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Geoinformatics_04-2009
article fig. 4 this diagram shows the geometric arrangement and ground coverage of the dimac wide twin-camera system. still sat side-by-side within the cylindrical drum but both were set in a vertical pointing position, so dispensing with the tilt blocks that were used previously to obtain the oblique pointing of the individual camera modules. the ccd arrays with their digital backs were then offset with respect to the optical axes of the camera lenses within the camera modules so that they covered the areas on the ground to the left and right of the flight line [fig. 4]. thus the wide cross-track coverage could still be maintained without the need to rectify the images. the two images are then merged using tie points in their common overlap in conjunction with the dimerge software. at the same time as this change was made, dimac systems entered into a business relationship with vx services of longmont, colorado, which manufactures and supports the vexcel vx 4000 film scanners. a new company, called dimac systems llc, was set up to sell the newly re-configured twin camera system - which is now called the dimac wide in the north american market. in this respect, it has been quite successful with several customers located in the u.s.a., canada and mexico. within europe, there is a customer in croatia, besides the two systems that are being utilized by cicade. another very new configuration is the dimac oblique system [fig. 5]. this employs six camera modules to generate the combination of vertical and oblique photography that gives rise to the maltese cross form of coverage of the ground that has become popular as a result of the activities of pictometry and its partners and competitors. the central vertical photograph is acquired using twin paired camera modules operating side-by-side as in the dimac wide system. the four oblique images are captured using four additional camera mod- allow between one and four camera modules to be mounted and operated simultaneously. internally within the drum, there is also a small support structure that can accommodate a gps/imu unit. the drum lid or cover contains the electronic controls that are needed to operate the camera modules. when the lid is closed, it ensures a temperature-controlled environment for the contents of the cylinder, the requisite warmth being generated by a built-in heating element. the cylindrical drum is designed to fit into a standard gyro-controlled mount. the cylinder also has a removable front carbon-fibre cover plate or cap that protects the lenses while the camera system is not in use in the air or on the ground. (iii) the electronics and it cabinet [fig. 3 (c)] has been designed by dimac, but is manufactured in the u.s.a. it contains the computers that carry out specific functions during the operation of the camera modules. it also includes the control board that provides the signals to the actuators for the fmc mechanism, based on the information about the aircraft speed over the ground that is provided by the system s flight management system. the cabinet also contains the removable storage unit that comprises a number of ruggedized and pressurized hard drives. associated with the cabinet and its contents is a touchscreen display monitor that is used by the camera operator to check and control the operation of the camera modules. the socalled diops software is provided to control the operation of the camera and the image data acquisition and to generate pre-view images for checking purposes. once the images have been exposed and stored on the hard drives, the data can then be downloaded via an external docking station. the capture one software that is provided by phase one is then used to convert the raw image data into tiff format. latest configurations in its original form, the dimac system could be used in a twin oblique camera configuration in order to provide a wide swath of coverage of the ground in the cross-track direction. in 2006, it was decided to re-configure this particular arrangement. the two cameras fig. 5 cad drawings of the dimac oblique camera system showing (a) the cross-track arrangement with the twin vertically pointing cameras in the lower part of the diagram and, mounted above them, the two oblique cameras pointing in opposite directions on either side of the flight line; and (b) the along-track arrangement showing the two oblique cameras pointing in opposite directions along the flight line. 46 june 2009
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