Based On Auto Cad Automatically Track The Scanning Vector System

The acquisition of precise geographical space data is essential to building the data base of GIS,ie,it is not only the vital part of constructing GIS,but also the bottleneck of GIS development .Generally,Vectorizing systems are utilized for digitizing existing topographic maps in order to build the data base of GIS.A new vectorizing system with automated tracing functions is developed for solving the problems such as low speed,poor precisition and fallibility in the manual tracing systems,and low accuracy in the automated vectorizing systems.Based upon general preliminary processing of raster images,such as converting the images to grey scale of 0 or 1,broadening of lines,orientating ..correcting and thinning,etc. a method of mobile rectangle is used to determine whether one line links up with another well or not,which results in connection of the fractured segments and ,therefore,perfect tracing of lines is achieved.Whatsmore,a new method ,selection from point to point,was put forward for data compression and extraction of characteristic points in the curves. The proposed methods are performed under the enviroment of AUTO CAD with visual Basic language and it is suitable for vectorizing topographic maps.