Patent Publication Number: US-10308374-B2

Title: Stereo distance measuring apparatus, stereo distance measuring method, and computer readable medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2016-204786 filed on Oct. 19, 2016, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The technology relates to a stereo distance measuring apparatus that measures a distance utilizing a stereo camera mounted on an aircraft, a stereo distance measuring method, and a computer readable medium having a stereo distance measuring program. 
     Aircrafts generally utilize radar mounted on their airframes, in a measurement of a distance from the own aircraft to a predetermined target. Distance measuring apparatuses that send out radio waves, e.g., the radar, however, have an issue that a position of the own aircraft may be detected by others. 
     For example, Japanese Patent (JP-B2) No. 4328551 makes a proposal for a distance measuring technique utilizing a stereo camera mounted on an airframe. This technique does not involve sending out the radio waves. In addition, this technique makes it possible to acquire image information. 
     Moreover, the technique described in JP-B2 No. 4,328,551 includes detecting posture information of the airframe, and controlling a posture of the stereo camera utilizing the posture information. This makes it possible to acquire images in a constant orientation, regardless of a posture of the airframe. 
     SUMMARY 
     In such a stereo distance measuring apparatus that measures a distance utilizing a stereo camera, high measurement precision is desired, with expectation of further enhancement in the measurement precision. 
     It is desirable to provide a stereo distance measuring apparatus, a stereo distance measuring method, and a computer readable medium having a stereo distance measuring program that make it possible to enhance measurement precision. 
     An aspect of the technology provides a stereo distance measuring apparatus including a first optical camera and a second optical camera, a position-posture calculator, an image corrector, and a stereo distance measuring unit. The first optical camera and the second optical camera are provided in an elastic structure part of an aircraft and separated from each other. The first optical camera and the second optical camera constitute a stereo camera. The position-posture calculator is configured to calculate, on the basis of a displacement amount of the elastic structure part, first position-posture information regarding a position and a posture of the first optical camera and second position-posture information regarding a position and a posture of the second optical camera. The image corrector is configured to generate a first corrected image by correcting, on the basis of the first position-posture information, a position and an orientation of an image taken by the first optical camera, and generates a second corrected image by correcting, on the basis of the second position-posture information, a position and an orientation of an image taken by the second optical camera. The stereo distance measuring unit is configured to calculate a distance to a photographing target, on the basis of the first corrected image and the second corrected image. 
     An aspect of the technology provides a stereo distance measuring method including: calculating, with a stereo distance measuring apparatus including a first optical camera and a second optical camera that are provided in an elastic structure part of an aircraft and separated from each other, first position-posture information regarding a position and a posture of the first optical camera and second position-posture information regarding a position and a posture of the second optical camera, on the basis of a displacement amount of the elastic structure part, the first optical camera and the second optical camera constituting a stereo camera; generating, with the stereo distance measuring apparatus, a first corrected image by correcting, on the basis of the first position-posture information, a position and an orientation of an image taken by the first optical camera, and a second corrected image by correcting, on the basis of the second position-posture information, a position and an orientation of an image taken by the second optical camera; and calculating, with the stereo distance measuring apparatus, a distance to a photographing target, on the basis of the first corrected image and the second corrected image. 
     An aspect of the technology provides a non-transitory computer readable medium having a stereo distance measuring program causing a computer to implement a method. The method includes: calculating, with a stereo distance measuring apparatus including a first optical camera and a second optical camera that are provided in an elastic structure part of an aircraft and separated from each other, first position-posture information regarding a position and a posture of the first optical camera and second position-posture information regarding a position and a posture of the second optical camera, on the basis of a displacement amount of the elastic structure part, the first optical camera and the second optical camera constituting a stereo camera; generating, with the stereo distance measuring apparatus, a first corrected image by correcting, on the basis of the first position-posture information, a position and an orientation of an image taken by the first optical camera, and a second corrected image by correcting, on the basis of the second position-posture information, a position and an orientation of an image taken by the second optical camera; and calculating, with the stereo distance measuring apparatus, a distance to a photographing target, on the basis of the first corrected image and the second corrected image. 
     An aspect of the technology provides a stereo distance measuring apparatus including a first optical camera and a second optical camera, a distance measuring unit, and circuitry. The first optical camera and a second optical camera are provided in an elastic structure part of an aircraft and separated from each other. The first optical camera and the second optical camera constitute a stereo camera. The distance measuring unit is provided in a highly-rigid part of the aircraft, and configured to measure a distance and a direction from the highly-rigid part to the first optical camera and a distance and a direction from the highly-rigid part to the second optical camera. The highly-rigid part has rigidity that is higher than rigidity of the elastic structure part. The circuitry is configured to calculate, on the basis of the distance and the direction from the highly-rigid part to the first optical camera, first position-posture information regarding a position and a posture of the first optical camera, and calculates, on the basis of the distance and the direction from the highly-rigid part to the second optical camera, second position-posture information regarding a position and a posture of the second optical camera. The circuitry is configured to generate a first corrected image by correcting, on the basis of the first position-posture information, a position and an orientation of an image taken by the first optical camera, and generates a second corrected image by correcting, on the basis of the second position-posture information, a position and an orientation of an image taken by the second optical camera. The circuitry is configured to calculate a distance to a photographing target, on the basis of the first corrected image and the second corrected image. 
     An aspect of the technology provides a stereo distance measuring apparatus including a first optical camera and a second optical camera, a displacement amount measuring unit, and circuitry. The first optical camera and a second optical camera are provided in an elastic structure part of an aircraft and separated from each other. The first optical camera and the second optical camera constitute a stereo camera. The displacement amount measuring unit is configured to measure a first displacement amount of the elastic structure part at a position, in the elastic structure part, at which the first optical camera is provided, and measures a second displacement amount of the elastic structure part at a position, in the elastic structure part, at which the second optical camera is provided. The circuitry is configured to calculate, on the basis of the first displacement amount, first position-posture information regarding a position and a posture of the first optical camera, and calculate, on the basis of the second displacement amount, second position-posture information regarding a position and a posture of the second optical camera. The circuitry is configured to generate a first corrected image by correcting, on the basis of the first position-posture information, a position and an orientation of an image taken by the first optical camera, and generate a second corrected image by correcting, on the basis of the second position-posture information, a position and an orientation of an image taken by the second optical camera. The circuitry is configured to calculate a distance to a photographing target, on the basis of the first corrected image and the second corrected image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of a functional configuration of a stereo distance measuring apparatus according to a first implementation of the technology. 
         FIG. 2  describes examples of a camera unit and a laser distance measuring device provided in the stereo distance measuring apparatus according to the first implementation. 
         FIG. 3A  is a flowchart illustrating an example of a flow of a stereo distance measuring process according to the first implementation. 
         FIG. 3B  is a flowchart illustrating an example of a flow of calibration for optical cameras in the stereo distance measuring process according to the first implementation. 
         FIG. 4  is a conceptual diagram describing an example of a procedure of calculating positions and postures of the respective optical cameras in the stereo distance measuring process according to the first implementation. 
         FIGS. 5A and 5B  are conceptual diagrams describing an example of a change in image before and after correction performed in the stereo distance measuring process. 
         FIG. 6  is a block diagram illustrating an example of a functional configuration of a stereo distance measuring apparatus according to a second implementation of the technology. 
         FIG. 7  describes examples of a camera unit and a strain gauge provided in the stereo distance measuring apparatus according to the second implementation. 
         FIG. 8A  is a flowchart illustrating an example of a flow of a stereo distance measuring process according to the second implementation. 
         FIG. 8B  is a flowchart illustrating an example of a flow of calibration for optical cameras in the stereo distance measuring process according to the second implementation. 
         FIG. 9  is a conceptual diagram describing an example of a procedure of calculating positions and postures of the respective optical cameras in the stereo distance measuring process according to the second implementation. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, some implementations of the technology are described with reference to the drawings. 
     [First Implementation] 
     A first implementation of the technology is described first. 
     [Configuration of Stereo Distance Measuring Apparatus  1 ] 
       FIG. 1  is a block diagram illustrating a functional configuration of a stereo distance measuring apparatus  1  according to the first implementation of the technology.  FIG. 2  describes a camera unit  14  and a laser distance measuring device  15  both provided in the stereo distance measuring apparatus  1 , which will be described later. 
     The stereo distance measuring apparatus  1  may be mounted on, for example but not limited to, an aircraft  30 , e.g., a fixed wing aircraft. The stereo distance measuring apparatus  1  may measure a distance from the aircraft  30  to a photographing target, on the basis of a stereo image acquired. 
     In one specific but non-limiting example, referring to  FIGS. 1 and 2 , the stereo distance measuring apparatus  1  may include a display unit  11 , an input unit  12 , two camera units  14 , two laser distance measuring devices  15 , a storage unit  16 , and a controller  18 . 
     The display unit  11  may include an unillustrated display. The display unit  11  may display various pieces of information on the display, on the basis of a display signal inputted from the controller  18 . 
     The input unit  12  may include unillustrated input receiving instrumentation. The input unit  12  may supply the controller  18  with a signal corresponding to an input operation made by an operator on the input receiving instrumentation. 
     The two camera units  14  may acquire a stereo image outside the aircraft  30 . As illustrated in  FIG. 2 , the two camera units  14  may be disposed separately at respective tips of both wings  32 , specifically, a right wing  32 R and a left wing  32 L, of the aircraft  30 , and widely separated from each other. The wings  32 , specifically, the right wing  32 R and the left wing  32 L may be an elastic structure part of the aircraft  30 . 
     As illustrated in  FIG. 1 , each of the camera units  14  may include an optical camera  141  and a global positioning system (GPS) receiver  142 . 
     It is to be noted that, in the following description, the reference characters of the camera unit  14  mounted on the right wing  32 R of the aircraft  30  and the parts of the relevant camera unit  14  are followed by “R”, while the reference characters of the camera unit  14  mounted on the left wing  32 L and the parts of the relevant camera unit  14  are followed by “L”, in order to distinguish one from the other. 
     The optical camera  141  may acquire, on the basis of a control instruction from the controller  18 , an image outside the aircraft  30 , and supply the controller  18  with image information acquired. The optical camera  141  may be provided in each of the two camera units  14 . Thus, the two optical cameras  141  may constitute a pair and function as a stereo camera. As illustrated in  FIG. 2 , the optical cameras  141  may be separated away from each other at a predetermined distance, with their visual fields or ranges VR overlapping with each other so as to be able to acquire the stereo image. 
     The GPS receiver  142  may acquire photographing time of images taken by the associated optical camera  141  of the same camera unit  14 , in this implementation. The GPS receiver  142  may receive, on the basis of a control instruction from the controller  18 , a GPS signal including GPS time information from a GPS satellite, and supply the GPS signal to the controller  18 . 
     The two laser distance measuring devices  15  may acquire position-posture information, i.e., information regarding positions and postures (i.e., orientations) of the pair of optical cameras  141 . The laser distance measuring devices  15  may be provided in a body  31 , of the aircraft  30 , that has rigidity higher than rigidity of the wings  32 . In one specific but non-limiting example, the two laser distance measuring devices  15  may be provided at the top of the substantial middle of the body  31 , in a front-rear direction of the airframe, in which base ends of both the wings  32  are located. 
     Each of the two laser distance measuring devices  15  may be associated with one of the two camera units  14 , specifically, one of the two optical cameras  141 . Each of the two laser distance measuring devices  15  may have a light reception-emission surface (i.e., a measuring surface) that is oriented to a side region of the airframe, i.e., outside of the aircraft  30 , and thus allow the associated optical camera  141  to be present in a measuring range of the relevant laser distance measuring device  15 . The light reception-emission surfaces or the measuring surfaces of the respective two laser distance measuring devices  15  may be oriented in directions opposite to each other. In one specific but non-limiting example, to address deformation of the wings  32  of the aircraft  30  in flight, the laser distance measuring devices  15  may be so provided that the laser distance measuring devices  15  allow the optical cameras  141  provided at the respective tips of the wings  32  to be present in scanning ranges S or the measuring ranges of the laser distance measuring devices  15  when the wings  32  are deformed, as illustrated in  FIG. 4 . Non-limiting example of the deformation of the wings  32  of the aircraft  30  in flight may include upward warp of the wings  32 . Each of the laser distance measuring devices  15  may measure, on the basis of a control instruction from the controller  18 , a distance and a direction or an angle from a position at which the relevant laser distance measuring device  15  is disposed to the tip of the wing  32  provided with the associated optical camera  141 , and supply the controller  18  with the distance and the direction (i.e., the angle) measured. 
     It is to be noted that, in the following description, the reference character of the laser distance measuring device  15  associated with the optical camera  141 R mounted on the right wing  32 R is followed by “R”, the reference character of the laser distance measuring device  15  associated with the optical camera  141 L mounted on the left wing  32 L is followed by “L”, in order to distinguish one from the other. 
     As illustrated in  FIG. 1 , the storage unit  16  may be a memory that stores programs and data to achieve various functions of the stereo distance measuring apparatus  1  and also serves as a work area. In this implementation, the storage unit  16  may store a stereo distance measuring program  160  and a wing deformation database  161 . 
     The stereo distance measuring program  160  may be a program that causes the controller  18  to execute a stereo distance measuring process described later. 
     The wing deformation database  161  may be a database that describes a relationship of a displacement amount (i.e., a warp amount) σz of the tip of each of the wings  32  in a wing thickness direction, i.e., a position at which the associated optical camera  141  is disposed, versus an angle (i.e., an orientation) of the tip of the relevant wing  32 , illustrated in  FIG. 4 . The wing thickness direction may be a top-bottom direction of the airframe. 
     In this implementation, the wing deformation database  161  may be used; however, this is non-limiting. As long as the relationship between the displacement amount σz of the tip of each of the wings  32  and the angle of the tip of the relevant wing  32  is expressed, the relationship is not necessarily expressed in a database format. In one specific but non-limiting example, a relational expression that expresses the relationship between the displacement amount σz of the tip of each of the wings  32  and the angle at the tip of the relevant wing  32  may be used instead of the wing deformation database  161 . 
     The controller  18  may be provided in the body  31  of the aircraft  30 . The controller  18  may execute, on the basis of an instruction inputted, a process based on a predetermined program, give instructions to each functional part or perform data transfer to each functional part, and perform a general control of the stereo distance measuring apparatus  1 . In one specific but non-limiting example, the controller  18  may read, in response to a signal such as an operation signal inputted from the input unit  12 , various programs stored in the storage unit  16 , and execute processes in accordance with the programs. The controller  18  may temporarily store results of the processes in the storage unit  16 , and output the results of the processes to the display unit  11  as appropriate. 
     [Operation of Stereo Distance Measuring Apparatus  1 ] 
     A description is given next of an operation of the stereo distance measuring apparatus  1  upon execution of the stereo distance measuring process. 
       FIG. 3A  is a flowchart illustrating a flow of the stereo distance measuring process according to the first implementation.  FIG. 3B  is a flowchart illustrating a flow of calibration for each of the optical cameras  141  included in the stereo distance measuring process, which will be described later.  FIG. 4  is a conceptual diagram describing a procedure of calculating positions and postures of the respective optical cameras  141  in the stereo distance measuring process according to the first implementation, specifically, the calibration for the respective optical cameras  141 .  FIGS. 5A and 5B  are conceptual diagrams describing a change in image before and after correction performed in the stereo distance measuring process. 
     It is to be noted that  FIG. 4  illustrates only components related to one of the pair of optical cameras  141 , and omits illustration of components related to the other. 
     The stereo distance measuring process may be a process that includes acquiring the stereo image with the pair of optical cameras  141 , and calculating, on the basis of the stereo image, the distance from the aircraft  30  to the photographing target. Upon an input of an instruction to execute the process by, for example, an operation by an operator, the controller  18  may read the stereo distance measuring program  160  from the storage unit  16  and develop the stereo distance measuring program  160 , to execute the stereo distance measuring process. 
     It is to be noted that it is assumed for this implementation that the photographing target, i.e., a target of a distance measurement, is on the ground below the airframe, and the photographing target is photographed from the aircraft  30  in flight. However, a location of the photographing target is not limited thereto. In one specific but non-limiting example, the photographing target may be level with or above the aircraft  30  in flight, or alternatively, the photographing target may be at the sea or in the air. 
     As illustrated in  FIG. 3A , upon the execution of the stereo distance measuring process, the controller  18  may, first, allow each of the pair of optical cameras  141  on the respective right and left wings  32  to acquire image information that represents an image outside the aircraft  30  (step S 1 ). The image outside the aircraft  30  may be either a still image or a moving image. At this occasion, in each of the camera units  14 , GPS time information acquired by the GPS receiver  142  may be associated with the image information taken by the associated optical camera  141 , and outputted to the controller  18 . 
     Thereafter, the controller  18  may perform calibration for the pair of optical cameras  141 , i.e., correct a pair of pieces of image information taken by the pair of optical cameras  141  (step S 2 ). 
     In the aircraft  30  in flight, both of the wings  32  of the airframe may be so deformed as to warp upward. This deformation may cause a change in relative positions and postures of the two camera units  14 R and  14 L disposed at the respective tips of both the wings  32  from a designed state. Therefore, simply utilizing the stereo image obtained by the pair of optical cameras  141  in the deformation state may become a hindrance to a precise measurement of the distance to the photographing target. 
     To address this, in step S 2 , the pair of pieces of image information taken by the pair of optical cameras  141  may be corrected separately from each other, on the basis of the position-posture information, i.e., the information regarding the positions and the postures, of the pair of optical cameras  141 . 
     In one specific but non-limiting example, the calibration may be performed as follows. Referring to  FIGS. 3B and 4 , the controller  18  may first calculate a vector A from the position at which each of the laser distance measuring devices  15  is disposed to the tip of the associated wing  32 , i.e., to the position at which the associated optical camera  141  is disposed (step S 21 ). The calculation of the vector A may be performed for both of the wings  32 , i.e., the right wing  32 R and the left wing  32 L. 
     In step S 21 , the controller  18  may calculate each of the vectors A by causing associated one of the laser distance measuring devices  15  to measure a distance and a direction or an angle from the position at which the associated laser distance measuring device  15  is disposed to the associated optical camera  141 . For the vector calculation, an assumed maximum distance Rmax from each of the laser distance measuring devices  15  to the associated optical camera  141  may be set in advance. The controller  18  may calculate, as the vector A, a maximum vector within a size range that is equal to or smaller than the assumed maximum distance Rmax. This prevents an error in measurement. Non-limiting examples of the error in measurement may include erroneously detecting that a position of an end of the vector A is located at a position that is farther than the end of the wing  32  in the side region of the airframe. 
     Thereafter, the controller  18  may calculate, as a position vector C of each of the optical cameras  141 , a vector from the base end to the tip of the associated wing  32  (step S 22 ). The calculation of the vector C may be performed for both of the wings  32 . 
     In step S 22 , the controller  18  may calculate the position vector C of each of the optical cameras  141  on the basis of the vector A calculated in step S 22  and a vector B. The vector B may be a vector from the position at which the associated laser distance measuring device  15  is disposed to the base end of the associated wing  32 . In this implementation, the vector B is a value known as a design value or a drawing value. 
     Thereafter, the controller  18  may calculate the displacement amount σz or a warp amount of the tip of each of the two wings  32  from a designed position Pd in the wing thickness direction, on the basis of the position vector C calculated in step S 22  (step S 23 ). The calculation of the displacement amount σz may be performed for both of the wings  32 . In this implementation, the designed position Pd may be a position at which the tip of the relevant wing  32  is located in the designed state, and a position of the tip of the relevant wing  32  in a state where the relevant wing  32  is not displaced. 
     Thereafter, the controller  18  may calculate, as a posture vector D of each of the optical cameras  141 , an angle (i.e., an orientation) of the tip of the associated wing  32  (step S 24 ). The calculation of the posture vector D may be performed for both of the wings  32 . 
     In step S 24 , the controller  18  may calculate the angle of the tip of each of the wings  32 , i.e., the posture vector D of the associated optical camera  141 , on the basis of the displacement amount σz of the tip of the associated wing  32  calculated in step S 23  and the wing deformation database  161  read from the storage unit  16 . 
     Thereafter, the controller  18  may correct the image information acquired in step S 1 , on the basis of the position vectors C of the respective optical cameras  141  calculated in step S 22  and the posture vectors D of the respective optical cameras  141  calculated in step S 24  (step S 25 ). 
     In one specific but non-limiting example, the controller  18  may calculate a change in position of each of the optical cameras  141  from the designed state, on the basis of the position vector C of the relevant optical camera  141 . Further, the controller  18  may calculate a change in posture of each of the optical cameras  141  from the designed state, on the basis of the posture vector D of the relevant optical camera  141 . Further, the controller  18  may correct a position and a posture of an image in the image information taken by the relevant optical camera  141  by the calculated amount of change in position and by the calculated amount of change in posture of the relevant optical camera  141 , respectively. The controller  18  may thereby acquire corrected image information. 
     As illustrated in  FIGS. 5A and 5B , this may correct the image taken by each of the optical cameras  141  whose position and posture are changed from those in the designed state to be an image that should have been taken by the relevant optical camera  141  in the designed state. 
     Thereafter, as illustrated in  FIG. 3A , the controller  18  may utilize, as the stereo image, the pair of pieces of the corrected image information thus acquired, and calculate the distance to the photographing target (step S 3 ). At this occasion, the controller  18  may refer to the GPS time information associated with each piece of the corrected image information, and select a pair of pieces of corrected image information whose timing of imaging coincide with each other. The situation where “the timing of the imaging coincide with each other” may encompass a situation where a time difference between points in time indicated by the two pieces of the GPS time information falls within a range in which the points in time are regarded as the same point in time. The controller  18  may collate the pair of pieces of the corrected image information, to calculate the distance. 
     In this way, the distance from the aircraft  30  to the photographing target is appropriately measured, with the stereo image based on the pair of pieces of the corrected image information whose timing of the imaging coincide with each other and in which the changes in the positions and the postures of the respective optical cameras  141  in flight are corrected. 
     In this connection, in applications of distance measurements utilizing a stereo camera mounted on an aircraft, distances to be measured are far longer than those in, for example, general applications such as monitoring applications on the ground. It is therefore desirable to also provide a large baseline length or a large visual axis interval between two cameras that constitute the stereo camera in the application of distance measurement from an aircraft. 
     However, with the two cameras separated apart from each other, it is generally difficult to support the two cameras integrally with high rigidity. For example, a possible method to space the two cameras as apart as possible from each other on a fixed wing aircraft may be to dispose the two cameras on respective two wings of an airframe. However, wings of an aircraft are deformed, or warp, in accordance with forces such as lift, and therefore fail in keeping relative states, e.g., positions and postures, of the two cameras constant. 
     As a result, the two cameras change in their relative positions and postures in accordance with flight states of the airframe. This results in lowered measurement precision as the stereo camera. Performing a posture control of the two cameras as in the technique described in JP-B2 4328551 is promising; however, it is still difficult to appropriately perform the posture control of the two cameras of different positions and postures with utilization of the posture information of the airframe that is common to the two cameras. 
     Directly acquiring information regarding the positions and the postures of the two cameras with utilization of a position-posture meter is also promising; however, a position-posture meter with high accuracy costs much, which increases a cost of the apparatus. 
     To address this, in the stereo distance measuring apparatus  1 , the pair of laser distance measuring devices  15  are utilized to calculate respective pieces of the position-posture information, i.e., the position vectors C and the posture vectors D, of the optical cameras  141 , on the basis of the displacement amounts of the wings  32 . On the basis of the two pieces of the position-posture information thus calculated, the respective positions and the respective orientations of the images in the pair of pieces of image information taken by the pair of optical cameras  141  are corrected. On the basis of the corrected pieces of image information, i.e., the two pieces of corrected image information, the distance from the aircraft  30  to the photographing target is obtained. This makes it possible for the stereo distance measuring apparatus  1  to obtain the distance on the basis of the corrected image information in which the positions and the orientations of the images are corrected, even in a case where the pair of optical cameras  141  have changed in the respective positions and the postures, due to the modification of the wings  32  of the aircraft  30  in accordance with forces such as lift. Hence, it is possible to enhance the measurement precision. 
     In particular, in the stereo distance measuring apparatus  1 , the pair of laser distance measuring devices  15  are utilized to calculate the respective pieces of position-posture information of the optical cameras  141  on the basis of the displacement amounts of the wings  32 . Therefore, it is possible to calculate the respective pieces of position-posture information of the optical cameras  141  without using an expensive position-posture meter. 
     [Effects] 
     As described, according to the first implementation, the images in the pair of pieces of image information taken by the pair of the optical cameras  141  configuring the stereo camera are separately corrected in position and orientation, on the basis of the two pieces of position-posture information, i.e., the position vectors C and the posture vectors D, of the respective optical cameras  141 . The two pieces of position-posture information, i.e., the position vectors C and the posture vectors D, of the respective optical cameras  141  are calculated on the basis of the displacement amounts of the two wings  32  on which the pair of optical cameras  141  are disposed. On the basis of the pair of pieces of the corrected image information thus corrected, the distance to the photographing target is calculated. 
     Accordingly, it is possible to appropriately correct the positions and the orientations of the images, even in a case where the pair of optical cameras  141  are mounted on the aircraft and separated from each other, and the positions and the postures of the optical cameras  141  have changed to different states from one another. Hence, it is possible to restrain the measurement precision from being lowered. Further, it is possible to calculate the position-posture information of the respective optical cameras  141  on the basis of the displacement amounts of the wings  32 , without necessity of utilizing the expensive position-posture meter. 
     Hence, it is possible to enhance the measurement precision of the stereo camera mounted on the aircraft  30  in an inexpensive configuration, as compared to a case where the position-posture meter is utilized. 
     Moreover, each piece of the image information taken by the pair of the optical cameras  141  may be associated with the GPS time information. On the basis of the GPS time information, the pair of pieces of the corrected image information whose timing of the imaging coincide with each other may be selected to calculate the distance to the photographing target. 
     Accordingly, it is possible to suitably restrain the shift in the timing of the imaging that is likely to occur because of the extension of the signal transmission paths and the manufacturing tolerances of the wiring lengths in the case with the pair of the optical cameras  141  separated apart from each other. Hence, it is possible to restrain the measurement precision from being lowered. 
     [Second Implementation] 
     A second implementation of the technology is described next. It is to be noted that components similar to those in the foregoing first implementation are denoted with the same numerals, and will not be further described. 
     [Configuration of Stereo Distance Measuring Apparatus  2 ] 
       FIG. 6  is a block diagram illustrating a functional configuration of a stereo distance measuring apparatus  2  according to the second implementation of the technology.  FIG. 7  describes a strain gauge unit  27  provided in the stereo distance measuring apparatus  2 , which will be described later. 
     The stereo distance measuring apparatus  2  may differ from the stereo distance measuring apparatus  1  according to the foregoing first implementation in that the position-posture information of the respective optical cameras  141  is obtained by using a strain gauge instead of the laser distance measuring device. 
     In one specific but non-limiting example, referring to  FIGS. 6 and 7 , the stereo distance measuring apparatus  2  may include two strain gauge units  27  instead of the two laser distance measuring devices  15  according to the foregoing first implementation. 
     The two strain gauge units  27  may acquire the position-posture information of the pair of optical cameras  141 . The strain gauge units  27  may be disposed separately on the respective two wings  32  of the aircraft  30 . Each of the strain gauge units  27  may include a plurality of strain gauges  271 . The plurality of strain gauges  271  may be continuously provided in a span direction (i.e., a wing length direction) from the base end of the associated wing  32  to the tip, of the associated wing  32 , at which the optical camera  141  is disposed. Further, the strain gauges  271  may be also attached onto an upper surface of the associated wing  32  so that the respective strain gauges  271  are able to measure bending strain and axial strain at positions to which the respective strain gauges  271  are attached. Each of the strain gauge units  27  may supply, via a component such as an unillustrated bridge circuit, the controller  18  with the displacement amounts, of the associated wing  32 , at the positions to which the respective strain gauges  271  are attached. 
     It is to be noted that, in the following description, the reference character of the strain gauge unit  27  disposed on the right wing  32 R is followed by “R”, and the reference character of the strain gauge unit  27  disposed on the left wing  32 L is followed by “L”, in order to distinguish one from the other. 
     [Operation of Stereo Distance Measuring Apparatus  2 ] 
     A description is given next of an operation of the stereo distance measuring apparatus  2  upon execution of the stereo distance measuring process. 
       FIG. 8A  is a flowchart illustrating a flow of the stereo distance measuring process according to the second implementation.  FIG. 8B  is a flowchart illustrating a flow of calibration for each of the optical cameras  141  included in the stereo distance measuring process.  FIG. 9  is a conceptual diagram describing a procedure of calculating positions and postures of the respective optical cameras  141  in the stereo distance measuring process according to the second implementation, specifically, the calibration for the respective optical cameras  141 . 
     It is to be noted that  FIG. 9  illustrates only components related to one of the pair of optical cameras  141 , and omits illustration of components related to the other. 
     As illustrated in  FIG. 8A , upon the execution of the stereo distance measuring process, the controller  18  may, first, allow each of the pair of optical cameras  141  on the respective right and left wings  32  to acquire image information that represents an image outside the aircraft  30 , as in the foregoing first implementation (step T 1 ). At this occasion, in each of the camera units  14 , GPS time information acquired by the GPS receiver  142  may be associated with the image information taken by the associated optical camera  141 , and outputted to the controller  18 . 
     Thereafter, the controller  18  may perform calibration for the pair of optical cameras  141 , i.e., correct a pair of pieces of image information taken by the pair of optical cameras  141  (step T 2 ). 
     In one specific but non-limiting example, as illustrated in  FIGS. 8B and 9 , in the calibration, the controller  18  may first cause each of the strain gauge units  27  to measure a displacement amount σx of the tip of the relevant wing  32 , i.e., the position at which the associated optical camera  141  is disposed, from the designed position Pd in the span direction, and a displacement amount σz of the tip of the relevant wing  32 , i.e., the position at which the associated optical camera  141  is disposed, from the designed position Pd in the wing thickness direction (step T 21 ). The measurement of the displacement amount σx and the displacement amount σz may be performed for both of the wings  32 , i.e. the right wing  32 R and the left wing  32 L. 
     In step T 21 , the controller  18  may calculate the displacement amounts σx and σz of the tip of each of the wings  32  by integrating the displacement amounts measured by the plurality of strain gauges  271  constituting the associated strain gauge units  27 . 
     Thereafter, the controller  18  may calculate a displacement vector E of the tip of each of the wings  32  from the designed position Pd, on the basis of the displacement amounts σx and σz measured in step T 21  (step T 22 ). The calculation of the displacement vector E may be performed for both of the wings  32 . 
     Thereafter, the controller  18  may calculate, as a position vector G of each of the optical cameras  141 , a vector from a reference position Pc on the body  31  to the tip of the associated wing  32  (step T 23 ). The calculation of the position vector G may be performed for both of the wings  32 . 
     In step T 23 , the controller  18  may calculate the position vector G of each of the optical cameras  141  on the basis of the displacement vector E of the tip of the associated wing  32  calculated in step T 22  and a vector F. The vector F may be a vector from the reference position Pc to the designed position Pd of the tip of the associated wing  32 . In one specific but non-limiting example, the reference position Pc may be a position that is on the body  31  which is less influenced by the deformation of the wings  32 , and is evenly away from the two wings  32 . In this implementation, the reference position Pc may be located at the top of the substantial middle in the front-rear direction of the airframe, as with the position at which the laser distance measuring devices  15  are disposed in the foregoing first implementation. Further, the vector F from the reference position Pc to the designed position Pd of the tip of the associated wing  32  is a value known as a design value or a drawing value. 
     Thereafter, the controller  18  may calculate, as a posture vector H of each of the optical cameras  141 , an angle (i.e., an orientation) of the tip of the associated wing  32  (step T 24 ). The calculation of the posture vector H may be performed for both of the wings  32 . 
     In step T 24 , the controller  18  may calculate the angle of the tip of each of the wings  32 , i.e., the posture vector H of the associated optical camera  141 , on the basis of the displacement amount σz of the tip of the associated wing  32  calculated in step T 21  and the wing deformation database  161  read from the storage unit  16 , as in step S 24  of the stereo distance measuring process in the foregoing first implementation. 
     Thereafter, the controller  18  may correct the image information acquired in step T 1 , on the basis of the position vectors G of the respective optical cameras  141  calculated in step T 23  and the posture vectors H of the respective optical cameras  141  calculated in step T 24  (step T 25 ). 
     In one specific but non-limiting example, as in step S 25  of the stereo distance measuring process in the foregoing first implementation, the controller  18  may calculate a change in position of each of the optical cameras  141  from the designed state, on the basis of the position vector G of the relevant optical camera  141 . Further, the controller  18  may calculate a change in posture of each of the optical cameras  141  from the designed state, on the basis of the posture vector H of the relevant optical camera  141 . Further, the controller  18  may correct a position and an orientation of an image in the image information taken by the relevant optical camera  141  by the calculated amount of change in position and by the calculated amount of change in posture of the relevant optical camera  141 , respectively. The controller  18  may thereby acquire corrected image information. 
     This may correct the image taken by each of the optical cameras  141  whose position and posture are changed from those in the designed state to an image that should have been taken by the relevant optical camera  141  in the designed state. 
     Thereafter, as illustrated in  FIG. 8A , the controller  18  may utilize, as the stereo image, the pair of pieces of the corrected image information thus acquired, and calculate the distance to the photographing target, as in step S 3  of the stereo distance measuring process in the foregoing first implementation (step T 3 ). At this occasion, the controller  18  may refer to the GPS time information associated with each piece of the corrected image information, and select a pair of pieces of corrected image information whose timing of imaging coincide with each other. The situation where “the timing of the imaging coincide with each other” may encompass a situation where a time difference between points in time indicated by the two pieces of the GPS time information falls within a range in which the points in time are regarded as the same point in time. The controller  18  may collate the pair of pieces of the corrected image information, to calculate the distance. 
     In this way, the distance from the aircraft  30  to the photographing target is appropriately measured, with the stereo image based on the pair of pieces of the corrected image information whose timing of the imaging coincide with each other and in which the changes in the positions and the postures of the respective optical cameras  141  in flight are corrected. 
     [Effects] 
     As described, according to the second implementation, effects similar to the effects of the foregoing first implementation are achieved. 
     Specifically, the images in the pair of pieces of image information taken by the pair of the optical cameras  141  configuring the stereo camera are separately corrected in position and orientation, on the basis of the two pieces of position-posture information, i.e., the position vectors G and the posture vectors H, of the respective optical cameras  141 . The two pieces of position-posture information, i.e., the position vectors G and the posture vectors H, of the respective optical cameras  141  are calculated on the basis of the displacement amounts of the two wings  32  on which the pair of optical cameras  141  are disposed. On the basis of the pair of pieces of the corrected image information thus corrected, the distance to the photographing target is calculated. 
     Accordingly, it is possible to appropriately correct the positions and the orientations of the images, even in a case where the pair of optical cameras  141  are mounted on the aircraft and separated from each other, and the positions and the postures of the optical cameras  141  have changed to different states from one another. Hence, it is possible to restrain the measurement precision from being lowered. Further, it is possible to calculate the position-posture information of the respective optical cameras  141  on the basis of the displacement amounts of the wings  32 , without necessity of utilizing the expensive position-posture meter. 
     Hence, it is possible to enhance the measurement precision of the stereo camera mounted on the aircraft  30  in an inexpensive configuration, as compared to a case where the position-posture meter is utilized. 
     [Modifications] 
     It is to be noted that the technology is not limitedly applicable to the foregoing first and second implementations. It should be appreciated that modifications and alterations may be made by persons skilled in the art without departing from the scope as defined by the appended claims. 
     For example, in the forgoing first and second implementations, the description is given referring to the example in which the displacement amount σz of only the tip of the wing  32  is used to calculate the posture vector of each of the optical cameras  141  with reference to the wing deformation database  161 . However, in one specific but non-limiting example, a deformation state (i.e., a warp state) of the wing  32  in a wider range may be detected and utilized to calculate the posture vector. 
     In this case, in one specific but non-limiting example, the deformation state of the wing  32  in the entire measurement range of the associated laser distance measuring device  15  may be detected by the associated laser distance measuring device  15 . In another specific but non-limiting example, the deformation state of the wing  32  as a whole in the span direction may be detected on the basis of the displacement amounts measured by the respective strain gauges  271 . In this case, in one specific but non-limiting example, a wing deformation database or a relational expression that describes a relationship between the deformation state of the wing  32  as a whole and the angle of the tip of the wing  32 , i.e., the posture vector of the optical camera  141 , may be used. 
     In this way, it is possible to calculate the posture vector of each of the optical cameras  141  more precisely even in a case where a load of a force such as lift on the wing  32  is uneven in the span direction, for example, in a case where the airframe of the aircraft  30  is inclined. 
     Moreover, in the forgoing first and second implementations, the description is given referring to the example in which the displacement amount of the tip of the wing  32  is calculated on the basis of the designed state utilized as a reference state, and is calculated as a value from the designed position Pd of the tip in the designed state. However, in one specific but non-limiting example, the reference state may be a stopped state in which the aircraft  30  is stopped on the ground. In this case, the position of the tip of the wing  32  in the stopped state of the aircraft  30  may be measured in advance, and the measured position may be used instead of the designed position Pd. However, in the stopped state of the aircraft  30 , the tip of the wing  32  warps downward due to its own weight. Therefore, in one specific but non-limiting example where the strain gauge unit  27  is utilized to measure the displacement amount of the wing  32 , the strain gauges  271  may be attached to both the upper and lower surfaces of the wing  32 . 
     Moreover, in the forgoing first and second implementations, the description is given referring to the example in which each of the two camera units  14  includes the GPS receiver  142 . However, in one specific but non-limiting example, the single GPS receiver  142  common to the two camera units  14  may be provided. In this case, time adjustment may be made in advance between each of the camera units  14 , i.e., the optical cameras  141  and the GPS receiver  142 , so as to allow the timing of the imaging in the two camera units  14  to coincide with each other. 
     Moreover, in the foregoing first implementation, the description is given referring to the example in which the laser distance measuring devices  15  are utilized to measure the distances and the directions to the tips of the wings  32 . However, instrumentation to be used to measure the distances and the directions to the tips of the wings  32  is not limited to optical instrumentation such as a laser. The measurement of the distances and the directions to the tips of the wings  32  may be performed by other instrumentation as long as the instrumentation is able to perform the measurement with high precision. 
     Moreover, in the forgoing first and second implementations, the description is given referring to the example in which the pair of the optical cameras  141  are disposed on both the wings  32 , i.e., the right wing  32 R and the left wing  32 L, of the aircraft  30 . However, the pair of the optical cameras  141  may be disposed anywhere as long as the pair of the optical cameras  141  are mounted on the aircraft  30  and separated from each other. There is no particular limitation on the positions of the optical cameras  141  on the airframe. 
     In one implementation described above, the controller  18  illustrated in  FIGS. 1 and 6  may be implemented by circuitry including at least one semiconductor integrated circuit such as at least one processor (e.g., a central processing unit (CPU)), at least one application specific integrated circuit (ASIC), and/or at least one field programmable gate array (FPGA). At least one processor can be configured, by reading instructions from at least one machine readable tangible medium, to perform all or a part of functions of the controller  18 . Such a medium may take many forms, including, but not limited to, any type of magnetic medium such as a hard disk, any type of optical medium such as a compact disc (CD) and a digital video disc (DVD), any type of semiconductor memory (i.e., semiconductor circuit) such as a volatile memory and a non-volatile memory. The volatile memory may include a dynamic random access memory (DRAM) and a static random access memory (SRAM), and the non-volatile memory may include a ROM and a non-volatile RAM (NVRAM). The ASIC is an integrated circuit (IC) customized to perform, and the FPGA is an integrated circuit designed to be configured after manufacturing in order to perform, all or a part of the functions of the units illustrated in  FIGS. 1 and 6 . 
     The implementation also provides a program as the stereo distance measuring program  160  that causes a computer to function as the controller  18 , and a recording medium that stores the program. The recording medium is computer readable. Non-limiting examples of the recording medium may include a flexible disk, a magneto-optical disk, ROM, CD, DVD (Registered Trademark) and BD (Registered Trademark). As used herein, the term “program” may refer to a data processor written in any language and any description method. 
     Although some preferred implementations of the technology have been described in the foregoing by way of example with reference to the accompanying drawings, the technology is by no means limited to the implementations described above. The use of the terms first, second, etc. does not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. It should be appreciated that modifications and alterations may be made by persons skilled in the art without departing from the scope as defined by the appended claims. The technology is intended to include such modifications and alterations in so far as they fall within the scope of the appended claims or the equivalents thereof.