THE RENDERING OF RELIEF IMAGES FROM DIGITAL CONTOUR DATA

Existing methods of modelling and rendering relief from digitised cont ours adopt either regular grid or triangulated irregular network appro aches. Both can have disadvantages which include imprecise terrain mod elling, ineffective visualisation, and/or heavy computing overheads. A n alternative approach has been developed which calculates profiles ac ross the contour model, typically at about 1 mm separation at the visu alisation scale, in the direction of an assumed illumination source. I ntensity values are calculated for the profile swathes by considering profile gradient and local slope characteristics. The resulting shaded model gives an effective visualisation, and offers a number of benefi ts for additional processing because of computational economy and effi ciency. Single light source images of shaded relief are often incomple te in their rendering because they favour relief trend lines in certai n directions only. A technique has been developed to overlay generated shaded images from a range of illumination directions using a multiba nd approach, which has been found to enhance visualisation.