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

K. Kundu, P Halder, J. K. Mandal


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.

Cite this Article

Kundu K, Halder P, Mandal JK. A GIS

Based Tool to Digitize Polygon and

Line Segments of a Black and White

Map. Journal of Remote Sensing & GIS.

2016; 7(1): 27–41p.


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

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