Patent Publication Number: US-8542286-B2

Title: Large format digital camera with multiple optical systems and detector arrays

Description:
BACKGROUND 
     Traditional methods and camera systems utilized for the optical airborne registration (photogrammetric mapping) of urban areas have typically suffered from several problems. For instance, the aviation regulations near urban airports typically do not allow aircraft to fly at altitudes low enough for achieving acceptable image scales using conventional camera systems. As another example, images generated by conventional airborne camera systems typically suffer from perspective foreshortening, which causes buildings to appear as if they are leaning. This is particularly problematic in urban areas that often have many tall buildings. 
     It is with respect to these and other considerations that the disclosure made herein is presented. 
     SUMMARY 
     Concepts and technologies are described herein for a large format digital camera having multiple optical systems and detector arrays. Through an implementation of the concepts and technologies presented herein, a large format digital camera having multiple optical systems and detector arrays is provided that is suitable for use in the airborne optical registration of urban areas. In particular, a large format digital camera is disclosed herein that is capable of producing images at different photographic scales. The large format digital camera presented herein can produce panchromatic images using a wide-angle geometry that are suitable for use in a photogrammetric workflow that includes image-based georeferencing and digital surface modeling. The large format digital camera disclosed herein can also produce color images using a narrow-angle geometry suitable for use in a photogrammetric workflow that includes ortho image production. An ortho image is an image that shows ground objects in an orthographic projection. 
     According to one aspect presented herein, a large format camera is provided that includes a primary camera system, which may be referred to herein as the “first camera system,” and a secondary camera system, which may be referred to herein as the “second camera system.” The primary camera system is configured for collecting panchromatic image data and the secondary camera system is configured for collecting color image data. The secondary camera system has an optical system that has a longer focal length than the optical system of the primary camera system. The primary camera system and the secondary camera system may be mounted within a common housing suitable for installation and use within an aircraft. 
     According to other aspects, the primary camera system has an electro optical detector array capable of capturing the panchromatic image data. The secondary camera system has an electro optical detector array capable of capturing the color image data. The resolution of the electro optical detector in the secondary camera system is greater than the resolution of the electro optical detector in the primary camera system. According to other aspects, the radiometric resolution of the secondary camera system may be greater than the radiometric resolution of the primary camera system. 
     According to other aspects, the primary camera system and the secondary camera system are configured such that the large format digital camera can produce images at two different image scales offering two different footprints. Images produced by the primary camera system have a larger footprint and are larger in size than those produced by the secondary camera system and offer information for performing image-based georeferencing by means of photogrammetric triangulation. Images produced by the secondary camera system have a smaller footprint and are smaller in size than those produced by the primary camera system and offer a high-resolution narrow angle color image. The color images produced by the secondary camera system may be utilized as a source data set for high-resolution ortho image production. The footprint of the secondary camera system may be configured to cover the center of the footprint of the primary camera system. 
     According to other aspects, the large format digital camera may be configured to generate a sequence of consecutive images along a flight line. The large format camera may be further configured such that the primary camera system produces a sequence of consecutive panchromatic images that overlap one another. The secondary camera system may be configured to produce a sequence of consecutive color images that overlap one another and the images produced by the primary camera system. The overlap between consecutive panchromatic images may be greater than the overlap between consecutive color images. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended that this Summary be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing aspects of a large format digital camera having multiple optical systems and detector arrays provided in one embodiment presented herein; 
         FIG. 2  is a schematic diagram showing the footprint of a primary camera system overlaid with the footprint of a secondary camera system in a large format digital camera presented in one embodiment disclosed herein; 
         FIG. 3  is a perspective diagram showing a perspective view of the footprint of a primary camera system and the footprint of a secondary camera system in a large format digital camera presented in one embodiment disclosed herein; 
         FIG. 4A  is a schematic diagram illustrating the overlap between the footprint of a sequence of consecutive images taken with a primary camera system and the footprint of a sequence of consecutive images taken with a secondary camera system in a large format digital camera presented one embodiment disclosed herein; 
         FIG. 4B  is a perspective diagram illustrating the overlap between the footprint of a sequence of consecutive images taken on several flight lines with a primary camera system and the footprint of a sequence of consecutive images taken with a secondary camera system in a large format digital camera presented one embodiment disclosed herein; and 
         FIG. 5  is a flow diagram showing one illustrative process presented herein for the airborne optical registration of urban areas using a large format digital camera having multiple optical systems and detector arrays provided in one embodiment presented herein. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is directed to a large format digital camera having multiple optical systems and detector arrays. In the following detailed description, references are made to the accompanying drawings that form a part hereof, and which are shown by way of illustration specific embodiments or examples. Referring now to the drawings, in which like numerals represent like elements throughout the several figures, aspects of a large format digital camera having multiple optical systems and detector arrays will be presented. 
       FIG. 1  is a schematic diagram showing aspects of a large format digital camera  100  having multiple optical systems  106 A- 106 B and detector arrays  110 A- 110 B provided in one embodiment presented herein. As shown in  FIG. 1 , the large format digital camera  100  includes a primary camera system  104 A, which might be referred to herein as the first camera system, and a secondary camera system  104 B, which might be referred to herein as the second camera system. Although  FIG. 1  illustrates only one secondary camera system  104 B, it should be appreciated that other embodiments might include multiple secondary camera systems  104 B. 
     According to one embodiment, the primary camera system  104 A includes an optical system  106 A that has a focal length  108 A. The secondary camera system  104 B includes an optical system  106 B that has a focal length  108 B that is longer than the focal length  108 A of the optical system  106 A. In this manner, the secondary camera system  104 B is configured to produce images having a narrower field of view than images produced by the primary camera system  104 A. Images produced by the primary camera system  104 A have a wider field of view than images produced by the secondary camera system  104 B. The optical systems  106 A- 106 B may include other conventional optical elements to produce a suitable image at the desired focal length. 
     According to one implementation, the primary camera system  104 A is configured with an electro optical detector array  110 A capable of capturing panchromatic image data  112 . As known in the art, a panchromatic image sensor, such as the electro optical detector array  110 A, is sensitive to all or most of the entire visible spectrum. According to embodiments, the secondary camera system  104 B is configured with an electro optical detector array  110 B capable of capturing color image data  116 . For instance, the secondary camera system  104 B might be equipped with a suitable charge coupled device (“CCD”) array configured for capturing the color image data  116 . According to embodiments, the camera system presented herein is a frame camera (also referred to as a framing camera), as opposed to a camera that utilizes push-broom sensing. 
     It should be appreciated that the detector arrays  110 A- 110 B comprise arrays of individual electro-optical detectors, e.g., semiconductor devices that output an electric signal, the magnitude of which is dependent on the intensity of light energy incident on such electro-optical detector. Therefore, the signal from each electro-optical detector in the arrays  110 A- 110 B is indicative of light energy intensity from a pixel area of the portion of the object or terrain being photographed, and the signals from all of the individual electro-optical detectors in the arrays  110 A- 110 B are indicative of light energy intensity from all of the pixel areas of the portion of the object or terrain being photographed. Consequently, the signals from the electro-optical detectors in each of the detector arrays  110 A- 110 B, together, are indicative of the pattern of light energy from the portion of the object being photographed, so a sub-image of the portion of the object can be produced from such signals. First, however, the signals are amplified, digitized, processed, and stored, as is well known to those of ordinary skill in the art. 
     The electro-optical detector arrays  110 A- 110 B are connected electrically by suitable conductors to a control circuit (not shown), which includes at least a microprocessor, input/output circuitry, memory, and a power supply for driving the electro-optical detector arrays  110 A- 110 B, retrieving image data from of the arrays  110 A- 110 B, and storing the image data. Other data processing functions, for example combining images and/or performing image display functions may be accomplished within the large format digital camera  100  or by other external data processing equipment. 
     According to implementations, the resolution of the electro optical detector array  104 B in the secondary camera system  104 B is greater than the resolution of the electro optical detector array  104 A in the primary camera system  104 A. In this manner, the large format digital camera  110  can produce a panchromatic image file  114  from the primary camera system  104 A using a wide-angle geometry that is suitable for use in a photogrammetric workflow that includes image-based georeferencing and digital surface modeling. The large format digital camera  110  can also simultaneously produce a higher-resolution color image file from the secondary camera system  104 B using a narrow-angle geometry suitable for use in a photogrammetric workflow that includes ortho image production. 
     As described briefly above, the primary camera system  104 A and the secondary camera system  104 B might be mounted within a common housing  102 . In this embodiment, a front glass plate  120  might be mounted within the housing  102  to protect the optical systems  106 A- 106 B. In alternate implementations, the primary camera system  104 A and the secondary camera system  104 B are mounted in separate housings (not shown). In both cases, the primary camera system  104 A, the secondary camera system  104 B, and the housing  102  are configured for mounting and use within an aircraft. 
       FIG. 2  is a schematic diagram showing the footprint  202  of the primary camera system  104 A overlaid with the footprint  204  of the secondary camera system  104 B in the large format digital camera  100  according in one embodiment disclosed herein. As illustrated in  FIG. 2 , the primary camera system  104 A and the secondary camera system  104 B are configured in one embodiment such that the large format digital camera  100  can produce overlapping images at two different image scales offering two different footprints  202  and  204 . 
     According to one embodiment, images produced by the primary camera system  104 A have a larger footprint  202  and are larger in size than those produced by the secondary camera system  104 B. Images produced by the secondary camera system  104 B have a smaller footprint  204  and are smaller in size than those produced by the primary camera system  104 A and offer a higher resolution narrow angle color image. 
     As also illustrated in  FIG. 2 , the footprint  204  of the secondary camera system  104 B may be configured to cover the center of the footprint  202  of the primary camera system  104 A. By overlapping the footprints  202  and  204  in the manner shown in  FIG. 2 , a portion of the images produced by the primary camera system  104 A can be enhanced by the images produced by the secondary camera system  104 B.  FIG. 3  provides a perspective view of the footprint  200  of the primary camera system  104 A and the footprint  204  of the secondary camera system  104 B when an image is taken from a common point  302  by both camera systems  104 A- 104 B. 
       FIG. 4A  shows a top-down view that illustrates the overlap between the footprint  200  of a sequence of consecutive images taken with the primary camera system  104 A and the footprint  204  of a sequence of consecutive images taken with the secondary camera system  104 B in the large format digital camera  100  in one embodiment disclosed herein. As discussed briefly above, the large format digital camera  100  may be mounted and configured for use within an aircraft (not shown). When the aircraft is flown according to a well-defined flight line  400 A, the large format digital camera  100  may be configured to capture a sequence of images along the flight line  400 A.  FIG. 4A  illustrates the footprints  202 A- 202 D of a sequence of images taken using the primary camera system  104 A and the footprints  204 A- 204 D of a sequence of images taken using the secondary camera system  104 B along the flight line  400 A. 
     As illustrated in  FIG. 4A , the large format camera  100  may be further configured such that the primary camera system  104 A produces a sequence of consecutive panchromatic images that have footprints  202 A- 202 D wherein consecutive sequential images overlap one another. The secondary camera system  104 B may similarly be configured to produce a sequence of consecutive color images that have footprints  204 A- 204 D wherein consecutive sequential images overlap one another and also overlap the images produced by the primary camera system  104 A. The overlap between the footprints of consecutive panchromatic images may be greater than the overlap between the footprints of consecutive color images. 
       FIG. 4B  is a perspective diagram illustrating the overlap between the footprints  200  of a sequence of consecutive images taken on several flight lines  400 A- 400 B with the primary camera system  104 A and the footprints  204  of a sequence of consecutive images taken with a secondary camera system  104 B in the large format digital camera  100  in one embodiment disclosed herein. If, as illustrated in  FIG. 4B , images are produced by the primary camera system  104 A and the secondary camera system  104 B along multiple well-defined flight lines  400 A- 400 B by means of aerial photogrammetric image acquisition, the footprints  202  of the primary camera system  104 A overlap one another in the sequence of exposures along the flight lines  400 A- 400 B. The footprints  204  of the secondary camera system  104 B also overlap with the footprints  202  of the primary camera system  104 A and the footprint  204  of the secondary camera system  104 B. 
     Along the flight lines  400 A- 400 B, images are therefore produced in such a way that the sequence of images produced by the primary camera system  104 A and the images produced by the secondary camera system  104 B create continuous image strips of overlapping images. The flight lines  400 A- 400 B may be defined in such a way that the large format digital camera  100  captures images covering an entire project area. 
     According to various embodiments, image acquisition by the secondary camera system  104 B may be triggered substantially simultaneously with image acquisition by the primary camera system  104 A and, accordingly, images from the secondary camera system  104 B may be acquired at the same position and with the same camera attitude as images from the primary camera system  104 A. Alternatively, the trigger for the secondary camera system  104 B may be independent from the primary camera system  104 A, e.g., may be at a higher rate than images captured by the primary camera system. Either embodiment, as well as any combination thereof, is contemplated to be within the scope of embodiments presented herein. 
     When the primary camera system  104 A and the secondary camera system  104 B are triggered at the same time, the images produced by the secondary camera system  104 B may be registered to the images produced by the primary camera system  104 A using the same trigger event. Additionally, images produced by the secondary camera system  104 B may be calibrated to images of the primary camera system  104 A through the use of a precisely surveyed and well-structured object (known as a “calibration object”). 
     The images of the secondary camera system  104 B may also be stitched to the images of the primary camera system  104 B using traditional methods. Additionally, the images generated by the primary camera system  104 A can be used to reconstruct the three dimensional form of an object (for instance, the buildings of a city by means of a digital surface model) and the images of the secondary camera system  104 B, with a higher geometric resolution, may be used to extract high resolution photo texture which can then used for the production of urban ortho image maps. 
     Referring now to  FIG. 5  additional details will be provided regarding the embodiments presented herein for a large format digital camera  100  having multiple optical systems and detector arrays. In particular,  FIG. 5  is a flow diagram showing a routine  500  that illustrates one process presented herein for the airborne optical registration of urban areas using the large format digital camera  100  described above. 
     The routine  500  begins at operation  502 , where the large format digital camera  100  is calibrated. As discussed above, the large format digital camera  100  may be calibrated using a calibration object such that the footprint of images produced by the secondary camera system  104 B overlap the central portion of the footprint of images produced by the primary camera system  104 A. As also discussed above, the large format digital camera  100  may be installed in an aircraft and utilized to capture ground images as the aircraft is flown along a well-defined flight line. Such images may be captured and stored in an appropriate digital storage device integrated with or external to the large format digital camera  100 . 
     From operation  502 , the routine  500  proceeds to operation  504  where panchromatic image files  114  are received from the primary camera system  104 A. The routine then proceeds to operation  506 , where color image files  118  are received from the secondary camera system  104 B. Once the images files have been received from both camera systems  104 A- 104 B, the routine  500  proceeds to operation  508 , where the image files  114  from the primary camera system  104 A are co-registered with the image files  118  from the secondary camera system  104 B. 
     From operation  508 , the routine  500  proceeds to operation  510 , where the image files  114  from the primary camera system  104 A are utilized in a photogrammetric workflow that includes image-based georeferencing and digital surface modeling. From operation  510 , the routine  500  proceeds to operation  512 , where the image files  118  from the secondary camera system  104 B are utilized for ortho image production. The routine  500  proceeds from operation  512  to operation  514 , where it ends. 
     Based on the foregoing, it should be appreciated that a large format digital camera  100  having multiple optical systems and detector arrays has been disclosed herein that is suitable for use in the airborne optical registration of urban areas. It should also be appreciated that the subject matter described above is provided by way of illustration only and should not be construed as limiting. Various modifications and changes may be made to the subject matter described herein without following the example embodiments and applications illustrated and described, and without departing from the true spirit and scope of the present invention, which is set forth in the following claims.