CARTOGRAPHIC RELIEF REPRESENTATIONS WITH DEM FILTERING TECHNIQUES 
Manfred F. Buchroithner 
Institute for Cartography, Dresden University of Technology, Germany 
Rolf Böhm 
Böhm Cartographic Publishing House, Bad Schandau, Germany 
Commission VIl, EARSeL Working Group 
KEY WORDS: Cartography, image map generation, DEM, digital filtering, relief shading, combined hill shading, 
elevation contour generation, elevation layer generation, aerial perspectives. 
ABSTRACT 
By means of various conventional digital filtering techniques a series of cartographic relief representations can be gen- 
erated from DEM data. We distinguish between basic depictions and representations of higher complexity. Simple filter 
matrices allow to produce all basic types: oblique hill shadings, vertical hill shadings, combined shadings, elevation 
layers, and elevation contours. By means of kernel size changes, contrast manipulations, turning of illumination direc- 
tion, changes of the neighbourhood definition and of the contour interval, and other methods a variety of design opera- 
tions are possible. Representations of higher complexity comprehend: elevation contours with shadow enhancement, 
Tanaka-Kitiro Lines, and representations generated by manipulations in the image domain. The latter ones can be per- 
formed by filters with finite pulse response. Low-pass, band-pass, directional, and "coarse" filters have been applied. 
Combinations of the above methods offer a variety of design possibilities like spectral combinations, aerial perspectives, 
and combinations of shading and elevation contours. Furthermore, geomorphological form representations have also 
been generated. They serve, at the same time, for the verification of the applied methods. 
1. INTRODUCTION 
"Mountain Ranges - Key Areas for the Next Century. Mountain regions gain increasing importance for the urban soci- 
ety". This is the headline of a paper published by Bruno Messerli, one of the world's leading highland experts (Messerli, 
1997). In his article he stresses the eminent and still growing ecological (e.g. biodiversity) and economic role (e.g. re- 
sources, last not least water) of alpine landscapes, an issue which goes along the line of the ISPRS Commission VII 
ICO BP'98 Symposium Theme "Resource and Environmental Monitoring". 
One of the prerequisites for an adequate spatial representation of mountain environments and resources is the exis- 
tence of the respective GIS data and (the derived) maps based on digital elevation model. The latter ones allow to gen- 
erate relief information like hill shadings or elevation contours etc. in various forms by means of different filtering tech- 
niques. 
Today the bias of remotely sensed image data of high-relief terrain through sun illumination can be compensated or 
eliminated by means of computer software. Furthermore, the three-dimensional impression of the resulting "flat" remote 
sensing imagery can subsequently be enhanced by the subtle integration of hill-shading. Since for the geocoding pro- 
cess of remote sensing data in mountainous terrain a digital elevation model has to be applied, these very data can 
easily be used for the generation of relief shading. 
2. DEM FILTERING FOR RELIEF REPRESENTATION 
It seems to be a rather surprising fact that to the authors, knowledge so far no in-depth study about the cartographic 
possibilities of "simple" filtering procedures applied to DEM data for the generation of hill shadings, elevation layers or 
elevation contours have been carried out. Rather previous studies merely concentrated on shading by illumination 
simulation (cf. Lukas & Weibel 1995). 
For the generation of the relief representations described in the following sections are only needed the following ele- 
mentary image processing operations: 
- Image combination by addition, subtraction, logical AND and logical OR, 
Geometric translation by an arbitrary number of pixels in horizontal and/or vertical direction, 
- Grey value transformation with arbitrary look-up tables. 
The above operations can be combined to filters in the spatial domain without any problems. By means of various kernel 
sizes, contrast manipulations, rotation of the illumination direction, changes of the neighbourhood definition and of the 
contour interval, and other methods a variety of design operations are possible. 
2.1 Hill Shadings 
By means of digital filtering all common hill shadings - oblique, vertical, and combined shadings - can be generated 
without any problem. To a great extent digitally generated shadings have been produced according to the traditional 
analogue manner. Apart from oblique and vertical shadings (Fig. 1, Fig. 2) attempts have been made to obtain good 
results for the following: 
Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 627