Automated Swiss-Style Relief Shading and Rock Hachuring

Abstract

Rock depiction in Swiss topographic maps has evolved from humble line drawings into expressive renderings indicating slope, aspect and traversability. In this paper, an automatic method to derive monochrome Swiss-style rock hachures from a raster elevation model is presented. The proper placement and light modulation of the linear strokes depend on the availability of sound foundations for both terrain generalization and relief shading, for which two novel methods are introduced. The generalization applies line integral convolution along slope lines to the elevation values. The resulting smoothed raster has the footprint of its steep faces enlarged to increase the map space available for steep faces. The shaded relief is generated with the focus on terrain edges, unlike common raster cell-based methods. The rock hachures are modulated according to the grey values of the shaded relief. Finally, we present two topographic maps that demonstrate this new method of depicting relief.

KEYWORDS:

• Relief representation
• analytical shading
• cartographic rock drawing
• terrain generalization
• topographic maps
• Swiss cartography

Acknowledgements

The authors would like to thank Jürg Gilgen (swisstopo) for his valuable contributions regarding terrain representation methods and techniques (including Figure 5), as well as Stefan Räber (ETH Zurich) for preparing the topographic map of ‘Mettelhorn’. Extracts of the Dufour map, the Swiss national map and corresponding digital elevation models: © swisstopo. Mount Everest Map: © Swiss World Atlas, EDK. Figures 3 and 5 by courtesy of the mentioned authors and institutions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on the contributor

Roman Geisthövel was born in Hildesheim, Germany. He holds an MSc degree in Computer Science from the University Hamburg, Germany and currently lives in Zurich, Switzerland. He first worked at the Institute of Cartography and Geoinformation of ETH Zurich as a software developer for the ‘Atlas of Switzerland’, the interactive Swiss national atlas. He then worked in the same institute in the project ‘Terrain analysis, feature extraction and model deformation for cartographic generalization and visualization’ (subproject ‘Terrain sketching’), funded by the ‘Swiss National Science Foundation’ (SNSF). In this context, he wrote his doctoral thesis on automatic rock depiction.

ORCID

Roman Geisthövel http://orcid.org/0000-0002-6485-7586

Lorenz Hurni http://orcid.org/0000-0002-0453-8743

Additional information

Funding

This work was supported by the ‘Swiss National Science Foundation’ (SNSF) under grant number 200021_127224.