Abstract:
A camera assembly is disclosed for mounting on a vehicle (e.g. an aircraft). An exemplary camera assembly can include: a fixture (e.g. a rotatable drum); a camera; and a mirror; wherein the fixture is arranged to be rotated relative to the vehicle about an axis; the camera is mounted on the fixture such that the camera has a substantially fixed position relative to the fixture; the mirror is mounted on the fixture such that, if the fixture rotates, the mirror rotates; the mirror is rotatable relative to the fixture about a further axis, the further axis being substantially perpendicular to the axis; and the camera is arranged to detect electromagnetic radiation reflected by the mirror. The axis and the further axis may intersect.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a camera assembly. 
     BACKGROUND 
     Unmanned Air Vehicles (UAVs) are commonly used in surveillance operations. 
     Typically, UAVs tend to use gimballed cameras (i.e. cameras mounted on moveable turrets) for reconnaissance. 
     However, only a small area of interest can be observed at any moment in time using such an approach. Furthermore, gimballed cameras tend to adversely affect the aerodynamic profile of an aircraft upon which it is mounted, e.g. by increasing drag. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the present invention provides a camera assembly for mounting on a vehicle, the camera assembly comprising: a fixture; a camera; and a mirror; wherein the fixture is arranged to be rotated relative to the vehicle about an axis; the camera is mounted on the fixture such that the camera has a substantially fixed position relative to the fixture; the mirror is mounted on the fixture such that, if the fixture rotates, the mirror rotates; the mirror is rotatable relative to the fixture about a further axis, the further axis being substantially perpendicular to the axis; and the camera is arranged to detect electromagnetic radiation reflected by the mirror. 
     The axis and the further axis may intersect. 
     The fixture may comprise a drum, the camera and the mirror are mounted inside the drum, and the axis is a longitudinal axis of the drum. 
     The camera assembly may further comprise a processor arranged to process images generated by the camera. 
     The camera assembly may further comprise storage means arranged to store images generated by the camera. 
     The camera assembly may further comprise transmitting means arranged to transmit images generated by the camera from the camera assembly for use by an entity remote from the camera assembly. 
     In a further aspect, the present invention provides a vehicle comprising a camera assembly according to the above aspect. 
     The vehicle may be an aircraft, and the camera assembly may be mounted on the aircraft such that the axis is substantially parallel to a roll axis of the aircraft. 
     The vehicle may further comprise a camera array, the camera array comprising: a plurality of array cameras having substantially fixed positions relative to each other, each array camera being arranged to, for each of a plurality of time-steps within a time period, generate an image of a respective portion of terrain, wherein the portions of terrain are such that the whole of a given area of terrain has been imaged by the end of the time period; and one or more processors arranged to: select a subset of the generated images such that the area of terrain is covered by the portions of the terrain in the images in the subset; and for an image not in the subset, if an object of interest is in that image, extracting a sub-image containing the object of interest from that image. 
     The fixture may be rotatable relative to the camera array. 
     A processor may be arranged to select a particular object of interest, and the camera assembly may be arranged to be operated depending on the selected particular object of interest so as to generate using the camera of the camera assembly one or more images of the selected a particular object of interest. 
     In a further aspect, the present invention provides a method of generating an image using a camera assembly according to any of the above aspects, the method comprising: selecting an object of interest; rotating the fixture about the axis and/or rotating the mirror about the further axis, such that a portion of terrain that the camera is able to image comprises the selected object of interest; and using the camera, generating one or more images of the portion of terrain comprising the selected object of interest. 
     The step of selecting an object of interest may comprise performing a method of capturing and processing images of an area of terrain, the method of capturing and processing images of an area of terrain comprising: for each of a plurality of time-steps within a time period, using each of a plurality of cameras in a camera array, generating an image of a respective portion of terrain, wherein the cameras in the camera array have substantially fixed positions relative to each other, and the portions of terrain are such that the whole of the terrain has been imaged by the end of the time period; selecting a subset of the generated images such that the whole of the terrain is covered by the portions of the terrain in the images in the subset; and for an image not in the subset, if an object of interest is in that image, extracting a sub-image containing the object of interest from that image. 
     In a further aspect, the present invention provides a program or plurality of programs arranged such that when executed by a computer system or one or more processors it/they cause the computer system or the one or more processors to operate in accordance with any of the above aspects. 
     In a further aspect, the present invention provides a machine readable storage medium storing a program or at least one of the plurality of programs according to the above aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration (not to scale) of an aircraft in which an example of a camera system is implemented; 
         FIG. 2  is a schematic illustration (not to scale) of an array of cameras; 
         FIG. 3  is a schematic illustration (not to scale) of an embodiment of a camera assembly; 
         FIG. 4  is a schematic illustration (not to scale) of a scenario in which the aircraft will be used to implement the embodiment of the camera system; 
         FIG. 5  is a process flow chart showing certain steps of a process by the camera system is implemented; 
         FIG. 6  is a schematic illustration (not to scale) of the images captured at step s 2  of the process shown in  FIG. 5 ; and 
         FIG. 7  is a process flow chart showing certain steps of a method of providing relatively high resolution images of a particular object to the ground base. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic illustration (not to scale) of an aircraft  2  in which an example of a camera system  3  is implemented. This example camera system  3  is useful in understanding an embodiment of a camera assembly  6  which will be described in more detail later below. 
     In this example, the aircraft  2  is an unmanned air vehicle (UAV). 
     In this example, the aircraft  2  comprises the camera system  3 . 
     The camera system  3  comprises an array of camera modules, hereinafter referred to as “the array  4 ”, and an assembly comprising a further camera, hereinafter referred to as “the assembly  6 ”. 
     An example of the array  4  is described in more detail later below with reference to  FIG. 2 . 
     An embodiment of the assembly  6  is described in more detail later below with reference to  FIG. 3 . 
     In this example, the array  4  is coupled to the assembly such that two-way communication is possible between the array  4  and the assembly  6 . 
       FIG. 2  is a schematic illustration (not to scale) of the array  4 . 
     In this example, the array  4  comprises four camera modules  8 . 
     In this example, each of the camera modules  8  comprises a camera  10 , a processor  12 , and a means for storing images which is hereinafter referred to as a “storage  13 ”. 
     In this example, each of the cameras  10  is coupled to the respective processor  12  and storage  13  such that images captured by a camera  10  are sent to the respective processor  12  and stored in the respective storage  13 . Each of the cameras  10  is a high pixel count, wide field of view camera. Moreover, in this example, each of the cameras  10  of the array  4  has a fixed position relative to the aircraft  2 . 
     In this example, the processors  12  of each of the camera modules  8  are coupled to one another such that two-way communication is possible between each of the processors  12 . 
     In this example, each of the cameras  10  is used to capture an image of an area of terrain that the aircraft  2  flies over, as described in more detail later below with reference to  FIG. 4 . The field of view of each of the cameras  10  is indicated in  FIG. 2  by dotted lines and the reference numeral  11 . Furthermore, in this example the array  4  is coupled to a navigation device (not shown in the Figures) which accurately provides aircraft location (e.g. in terms of latitude, longitude and altitude) and aircraft orientation (e.g. in terms of aircraft roll, pitch, and yaw angles). Using the aircraft&#39;s location, the aircraft&#39;s orientation, the fixed position of the cameras  10  of the array  4  relative to the aircraft  2 , and a ground elevation, a location for the image pixels that intercept the ground can be determined for any image taken, for example using a process such as geolocation. This provides a common reference (i.e. latitude, longitude and altitude) for objects are identified and distributed to other systems (as described in more details later below). 
       FIG. 3  is a schematic illustration (not to scale) of the assembly  6  according to an embodiment of the present invention. 
     In this embodiment, the assembly  6  comprises a camera (hereinafter referred to as “the assembly camera  14 ”), a processor (hereinafter referred to as “the assembly processor  15 ”) means for storing images which is hereinafter referred to as the “assembly storage  17 ”, a mirror  16 , and a drum  18 . 
     In this embodiment, the assembly camera  14  is a high pixel count, narrow field of view camera. The assembly camera  14  is coupled to the assembly processor  15  such that images captured by the assembly camera  14  are sent to the assembly processor  15  and assembly storage  17 . 
     In this embodiment, the assembly camera  14  is used to capture an image of an area of terrain that the aircraft  2  flies over, as described in more detail later below with reference to  FIG. 4 . The field of view of the assembly camera  14  is indicated in  FIG. 3  by dotted lines and the reference numeral  20 . Images are captured by the assembly camera  14  from light reflected from the terrain, passing through an aperture  22  in the drum  18 , and reflected by the mirror  16  to the assembly camera  14 . 
     In this embodiment, the assembly camera  14 , the assembly processor  15 , the assembly storage  17  and the mirror  16  are each mounted inside the drum  18 . 
     In this embodiment, the assembly camera  14  has a substantially fixed position relative to the drum  18 . 
     In this embodiment, the drum  18  is rotatable about its axis  24 . The axis  24  of the drum  18  is indicated in  FIG. 3  by dotted lines. Thus, the assembly camera  14 , the assembly processor  15 , the assembly storage  17  and the mirror  16  rotate with the drum  18 . The rotation of the assembly  6  within the aircraft  2  about the axis  24  has an effect that is described in more detail later below with reference to  FIG. 4 . 
     In this embodiment, the drum  18  is mounted in the aircraft  2  such that the drum  18  is rotatable about its axis  24  relative to the aircraft  2 . Furthermore, the drum  18  is mounted in the aircraft  2  such that the axis  24  of the drum  18  is substantially parallel to a roll axis of the aircraft  2 , (i.e. to a direction of travel of the aircraft  2  when the aircraft  2  flies in a straight line). 
     In this embodiment, the mirror  16  is rotatable about an axis, hereinafter referred to as the “further axis” and indicated by a dotted line and the reference numeral  26  in  FIG. 3 . In this embodiment, the further axis  26  is substantially perpendicular to the axis  24 . Furthermore, the further axis  26  is substantially fixed relative to the drum  18 . Rotation of the mirror  16  about the further axis  26  provides that the mirror  16  is able to tilt back and forward (as indicated by solid arrows in  FIG. 3  and indicated by the reference numeral  28 ). The tilting of the mirror  16  has an effect that is described in more detail later below with reference to  FIG. 4 . 
       FIG. 4  is a schematic illustration (not to scale) of a scenario in which the aircraft  2  will be used to implement the camera system  3 . The method by which the camera system  3  is implemented is described in more detail later below with reference to  FIGS. 5 and 7 . 
     In this scenario, the aircraft  2  files over an area of terrain  30 . The aircraft  2  flies in a direction of travel indicated in  FIG. 4  by solid arrows and the reference numeral  31 . 
     In this scenario, each of the respective cameras  10  of the array  4  takes an image of a respective portion of terrain  30 . The process by which the portions of the terrain  30  are imaged using the array  4  is described in more detail later below with reference to  FIG. 5 . Each of the respective portions of the terrain is indicated in  FIG. 4  by the reference numeral  32 . 
     In this embodiment, the array  4  captures an image of a strip of the terrain. The strip of terrain is formed of four respective portions  32 . An image is captured of each of the respective portions  32  by a respective camera  10  of the array  4 . In this embodiment, the adjacent portions  32  partially overlap such that the strip of the terrain  30  imaged by the cameras  10  is continuous. In this embodiment, the strip of terrain formed by the portions is substantially perpendicular to the direction of travel  31  of the aircraft  2 . 
     In this scenario, the cameras  10  take images of the terrain for a pre-determined time period, T. The time period T comprises time steps t 1 , . . . , t N . 
     During the time period T, as the aircraft  2  flies over the terrain  30  the cameras  10  each capture an image at each time-step t i  in T, i.e. discrete images are taken by each camera  10  of the terrain  30  such that a continuous image of the terrain  30  is captured over the time-period T. 
     The images captured by the cameras  10  of the array  4  are processed by the processors  12  of the array  4  as described in more detail later below with reference to  FIG. 5 . 
     Furthermore, in this scenario, the assembly camera  14  (of the assembly  6 ) takes an image of a portion of the terrain. The portion of the terrain of which an image is captured by the assembly camera  14  is hereinafter referred to as the “assembly portion” and is indicated in  FIG. 4  by the reference numeral  34 . As mentioned above, in this embodiment, the ground pixel footprint of the assembly camera  14  (i.e. the size of the assembly portion  34 ) is smaller than the ground pixel footprint of a portion  32 . 
     In this embodiment, because the assembly camera  14  is mounted inside a drum  18  that is rotatable about the roll axis of the aircraft  2 , the assembly portion  34  is moveable relative to the portions  32 . In particular, rotating the drum  18  about its axis  24 , causes the position of the assembly portion  34  to move on the surface of the terrain  30  in a direction that is substantially perpendicular to the direction of travel  31  of the aircraft  2 . Such directions are indicated by solid arrows and by reference numerals  36  in  FIG. 4 . 
     In this embodiment, because the mirror  16  in the assembly  6  is rotatable (i.e. can be tilted) about the further axis  26 , the assembly portion  34  is moveable relative to the portions  32 . In particular, tilting the mirror  16  about the further axis  26 , causes the position of the assembly portion  34  to move on the surface of the terrain  30  in a direction that is substantially parallel to the direction of travel  31  of the aircraft  2 . Such directions are indicated by solid arrows and by reference numerals  38  in  FIG. 4 . 
     Thus, by rotating the drum  18  about the axis  24  by a particular amount, and by tilting the mirror  16  about the further axis  26  to have a particular angle within the drum  18 , the position of the assembly portion  34  relative to the portions  32  may be changed. In this embodiment, the assembly portion  34  may overlap one or more portions  32  to any extent, or may not overlap a portion  32 . 
     In this embodiment, the position of the assembly portion  34  on the terrain  30 , i.e. the portion of the ground imaged by the assembly  6 , is determined as described below with reference to  FIG. 7 . Also, the images captured by the assembly camera  14  are processed by the assembly processor  15  as described in more detail later below with reference to  FIG. 7 . 
     In this scenario, identities and locations of the images taken using the array  4  and the assembly  6  are sent from the aircraft  2  to a ground station  40 . The aircraft  2  is in two-way communication with the ground station  40 . Also, on request, processed images taken using the array  4  and the assembly  6  are sent from the aircraft  2  to a ground station  40 . 
       FIG. 5  is a process flow chart showing certain steps of a process by which the camera system  3  is implemented. 
     At step s 2 , an image of each respective portion  32  of the area of terrain  30  is captured by each respective camera  10  of the array  4 . In this embodiment, images are taken by the cameras  10  at each time-step in the time-period T. In this embodiment, the cameras  10  of the array  4  take images as quickly as possible. In this embodiment, the cameras  10  each take images at a rate of 4 frames per second, i.e. the time-steps t 1  to t N  are 4 s apart. However, in other embodiments, a camera may take images at a different rate. 
     The aircraft  2  files over the terrain  30  during the time period T. The cameras  10  have substantially fixed positions relative to the aircraft  2 . Thus, in this embodiment, at each time-step the portions  32  of the terrain  30  have different positions on the surface of the terrain  30 . 
     In this embodiment, a portion  32  imaged by a camera  10  at one time-step partially overlaps the portion  32  taken by the same camera at the next time-step. In particular, in this embodiment portions  32  imaged at some of the time-steps in the time period T are covered by images taken at other time-steps. 
     In other words, continuous coverage of the terrain  30  that the aircraft  2  flies over is provided by a sub-set of the images taken by the cameras  10 . Depending on camera optic geometry, aircraft position, altitude and orientation and the terrain the rate at which images can be taken to achieve continuous coverage varies. In this embodiment, the cameras  10  of the array  4  take images at a rate of 4 frames per second. However, in this embodiment the rate at which images can be taken to achieve continuous coverage of the terrain  30  is a different (smaller) value, for example 0.2 frames per second (i.e. one image every 5 seconds). 
     In this embodiment, images taken by the cameras  10  of the array  4  at the time-steps t i , t j , t k , and t l  provide a continuous image of the terrain  30  that the aircraft  2  flies over in the time period T. The set of images taken at the time-steps t i , t j , t k , and t l  is a sub-set of the set of images taken at the time-steps t 1 , . . . , t N . 
     The portions  32  of the terrain  30  that images are taken of between the time-steps t i  and t j  are covered by the images taken at t i  and t j . Likewise, the portions  32  of the terrain  30  that images are taken of between the time-steps t j  and t k  are covered by the images taken at t j  and t k . Likewise, the portions  32  of the terrain  30  that images are taken of between the time-steps t k  and t l  are covered by the images taken at t k  and t l . 
     Thus, in this embodiment, a substantially complete image of the surface of the terrain  30  under the aircraft  2  during the time period T is captured using the cameras  10  of the array  4 . In other words, contiguous coverage of the surface of the terrain  30  under the aircraft&#39;s flight path is provided over the time period T. 
     At step s 4 , the sub-set of the images that provide a continuous image of the terrain  30  that the aircraft  2  flies over in the time period T are stored at the storages  13 . 
     In this embodiment, images taken by a camera  10  at each of the time-steps t i , t j , t k , and t l  are sent to, and stored at, the respective storage  13  for that camera  10 . The images taken at time-steps other than t i , t j , t k , and t l , which may be conveniently referred to as “intermediate images”, are not stored at this stage. 
       FIG. 6  is a schematic illustration (not to scale) of the images stored at step s 4 . In  FIG. 6 , the rows of four images taken by the four cameras  10  of the array  4  at each of the time steps t i , t j , t k , and t l  are indicated. Overlaps between the images are indicated in  FIG. 6  by the reference numeral  44 . 
     At step s 6 , all the images captured at step s 2  by a camera  10  (i.e. at each time-step) are sent to the processor  12  corresponding to that camera  10 . The images may be sent as they are captured by the camera  10 , or e.g. after a certain number of images have been captured. The images received by the processors  12  are processed to identify objects of interest in those images. In this embodiment, a conventional object identification process is implemented, for example a feature extraction, or change detection process. 
     In this embodiment, each object that is identified is assigned, by a processor  12 , an object ID, such that the objects can be identified at later stages. 
     At step s 7 , each camera module  8  transmits the identity and location of each subset of images stored in that camera module  8 , and the identity and location of all the objects of interest identified by that camera module  8  (at step s 6  above), to each of the other camera modules  8 , the assembly  6 , and the ground station  40 . 
     At step s 8 , from each image in which an object of interest has been identified at step s 6 , a sub-image is extracted containing the object of interest by the processor  12  corresponding to the camera  10  that captured that image. 
     The sub-images that include the identified objects may be extracted using any appropriate process. 
     At step s 10 , the sub-images extracted (at step s 8 ) from the images taken by a camera  10  are stored in sequence (i.e. in time-order) at the storage  13  corresponding to that camera  10 . 
     In this embodiment, the sub-images are stored in sequence. Thus, in this embodiment the stored sequences of sub-images form video of the identified objects of interest, as described in more detail below. 
     At step s 12 , on request, the images that were stored at step s 4  (i.e. the images taken at time-steps t i , t j , t k , or t l ), and the sub-images stored at step s 10  are transmitted from the camera module  8  at which the images/sub-images are stored to the other camera modules  8  of the array  4 . Thus, in this embodiment information about the identified objects of interests is broadcast between the processors  12 , i.e. between the camera modules  8 . Moreover, each camera module  8  tracks the positions of each identified object within the field of view of its camera  10 . In this embodiment, a conventional object tracking processes is used. 
     Furthermore, at step s 12 , on request from the ground base station  40 , the image footprints for the images that were stored at step s 4  (i.e. the images taken at time-steps t i , t j , t k , or t l ), and the sub-images stored at step s 10  are transmitted to the ground station  40 . The ground station  40  may request images either automatically, or in response to operator intervention, and may request images in either reduced or full resolution. 
     In this embodiment, once all the images/sub-images containing a particular object of interest have been downloaded by the ground station  40 , they are compiled at the ground station  40  into a low frame rate video sequence of that object of interest. In this embodiment, the frame rate of the video of a particular object is 4 frames per second. Also, in this embodiment, a duration of a video of an object depends on whether or not the object is moving relative to the terrain  30 , and, if it is moving, with its velocity relative to the aircraft&#39;s direction of flight. 
     Furthermore, at step s 12 , on request the images that were stored at step s 4  (i.e. the images taken at time-steps t i , t j , t k , or t l ), and the sub-images stored at step s 10  are transmitted to the assembly  6 . In this embodiment, the assembly  6  performs a process of capturing further images or video of particular objects using the received sequences of sub-images, as described below with reference to  FIG. 7 . 
     The images stored at step s 4  and/or the sub-images stored at step s 10  may be sent to the ground station  40  and/or the assembly  6  at the same time, or at different times. 
     Thus, a method of implementing the camera system  3  in which an objects of interest are identified in images taken by cameras  10  on the aircraft  2  is identified, and a relatively images/video of the objects are generated and provided to other systems (e.g. the ground station  40 , which is remote from the aircraft  2 , or the assembly  6 , which is onboard the aircraft  2 ). 
     In this embodiment, a process by which further images and/or videos of one or more identified objects of interest are captured is performed. 
       FIG. 7  is a process flow chart showing certain steps of a method of capturing further images and/or video of identified objects. 
     In this embodiment, the steps of the process shown in  FIG. 7  are performed after those steps shown in  FIG. 5 , i.e. after performing step s 12  described above. 
     At step s 14 , the identities and locations of all identified objects of interest that were transmitted to the assembly  6  at step s 7 , as described in more detail above, are received by the assembly  6  and analysed by the assembly processor  15 . 
     At step s 16 , the assembly processor  15  identifies one or more particular objects of interest of which further images and/or video are to be taken. 
     In this embodiment, the assembly  6  (i.e. the assembly processor  15 ) decides which objects of interest to capture high ground resolution image(s) of. 
     In this embodiment, this decision by the assembly processor  15  is made solely by the assembly processor  15 . The further images and/or video that are to be taken using the assembly  6  could be, for example, a single still image of each object of interest or a sequence of still images (i.e. to provide video) of one or more particular objects of interest. 
     In this embodiment, the images/video taken by the assembly camera  14  have higher resolution and are taken for a longer duration than those of the cameras  10  of the array  4 . In this embodiment, a particular object of interest can be identified, e.g. by the assembly  6  or ground station  40 , using the object ID assigned to it at step s 6  above (if that object was identified at step s 6 ), or an object could be referenced by its location on the surface of the terrain (e.g. if the object was not identified at step s 6  above). 
     In other embodiments, instructions regarding which object(s) further images and/or video are to be taken of, by the assembly  6 , may be provided to the aircraft  2  from an entity remote from the aircraft  2 , e.g. the ground station  40 . For example, an operator at the ground station  40  may analyse the images and sub-images that were transmitted to the ground station  40  from the aircraft  2  at step s 12  above, and identify one or more particular objects of interest and request further images/video of those objects from the aircraft  2 . 
     In this embodiment, at step s 16  the assembly processor  15  decides to take a sequence of images of a single particular object of interest to produce video footage of that object of interest. 
     At step s 18 , the drum  18  is rotated, and the mirror  16  is tilted, such that the assembly portion  34  (i.e. the area on the surface of the terrain  30  that is imaged by the assembly camera  14 ) is moved. This is done so that the particular object of interest on the surface of the terrain  30  lies within the assembly portion  34 . 
     In this embodiment, rotating the drum  18  about its axis  24  moves the assembly portion  34  on the surface of the terrain  30  in a direction that is substantially perpendicular to the direction of travel  31  of the aircraft  2  (such directions are indicated by arrows and the reference numeral  36  in  FIG. 4  as described above). 
     In this embodiment, rotating the mirror  16  about the further axis  26  moves the assembly portion  34  on the surface of the terrain  30  in a direction that is substantially parallel to the direction of travel  31  of the aircraft  2  (such directions are indicated by arrows and the reference numeral  38  in  FIG. 4  as described above). 
     At step s 19 , once the assembly portion has been moved such that an object on the surface of the terrain  30  lies within the assembly portion  34 , images/video are taken of that object using the assembly camera  14 . In this embodiment, these images have a higher resolution than those images taken by the cameras  10  of the array  4 . 
     In this embodiment, a conventional object tracking process is used so that the assembly camera  14  tracks an object as it moves relative to the aircraft  2 . This advantageously tends to provide that a period of time in which the relatively high resolution images are taken of an object is maximised. This period is from a time-step at which the object first coincides with the assembly portion  34 , to a subsequent time-step at which either the object is at a position that is not within the field of view of the assembly camera  14  or the assembly  6  is requested to provide images/video of a different target. 
     Thus, in this way, further images and/or video can be taken of one or more objects of interest identified at step s 16  above. 
     At step s 20 , the images of the object from the assembly camera  14  are stored in sequence (i.e. in time-order) at the assembly storage  17 . This stored sequence of assembly camera images provides a further images/video of the particular object of interest. 
     At step s 22 , the images captured at step s 18  by the assembly camera  14  are sent to the assembly processor  15 . The images are then processed. 
     At step  23 , the assembly processor  15  processes the received images to identify an object of interest. 
     At step s 24 , the assembly  6  transmits the identity and location of each image captured and stored by the assembly  6  to each of the camera modules  8 , and the ground station  40 . 
     At step s 6 , on request the stored assembly camera images are transmitted from the assembly  6  to the camera modules  8  and/or the ground station  40 . 
     Thus, a method of implementing the camera system  3  in which further (relatively high resolution) images and/or videos of one or more identified objects of interest are captured, and transmitted to the ground station  40 , is provided. 
     An advantage provided by the above described camera array is that the images/video taken of the terrain under the aircraft using the cameras of the array tends to be continuous and covers a relatively large area of the terrain surface. This is provided by the relatively wide field of view of the cameras of the array. Also, this is provided by, at step s 4 , selecting a sub-set of images from the set of all images taken, such that the sub-set provides continuous coverage of the terrain for storage. 
     A further advantage provided by the above described system is that the system is modular. In particular, each of the camera modules are separate and distinct modules. Also, the assembly is a separate module to the camera modules of the array. This tends to provides that, if desired, any of the modules of the camera system can be updated, repaired, replaced, or changed independently of the other modules of the system. 
     Moreover, the modularity of the system tends to provide that additional camera modules can easily be incorporated into the array, or existing camera modules can be removed from the array, as required (e.g. depending on the application or any constraints on the system such as spatial constraints imposed by the aircraft). Furthermore, due to its modularity the array is scalable so that it can be implemented on a variety of platforms. 
     Moreover, the modularity of the system tends to provide that processing of images etc. is not performed at a central location (i.e. by a central processor). Thus, the number of camera modules that are used in an implementation of the camera system is not limited by the processing capabilities of a central processor. 
     A further advantage provided by the above described system and method is that of a reduction in memory/storage requirements, and also communication bandwidth requirements, compared with that of a conventional system. This reduction in memory and communication bandwidth tends to be facilitated by not storing the whole of all of the images taken by the cameras of array. In the above embodiments, only a subset of these whole images is stored, e.g. the minimum number of images that provides a continuous coverage of the terrain that the aircraft flies over is stored. In other words, in the above embodiments, the images taken between the time-steps t i , t j , t k , or t l  (i.e. the so called ‘intermediate images’) are not stored, but a continuous image of the terrain is still stored. Thus, storage requirements tends to be reduced compared to conventional techniques, for example those in which all images captured are stored and/or transmitted to another system. The reduction in memory, and communication bandwidth tends to be further facilitated by only storing and/or transmitting sub-images that contain objects of interest (i.e. as opposed to the whole image that contain the object). 
     An advantage provided by the assembly is that the components of the assembly tend to be mounted inside a cylindrical drum. This advantageously tends to provide the assembly has a relatively aerodynamic shape compared to conventional systems (e.g. systems in which one or more cameras are mounted in a turret on an aircraft). Thus, problems caused by increased drag or air resistance, or caused by changing an aerodynamic profile of an aircraft by affixing the assembly to it, tend to be alleviated. 
     A further advantage provided by the above described system and method is that, by using the array of cameras (as opposed to, for example, a camera mounted on turret) is that video of more than one object of inertest can be extracted simultaneously from within the field of view of a single camera. Furthermore, the extracted video of objects of interest from all the cameras in the array may be coupled together such that a capability of ‘videoing’ multiple objects of interest at the same time tends to be advantageously provided. 
     Apparatus, including the processors  12 , storage  13 , the assembly processor  15 , and assembly storage  17 , for implementing the above arrangement, and performing the above described method steps, may be provided by configuring or adapting any suitable apparatus, for example one or more computers or other processing apparatus or processors, and/or providing additional modules. The apparatus may comprise a computer, a network of computers, or one or more processors, for implementing instructions and using data, including instructions and data in the form of a computer program or plurality of computer programs stored in or on a machine readable storage medium such as computer memory, a computer disk, ROM, PROM etc., or any combination of these or other storage media. 
     It should be noted that certain of the process steps depicted in the flowcharts of  FIGS. 5 and 7  and described above may be omitted or such process steps may be performed in differing order to that presented above and shown in the Figures. Furthermore, although all the process steps have, for convenience and ease of understanding, been depicted as discrete temporally-sequential steps, nevertheless some of the process steps may in fact be performed simultaneously or at least overlapping to some extent temporally. 
     In the above embodiments, the camera system is implemented on an aircraft. The aircraft is a UAV. However, in other embodiments the camera system is implemented on a different entity or system. For example, in other embodiments the camera system is implemented on a different type of vehicle (e.g. a manned aircraft, or a land-based vehicle), or a building. 
     In the above embodiments, the positions of the camera modules are substantially fixed relative to the aircraft. However, in other embodiments the camera modules may be moveable relative to the aircraft. For example, in other embodiments the cameras of the camera modules are substantially fixed relative to one another, but are movable (e.g. by mounting on a turret) relative to the vehicle/building they are mounted on. 
     In the above embodiments, the camera modules are separate modules comprising separate processors. However, in other embodiments the processing of the images captured by the cameras of the array may be performed centrally, i.e. at a central processor. Such a central processor may be on-board the aircraft, or remote from the aircraft. The use of a central processor advantageously tends to reduce the weight and size of the array. However, the above described advantages provided by the modularity of the array tend to be reduced. 
     In the above embodiments, the array comprises four camera modules, i.e. four cameras each coupled to a separate processor. However, in other embodiments the array comprises a different number of camera modules. In other embodiments, the array comprises a different number of cameras coupled to any number of processors. The number of camera modules, cameras and/or processors may be advantageously selected depending on any spatial/weight limitations or constraints, or depending on the scenario in which the camera system is to be implemented. 
     In the above embodiments, the cameras of the array are relatively wide field of view, visible light sensors. However, in other embodiments one or more of the cameras of the array is a different type of camera. For example, the cameras of the array could be infrared sensors, ultraviolet sensors, or any other type of sensor or camera. 
     In the above embodiments, the assembly camera is a visible light camera. However, in other embodiments the assembly camera is a different type of camera. For example, the assembly camera could be an infrared sensor, ultraviolet sensor, or any other type of sensor or camera. 
     In the above embodiments, the components of the assembly are mounted in a cylindrical drum. Also, the functionality that the assembly portion is moveable relative to the portions of the terrain imaged by the cameras of the array is provided by the drum being rotatable about the roll axis of the aircraft, and by a mirror that reflects light being received by the assembly camera. However, in other embodiments the functionality provided by the assembly is provided by different means. For example, in other embodiments, the assembly camera is mounted in a turret that can be operated so as to point the assembly camera in a desired direction. 
     In the above embodiments, the camera system is implemented in the scenario described above with reference to  FIG. 4 . However, in other embodiments the camera system is implemented in a different scenario. 
     In the above embodiments, as the aircraft flies over the terrain, the cameras of the array are arranged to capture images of a strip of the terrain at each of a number of time-steps. In the above embodiments, the strip of terrain is substantially perpendicular to the direction of travel of the aircraft. However, in other embodiments the cameras of the array are arranged differently (i.e. are in a different configuration) so as to capture images of a differently shaped area of the terrain. 
     In the above embodiments, images are sent from the aircraft to a single ground base. The ground base is remote from the aircraft. However, in other embodiments, images are sent from the aircraft to a different number of ground bases. Also, in other embodiments, images are sent from the aircraft to a different type of entity (e.g. an airborne platform) remote from the aircraft. Also, in other embodiments one or more of the entities that the images are sent to, and/or the requests are received from are not remote from the aircraft, e.g. a pilot of the aircraft, or other onboard system of the aircraft. 
     In the above embodiments, further images and/or video of one or more particular objects of interest are captured using the assembly, and provided to the ground base, if it is determined by the assembly processor that those one or more objects are of particular interest. However, in other embodiments further images and/or video of one or more particular objects of interest are captured using the assembly, and/or provided to the ground base, if a different criteria is satisfied. For example, in other embodiments high resolution images of a particular object of interest are captured using the assembly, and/or provided to the ground base if it is determined by the processor that the object is moving with relative speed that is above a predefined threshold value, or if a request for high-resolution images is received by the aircraft/assembly from the ground station, or a source other than the ground station. 
     In the above embodiments, a single camera assembly is used to capture relatively high ground resolution images/video of one or more particular object of interest. However, in other embodiments, a different number of such assemblies are used, e.g. to track and/or provide images/video of a plurality of objects at the same time. 
     In the above embodiments, the camera assembly is used in conjunction with the array, i.e. to take images/video of objects identified by the processors of the array. However, in other embodiments, the assembly is used in conjunction with, or alongside, a different apparatus. Also, in other embodiments, the assembly is implemented independently from such an apparatus.