Multidirectional Visibility Index for Analytical Shading Enhancement

Abstract

A novel method called multidirectional visibility index (MVI) has been developed and verified. The MVI improves standard cartographic analytical shading with a number of enhancements to topographic detail and prominent structures, i.e. the portrayal of flat areas in lighter tones, the accentuation of morphologic edges, and the multiscale visualisation of morphologic terrain features. The procedure requires a digital elevation model (DEM) and involves the following steps: visibility mask computation; the respective multidirectional altering of the azimuth and elevation angle; the generation of continuous grid MVIs that indicate upper/lower views, quasi-slope, and relative relief; and an appropriate visualisation of the relevant MVI as a standalone technique or in combination with standard hill-shaded relief. The modelling parameters are robust and therefore highly adaptive to different landforms.Analytical shading is a computer-based method for the visualisation of landforms. It enables a rapid and accurate perception of shapes, structures and proportions of terrain on topographic and thematic maps. Analytical shading methods are increasingly complex, utilizing local or global illumination (and reflectance) models, with the support of various techniques to enhance the topographic details (graphical improvements).A cartographic visualisation requires standard topographical rules for landform representation as part of an appropriate abstraction of reality (Imhof, 1982). The plasticity and comprehension of three-dimensional landforms by visualisations in two-dimensional cartography can be efficiently demonstrated using manual -or hand-shading methods. Wiechel (1878) developed a mathematical shading methodology that used oblique illumination of a diffusely reflecting surface for terrain elevations. Analytical shading, i.e. the technique adapted to digital computers, was introduced by Yoëli (1967b), who applied a diffuse reflection illumination model to a digital elevation model (DEM). Brassel (1974) suggested and applied various computational and graphic procedures -enhancements that were intended to imitate the complex hand-shading processes. Many methods based on analytical shading have been developed to implement the various styles of landform visualisation (

General sky models for illuminating terrains

“…These methods, however, require expert cartographic knowledge of how variations in shades of gray of secondary landforms will work in concert with the overall hill-shading effect. Podobnikar (2012) achieves interesting and striking effects with visibility masks, but this method does not directly relate to illumination principles. Another method uses variations in luminosity based on aspect direction (Kennelly and Kimerling, 2004), but this is only possible for certain color combinations and bases colors on maximizing variations in luminosity.…”

Detecting Mountain Peaks and Delineating Their Shapes Using Digital Elevation Models, Remote Sensing and Geographic Information Systems Using Autometric Methodological Procedures

“…The possible applications of this research are numerous, for example (some of which have already been applied): to improve DEM production [22]; the comprehensive quality control of DEMs; enhanced automatic generalization of DEM [44]; landscape classification; an increased knowledge of multi-scale morphology [45], applicable to geological and tectonic studies; karst research; generic prominence analysis [46,47]; silhouette generation; the improved cartographic presentation of terrain [8]; examining anthropogenic influences on the landscape morphology; and ethnophysiographic, sociolinguistic, cognitive psychologic, psycholinguistic, or ergonomic [11] studies.…”

“…An image processing technique of multidirectional visibility index (MVI) [8] shows another aspect in appearance of peaks and other terrain features (a composition of series of 57 photograph visibility masks between 6:30 AM and 17:15 PM (GMT+1), 26 September; view from Kredarica to peak Tosc; webcam of ARSO).…”

“…A mountain can be defined as a natural rise in the Earth's surface that usually has a peak (or a summit) [8]. Similarly, the term mountain is defined as a landform that sufficiently extends above the surrounding terrain over a limited area with comparatively steep sides and a peak.…”

“…The following innovative variables have been derived (see Table 4 [5]) One of the most applicable variables that was developed is a relative relief based on a "multidirectional visibility index" (MVI). It is based on a visibility masks calculation with regard to the variations in azimuths and zenith angles [8]. The catchment analysis (CA) is based on a calculation of cost surfaces around the peaks.…”