Abstract
As relief influences disposition of all the other objects displayed on maps, terrain representation plays one of the key roles in the map creation process. Originally a manual technique, relief shading creates the three-dimensional effect and allows the user to read the terrain in an intuitive way. With the advent of digital elevation models (DEMs) analytical relief shading came into a wider use, since it is faster, requires less effort, and delivers reproducible results. In contrast to manual relief shading, however, it often lacks clarity when representing heterogeneous landscapes with diverse landforms. The aim of this work is to evaluate analytical hillshading methods against a set of landforms within an online survey. The responses revealed that the clear sky model performs best applied to most of the landforms included in the survey, in particular all the mountain and valley types. Cluster shading proved to work well for the mountainous and hilly areas but less so in the depiction of valleys. Texture shading and the multidirectional, oblique-weighted (MDOW) method deliver too much detail for most of the landforms presented. Glaciers were depicted in the best way using the aspect tool. For alluvial fans, the standard relief shading with custom lighting direction proved to work best compared to the other methods.
Highlights
To achieve a proper visual look and easy interpretation of maps with manual relief shading, a cartographer is required to skilfully interpret the terrain and to represent it in an artistic way
The survey was designed with the aim of identifying which analytical relief shading methods are efficient with regard to particular landforms
The authors primarily addressed the common lighting approaches such as using one light source with the improved NNW direction, applying several light sources, adjusting the light direction depending on the orientation of the slope, deploying the custom illumination direction to highlight certain terrain features, and illuminating terrain by means of the sky model with the 250 lighting directions
Summary
To achieve a proper visual look and easy interpretation of maps with manual relief shading, a cartographer is required to skilfully interpret the terrain and to represent it in an artistic way. For that reason, shaded relief is nowadays generated mostly automatically, sometimes with further optional enhancements in Photoshop [1] or by rendering using e.g., Blender software combined with Photoshop filters [2], and the goal of cartographers is to transfer manual techniques, which are often superior, into the automated form. With this aim in mind, the authors set up an online survey in an attempt to evaluate the perceived effectiveness of a selection of analytical relief shading methods, which is the respondents’ satisfaction and graphical attractiveness of shaded relief images. In contrast to effectiveness or efficiency of those methods, the graphical attractiveness deals with subjectivity, and it addresses subjective as opposed to objective usability
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