Standard techniques for representing the terrain, such as shading, are sufficient for many applications, but with Terrain Tools you can represent the terrain under different lighting conditions, or use more artistic techniques. This set of tools complete or extend what you find in the default software. These techniques are often difficult to find or to put into work. The Terrain Tools project brings together some of these ideas in a toolkit which provides the features to create alternative representations of the terrain with ArcGIS.
The Terrain Tools are included in a toolbox to be used either with ArcGIS Desktop 10.3 or ArcGIS Pro 1.0.
To download Terrain Tools, follow this link: https://www.arcgis.com/home/item.html?id=4b2ea7c5f87d476a8849c804b81667aa Once installed, the toolbox contains the following tools:
Here is a short explanation of each tool.
Multidirectional oblique weighted Shading (MDOW)
This technique applies an oblique lighting on all surfaces by using four light sources unlike classical shading where only one is used. It allows to highlight more details. Once the four different shadings are created (one per light source) they are mathematically weighted and added to create the final shading.
This style of shading combines many types of shading in one output with yellow- blue tones. Grey shading (as those created by the Default shading tool) is combined with yellow lively shading on the slopes sunny and blue-grey tones in less bright areas. Blue simulates atmospheric haze and provides the possibility of blue pale shadows to colour the valleys, flat terrains and uneven regions. Colour yellow gives the impression of warmer colours in the sunny slopes.
The Swiss shading model combines a set of tools by chaining them. From the MNT original two new layers are created (one for blues, the other for yellows). The original DTM and the two new rasters are then combined to create the final shading.
Shading by segmentation (hillshade cluster)
Most shading techniques fail to reproduce local variations. For example, shading can generate areas without slight differences, especially when the light source is parallel to the mountain peaks.
The shading by segmentation technique ensures that slight differences in shading throughout the scene are obvious.
Clustering is a technique that allows the division of a data set into homogeneous subsets. The objective is to create subsets of a variable that are most similar within the subset and, at the same time, the most different possible between subsets.
The classic algorithm to solve this problem, sometimes called k- means method, is very much used and is considered to be effective although does not guarantee optimality, nor a limited calculation time.
The process starts at random by selecting a series of centroids and assigns each element of the data set to the nearest gravity centre. Then, by successive iterations, recalculates the centroids and reallocates the cluster members, until the degree of similarity is maximal within clusters and minimum among them. You will find a suite of three tools that uses the k- mean method to create a continuous change of local lighting conditions and produces a final shading: the original classic method, a modification of this method for heights, and another modification for the slope.
Classic segmentation shading
This is the original method described above. Its problem is that does not put in evidence the terrain structures considered less important, such as valleys.
Modified segmentation shading for heights In both additional methods, the light is placed perpendicular to the terrain, resulting in darker areas when the slope is steep while illuminating the valleys and mountainous ridges. The modified method for the heights emphasizes the lighting changes with altitude. The modified method for slopes emphasizes the slope as the element to be illuminated. These are changes to the segmentation method by default and transform the weight of elevation and. Weights are used to continuously correct the values of Zenith in the landscape . The results give white brilliant tones for the valleys. The modified method for heights gives tones gradually darker with increased altitude what improves the sharpness of the peaks.
Modified segmentation shading for slopes The modified segmentation technique for slopes results, also, in white bright tones for valleys and channels and darker tones for steep slopes such as rocky bassets.
All the shading models we have discussed up till now use, only, one lighting source to derive a final shading by combination of a certain number of shading intermediaries.
But in reality the light does not illuminate the world this way. Illumination takes place from every angle, but with varying intensity and under different atmospheric conditions. A landscape will be different on a sunny day or a cloudy day. Likewise it will be different in the early morning or late afternoon versus midday when the sun is perpendicular.
This method uses an external program ( SkyLuminance.exe) , supplied with the Terrain Tools, to calculate a file with the lighting parameters. The program builds a dome with a very large number of lighting sources:
The result of this method will depend on the number of light sources and the type of lighting (clear sky, cloudy , etc. ) The following image shows the result with 200 lighting points per sky covered:
This method creates and symbolizes the contours with a “traditional” dotted symbol while changing the overall appearance by removing contours for surfaces with slopes of less than 5 °
This tool creates contours by generating a layer of polygons where the space between the isolines is colour filled.
Illuminated contours (Tanaka)
This method applies a north-west light source to a contour map. The result is a 3D style representation of the terrain. The method involves changing the width and colour of the contour lines based on their position relative to the light source: The contour lines that face the light source are drawn white while those found in the shadow are traced in black; the lines perpendicular to the light source are drawn thinner than the parallels. In summary, this method gives a very realistic shadow effect to terrain maps and allows the viewer to better understand the features of the landscape.
A classic cartographic technique to represent the topography in three dimensions on a map is the use of hatching. Hatching is drawn following the direction of the steepest slope. Hatching a territory creates tonal variations on the whole map. These tonal variations are a shading technique to represent the topography in three dimensions.
The tool generates a layer of dots that are represented by a hatched symbol. The symbol is given a size proportional to the slope and oriented according to it. The problem of this method is that the generation of the layer of points is done with a default scale of 1:36 000. If you want to represent a territory with a different scale, it gets very complicated to adapt the result in order to get a correct representation. In any event, the Terrain Toolbox method only applies for scales between 1:10 000 and 1: 150 000.
This type of hatching is an artistic drawing method that uses lines of varying thickness and orientation to produce shading variations. Two light sources (azimuths 315 and 360) are applied with angles of incidence between 5 and 30 ° above the horizon line. For each of them the schema lines are calculated as follows:
The thickness of the lines produced depends on the number of inclinations “in the shade”. The result is the following:
Chroma Stereoscopic Colors
A technique that codes the elevation values in colours which viewed through special glasses, gives a 3D holographic view of the data.
3D choropleths This method is not used for field data, but is useful to give “relief” to layers of polygons, usually statistics, creating a shadow scope proportional to a value.