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Geoinformatics_06-2009
article [a] [b] [a] fig. 7 a plan view of the geometric configuration and ground coverage of a triple-digicam system with its single vertical photo and twin oblique photos providing a very wide angular coverage of the terrain. [b] a third configuration using twin digicam cameras that is being offered by igi is the so-called dual-digicam oblique system. like the previous dual digicam system, it uses a pair of oblique pointing digicam cameras. however these are operated with their optical axes set at the high tilt angles of 45 degrees to the vertical and without any attempt to overlap the two resulting high oblique images [fig. 6]. this arrangement is designed specifically to produce highly oblique images that can provide detailed information about the characteristics of buildings and other structures that can be used for 3d city modelling. end of the year, when the 60 megapixel backs become available, the final stitched composite image will be 220 megapixels in size. a series of overlapping large-format composite images, each of which has been taken from a single position in the air, can readily be acquired using the quattro-digicam system. these images can then be accommodated as stereo[a] three camera systems igi has also designed a triple-digicam airborne digital camera system. this comprises three digicam cameras that can be placed within a standard mount in a configuration that provides one vertical and two low oblique frames, again with the same highly synchronized exposures as for the twin camera systems [fig. 7]. by selecting lenses of a suitable (short) focal length from the available range, an extremely wide angular coverage of the ground can be achieved in the cross-track direction from horizon-tohorizon if required. as with all the previous configurations, an aerocontrol gps/imu system can be supplied and integrated to provide continuous measurement of the position and attitude values of the airborne platform on which the triple-digicam system has been mounted. fig. 5 (a) an igi dual-digicam system with the twin cameras tilted so that their optical axes are pointing obliquely to either side of the flight line in the cross-track direction. again with an aerocontrol imu unit mounted on the shelf above the two cameras. (b) a diagram providing plan view of the geometric configuration and ground coverage of a dual-digicam twin-camera system. [b] four camera systems igi has also introduced four camera systems based on two alternative and quite different geometric configurations of the oblique pointing digicam cameras. (i) in the first of these called the quattro-digicam system [fig. 8(a)] the four cameras are closely coupled together in a block configuration such that all four tilted images are acquired simultaneously and overlap slightly along two of their edges [fig. 8(b)]. the resulting four low oblique images can then be rectified post-flight. after rectification, the four individual rectified images can then be stitched together to produce a single composite near-vertical image with a large rectangular format that is 145 megapixels in size. by the fig. 6 an igi dual-digicam oblique system showing the pair of cameras tilted at angles of 45 degrees to the vertical to acquire images on either side of the flight line. fig. 8 (a) a quattro-digicam system with its four closely-coupled digigcam medium-format cameras that have been configured to produce a single composite large-format frame image - after the rectification and stitching together of the four oblique images has been undertaken. (b) this diagram shows the geometric arrangement, ground coverage and overlaps of the four oblique images that are [c] generated by a quattro-digicam system. (c) a cad drawing of the cylindrical adapter unit that is used to fit the four digicam cameras into a standard camera mount. 62 september 2009
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