at least a region directly below one image capturing apparatus  50   b  is captured by the other image capturing apparatus  50   a  of the two image capturing apparatuses  50 . An image of at least a region directly below the other image capturing apparatus  50   a  is captured by the one image capturing apparatus  50   b . With such an arrangement, the arrangement of the image capturing apparatus  50  more suitable for surveillance is realized. 
     In this example, the image capturing apparatuses  50  are arranged so that a first region (for example, region S 1 ) and a second region (for example, region S 2 ) are not directly adjacent to each other and are not adjacent to each other with only a blind spot region interposed between the first region and second region. The first region is a region in which the difficulty of surveillance indicated by the surveillance index is higher than a predetermined reference, or the easiness of surveillance indicated by the surveillance index is lower than the reference. In addition, in a case where the target object  70  is placed in the first region, an image of the target object  70  is captured by a first image capturing apparatus  50   a . The second region is a region in which the difficulty of surveillance indicated by the surveillance index is higher than the reference, or the easiness of surveillance indicated by the surveillance index is lower than the reference. In addition, in a case where the target object  70  is placed in the second region, an image of the target object  70  is captured by a second image capturing apparatus  50   b  located within a predetermined range (for example, within 30 m) from the first image capturing apparatus  50   a . In a case where the target object  70  is placed in the blind spot region, an image of at least a portion of the target object  70  is not captured by any of one or more image capturing apparatuses  50 . With such an arrangement, the arrangement of the image capturing apparatus  50  more suitable for surveillance is realized. 
     In the fifth example illustrated in  FIG. 9( c ) , the environmental information includes information indicating that there is an elongated passage in the target region  60 . The image capturing apparatuses  50  are arranged so that the orientations of the image capturing apparatuses  50  coincide with each other in the elongated passage. In this example, all the image capturing apparatuses  50  are directed in the same direction, specifically, in a direction parallel to the long side of the rectangle. A region close to one image capturing apparatus  50  is in the immediate vicinity of a region far from another image capturing apparatus  50 . Specifically, for example, the distance between two adjacent image capturing apparatuses  50  is equal to or longer than 5 m or equal to or shorter than 30 m. With such an arrangement, it is possible to avoid an occurrence of a situation in which a region with a high surveillance-unsuitability index is continuously formed to be long. Thus, the suitability A tends to be high. As described above, in a case where the suitability computation unit  140  computes the suitability A using a plurality of references and further obtains the amount of change in the suitability A in response to the change of the reference, the amount of change in the fifth example is smaller than the amount of change in the third example. That is, this means that it is difficult to decrease the suitability even though a strict reference is set, in the fifth example, and thus the arrangement in the fifth example is more preferable. 
       FIGS. 10( a ) and 10( b )  are diagrams illustrating a sixth example and a seventh example of the arrangement of the image capturing apparatus  50 , respectively. In the sixth example and the seventh example, the target region  60  is, for example, a passage, and a bent portion  601  is in the planar shape of the target region  60 . Each of  FIGS. 10( a ) and 10( b )  illustrates a state where the target region  60  being a passage with the bent portion  601  is viewed from the top. The bent portion  601  is, for example, the corner of a passage. In  FIGS. 10( a ) and 10( b ) , the bent portion  601  is bent at 90°, but the bending angle is not particularly limited. 
     In the sixth example illustrated in  FIG. 10( a ) , two image capturing apparatuses  50  are arranged toward the bent portion  601 . The two image capturing apparatuses  50  are located at the ends of the target region  60 , respectively. A large surveillance-unsuitable region  620  is formed in and around the bent portion  601 . As a result, the suitability A tends to be low for the arrangement as in this example. 
     In the seventh example illustrated in  FIG. 10( b ) , at least one image capturing apparatus  50  is located near the bent portion  601  and faces the end of the target region  60 . With such an arrangement, it is possible to avoid an occurrence of a situation in which the surveillance-unsuitable region  620  near the bent portion  601  is formed largely. In the example in  FIG. 10( b ) , the surveillance-unsuitable region  620  is formed at one end of the target region  60 , but the region-passing route length in the surveillance-unsuitable region  620  is not as long as the region-passing route length in the surveillance-unsuitable region  620  around the bent portion  601  in the sixth example. Therefore, the suitability A in the seventh example is higher than the suitability A in the sixth example. In addition, since a region close to one image capturing apparatus  50  is in the immediate vicinity of a region far from another image capturing apparatus  50 , the arrangement in the seventh example is preferable. 
       FIGS. 11( a ) and 11( b )  are diagrams illustrating an eighth example and a ninth example of the arrangement of the image capturing apparatus  50 , respectively. In the eighth and ninth examples, the environmental information includes information indicating that a plurality of passages  603  interposing one or more objects  660  arranged in the target region  60  are present substantially in parallel in the target region  60 . In the eighth and ninth examples, the target region  60  is, for example, a room in which shelves are arranged.  FIGS. 11( a ) and 11( b )  illustrate a state where the room is viewed from the top. In the eighth and ninth examples, the planar shape of the target region  60  is rectangular, and the objects  660  having a rectangular planar shape are arranged in parallel in the target region  60 . The long side of the object  660  is parallel to any side of the target region  60 . There are a plurality of passages  603  in the target region  60 . Each of the passages  603  is rectangular and is interposed between the object  660  and the object  660 , or between the object  660  and the end of the target region  60 . 
     In the eighth example illustrated in  FIG. 11( a ) , the image capturing apparatus  50  is provided for each passage  603  so as to capture an image of all the passages  603  from the same direction. That is, a plurality of image capturing apparatuses  50  are arranged in the vicinity of the same side of the target region  60 . As a result, a wide surveillance-unsuitable region  620  is formed around the side facing the side on which the image capturing apparatus  50  is provided, and the region-passing route length becomes long. Therefore, the suitability A tends to decrease for such an arrangement. 
     In the ninth example illustrated in  FIG. 11( b ) , one image capturing apparatus  50  is provided for each of a plurality of passages  603 , and the image capturing apparatuses  50  are arranged so that images of adjacent passages  603  are captured from different directions. That is, one or more image capturing apparatuses  50  are located in the vicinity of the two sides of the target region  60 , which face each other. As a result, the surveillance-unsuitable region  620  is divided, and the region-passing route length is reduced. Thus, the suitability A tends to increase. As described above, the arrangement in the ninth example is more preferable than the arrangement in the eighth example. 
     &lt;Hardware Configuration&gt; 
     A hardware configuration of the evaluation apparatus  10  will be described below. Each functional component of the evaluation apparatus  10  may be realized by hardware (for example, hard-wired electronic circuit) that realizes each functional component, or may be realized by a combination of hardware and software (for example, combination of an electronic circuit and a program of controlling the electronic circuit). A case where each functional component of the evaluation apparatus  10  is realized by a combination of hardware and software will be further described below. 
       FIG. 12  is a diagram illustrating a computer  1000  of realizing the evaluation apparatus  10 . The computer  1000  is any computer. For example, the computer  1000  is a personal computer (PC), a server machine, a tablet terminal, or a smartphone. The computer  1000  may be a dedicated computer designed to realize the evaluation apparatus  10  or a general-purpose computer. 
     The computer  1000  includes a bus  1020 , a processor  1040 , a memory  1060 , a storage device  1080 , an input and output interface  1100 , and a network interface  1120 . The bus  1020  is a data transmission path used when the processor  1040 , the memory  1060 , the storage device  1080 , the input and output interface  1100 , and the network interface  1120  transmit and receive data to and from each other. A method of connecting the processor  1040  and the like to each other is not limited to bus connection. The processor  1040  includes various processors such as a Central Processing Unit (CPU), a Graphics Processing Unit (GPU), and a Field-Programmable Gate Array (FPGA). The memory  1060  is a main storage realized using a Random Access Memory (RAM) or the like. The storage device  1080  is an auxiliary storage realized using a hard disk, a Solid State Drive (SSD), a memory card, a Read Only Memory (ROM), or the like. 
     The input and output interface  1100  is an interface for connecting the computer  1000  with input and output devices. For example, an input device such as a keyboard or an output device such as a display device is connected to the input and output interface  1100 . 
     The network interface  1120  is an interface for connecting the computer  1000  to the network. The communication network is, for example, a Local Area Network (LAN) or a Wide Area Network (WAN). A method of the connection of the network interface  1120  to the network may be wireless connection or wired connection. 
     The storage device  1080  stores program modules that realize the acquisition unit  110 , the index computation unit  120 , and the suitability computation unit  140  in the evaluation apparatus  10 . The processor  1040  realizes the function corresponding to each program module by reading each program module into the memory  1060  and executing the program module. 
     In a case where the storage unit  100  is provided in the evaluation apparatus  10 , for example, the storage unit  100  is realized using the storage device  1080 . 
     Next, the operation and the advantageous effect of the present example embodiment will be described. According to the evaluation apparatus  10  according to the present example embodiment, the surveillance index for each position p i  in the target region  60  is computed, and the suitability of the arrangement of the image capturing apparatus  50  is obtained from the distribution of the surveillance index in the target region  60 . With such a method, it is possible to evaluate the quality of the arrangement of the image capturing apparatus  50  in consideration of a situation of the entire target region  60 . As a result, it is possible to obtain the arrangement of the image capturing apparatus  50  in the target region  60  in which overlooking of the target object  70  occurs less frequently. 
     Second Example Embodiment 
     An evaluation apparatus  10  according to the second example embodiment is the same as the evaluation apparatus  10  according to the first example embodiment except that the acquisition unit  110  further acquires target object information being information regarding the target object  70 , and the index computation unit  120  further uses the target object information to compute the surveillance index. 
     The target object information includes, for example, at least any of information indicating the movement characteristics of the target object  70  and information indicating the density of a plurality of target objects  70  in the target region  60 . The movement characteristics of the target object  70  are, for example, at least one of the direction and the speed of movement. In a case where the target object information includes information indicating the direction of the target object  70  moving, the target object information may further include information indicating the ratio (frequency) of the target object  70  moving in each movement direction. 
     At least one of the information indicating the movement characteristics and the information indicating the density may be given to each position p i . At this time, the target object information is distribution information within the target region  60 . At least one of the information indicating the movement characteristics and the information indicating the density may be given as a representative value in each region r i . Here, each region r i  is a set of a plurality of continuous position p i , and can be freely defined. The target region  60  is partitioned into a plurality of regions r i . 
     In a case where there are a plurality of expected movement routes of the target object  70  in the target region  60 , at least one of the information indicating the movement characteristics and the information indicating the density may be given for each route. The target object information may further include information indicating the frequency with which each route is selected by the target object  70 . Each route is associated with a plurality of continuous positions p i  that overlap the route. 
     The acquisition unit  110  can acquire the target object information from the outside of the evaluation apparatus  10  or in the evaluation apparatus  10 . For example, the user may perform an input operation on the evaluation apparatus  10 , and the acquisition unit  110  may acquire the target object information based on the input contents of the user. The acquisition unit  110  may acquire the target object information from a detection unit such as a sensor or a camera. Further, the target object information may be stored in advance in the storage unit  100  provided outside or inside the evaluation apparatus  10 , and the acquisition unit  110  may read and acquire the target object information. 
     The target object information may be obtained, for example, by prior research or simulation. Specifically, the target object information can be generated based on the average movement velocity and the average density of the target object  70  in the passage. In addition, in an open space such as a plaza, the target object information can be generated based on data such as how many target objects  70  move in which direction and by what route. 
     The target object information may be generated based on the environmental information and reference information. Specifically, in a case where the target object  70  is a person, the velocity on the stairs or slope is different from the velocity on a flat place. Thus, information indicating how the velocity of a person changes in accordance with the incline is prepared as the reference information. When the information is prepared as the reference information, and the environmental information includes information indicating the incline, it is possible to compute the velocity of the person by using the incline and the reference information. In a case where an apparatus such as an escalator or a moving walkway that automatically moves the target object  70  is provided in the target region  60 , the movement velocity of the target object  70  can be obtained using the average velocity of the apparatus as the reference information. For example, the reference information is stored in the storage unit  100  in advance, and the acquisition unit  110  can acquire the target object information generated outside the evaluation apparatus  10  or inside the evaluation apparatus  10 . 
     The target object information may be provided for each time slot (time range). For example, the amount of movement and the main movement direction of the target object  70  may differ depending on the morning, the daytime, and the evening. Therefore, the acquisition unit  110  may acquire the target object information for each time slot, and the index computation unit  120  may compute the surveillance index for each time slot. 
     The target object information may include information regarding the stop of the target object  70 . The information regarding the stop is information indicating how frequency the target object  70  stops for each position p i  or for each region r i  in the target region  60  and how long the stopped state continues. The information regarding the stop may be handled separately from other target object information, as dwell information of the target object  70 . The information regarding the stop may be information indicating the number of target objects  70 , the frequency of the target object  70  staying at the position p i  or in the region r i , and the length of a staying time. 
     A first example of a method of computing the surveillance index using the target object information in the evaluation apparatus  10  according to the present example embodiment will be described below. In an acquisition step S 110  in this example, the acquisition unit  110  acquires information indicating the movement direction of the target object  70  as the target object information. In an index computation step S 120 , the index computation unit  120  computes the surveillance index by assuming that it is easier to surveil the target object  70  as the movement direction of the target object  70  becomes closer to the direction toward the image capturing apparatus  50 . The specific method is as follows. 
     In general, the easiness of identifying the target object  70  changes depending on the orientation of the target object  70 . For example, in a case where the target object  70  is a person and the person faces the front of the image capturing apparatus  50 , an image of the face is captured, and thus the person can be easily identified. On the other hand, in a case where the person faces the image capturing apparatus  50  sideways or backwards, identifying has more difficulty. Therefore, as the movement direction of the target object  70  for the position p i  is closer to the direction toward the image capturing apparatus  50 , it can be considered as being easier to surveil the target object  70  located at the position p i . Specifically, in a case where the moving element in the direction toward the image capturing apparatus  50  is large, the surveillance-unsuitability index is decreased. In a case where the moving element away from the image capturing apparatus  50  is large, the surveillance-unsuitability index is increased. 
     In a case where the movement characteristics of a plurality of directions are mixed in the information indicating the movement direction at the position p i , the index computation unit  120  computes the surveillance index by performing statistical processing (for example, averaging) for the plurality of directions. In the statistical processing, for example, weighting is performed using the density of the target object  70  moving in each direction. The index computation unit  120  may compute the surveillance index based on the direction having the most difficult in surveillance among the plurality of directions. 
     A second example of the method of computing the surveillance index by using the target object information in the evaluation apparatus  10  according to the present example embodiment will be described below. In the acquisition step S 110  in this example, the acquisition unit  110  acquires the information indicating the density of a plurality of target objects  70 , as the target object information. In the index computation step S 120 , the index computation unit  120  can compute the surveillance index by considering that it is more difficult to surveil the target object  70  as the density of the plurality of target objects  70  becomes higher. The specific method is as follows. 
     When the density of the target objects  70  becomes high, the target objects  70  tend to overlap in the image captured by the image capturing apparatus  50 . Therefore, it is easy to lose sight of a tracking target. In addition, an error in association easily occurs between the plurality of target objects  70 . Thus, the index computation unit  120  increases the surveillance-unsuitability index as the density of the target object  70  becomes higher. It should be noted that, the depression angle of the image capturing apparatus  50  and an angle θ formed by an optical axis of the image capturing apparatus  50  and the movement direction of the target object  70  have an influence on the easiness of overlapping and the degree of hiding of the target object  70 , in addition to the density of the target object  70 . For example, when the depression angle and θ become smaller, overlapping occurs more easily, and the degree of hiding increases. Thus, the surveillance-unsuitability index becomes higher. Therefore, the index computation unit  120  may compute the surveillance index based on the relation. For example, reference data (mathematical expression, graph, table, and the like) indicating the relation between the density of the target object  70 , the depression angle of the image capturing apparatus  50 , the angle θ, and the surveillance index is generated in advance based on experiments, simulations, computations, or the like. The reference data is stored in the storage unit  100 . The index computation unit  120  can compute the surveillance index by using the density of the target object  70 , the depression angle and the angle θ based on the arrangement information and the target object information, and the reference data read from the storage unit  100 . 
     In a case where the target object information includes the dwell information of the target object  70 , the index computation unit  120  may obtain the degree of a state where the target objects  70  overlap each other continuing, by using the density of the target object  70  and the average dwell time. Then, the index computation unit may compute the surveillance index by using the degree. 
     It should be noted that, the target object information may include both information indicating the movement direction of the target object  70  and the information indicating the density. The index computation unit  120  may compute the surveillance index by using both the information indicating the movement direction of the target object  70  and the information indicating the density. In the evaluation apparatus  10  according to the present example embodiment, the index computation unit  120  may compute the surveillance index in combination with the method described in the first example embodiment. Such a plurality of types of information and factors can be applied to the surveillance index by a method similar to the method described in the first example embodiment. 
     Next, the operation and the advantageous effect of the present example embodiment will be described. In the present example embodiment, the operation and the advantageous effect similar to those in the first example embodiment can be obtained. In addition, the index computation unit  120  computes the surveillance index at each position p i  by further using the information regarding the target object  70 , and thus it is possible to evaluate the arrangement of the image capturing apparatus  50  with higher accuracy. 
     Third Example Embodiment 
     An evaluation apparatus  10  according to a third example embodiment is the same as the evaluation apparatus  10  according to at least any of the first and second example embodiments except for points described below. 
     In the present example embodiment, the acquisition unit  110  further acquires information indicating the speed of movement of the target object  70 . The suitability computation unit  140  computes the transit time t n  taken when the target object  70  passes through the surveillance-unsuitable region based on the length d n  of the route and the information indicating the speed of the target object  70  moving. The suitability computation unit computes the suitability based on the transit time t n . 
     The suitability computation unit  140  computes the suitability based on the length d n  of the route for passing through the surveillance-unsuitable region S n . Here, even though the lengths d n  of the route are equal to each other, the time taken to pass through the surveillance-unsuitable region S n  varies when the velocity of the target object  70  varies. In a case where the target object  70  as a tracking target enters the surveillance-unsuitable region S n , as the time taken to pass becomes longer, the ambiguity of the position estimation of the target object  70  increases, and a possibility of losing sight of the target object  70  as the tracking target increases. Thus, it is possible to perform the evaluation with higher accuracy by performing the evaluation with the time taken to move on the route, than the accuracy of the evaluation with the region-passing route length d n  itself. 
     Specifically, in the acquisition step S 110  in the present example embodiment, the acquisition unit  110  acquires information indicating the movement speed of the target object  70  as the target object information. The target object information is as described in the second example embodiment. In the target object information, each position p i  or each region r i  is associated with the speed of the target object  70 . Then, the index computation step S 120  is performed in a manner similar to the method according to at least any of the first and second example embodiments. In the suitability computation step S 130 , the suitability computation unit  140  firstly computes the speed of the target object  70  in each surveillance-unsuitable region S n . The suitability computation unit  140  can set the speed of the target object  70  in the surveillance-unsuitable region S n  by using the speed associated with any position p i  or any region r i  in the surveillance-unsuitable region S n . The suitability computation unit  140  may set the average value, the mode value, the median value, or the like of the speed associated with the plurality of positions p i  or the plurality of regions r i  included in the surveillance-unsuitable region S n , as the speed of the target object  70  in the surveillance-unsuitable region S n . The suitability computation unit  140  obtains the transit time t n  by dividing the region-passing route length d n  by the speed of the target object  70  in the surveillance-unsuitable region S n . 
     In a case where the velocity of the target object  70  varies for each section of the route for passing through the surveillance-unsuitable region S n , it is possible to obtain the transit time t n  by dividing the route into a plurality of sections, computing the transit time for each section, and summing up the transit times of all the sections. A plurality of routes may be provided in one surveillance-unsuitable region S n , and a route may be provided which requires longer transit time than that of a case where the target object moves along the route corresponding to the region-passing route length d n . Therefore, the transit time for all available routes may be computed, and the representative value may be set as the transit time t n  of the surveillance-unsuitable region S n . 
     Then, the suitability computation unit  140  performs statistical processing on t n  and computes the suitability A based on the obtained statistical value τ. For example, the suitability computation unit sets the maximum value of all the obtained t n  as the statistical value τ in accordance with Expression (4). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                         
                     4 
                   
                   ] 
                 
               
               
                  
               
             
             
               
                 
                   τ 
                   = 
                   
                     
                       
                         max 
                            
                       
                       
                         
                           n 
                           = 
                           1 
                         
                         , 
                         … 
                             
                         , 
                         N 
                       
                     
                     ⁢ 
                     
                       t 
                       n 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     The suitability computation unit  140  may obtain the statistical value τ by using Expression (5) instead of Expression (4). That is, the suitability computation unit  140  may set the result of weighting and averaging the obtained plurality of t n  as the statistical value τ. Here, the weight w n  may be constant, and the weight w n  may be set to increase as the estimated frequency of use of the route becomes more. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                         
                     5 
                   
                   ] 
                 
               
               
                  
               
             
             
               
                 
                   τ 
                   = 
                   
                     
                       
                         ∑ 
                         
                           n 
                           = 
                           1 
                         
                         N 
                       
                         
                       
                         
                           w 
                           n 
                         
                         ⁢ 
                         
                           t 
                           n 
                         
                       
                     
                     
                       
                         ∑ 
                         
                           n 
                           = 
                           1 
                         
                         N 
                       
                       
                         w 
                         n 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Then, the suitability computation unit  140  computes the suitability A from the statistical value τ by using the monotonous non-increasing function f(τ). Here, A=f(τ). That is, as the statistical value τ becomes smaller, the suitability A increases. 
     Next, the operation and the advantageous effect of the present example embodiment will be described. In the present example embodiment, the operation and the advantageous effect similar to those in the first example embodiment can be obtained. In addition, since the suitability computation unit  140  further uses the information indicating the movement speed of the target object  70  to compute the suitability, it is possible to evaluate the arrangement of the image capturing apparatus  50  with higher accuracy. 
     Fourth Example Embodiment 
       FIG. 13  is a block diagram illustrating a configuration of an obtaining apparatus  20  according to a fourth example embodiment. The obtaining apparatus  20  according to the present example embodiment obtains the arrangement of one or more image capturing apparatuses  50  that surveil the target region  60 . The obtaining apparatus  20  includes an acquisition unit  220 , an arrangement information generation unit  240 , an evaluation unit  260 , and a selection unit  280 . The acquisition unit  220  acquires condition information indicating a condition regarding the arrangement of the image capturing apparatus  50  and environmental information indicating an environment of the target region  60 . The arrangement information generation unit  240  generates a plurality of pieces of arrangement information including at least any of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 , based on the condition information and the environmental information. The evaluation unit  260  evaluates the arrangement of the image capturing apparatus  50 , which is indicated by the plurality of pieces of arrangement information. The selection unit  280  selects one or more pieces of the arrangement information from the plurality of pieces of the arrangement information, based on the evaluation result of the evaluation unit  260 . The evaluation unit  260  includes an index computation unit  120  and a suitability computation unit  140 . The index computation unit  120  computes, for each of a plurality of positions p i  in the target region  60 , a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling the target object  70  in a case where the target object  70  is located at each of the plurality of positions p i . Thus, the suitability computation unit  140  computes the suitability of the arrangement of the image capturing apparatus  50  indicated by the arrangement information, based on the distribution of the surveillance index in the target region  60 . 
     The index computation unit  120  according to the present example embodiment is the same as the index computation unit  120  according to at least any of the first to third example embodiments. The suitability computation unit  140  according to the present example embodiment is the same as the suitability computation unit  140  according to at least any of the first to third example embodiments. 
       FIG. 14  is a flowchart illustrating an obtaining method according to the fourth example embodiment.  FIG. 15  is a flowchart illustrating contents of an evaluation step S 230  according to the fourth example embodiment. The obtaining method in the present example embodiment is a method of obtaining the arrangement of one or more image capturing apparatuses  50  that surveil the target region  60 . The present method includes an acquisition step S 210 , an arrangement information generation step S 220 , the evaluation step S 230 , and a selection step S 240 . In the acquisition step S 210 , the condition information indicating a condition regarding the arrangement of the image capturing apparatus  50  and the environmental information indicating the environment of the target region  60  are acquired. In the arrangement information generation step S 220 , a plurality of arrangement information including at least any of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50  are generated based on the condition information and the environmental information. In the evaluation step S 230 , the arrangement of the image capturing apparatuses  50  indicated by the plurality of pieces of arrangement information is evaluated. In the selection step S 240 , one or more pieces of arrangement information are selected from the plurality of pieces of arrangement information based on the evaluation result in the evaluation step S 230 . The evaluation step S 230  includes an index computation step S 232 , and a suitability computation step S 234 . In the index computation step S 232 , for each of a plurality of positions p i  in the target region  60 , the surveillance index indicating difficulty or easiness of surveilling the target object  70  in a case where the target object  70  is located at each of the plurality of positions p i  is computed using the arrangement information and the environmental information. In the suitability computation step S 234 , the suitability of the arrangement of the image capturing apparatus  50  indicated by the arrangement information is computed based on the distribution of the surveillance index in the target region  60 . 
     The obtaining method according to the present example embodiment is realized by the obtaining apparatus  20 . The index computation step S 232  according to the present example embodiment is the same as the index computation step S 120  according to at least any of the first to third example embodiments. The suitability computation step S 234  according to the present example embodiment is the same as the suitability computation step S 130  according to at least any of the first to third example embodiments. This will be described in detail below. 
     The obtaining apparatus  20  according to the present example embodiment obtains the arrangement of the image capturing apparatus  50  in the target region  60 . The obtaining apparatus  20  can obtain the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 , as the arrangement of the image capturing apparatus  50 . Some of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50  may be predetermined, and the obtaining apparatus  20  may obtain the remaining of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 . For example, the position and the field angle of the image capturing apparatus  50  have already been defined, and a suitable orientation of the image capturing apparatus  50  may be obtained on the premise of the position and the field angle. 
     In the acquisition step S 210 , the acquisition unit  220  acquires the condition information and the environmental information from the outside of the obtaining apparatus  20  or inside the obtaining apparatus  20 . For example, the user may perform an input operation on the obtaining apparatus  20 , and the acquisition unit  220  may acquire the condition information and the environmental information based on the input contents of the user. The arrangement information and the environmental information may be stored in advance in the storage unit  100  provided outside or inside the obtaining apparatus  20 , and the acquisition unit  220  may read and acquire the arrangement information and the environmental information. The storage unit  100  refers to any storage device.  FIG. 13  illustrates an example in which the obtaining apparatus  20  includes the storage unit  100 . It should be noted that, the acquisition unit  220  may further acquire the target object information in the acquisition step S 210 , similar to the acquisition step S 110  in the second and third example embodiments. The acquisition unit  220  may acquire at least one of the environmental information and the target object information from the detection unit such as the sensor and the camera. 
     The condition information indicates restrictions on the arrangement of the image capturing apparatus  50 . For example, the condition information includes at least any of the coordinate range of the region in which the image capturing apparatus  50  can be arranged, the angle range of the orientation that can be taken by the image capturing apparatus  50 , the range of the field angle that can be taken by the image capturing apparatus  50 , and the range of the number of the available image capturing apparatuses  50 . The region in which the image capturing apparatus  50  can be arranged is defined in accordance with, for example, whether or not power can be supplied to the image capturing apparatus  50  or whether or not a fixing tool for the image capturing apparatus  50  can be attached. It should be noted that, the condition information may include at least any of the coordinate range in a region in which it is not possible to arrange the image capturing apparatus  50 , and the angle range of the orientation of which adoption by the image capturing apparatus  50  is not possible. The coordinate space may be a coordinate system relative to the target region  60 , or may be a real world coordinate system. 
     The environmental information is as described in the first example embodiment. 
     The arrangement information generation unit  240  generates a plurality of pieces of arrangement information in the arrangement information generation step S 220 . It should be noted that, one piece of arrangement information indicates arrangement of one pattern. Each piece of arrangement information is as described in the first example embodiment. In a case where the target region  60  is surveilled by a plurality of image capturing apparatuses  50 , each piece of arrangement information includes information indicating the arrangement of the plurality of image capturing apparatuses  50 . The arrangement information generation unit  240  generates the arrangement information indicating an arrangement pattern of the image capturing apparatus  50  that satisfies the conditions indicated by the condition information. It should be noted that, the arrangement information is associated with the environmental information. Thus, the arrangement of the image capturing apparatus  50  for the target region  60  is indicated by the arrangement information and the environmental information. It should be noted that, the position of the image capturing apparatus  50 , which is indicated by the arrangement information is not necessarily required to be in the target region  60  as long as the image capturing apparatus  50  is capable of capturing an image of at least a portion of the target region  60 . 
     Specifically, for example, the arrangement information generation unit  240  arranges a plurality of arrangement points of the image capturing apparatuses  50  that satisfy the conditions indicated by the condition information at regular intervals, and selects points corresponding to the number of available image capturing apparatuses  50 , from the plurality of arrangement points. Then, information of the possible orientation taken by each image capturing apparatus  50  is added thereto and the arrangement information is set. The positions and the orientations of the available image capturing apparatuses  50  may be randomly defined in a range satisfying the condition indicated by the condition information. 
     In the evaluation step S 230 , the evaluation unit  260  evaluates the arrangement of the image capturing apparatus  50  indicated by each piece of arrangement information, by an evaluation method similar to the method performed by the evaluation apparatus  10  according to at least any of the first to third example embodiments. The evaluation unit  260  outputs the suitability for each piece of arrangement information. It should be noted that, the evaluation unit  260  may compute the suitability for each piece of arrangement information after acquiring all of the plurality of arrangement information from the arrangement information generation unit  240 , or repeat acquisition of some pieces of the arrangement information and computation of the suitability. 
     The selection unit  280  acquires the suitability from the evaluation unit  260  as the evaluation result of each arrangement. Further, the selection unit  280  also acquires a plurality of pieces of arrangement information generated by the arrangement information generation unit  240 . The suitability is associated with each piece of the plurality of arrangement information generated by the arrangement information generation unit  240 . In the selection step S 240 , the selection unit  280  selects the arrangement information in which the suitability is the maximum among the plurality of pieces of arrangement information. The selected arrangement information is output from the selection unit  280 . The suitability of the arrangement information may be output from the selection unit  280 . The output arrangement information or the like is displayed by the display unit such as a display. The arrangement information is displayed, for example, by displaying a drawing illustrating a mark indicating the position, the orientation, and the like of the image capturing apparatus  50  on the plan view of the target region  60 . The arrangement information and the like may be stored in the storage unit  100 , or may be input to a device outside the obtaining apparatus  20 . 
     It should be noted that, the selection unit  280  may output a plurality of pieces of arrangement information. The selection unit  280  can select and output the plurality of pieces of arrangement information the number of which is within a range of a predetermined value, for example, in descending order of suitability. The number of pieces of arrangement information to be output is input to the obtaining apparatus  20  by the user, for example. The user can adopt the freely-selected arrangement from the arrangements indicated by the plurality of pieces of output arrangement information. 
     The suitability computed by the evaluation unit  260  may be fed back to the arrangement information generation unit  240 . That is, the arrangement information generation unit  240  acquires the suitability computed by the evaluation unit  260 , and generates the arrangement information indicating the different arrangement based on the acquired suitability and the arrangement associated with the suitability. For example, the arrangement information generation unit  240  suppresses the generation of an arrangement similar to the arrangement having low suitability. As an example, the arrangement information generation unit  240  can roughly set the parameters used for generating the arrangement in the vicinity of the arrangement having low suitability. 
     Specifically, for example, in a case where points corresponding to the number of image capturing apparatuses  50  are selected from a plurality of arrangement points as described above, the arrangement information is not generated for combinations for all the arrangement points, but the arrangement points are selected from the rest obtained by excluding some arrangement points therefrom. Examples of the arrangement points to be excluded include arrangement points selected in the arrangement having low suitability. The arrangement information generation unit  240  may generate arrangement information by widening the interval between a plurality of arrangement points for an arrangement close to the arrangement having low suitability. 
     On the contrary, the arrangement information generation unit  240  may increase the generation of arrangements similar to the arrangements having high suitability. As an example, the arrangement information generation unit  240  finely sets the parameters used for generating the arrangement in the vicinity of the arrangement having high suitability. It should be noted that, the arrangement having high suitability means, for example, the arrangement having suitability which is higher than the predetermined reference. The arrangement having low suitability means, for example, the arrangement having suitability which is lower than the predetermined reference. 
     In addition, generation of the arrangement information and computation of the suitability may be performed by a coarse to fine search approach. That is, firstly, a plurality of arrangements are roughly set, and the suitability of the arrangement is computed. Then, the finer arrangement is set in the vicinity of the arrangement having high suitability, and the suitability is computed. Specifically, for example, in a case where points corresponding to the number of image capturing apparatuses  50  are selected from a plurality of arrangement points as described above, in a first step, a plurality of arrangement points are determined at wide intervals, and one or more arrangements having high suitability are obtained. Then, as a second step, the interval between the plurality of arrangement points is made narrower than the interval in the first step, and the arrangement information of the arrangement similar to the arrangement obtained in the first step is generated. In the next step, the similar process may be continued at a narrower arrangement point interval. In this manner, the arrangement having high suitability can be efficiently obtained. 
     The obtaining apparatus  20  may obtain the arrangement of the image capturing apparatus  50  for each of the plurality of time ranges. In this case, at least any type of information acquired by the acquisition unit  220  is defined for each of the plurality of time ranges. Here, the information acquired by the acquisition unit  220  is either a case of the condition information and the environmental information, or a case of the condition information, the environmental information, and the target object information. In a case where at least one of the condition information and the environmental information is defined for each time range, the arrangement information generation unit  240  generates a plurality of pieces of arrangement information for each time range. In a case where at least any of the arrangement information, the environmental information, and the target object information is defined for each time range, the evaluation unit  260  outputs the evaluation result for each time range. Thus, in a case where the evaluation unit  260  outputs the evaluation result for each time range, the selection unit  280  selects and outputs the arrangement for each time range. In this manner, the user can know the suitable arrangement for each time range. 
     As described above, the obtaining apparatus  20  according to the present example embodiment can obtain the arrangement of the image capturing apparatus  50  suitable for surveilling the target region  60  within the range satisfying the predetermined conditions. 
     For example, the user of the evaluation apparatus  10  can input the information regarding the target region  60  intended to be surveilled and the arrangement conditions of the image capturing apparatus  50  to the obtaining apparatus  20  and adopt the output arrangement. According to the obtaining apparatus  20  and the obtaining method according to the present example embodiment, for example, in the first example embodiment, the arrangements described in the first to ninth examples of the arrangement of the image capturing apparatus  50  can be obtained. 
     The obtaining apparatus  20  according to the present example embodiment can be realized by, for example, the computer  1000  as illustrated in  FIG. 12 . The storage device  1080  stores program modules that realize the acquisition unit  220 , the arrangement information generation unit  240 , the evaluation unit  260 , the index computation unit  120 , the suitability computation unit  140 , and the selection unit  280  in the obtaining apparatus  20 . The processor  1040  realizes the function corresponding to each program module by reading each program module into the memory  1060  and executing the program module. 
     Next, the operation and the advantageous effect of the present example embodiment will be described. According to the obtaining apparatus  20  according to the present example embodiment, the preferable arrangement of the image capturing apparatus  50  is obtained based on the evaluation result in consideration of the situation of the entire target region  60 . In this manner, it is possible to know the arrangement of the image capturing apparatus  50  in the target region  60  in which overlooking of the target object  70  occurs less frequently. 
     Fifth Example Embodiment 
     In a surveillance method according to a fifth example embodiment, the image capturing apparatus  50  is arranged based on the arrangement determined using the evaluation apparatus  10  according to at least any of the first to third example embodiments or the obtaining apparatus  20  according to the fourth example embodiment, and the target region  60  is surveilled. 
     In a case using the evaluation apparatus  10 , the user prepares a plurality of candidates for the arrangement of the image capturing apparatus  50 . Then, information of each arrangement candidate is input to the evaluation apparatus  10 , and the acquisition unit  110  acquires the arrangement information. The user inputs information regarding the target region  60  to the evaluation apparatus  10 , and the acquisition unit  110  acquires the environmental information. The user may further input the target object information to the evaluation apparatus  10 . The evaluation apparatus  10  outputs the suitability of each candidate. The user compares a plurality of pieces of the suitability of a plurality of output candidates with each other, and determines the candidate having the highest suitability as the arrangement of the image capturing apparatus  50 . Then, the user installs the image capturing apparatus  50  in accordance with the determined arrangement. 
     On the other hand, in a case using the obtaining apparatus  20 , the user inputs the arrangement conditions for the image capturing apparatus  50  to the obtaining apparatus  20 , and the acquisition unit  220  acquires the condition information. The user inputs information regarding the target region  60  to the obtaining apparatus  20 , and the acquisition unit  220  acquires the environmental information. The user may further input the target object information to the obtaining apparatus  20 . The obtaining apparatus  20  outputs information indicating the arrangement of the image capturing apparatus  50  suitable for surveilling the target region  60 . The user installs the image capturing apparatus  50  in accordance with the arrangement of the image capturing apparatus  50  output by the obtaining apparatus  20 . 
       FIG. 16  is a block diagram illustrating a configuration of a surveillance apparatus  30  according to the fifth example embodiment. In the example in  FIG. 16 , the surveillance apparatus  30  includes an analysis unit  380 , a display unit  360 , a storage unit  100 , and a plurality of image capturing apparatuses  50 . The image capturing apparatuses  50  are arranged based on the arrangement determined using the evaluation apparatus  10  according to at least any of the first to third example embodiments or the obtaining apparatus  20  according to the fourth example embodiment. 
     In the surveillance apparatus  30  and a surveillance method according to the present example embodiment, for example, in the first example embodiment, the image capturing apparatuses  50  can be arranged as described in the first to ninth examples of the arrangement of the image capturing apparatus  50 . 
     Each image capturing apparatus  50  captures an image of at least a portion of the target region  60 . It should be noted that, the position, the orientation, the field angle, and the like of the image capturing apparatus  50  may be further finely adjusted by the user, an observer, or the like. In a case where the arrangement that varies depending on the time slot is preferable as a result of the processing of the evaluation apparatus  10  or the obtaining apparatus  20 , the arrangement of the image capturing apparatus  50  may be changed in a timely manner by the user, the observer, or the like. 
     Image information output from each image capturing apparatus  50  is input to the analysis unit  380 . The analysis unit  380  analyzes the image information from the image capturing apparatus  50 . The analysis performed by the analysis unit  380  is, for example, detection or tracking of the target object  70 . For example, the image captured by the image capturing apparatus  50  and the analysis result by the analysis unit  380  are displayed on the display unit  360  and are provided for the observer. Thus, the observer can recognize the situation of the target object  70  in the target region  60 . 
     In the image displayed on the display unit  360 , for example, a frame surrounding the target object  70  may also be displayed based on the detection result by the analysis unit  380 , or an ID assigned to the target object  70  may also be displayed based on the tracking result by the analysis unit  380 . An abnormal movement of the target object  70  may be detected based on the result of detecting and tracking the target object  70 . An alert may be given. 
     It should be noted that, not an image itself captured by the image capturing apparatus  50  may be displayed, but only the analysis result by the analysis unit  380  may be displayed, on the display unit  360 . For example, the position and movement trajectory of the target object  70  may be displayed on a map based on the tracking result. Then, when the observer wants to check the image captured by the specific image capturing apparatus  50 , the image may be displayed by performing an operation for issuing a display processing command. 
     It should be noted that, the image information output from each image capturing apparatus  50  may be stored in the storage unit  100 . The surveillance apparatus  30  may not include the analysis unit  380 . The image information output from each image capturing apparatus  50  may be directly input to and displayed on the display unit  360  without passing through the analysis unit  380 . 
     The surveillance apparatus  30  according to the present example embodiment can be realized using, for example, the computer  1000  as illustrated in  FIG. 12 . The storage device  1080  stores a program module that realizes the analysis unit  380  in the surveillance apparatus  30 . The processor  1040  realizes the function corresponding to each program module by reading each program module into the memory  1060  and executing the program module. 
     The display unit  360  is, for example, a display device connected to the input and output interface  1100 . It should be noted that, the display unit  360  may be connected to the computer  1000  through the network interface  1120 . 
     Next, the operation and the effect of the present example embodiment will be described. According to the surveillance apparatus  30  according to the present example embodiment, the surveillance is performed in the preferable arrangement of the image capturing apparatus  50 , which is obtained based on the evaluation result in consideration of the situation of the entire target region  60 . In this manner, it is possible to surveil the target region  60  in which overlooking of the target object  70  occurs less frequently. 
     Sixth Example Embodiment 
       FIG. 17  is a block diagram illustrating a configuration of a surveillance apparatus  30  according to a sixth example embodiment. The surveillance apparatus  30  according to the present example embodiment is the same as the surveillance apparatus  30  according to the fifth example embodiment except for the points described below. 
     The surveillance apparatus  30  according to the present example embodiment surveils the target region  60  with one or more image capturing apparatuses  50 . The surveillance apparatus  30  includes an obtaining unit  320  and an arrangement control unit  340 . The obtaining unit  320  obtains an arrangement of the image capturing apparatus  50 . The arrangement control unit  340  controls the arrangement of the image capturing apparatus  50  based on the arrangement of the image capturing apparatus  50  obtained by the obtaining unit  320 . The obtaining unit  320  includes an acquisition unit  220 , an arrangement information generation unit  240 , an evaluation unit  260 , and a selection unit  280 . The acquisition unit  220  acquires condition information indicating a condition regarding the arrangement of the image capturing apparatus  50  and environmental information indicating an environment of the target region  60 . The arrangement information generation unit  240  generates a plurality of pieces of arrangement information including at least any of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 , based on the condition information and the environmental information. The evaluation unit  260  evaluates the arrangement of the image capturing apparatus  50 , which is indicated by the plurality of pieces of arrangement information. The selection unit  280  selects one or more pieces of the arrangement information from the plurality of pieces of the arrangement information, based on the evaluation result of the evaluation unit  260 . The evaluation unit  260  includes an index computation unit  120  and a suitability computation unit  140 . The index computation unit  120  computes, for each of a plurality of positions p i  in the target region  60 , a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling the target object  70  in a case where the target object  70  is located at each of the plurality of positions p i . The suitability computation unit  140  computes the suitability of the arrangement of the image capturing apparatus  50  indicated by the arrangement information, based on the distribution of the surveillance index in the target region  60 . 
     In the present example embodiment, the surveillance apparatus  30  further includes an image capturing apparatus  50 , an analysis unit  380 , and a display unit  360 . 
     The surveillance apparatus  30  according to the present example embodiment is also described as follows, for example. The surveillance apparatus  30  surveils the target region  60  with one or more image-capturing-apparatus  50 . The surveillance apparatus includes at least one of the analysis unit  380  that analyzes an image captured by the image capturing apparatus  50  and the display unit  360  that displays the image. The image capturing apparatus  50  is placed based on the arrangement information obtained based on the distribution of the surveillance index in the target region  60 . The surveillance index is computed based on the environmental information indicating the environment of the target region  60  for each of a plurality of positions p i  in the target region  60 , and indicates the difficulty or the easiness of surveillance of the target object  70  in a case where the target object  70  is located at each of the plurality of positions p i . In addition, the arrangement information indicates at least any of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 . 
     The index computation unit  120  according to the present example embodiment is the same as the index computation unit  120  according to at least any of the first to third example embodiments. The suitability computation unit  140  according to the present example embodiment is the same as the suitability computation unit  140  according to at least any of the first to third example embodiments. The acquisition unit  220 , the arrangement information generation unit  240 , the evaluation unit  260 , and the selection unit  280  according to the present example embodiment are the same as the acquisition unit  220 , the arrangement information generation unit  240 , the evaluation unit  260 , and the selection unit  280  according to the fourth example embodiment, respectively. The analysis unit  380  and the display unit  360  according to the present example embodiment are the same as the analysis unit  380  and the display unit  360  according to the fifth example embodiment, respectively. 
       FIG. 18  is a flowchart illustrating a surveillance method according to the sixth example embodiment. It should be noted that, the content of an obtaining step S 330  in the present example embodiment is illustrated by the flowchart which is the same as the flowchart in  FIG. 14 . The content of an evaluation step S 230  in the present example embodiment is illustrated by the flowchart which is the same as the flowchart in  FIG. 15 . 
     The surveillance method according to the present example embodiment is a method of surveilling the target region  60  with one or more image capturing apparatuses  50 . The method includes the obtaining step S 330  and an arrangement control step S 340 . In the obtaining step S 330 , the arrangement of the image capturing apparatus  50  is obtained. In the arrangement control step S 340 , the arrangement of the image capturing apparatus  50  is controlled based on the arrangement of the image capturing apparatus  50 , which is obtained in the obtaining step S 330 . The obtaining step S 330  includes an acquisition step S 210 , an arrangement information generation step S 220 , the evaluation step S 230 , and a selection step S 240 . In the acquisition step S 210 , the condition information indicating a condition regarding the arrangement of the image capturing apparatus  50  and the environmental information indicating the environment of the target region  60  are acquired. In the arrangement information generation step S 220 , a plurality of arrangement information indicating at least any of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50  are generated based on the condition information and the environmental information. In the evaluation step S 230 , the arrangement of the image capturing apparatuses  50  indicated by the plurality of pieces of arrangement information is evaluated. In the selection step S 240 , one or more pieces of arrangement information are selected from the plurality of pieces of arrangement information based on the evaluation result in the evaluation step S 230 . The evaluation step S 230  includes an index computation step S 232 , and a suitability computation step S 234 . In the index computation step S 232 , the surveillance index indicating difficulty or easiness of surveilling the target object  70  in a case where the target object  70  is located at each of a plurality of positions p i  in the target region  60  is computed using the arrangement information and the environmental information for each of the plurality of positions p i . In the suitability computation step S 234 , the suitability of the arrangement of the image capturing apparatus  50  indicated by the arrangement information is computed based on the distribution of the surveillance index in the target region  60 . 
     The surveillance method according to the present example embodiment is realized by the surveillance apparatus  30  according to the present example embodiment. The index computation step S 232  according to the present example embodiment is the same as the index computation step S 120  according to at least any of the first to third example embodiments. The suitability computation step S 234  according to the present example embodiment is the same as the suitability computation step S 130  according to at least any of the first to third example embodiments. The acquisition step S 210 , the arrangement information generation step S 220 , the evaluation step S 230 , and the selection step S 240  according to the present example embodiment are the same as the acquisition step S 210 , the arrangement information generation step S 220 , the evaluation step S 230 , and the selection step S 240  according to the fourth example embodiment, respectively. This will be described in detail below. 
     In the present example embodiment, at least any of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50  can be controlled by the arrangement control unit  340 . For example, the image capturing apparatus  50  is attached to a drive device that changes at least one of the position and the orientation of the image capturing apparatus. In addition, the field angle of the image capturing apparatus  50  can be adjusted by a signal from the arrangement control unit  340 . Specifically, for example, the image capturing apparatus  50  is a mobile camera capable of changing the position or the pose of the image capturing apparatus by the external control. The image capturing apparatus  50  may be an apparatus such as a PZT camera, of which the orientation and the zoom ratio can be controlled from the outside, or may be an apparatus such as an Unmanned Aerial Vehicle (UAV), which is capable of floating in the air and capturing an image. The image capturing apparatus  50  may be a camera installed on a wall or ceiling to be able to move in the shape of a laid rail. Alternatively, the image capturing apparatus  50  may be a camera mounted on a movable robot. 
     In the obtaining step S 330 , the obtaining unit  320  obtains the arrangement of the image capturing apparatus  50  by the same obtaining method as that performed by the obtaining apparatus  20  according to the fourth example embodiment. In the present example embodiment, the range that can be controlled by the arrangement control unit  340  is applied as the range in which image capturing apparatus  50  can be arranged, to the condition information acquired by the acquisition unit  220 . 
     The arrangement information output from the obtaining unit  320  is input to the arrangement control unit  340 . It should be noted that, the arrangement information output from the obtaining unit  320  may be stored once in the storage unit  100 , and the arrangement control unit  340  may read and acquire the information. The arrangement control unit  340  controls at least any of the position of the image capturing apparatus  50 , the orientation of the image capturing apparatus  50 , and the field angle of the image capturing apparatus  50 , based on the acquired arrangement information. Specifically, for example, a control signal is transmitted from the arrangement control unit  340  to the drive device or the like to which the image capturing apparatus  50  is attached.  FIG. 17  illustrates an example in which the surveillance apparatus  30  includes the storage unit  100 . 
     The image capturing apparatus  50  surveils the target region  60  in an arrangement adjusted by the arrangement control unit  340 . An image captured by the image capturing apparatus  50  is processed in the similar manner to that in the fifth example embodiment. 
     The obtaining unit  320  may obtain the arrangement of the image capturing apparatus  50  for each of a plurality of time ranges, and the arrangement control unit  340  may control the arrangement for each time range. The method of evaluating and obtaining the arrangement for each time range is as described, for example, in the first, second, and fourth example embodiments. The obtaining unit  320  obtains the arrangement of the image capturing apparatus  50  for each of the plurality of time ranges, and generates a timetable for the arrangement of the image capturing apparatus  50 . The generated timetable is stored in, for example, the storage unit  100 . The arrangement control unit  340  changes the arrangement of the image capturing apparatus  50  for each time range, in accordance with the timetable read from the storage unit  100 . In this manner, the surveillance is normally performed with the suitable arrangement of the image capturing apparatus  50 . 
     The surveillance apparatus  30  according to the present example embodiment can be realized using, for example, the computer  1000  as illustrated in  FIG. 12 . The storage device  1080  stores program modules that realize the obtaining unit  320 , the acquisition unit  220 , the arrangement information generation unit  240 , the evaluation unit  260 , the index computation unit  120 , the suitability computation unit  140 , the selection unit  280 , the arrangement control unit  340 , and the analysis unit  380  in the surveillance apparatus  30 . The processor  1040  realizes the function corresponding to each program module by reading each program module into the memory  1060  and executing the program module. 
     Next, the operation and the advantageous effect of the present example embodiment will be described. In the present example embodiment, the operation and the advantageous effect similar to those in the fifth example embodiment can be obtained. 
     Seventh Example Embodiment 
       FIG. 19  is a block diagram illustrating a configuration of a surveillance apparatus  30  according to a seventh example embodiment. The surveillance apparatus  30  according to the present example embodiment is the same as the surveillance apparatus  30  according to the sixth example embodiment except for the points described below. In the surveillance apparatus  30  according to the present example embodiment, the obtaining unit  320  obtains the arrangement of the image capturing apparatus  50  at a plurality of timings based on predetermined conditions. Then, the arrangement control unit  340  controls the arrangement of the image capturing apparatus  50  every time the obtaining unit  320  obtains the arrangement of the image capturing apparatus  50 . This will be described in detail below. 
     The surveillance apparatus  30  according to the present example embodiment acquires real-time information obtained on the spot and applies the information to the arrangement of the image capturing apparatus  50 . In this manner, it is possible to realize an appropriate arrangement of the image capturing apparatus  50  in accordance with the actual situation. 
     The surveillance apparatus  30  according to the present example embodiment further includes a detection unit  330  and an update determination unit  310 . The detection unit  330  is a camera, a sensor, or the like that detects the status of the target region  60 . A portion of the detection unit  330  may also serve as the image capturing apparatus  50 . The surveillance apparatus  30  may include a plurality of detection units  330 . The detection unit  330  detects, for example, at least any of the density, the distribution, and the movement status of the target object  70  in the target region  60 . Then, the obtained detection result is acquired by the acquisition unit  220  as the target object information. The detection unit  330  may detect, for example, the illuminance in at least a portion of the target region  60  and the position of the object  660 . In this case, the obtained detection result is acquired by the acquisition unit  220  as the environmental information. It should be noted that, the detection target of the detection unit  330  is not limited to the above examples. The detection unit  330  can detect information that can be included in the arrangement information or the target object information described above, and the acquisition unit  220  can acquire the detection result as at least a portion of the arrangement information or the target object information. 
     The update determination unit  310  determines whether or not the arrangement of the image capturing apparatus  50  is to be updated. For example, update condition information indicating a condition of whether or not the arrangement is to be updated is stored in the storage unit  100  in advance. The update determination unit  310  reads the update condition information from the storage unit  100  and uses the update condition information for the determination. The update condition information is, for example, a time indicating an update interval or a time at which the update is to be performed. In a case where the update condition information is the time indicating the update interval, the update determination unit  310  causes the obtaining unit  320  to obtain the arrangement again when the elapsed time from the previous obtaining of the arrangement information is equal to or longer than the time indicating the update interval. In a case where the update condition information is the time at which the update is to be performed, the update determination unit  310  causes the obtaining unit  320  to obtain the arrangement again when the current time is the time at which the update is to be performed. 
     The update condition information may be, for example, a reference value regarding a difference between the environmental information or the target object information used for previously obtaining the arrangement information and the latest detection result obtained by the detection unit  330 . For example, in a case where the difference is equal to or more than the reference value, the update determination unit  310  causes the obtaining unit  320  to obtain the arrangement again. This is because, in a case where the difference is large, the arrangement may not be suitable for the current situation. 
     It should be noted that, the user or the observer may perform an operation on the surveillance apparatus  30  to update the arrangement. In a case where the operation is performed, the update determining unit  310  may determine that the update condition is satisfied. 
       FIG. 20  is a flowchart illustrating contents of processing of updating the arrangement, which is performed by the surveillance apparatus  30  according to the seventh example embodiment. The surveillance method according to the present example embodiment includes the step S 310 , the step S 320 , the obtaining step S 330 , and the arrangement control step S 340 . When the surveillance apparatus  30  starts to update the arrangement, the update determination unit  310  determines, in Step S 310 , whether or not an end operation has been performed. In a case where the end operation has not been performed (N in Step S 310 ), the update determination unit  310  then performs Step S 320 . 
     In Step S 320 , the update determination unit  310  determines whether or not the update condition is satisfied. In a case where the update condition is not satisfied (N in Step S 320 ), the process returns to Step S 310 . In a case where the update condition is satisfied (Y in Step S 320 ), the update determination unit  310  causes the obtaining unit  320  to obtain the arrangement of the image capturing apparatus  50 . The obtaining unit  320  obtains the arrangement of the image capturing apparatus  50  in the obtaining step S 330 , and then the arrangement control unit  340  controls the arrangement of the image capturing apparatus  50  in the arrangement control step S 340 . The contents of the obtaining step S 330  and the arrangement control step S 340  are the same as the contents of the obtaining step S 330  and the arrangement control step S 340  in the sixth example embodiment, respectively. At this time, the obtaining unit  320  obtains the arrangement by using the latest detection result by the detection unit  330 . It should be noted that, as a result of re-obtaining, the same arrangement may be obtained as the suitable arrangement. 
     Following the arrangement control step S 340 , the update determination unit  310  performs Step S 310  again and repeats the above process until the end operation is performed. It should be noted that, in a case where the end operation is performed (Y in Step S 310 ), the surveillance apparatus  30  ends the update of the arrangement. 
     It should be noted that, the image capturing apparatus  50 , the analysis unit  380 , and the display unit  360  continue to operate for surveilling the target region  60 , while the step S 310 , the step S 320 , the obtaining step S 330 , and the arrangement control step S 340  are performed. 
     The update determination unit  310  in the surveillance apparatus  30  according to the present example embodiment can be realized by, for example, the computer  1000  as illustrated in  FIG. 12 . The storage device  1080  further stores a program module that realizes the update determination unit  310  in the surveillance apparatus  30 . The processor  1040  realizes the function corresponding to the program module by reading the program module into the memory  1060  and executing the program module. The detection unit  330  may be, for example, a sensor connected to the input and output interface  1100  or the network interface  1120 . 
     Next, the operation and the advantageous effect of the present example embodiment will be described. In the present example embodiment, the operation and the advantageous effect similar to those in the fifth example embodiment can be obtained. In addition, it is possible to control the arrangement to which the real-time information by the detection unit  330  has been applied. 
     Hitherto, the example embodiments of the present invention have been described above with reference to the drawings. These are merely examples of the present invention, and various configurations other than the above description may be adopted. For example, in the sequence diagram and the flowchart used in the above description, a plurality of steps (processes) are described in order, but the execution order of the steps executed in each example embodiment is not limited to the order of the description. In the example embodiments, the order of the illustrated steps can be changed within a range without hindering the contents. In addition, the above-described example embodiments can be combined as long as the contents do not conflict with each other. 
     Some or all of the example embodiments described above can be described as the supplementary notes as follows, but the present invention is not limited to the followings. 
     1. An evaluation apparatus that evaluates an arrangement of one or more image capturing apparatuses that surveil a target region, the apparatus including: 
     an acquisition unit that acquires arrangement information and environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, and the environmental information indicating an environment of the target region; 
     an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position; and 
     a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     2. The evaluation apparatus according to 1., in which 
     the environmental information indicates at least any of a shape of the target region, a size of the target region, a position of an object placed in the target region, a shape of the object, a size of the object, and an orientation of the object. 
     3. The evaluation apparatus according to 1. or 2., in which 
     the index computation unit computes the surveillance index based on at least any of a size, brightness, a hiding degree of the target object captured by the image capturing apparatus in a case where the target objects is located at each of the plurality of positions in the target region. 
     4. The evaluation apparatus according to any one of 1. to 3., in which 
     the suitability computation unit 
     specifies one or more surveillance-unsuitable regions based on distribution of the surveillance index in the target region, the surveillance-unsuitable regions in which it is difficult to surveil the target object by the image capturing apparatus, 
     obtains a length of a route in a case where the target object passes through the surveillance-unsuitable region, for each of the surveillance-unsuitable regions, and 
     computes the suitability based on the length of the route. 
     5. The evaluation apparatus according to 4., in which 
     the acquisition unit further acquires information indicating a speed of a movement of the target object, and 
     the suitability computation unit 
     computes a transit time taken for the target object to pass through the surveillance-unsuitable region, based on the length of the route and the information indicating the speed of the target object, and 
     computes the suitability based on the transit time. 
     6. The evaluation apparatus according to any one of 1. to 5., in which 
     the acquisition unit further acquires information indicating a direction of a movement of the target object, and 
     the index computation unit computes the surveillance index on the assumption that, as the direction of the movement of the target object becomes closer to a direction toward the image capturing apparatus, it is easier to surveil the target object. 
     7. The evaluation apparatus according to any one of 1. to 6., in which 
     the acquisition unit further acquires information indicating density of a plurality of the target objects, and 
     the index computation unit computes the surveillance index on the assumption that, as the density of the plurality of the target objects becomes higher, it is more difficult to surveil the target object. 
     8. An obtaining apparatus that obtains an arrangement of one or more image capturing apparatuses that surveil a target region, the apparatus including: 
     an acquisition unit that acquires condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region; 
     an arrangement information generation unit that generates a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus; 
     an evaluation unit that evaluates each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information; and 
     a selection unit that selects one or more pieces of the arrangement information from among the plurality of pieces of arrangement information, based on an evaluation result of the evaluation unit, in which 
     the evaluation unit includes 
     an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and 
     a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     9. The obtaining apparatus according to 8., in which 
     the environmental information indicates at least any of a shape of the target region, a size of the target region, a position of an object placed in the target region, a shape of the object, a size of the object, and an orientation of the object. 
     10. The obtaining apparatus according to 8. or 9., in which 
     the index computation unit computes the surveillance index based on at least any of a size, brightness, a hiding degree of the target object captured by the image capturing apparatus in a case where the target objects is located at each of the plurality of positions in the target region. 
     11. In the obtaining apparatus according to any one of 8. to 10., in which 
     the suitability computation unit 
     specifies one or more surveillance-unsuitable regions based on distribution of the surveillance index in the target region, the surveillance-unsuitable regions in which it is difficult to surveil the target object by the image capturing apparatus, 
     obtains a length of a route in a case where the target object passes through the surveillance-unsuitable region, for each of the surveillance-unsuitable regions, and computes the suitability based on the length of the route. 
     12. The obtaining apparatus according to 11., in which 
     the acquisition unit further acquires information indicating a speed of a movement of the target object, and 
     the suitability computation unit 
     computes a transit time taken for the target object to pass through the surveillance-unsuitable region, based on the length of the route and the information indicating the speed of the target object, and 
     computes the suitability based on the transit time. 
     13. The obtaining apparatus according to any one of 8. to 12., in which 
     the acquisition unit further acquires information indicating a direction of a movement of the target object, and 
     the index computation unit computes the surveillance index on the assumption that, as the direction of the movement of the target object becomes closer to a direction toward the image capturing apparatus, it is easier to surveil the target object. 
     14. The obtaining apparatus according to any one of 8. to 13., in which 
     the acquisition unit further acquires information indicating density of a plurality of the target objects, and 
     the index computation unit computes the surveillance index on the assumption that, as the density of the plurality of the target objects becomes higher, it is more difficult to surveil the target object. 
     15. A surveillance method of arranging the image capturing apparatus based on the arrangement determined using the evaluation apparatus according to any one of 1. to 7. or the obtaining apparatus according to any one of 8. to 14., and surveilling the target region. 
     16. A surveillance apparatus that surveils a target region with one or more image capturing apparatuses, the apparatus including: 
     an obtaining unit that obtains an arrangement of the image capturing apparatus; and 
     an arrangement control unit that controls the arrangement of the image capturing apparatus based on the arrangement of the image capturing apparatus obtained by the obtaining unit, in which 
     the obtaining unit includes 
     an acquisition unit that acquires condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region, 
     an arrangement information generation unit that generates a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, 
     an evaluation unit that evaluates each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information, and 
     a selection unit that selects one or more pieces of the arrangement information from among the plurality of pieces of arrangement information, based on an evaluation result of the evaluation unit, and 
     the evaluation unit includes 
     an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and 
     a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     17. The surveillance apparatus according to 16., in which 
     the obtaining unit obtains the arrangement of the image capturing apparatus for each of a plurality of time ranges, and 
     the arrangement control unit controls the arrangement of the image capturing apparatus for each time range. 
     18. The surveillance apparatus according to 16., in which 
     the obtaining unit obtains the arrangement of the image capturing apparatus at a plurality of timings based on a predetermined condition, and 
     the arrangement control unit controls the arrangement of the image capturing apparatus every time the obtaining unit obtains the arrangement of the image capturing apparatus. 
     19. The surveillance apparatus according to any one of 16. to 18., in which 
     the environmental information indicates at least any of a shape of the target region, a size of the target region, a position of an object placed in the target region, a shape of the object, a size of the object, and an orientation of the object. 
     20. The surveillance apparatus according to any one of 16. to 19., in which 
     the index computation unit computes the surveillance index based on at least any of a size, brightness, a hiding degree of the target object captured by the image capturing apparatus in a case where the target object is located at each of the plurality of positions in the target region. 
     21. The surveillance apparatus according to any one of 16. to 20., in which 
     the suitability computation unit 
     specifies one or more surveillance-unsuitable regions based on distribution of the surveillance index in the target region, the surveillance-unsuitable regions in which it is difficult to surveil the target object by the image capturing apparatus, 
     obtains a length of a route in a case where the target object passes through the surveillance-unsuitable region, for each of the surveillance-unsuitable regions, and 
     computes the suitability based on the length of the route. 
     22. The surveillance apparatus according to 21., in which 
     the acquisition unit further acquires information indicating a speed of a movement of the target object, and 
     the suitability computation unit 
     computes a transit time taken for the target object to pass through the surveillance-unsuitable region, based on the length of the route and the information indicating the speed of the target object, and 
     computes the suitability based on the transit time. 
     23. The surveillance apparatus according to any one of 16. to 22., in which 
     the acquisition unit further acquires information indicating a direction of a movement of the target object, and 
     the index computation unit computes the surveillance index on the assumption that, as the direction of the movement of the target object becomes closer to a direction toward the image capturing apparatus, it is easier to surveil the target object. 
     24. The surveillance apparatus according to any one of 16. to 23., in which 
     the acquisition unit further acquires information indicating density of a plurality of the target objects, and 
     the index computation unit computes the surveillance index on the assumption that, as the density of the plurality of the target objects becomes higher, it is more difficult to surveil the target object. 
     25. An evaluation method of evaluating an arrangement of one or more image capturing apparatuses that surveil a target region, the method including: 
     an acquisition step of acquiring arrangement information and environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, and the environmental information indicating an environment of the target region; 
     an index computation step of computing, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position; and 
     a suitability computation step of computing suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     26. The evaluation method according to 25., in which 
     the environmental information indicates at least any of a shape of the target region, a size of the target region, a position of an object placed in the target region, a shape of the object, a size of the object, and an orientation of the object. 
     27. The evaluation method according to 25. or 26., in which 
     in the index computation step, the surveillance index is computed based on at least any of a size, brightness, a hiding degree of the target object captured by the image capturing apparatus in a case where the target object is located at each of the plurality of positions in the target region. 
     28. The evaluation method according to any one of 25. to 27., in which 
     in the suitability computation step, 
     one or more surveillance-unsuitable regions are specified based on distribution of the surveillance index in the target region, the surveillance-unsuitable regions in which it is difficult to surveil the target object by the image capturing apparatus, 
     a length of a route in a case where the target object passes through the surveillance-unsuitable region is obtained for each of the surveillance-unsuitable regions, and 
     the suitability is computed based on the length of the route. 
     29. The evaluation method according to 28., in which 
     in the acquisition step, information indicating a speed of a movement of the target object is further acquired, and 
     in the suitability computation step, 
     a transit time taken for the target object to pass through the surveillance-unsuitable region is computed based on the length of the route and the information indicating the speed of the target object, and 
     the suitability is computed based on the transit time. 
     30. The evaluation method according to any one of 25. to 29., in which 
     in the acquisition step, information indicating a direction of a movement of the target object is further acquired, and 
     in the index computation step, the surveillance index is computed on the assumption that, as the direction of the movement of the target object becomes closer to a direction toward the image capturing apparatus, it is easier to surveil the target object. 
     31. The evaluation method according to any one of 25. to 30., in which 
     in the acquisition step, information indicating density of a plurality of the target objects is further acquired, and 
     in the index computation step, the surveillance index is computed on the assumption that, as the density of the plurality of the target objects becomes higher, it is more difficult to surveil the target object. 
     32. A computer program for realizing an evaluation apparatus that evaluates an arrangement of one or more image capturing apparatuses that surveil a target region, the program causing a computer to function as: 
     an acquisition unit that acquires arrangement information and environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, and the environmental information indicating an environment of the target region; 
     an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position; and 
     a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     33. The computer program according to 32., in which 
     the environmental information indicates at least any of a shape of the target region, a size of the target region, a position of an object placed in the target region, a shape of the object, a size of the object, and an orientation of the object. 
     34. The computer program according to 32. or 33., in which 
     the index computation unit computes the surveillance index based on at least any of a size, brightness, a hiding degree of the target object captured by the image capturing apparatus in a case where the target object is located at each of the plurality of positions in the target region. 
     35. The computer program according to any one of 32. to 34., in which 
     the suitability computation unit 
     specifies one or more surveillance-unsuitable regions based on distribution of the surveillance index in the target region, the surveillance-unsuitable regions in which it is difficult to surveil the target object by the image capturing apparatus, 
     obtains a length of a route in a case where the target object passes through the surveillance-unsuitable region, for each of the surveillance-unsuitable regions, and 
     computes the suitability based on the length of the route. 
     36. The computer program according to 35., in which 
     the acquisition unit further acquires information indicating a speed of a movement of the target object, and 
     the suitability computation unit 
     computes a transit time taken for the target object to pass through the surveillance-unsuitable region, based on the length of the route and the information indicating the speed of the target object, and 
     computes the suitability based on the transit time. 
     37. The computer program according to any one of 32. to 36., in which 
     the acquisition unit further acquires information indicating a direction of a movement of the target object, and 
     the index computation unit computes the surveillance index on the assumption that, as the direction of the movement of the target object becomes closer to a direction toward the image capturing apparatus, it is easier to surveil the target object. 
     38. The computer program according to any one of 32. to 37., in which 
     the acquisition unit further acquires information indicating density of a plurality of the target objects, and 
     the index computation unit computes the surveillance index on the assumption that, as the density of the plurality of the target objects becomes higher, it is more difficult to surveil the target object. 
     39. An obtaining method of obtaining an arrangement of one or more image capturing apparatuses that surveil a target region, the method including: 
     an acquisition step of acquiring condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region; 
     an arrangement information generation step of generating a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus; 
     an evaluation step of evaluating each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information; and 
     a selection step of selecting one or more pieces of the arrangement information from among the plurality of pieces of arrangement information, based on an evaluation result in the evaluation step, in which 
     the evaluation step includes 
     an index computation step of computing, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and 
     a suitability computation step of computing suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     40. The obtaining method according to 39., in which 
     the environmental information indicates at least any of a shape of the target region, a size of the target region, a position of an object placed in the target region, a shape of the object, a size of the object, and an orientation of the object. 
     41. The obtaining method according to 39. or 40., in which 
     in the index computation step, the surveillance index is computed based on at least any of a size, brightness, a hiding degree of the target object captured by the image capturing apparatus in a case where the target object is located at each of the plurality of positions in the target region. 
     42. The obtaining method according to any one of 39. to 41., in which 
     in the suitability computation step, 
     one or more surveillance-unsuitable regions in which it is difficult to surveil the target object by the image capturing apparatus is specified based on distribution of the surveillance index in the target region, 
     a length of a route in a case where the target object passes through the surveillance-unsuitable region is obtained for each of the surveillance-unsuitable regions, and 
     the suitability is computed based on the length of the route. 
     43. The obtaining method according to 42., in which 
     in the acquisition step, information indicating a speed of a movement of the target object is further acquired, and 
     in the suitability computation step, 
     a transit time taken for the target object to pass through the surveillance-unsuitable region is computed based on the length of the route and the information indicating the speed of the target object, and 
     the suitability is computed based on the transit time. 
     44. The obtaining method according to any one of 39. to 43., in which 
     in the acquisition step, information indicating a direction of a movement of the target object is further acquired, and 
     in the index computation step, the surveillance index is computed on the assumption that, as the direction of the movement of the target object becomes closer to a direction toward the image capturing apparatus, it is easier to surveil the target object. 
     45. The obtaining method according to any one of 39. to 44., in which 
     in the acquisition step, information indicating density of a plurality of the target objects is further acquired, and 
     in the index computation step, the surveillance index is computed on the assumption that, as the density of the plurality of the target objects becomes higher, it is more difficult to surveil the target object. 
     46. A computer program for realizing an obtaining apparatus that obtains an arrangement of one or more image capturing apparatuses that surveil a target region, the program causing a computer to function as: 
     an acquisition unit that acquires condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region; 
     an arrangement information generation unit that generates a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus; 
     an evaluation unit that evaluates each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information; and 
     a selection unit that selects one or more pieces of the arrangement information from among the plurality of pieces of arrangement information, based on an evaluation result of the evaluation unit, in which 
     the evaluation unit includes 
     an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and 
     a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     47. The computer program according to 46., in which 
     the environmental information indicates at least any of a shape of the target region, a size of the target region, a position of an object placed in the target region, a shape of the object, a size of the object, and an orientation of the object. 
     48. The computer program according to 46. or 47., in which 
     the index computation unit computes the surveillance index based on at least any of a size, brightness, a hiding degree of the target object captured by the image capturing apparatus in a case where the target objects is located at each of the plurality of positions in the target region. 
     49. The computer program according to any one of 46. to 48., in which 
     the suitability computation unit 
     specifies one or more surveillance-unsuitable regions based on distribution of the surveillance index in the target region, the surveillance-unsuitable regions in which it is difficult to surveil the target object by the image capturing apparatus, 
     obtains a length of a route in a case where the target object passes through the surveillance-unsuitable region, for each of the surveillance-unsuitable regions, and computes the suitability based on the length of the route. 
     50. The computer program according to 49., in which 
     the acquisition unit further acquires information indicating a speed of a movement of the target object, and 
     the suitability computation unit 
     computes a transit time taken for the target object to pass through the surveillance-unsuitable region, based on the length of the route and the information indicating the transit time, and 
     computes the suitability based on the length of the route. 
     51. The computer program according to any one of 46. to 50., in which 
     the acquisition unit further acquires information indicating a direction of a movement of the target object, and 
     the index computation unit computes the surveillance index on the assumption that, as the direction of the movement of the target object becomes closer to a direction toward the image capturing apparatus, it is easier to surveil the target object. 
     52. The computer program according to any one of 46. to 51., in which 
     the acquisition unit further acquires information indicating density of a plurality of the target objects, and 
     the index computation unit computes the surveillance index on the assumption that, as the density of the plurality of the target objects becomes higher, it is more difficult to surveil the target object. 
     53. A surveillance method of surveilling a target region with one or more image capturing apparatuses, the method including: 
     an obtaining step of obtaining an arrangement of the image capturing apparatus, and 
     an arrangement control step of controlling the arrangement of the image capturing apparatus based on the arrangement of the image capturing apparatus obtained in the obtaining step, in which 
     the obtaining step includes 
     an acquisition step of acquiring condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region, 
     an arrangement information generation step of generating a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, 
     an evaluation step of evaluating each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information, and 
     a selection step of selecting one or more pieces of the arrangement information from among the plurality of pieces of arrangement information, based on an evaluation result in the evaluation step, in which 
     the evaluation step includes 
     an index computation step of computing, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and 
     a suitability computation step of computing suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     54. The surveillance method according to 53., in which 
     in the obtaining step, the arrangement of the image capturing apparatus is obtained for each of a plurality of time ranges, and 
     in the arrangement control step, the arrangement of the image capturing apparatus is controlled for each time range. 
     55. The surveillance method according to 53., in which 
     in the obtaining step, the arrangement of the image capturing apparatus at a plurality of timings is obtained based on a predetermined condition, and 
     in the arrangement control step, the arrangement of the image capturing apparatus is controlled every time the arrangement of the image capturing apparatus is obtained in the obtaining step. 
     56. The surveillance method according to any one of 53. to 55., in which 
     the environmental information indicates at least any of a shape of the target region, a size of the target region, a position of an object placed in the target region, a shape of the object, a size of the object, and an orientation of the object. 
     57. The surveillance method according to any one of 53. to 56., in which 
     in the index computation step, the surveillance index is computed based on at least any of a size, brightness, a hiding degree of the target object captured by the image capturing apparatus in a case where the target object is located at each of the plurality of positions in the target region. 
     58. The surveillance method according to any one of 53. to 57., in which 
     in the suitability computation step, 
     specifies one or more surveillance-unsuitable regions based on distribution of the surveillance index in the target region, the surveillance-unsuitable regions in which it is difficult to surveil the target object by the image capturing apparatus, 
     obtains a length of a route in a case where the target object passes through the surveillance-unsuitable region, for each of the surveillance-unsuitable regions, and the suitability is computed based on the length of the route. 
     59. The surveillance method according to 58., in which 
     in the acquisition step, information indicating a speed of a movement of the target object is further acquired, and 
     in the suitability computation step, 
     a transit time taken for the target object to pass through the surveillance-unsuitable region is computed based on the length of the route and the information indicating the speed of the target object, and 
     the suitability is computed based on the transit time. 
     60. The surveillance method according to any one of 53. to 59., in which 
     in the acquisition step, information indicating a direction of a movement of the target object is further acquired, and 
     in the index computation step, the surveillance index is computed on the assumption that, as the direction of the movement of the target object becomes closer to a direction toward the image capturing apparatus, it is easier to surveil the target object. 
     61. The surveillance method according to any one of 53. to 60., in which 
     in the acquisition step, information indicating density of a plurality of the target objects is further acquired, and 
     in the index computation step, the surveillance index is computed on the assumption that, as the density of the plurality of the target objects becomes higher, it is more difficult to surveil the target object. 
     62. A computer program for realizing a surveillance apparatus that surveils a target region with one or more image capturing apparatuses, the program causing a computer to function as: 
     an obtaining unit that obtains an arrangement of the image capturing apparatus; and 
     an arrangement control unit that controls the arrangement of the image capturing apparatus based on the arrangement of the image capturing apparatus obtained by the obtaining unit, in which 
     the obtaining unit includes 
     an acquisition unit that acquires condition information indicating a condition regarding the arrangement of the image capturing apparatus and environmental information indicating an environment of the target region, 
     an arrangement information generation unit that generates a plurality of pieces of arrangement information based on the condition information and the environmental information, the arrangement information indicating at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus, 
     an evaluation unit that evaluates each of the arrangements of the image capturing apparatus, which are indicated by the plurality of pieces of arrangement information, and 
     a selection unit that selects one or more pieces of the arrangement information from among the plurality of pieces of arrangement information, based on an evaluation result of the evaluation unit, and 
     the evaluation unit includes 
     an index computation unit that computes, for each of a plurality of positions in the target region, a surveillance index by using the arrangement information and the environmental information, the surveillance index indicating difficulty or easiness of surveilling a target object in a case where the target object is located at the position, and 
     a suitability computation unit that computes suitability of the arrangement of the image capturing apparatus, which is indicated by the arrangement information, based on distribution of the surveillance index in the target region. 
     63. The computer program according to 62., in which 
     the obtaining unit obtains the arrangement of the image capturing apparatus for each of a plurality of time ranges, and 
     the arrangement control unit controls the arrangement of the image capturing apparatus for each time range. 
     64. The computer program according to 62., in which 
     the obtaining unit obtains the arrangement of the image capturing apparatus at a plurality of timings based on a predetermined condition, and 
     the arrangement control unit controls the arrangement of the image capturing apparatus every time the obtaining unit obtains the arrangement of the image capturing apparatus. 
     65. The computer program according to any one of 62. to 64., in which 
     the environmental information indicates at least any of a shape of the target region, a size of the target region, a position of an object placed in the target region, a shape of the object, a size of the object, and an orientation of the object. 
     66. The computer program according to any one of 62. to 65., in which 
     the index computation unit computes the surveillance index based on at least any of a size, brightness, a hiding degree of the target object captured by the image capturing apparatus in a case where the target object is located at each of the plurality of positions in the target region. 
     67. The computer program according to any one of 62. to 66., in which 
     the suitability computation unit 
     specifies one or more surveillance-unsuitable regions based on distribution of the surveillance index in the target region, the surveillance-unsuitable regions in which it is difficult to surveil the target object by the image capturing apparatus, 
     obtains a length of a route in a case where the target object passes through the surveillance-unsuitable region, for each of the surveillance-unsuitable regions, and 
     computes the suitability based on the length of the route. 
     68. The computer program according to 67., in which 
     the acquisition unit further acquires information indicating a speed of a movement of the target object, and 
     the suitability computation unit 
     computes a transit time taken for the target object to pass through the surveillance-unsuitable region, based on the length of the route and the information indicating the speed of the target object, and 
     computes the suitability based on the transit time. 
     69. The computer program according to any one of 62. to 68., in which 
     the acquisition unit further acquires information indicating a direction of a movement of the target object, and 
     the index computation unit computes the surveillance index on the assumption that, as the direction of the movement of the target object becomes closer to a direction toward the image capturing apparatus, it is easier to surveil the target object. 
     70. The computer program according to any one of 62. to 69., in which 
     the acquisition unit further acquires information indicating density of a plurality of the target objects, and 
     the index computation unit computes the surveillance index on the assumption that, as the density of the plurality of the target objects becomes higher, it is more difficult to surveil the target object. 
     71. A surveillance apparatus that surveils a target region with one or more image capturing apparatuses, the apparatus including: 
     at least one of an analysis unit that analyzes an image captured by the image capturing apparatus and a display unit that displays the image, in which 
     the image capturing apparatus is placed based on arrangement information obtained based on distribution of a surveillance index in the target region, 
     the surveillance index is computed based on environmental information indicating an environment of the target region for each of a plurality of positions in the target region, and indicates difficulty or easiness of surveillance of a target object in a case where the target object is located at the position, and 
     the arrangement information indicates at least any of a position of the image capturing apparatus, an orientation of the image capturing apparatus, and a field angle of the image capturing apparatus. 
     72. The surveillance apparatus according to 71., 
     the environmental information includes information indicating that there is an elongated passage in the target region, and 
     the image capturing apparatuses are arranged so that the orientations of the image capturing apparatuses coincide with each other in the elongated passage. 
     73. The surveillance apparatus according to 71. or 72., in which the environmental information includes information indicating that there is an elongated passage in the target region, 
     two image capturing apparatuses are arranged in directions opposite to each other in a vicinity of a center of the elongated passage, 
     an image of at least a region directly below one image capturing apparatus is captured by the other image capturing apparatus of the two image capturing apparatuses, and 
     an image of at least a region directly below the other image capturing apparatus is captured by the one image capturing apparatus. 
     74. The surveillance apparatus according to any one of 71. to 73., in which 
     the image capturing apparatus is placed so that a first region and a second region are not directly adjacent to each other and not adjacent to each other with only a blind spot region interposed between the first region and the second region, 
     the first region is a region in which difficulty of surveillance indicated by the surveillance index is higher than a predetermined reference or easiness of the surveillance indicated by the surveillance index is lower than the reference, 
     a first image capturing apparatus captures an image of the target object in a case where the target object is placed in the first region, 
     the second region is a region in which the difficulty of the surveillance indicated by the surveillance index is higher than the reference or the easiness of the surveillance indicated by the surveillance index is lower than the reference, 
     a second image capturing apparatus located within a predetermined range from the first image capturing apparatus captures the image of the target object in a case where the target object is placed in the second region, and 
     any of the one or more image capturing apparatuses does not capture an image of at least a portion of the target object when the target object is placed in the blind spot region. 
     75. The surveillance apparatus according to any one of 71. to 74., in which 
     the environmental information includes information indicating that a rectangular region is in the target region, and 
     the image capturing apparatus is placed near a point closer to a center than to an end of a long side of the rectangle. 
     76. The surveillance apparatus according to any one of 71. to 75., in which 
     the environmental information includes information indicating that a plurality of passages interposing one or more objects arranged in the target region are substantially in parallel in the target region, 
     one image capturing apparatus is provided for each of the plurality of passages, and 
     the image capturing apparatuses are arranged so that images of adjacent passages are captured from different directions.