DIGITAL CHART PRODUCTION BY SCANNING DIGITIZING METHOD
C.X. Yu, Y.D. Zheng, W.Q. Huang
Dalian Naval Academy,Department of Hydrography and Cartography,Dalian,China
With the popularization of computer technique and the development of GIS, the demanding number of digital charts is more and larger, so it is the important key task to establish GIS that producing the high quality digital charts fitting the GIS demands. At present, one of the main methods to produce digital chars is digitalizing the former charts. Because of the higher performance and the lower price of engineering scanners, and it proves by practice that scanning digitizing method has the advantages of few investment, less labour intensity, shorter working period, and higher quality, scanning digitizing method is more and more popular.
The task flow of scanning digitizing is firstly to gain image files by scanning the former charts, then to digitize them. Generally digitizing is done by the special software (called as vectorization software). On the premise of satisfying scanner technical parameter (mostly is scanning resolution), the key to guarantee chart quality is the performance of vectorization software and the relevant technical scheme. And that GeoScan, as the product of ESRI company, aiming at the definite demanding of digital charts by GIS, provides the full functions of spatial data digitizing, attribute recording, layer controlling and data quality.
In the paper, taking Geoscan as example, firstly the customization methods are introduced, including layer structure customization, code system customization, symbol system customization and attribute defining customization, so different GIS projects can set the proper systematic layout according to their different demands. Then the whole processes of scanning digitization charts are discussed, including the preparative job that is Geoscan customization, image files calling, parameter and numeral condition setting, map sheet information inputting, map sheet orientation, classification and layer digitization, files saving and so on. And then methods of digitizing several typical chart elements are detailedly discussed, such as SOUDPT, OCLDNT, BULDPT, TRSPNT and RELFNT. Lastly, the operations easily leading the error in the digitizing process and the matters needing attention when digitizing the special elements are pointed.