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The extraction of topological features from LIDAR DEM data with the application of wireless systems design
III. Topological feature extraction (TOFEX) system
The ultimate goal is to extract terrain features solely from the LIDAR dataset using GIS software. The features would be represented within the software applications as vector polygons which can then be exported as a vector output file. The vector information can be exported to an external data file for various purposes. Various GIS software applications were used in the implementation of the features. The method includes various GIS and image processing techniques including filtering, smoothing, edge detection, vectorisation, and feature enhancing techniques. In Figure 2, features represented in brown, can be seen, superimposed onto a 2D image of the DEM.  Figure 2. Extracted Polygons with height data from LIDAR DEM data The yellow outlines depict the idealised feature outlines from the Ordnance Survey LandLine.Plus vector data. Replication of these vector outlines is the ultimate goal of the TOFEX system. The features can be classified using pattern recognition or mathematical morphology. IV. Wireless communication as an application of the GIS ‘TOFEX’ system Various applications of the extracted features exist. One such application is in the wireless communication systems design. The extracted features can be used in existing microcell ray tracing models and propagation modelling. Work in this project has involved the implementation of a visibility analysis of the DEM data, implementation of LOS and single knife-edge diffraction propagation techniques as depicted in Figure 3.  Figure 3. Signal Strength Minus LOS and diffraction losses
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