Rendering Mass with a Structuring Framework

To effectively communicate the form of terrain, a number of visual cues need to be rendered so our brain can construct an internal representation from the image presented to our retina. The aim of the Blue Mountains Revealed project was to achieve this through balancing clarity of depiction with an illustrative/cartographic aesthetic. This post will illustrate the separate cue layers that go into the final rendered Blue Mountains tileset. For a boarder review of relief depictions techniques please see Whelan (2011) or refer to Cartographic Relief Depiction, by Eduard Imhof.

The rendered tileset uses a combination of mass (continuous shading) and line to suggest and delineate features. Surface altitude and slope, both object-based visual cues are represented through a continuous tonal shade whilst a view-dependent line-set is created from detecting edges in a specially rendered z-buffer (described in an earlier post).

Frontal breaks of slope are suggested by the continuous shading of terrain slope, whereas rear-facing breaks of slope are highlighted through the linear cues.  A hypsometric weighting orders the surface into a visual hierarchy. No interpolation across the shaded areas was applied and, as previously mentioned, the low resolution data patches have had an impact on the slope rendering. These artefacts in slope can be seen in Fig 6. The various layers are shown below along with a combination of the slope and the linear framework.

 

Refs:

Imhof, E. (H. J. Steward (Ed)), 1982, Cartographic Relief Representation, Walter de Gruyter

Whelan J. C., 2011, Web-based Vector Terrain Exploration, Proceedings of SVG Open 2011, Cambridge MA