A GIS Based Tool to Digitize Polygon and Line Segments of a Black and White Map

Abstract

In this paper, a GIS based tool has been proposed to digitize polygon and line objects through efficient usage of RGB values of the segments of raster maps. For digitization of polygon, initially a closed loop is drawn inside the polygon segment. Beginning from the initial point of the closed loop, eight connected pixels calculation is incorporated to obtain the points existing in between the loop and the actual boundary. The points which exist outside the loop are compared with the RGB value of the boundary points to calculate the boundary. The boundary points are stored in the boundary array after arranging them in the cyclic order. In the existing tool, the polygon segment is digitized using the single click but the drawback is that lot of memory space is required for the processing. The concept of single click boundary calculation is also integrated in this tool to vectorise the small and/or narrow segments where drawing of closed loop inside the segment is difficult. For digitization of line, initially a point is selected on the line. Then, gradually scanning is performed from that point to both sides of selected point until it reaches the junction points. After that two arrays for both directions are merged to obtain the actual line coordinates. The polygon boundary and line segments points are minimized by obtaining minimum number of points of the segment which reduce the space complexity and minimize to the essential boundary points compared to the existing tools.

Keywords: GIS, digitization, spatial data, vector map, raster map