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It does not show the effect of terrain that may block light from the sun. The illumination behavior model has significant differences from hillshading in Spatial Analyst, though with both there is a slight amount of shading that is independent of the sun.Ī major difference between these two methods of giving a hillshading effect is that illumination does not generate shadows. The process used in 3D Analyst to give the effect of hillshading is called illuminating faces. Lowering the sun's position darkens the colors in a hillshaded image. Thus the user may end up with hillshade colors that are vastly lighter and/or darker than those specified with the Legend Editor for the grid theme. Brightness settings can take complete control of the value portion of a color.
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The sun's altitude setting also has an effect on overall theme brightness, but this effect is very slight. The amount of this adjustment is controlled by the minimum and maximum cell brightness settings that can be modified using the Advanced Options menu in the Legend Editor. Shaded relief in a hillshade is constructed by adjusting the value component of a grid theme's cell colors in proportion to the values of the related brightness theme cells. Grayscale values range from 255 for white to 0 for black with gray making up the middle values. In terms of the hue, saturation, and value (HSV) color model, grayscale colors have a hue of 0 and a saturation of 0. Regardless of the colors applied to the hillshade theme, when a hillshade is used as a brightness theme for another theme to produce a relief map, the hillshade is applied with grayscale values. The shadow direction is affected by the sun's azimuth setting and shadow length is affected by the altitude component. The shadowing effect of adjacent terrain is also used in generating a hillshade. Hillshading in Spatial Analyst results from the program evaluating the aspect and slope of the terrain relative to the sun's azimuth (the sun's location on the horizon) and sun's altitude (the sun elevation above the horizon). However, these models appear to adequately serve as a framework for describing both the problems encountered and the solutions suggested.
HILL SHADED DIGITAL TERRAIN MODEL CODE
The following discussion is based on observations made while using these two extensions rather than any knowledge of the theory behind the development of these extensions or the code used to produce them.
HILL SHADED DIGITAL TERRAIN MODEL HOW TO
To understand how to best use these solutions, it is desirable to understand a little about how Spatial Analyst and 3D Analyst work with light. ShadeMax provides some solutions to this problem. It can be difficult to match the colors generated using the hillshade feature in Spatial Analyst with a representation of the same area displayed in 3D Analyst without introducing undesirable visual effects. Matching Color in Spatial Analyst and 3D Analyst Using seemingly continuous color versus discrete color sets for portraying elevation noticeably enhanced the visual effect. This test palette, SM08vermonter.avp, became the first component of the ShadeMax color set. In early 1998 the author developed a test palette of 48 light, closely spaced colors that was initially tested at the Vermont Agency of Transportation with very acceptable results. The core concept that led to the development of ShadeMax is that elevation is continuous data and can best be portrayed with a color set that gives at least the illusion of a continuous change in color as elevation changes. These ramps are discrete color sets with very noticeable color demarcations. The standard method for coloring shaded relief in Spatial Analyst and 3D Analyst has been to use one of the color ramps that come with ArcView GIS such as Elevation #1. The source data included 12 7.5-minute, 30-meter DEMs downloaded from the United States Geological Survey Web site. Unless otherwise noted, the accompanying illustrations show the Mt. This article describes how and why ShadeMax was developed and gives some tips on using its components.
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ShadeMax is available at no charge from the ArcScripts pages of the Esri Web site. The ShadeMax palette gives the illusion of a continuous change in color. The default elevation color ramps produce noticeable banding. While primarily created to portray elevation for maps created from digital elevation model (DEM) data, concepts used in its development can be applied to any mapping situation that uses ArcView Spatial Analyst or ArcView 3D Analyst with continuous data. These palettes can be customized to meet individual terrain mapping needs. The ShadeMax Color System is a set of color palettes and legends that significantly enhance shaded relief maps produced with the ArcView Spatial Analyst and ArcView 3D Analyst extensions to ArcView GIS. New Color System Enhances Relief Maps By Jim Mossman, Data Deja View