On the Use of Dtp Scanners for Cartographic Applications

Scanners have been used as input devices in cartographic applications mainly for digitisation and eventually subsequent vectorisation of existing hardcopy maps. Other applications that can increasingly be found, particularly in relation to cartographic work within a GIS, make use of scanned images, especially aerial imagery, which are usually transformed into orthoimages and are subsequently used for generation or update of cartographic databases, and creation of different visual products in digital or analogue form like orthoimage maps and 3D perspective views. This paper deals with the use and applicability of DeskTop Publishing (DTP) scanners for cartographic applications. The motivation of the paper is the investigation as to what extent lower-priced DTP scanners, which are rapidly improving during the few last years, can be used for such applications. DTP scanners can be roughly divided into two groups: (a) flatbed scanners that are generally low-cost and up to A3 format, and (b) drum scanners that are generally more expensive and geometrically less accurate than flatbed ones, but with better radiometric performance and larger scan size. The paper will mainly concentrate on flatbed scanners with aim the scanning of aerial images. However, many of the topics mentioned in the paper are also valid for drum scanners and applications involving scanning of maps or layers thereof. The paper gives a review of recent technological developments with respect to these scanners, describes advantages and disadvantages, presents characteristics, tests and problems of such scanners, and investigations on their geometric accuracy. For certain applications, e.g. production of analogue orthoimages or orthoimage maps, the geometric accuracy of such scanners may suffice, while for others like updating of digital databases it is generally insufficient. Thus, test patterns for calibration of such scanners and some first results will also be presented.