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Changing the Light Azimuth in Shaded Relief Representation by Clustering Aspect


Manual shading, traditionally produced manually by specifically trained cartographers, is still considered superior to automatic methods, particularly for mountainous landscapes. However, manual shading is time-consuming and its results depend on the cartographer and as such difficult to replicate consistently. For this reason there is a need to create an automatic method to standardize its results. A crucial aspect of manual shading is the continuous change of light direction (azimuth) and angle (zenith) in order to better highlight discrete landforms. Automatic hillshading algorithms, widely available in many geographic information systems (GIS) applications, do not provide this feature. This may cause the resulting shaded relief to appear flat in some areas, particularly in areas where the light source is parallel to the mountain ridge. In this work we present a GIS tool to enhance the visual quality of hillshading. We developed a technique based on clustering aspect to provide a seamless change of lighting throughout the scene. We also provide tools to change the light zenith according to either elevation or slope. This way the cartographer has more room for customizing the shaded relief representation. Moreover, the method is completely automatic and this guarantees consistent and reproducible results. This method has been embedded into an ArcGIS toolbox.



The toolbox is available from the following link: Cluster Shading Toolbox

The toolbox was developed and tested on ArcGIS 10.0 SP1.
To install the toolbox you can follow these instructions:

This tool creates several temporary files that are needed to finish the process, it computes aspect and slope for example.
The toolbox is programmed to save each temporary file into the local folder: “C:/temp”
Therefore, please be sure that you create a folder named “temp” in your local hard disk.