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Geoinformatics_06-2009
article modular cameras; multiple configurations the igi digicam range a previous article in geoinformatics (published in the october/november 2006 issue) highlighted the expansion of igi s product range into the areas of airborne digital frame cameras and laser scanners. since then, igi has pursued a vigorous development of its airborne camera technology. this has resulted in numerous alternative configurations based on the use of multiple cameras with both vertical and oblique imaging capabilities. by gordon petrie [a] end of this year (2009) will feature a 60 megapixel digital back that is based on the new chip from dalsa. to meet the varied needs of its customers, igi offers a very wide range of lenses for use with its digicam cameras with focal length values ranging between 28 and 300 mm. these lenses have been developed by hasselblad specifically for use in digital cameras. each lens in the range is operated in conjunction with an electronically-controlled leaf shutter that is housed in the lens and provides shutter speeds over the range 1/800th to 1/125th second. the minimum time between successive exposures with the digicam-39 camera is 1.9 seconds; the new digicam-60 camera will have an image repetition rate of 1.6 seconds. besides the actual camera unit, a complete digicam system also comprises a digicontrol sensor management unit (smu) together with twin solid-state (ssd) storage units that have the capacity to record 6,400 images. the complete system also includes an 8-inch tft touchscreen display monitor that provides on-line information such as preview images and histograms to the camera operator [fig. 1(b)]. integration of a digicam camera system with igi s own ccns4 airborne navigation and guidance system provides fully automated operation of the camera system. the addition and further integration of the company s aerocontrol gps/imu system provides both the measured position and height coordinates and the attitude values of the camera (providing external orientation parameters) at the moment of exposure as needed for direct geo-referencing or for use in aerial triangulation operations. [b] fig. 1 (a) on the right half of this photo are the individual modular components lens, camera body and digital back of an individual digicam camera; while, at the left, is the assembled camera unit. (b) this photo shows the main elements of a complete digicam system. at the left side of the photo is the tft touch-screen display monitor; in the centre is the digicontrol control unit with its twin storage units for the recording of the acquired images; while the digicam camera unit with two filters placed in front of it is shown at the right side of the photo. basic camera & system the basic building block for the construction of igi s multiple camera systems is its digicam medium-format digital frame camera. this is based on the hasselblad camera and has a modular construction comprising three main units (i) a modified camera body; (ii) a digital back; and (iii) and a range of lenses that have been calibrated by igi [fig. 1(a)]. initial versions of the digicam camera featured a 22 megapixel digital back. however the vast majority of those built to date have utilized the later 39 megapixel digital back generating a frame image with a rectangular format of 7,216 x 5,412 pixels. the next production series of digicam cameras which will become available by the single camera systems the use of individual digicam camera systems is of course possible in a stand-alone mode in order to acquire overlapping near-vertical frame images of the terrain. for such a basic operation, a simple mount can be fitted to the aircraft floor to allow the pointing of the camera in the nadir direction [fig. 2(a)]. however, more usually, the digicam camera will be mounted on and operated from one of the purpose-built camera mounts that are readily available. these include a non-gyroscopically-controlled mount such as the older wild/leica pav10/20 models [fig. 2(b)] or one of the more modern gyro-controlled mounts such as the leica pav30, zeiss t-as & september 2009 [a] [b] fig. 2 (a) this particular digicam camera has been placed in a simple mount over a hole cut in the floor of a cessna 208 caravan aircraft. (b) this single digicam camera has been placed in a cylindrical adapter unit that fits into a wild/leica pav10 camera mount. an aerocontrol imu unit has been placed on a shelf on the top of the adapter unit so that it is mounted directly above the camera. 60
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