Origins and applications
This chapter addresses the problem of vector to raster conversion, also known as rasterisation and scan conversion, and secondly the problem of raster to vector conversion, which is also known as vectorisation. Conversions between vector and raster representations occur in several contexts of Geographical Information Systems (GIS) and cartography. The task of vector to raster conversion is one of finding a set of pixels in the raster space which coincide with the location of a point, line, curve or polygon in its vector representation. Straight-line rasterising algorithms usually work in an incremental manner starting at one end of the line and stepping along it, setting one pixel at each increment. Raster to vector conversion involves several image-processing techniques, the use of which varies according to the type of data being vectorised. Scanned images are often converted, by the process of thresholding, to bilevel images in which the pixels are classified as either foreground or background.