Line of sight

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Line of sight

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Line of sight computations provide point-to-point information on visibility by means of: (a) mapped lines ― variable coloring of a line drawn on the map between the source and target points; (b) tabulated data for the selected transect; and (c) profiles. Lines of sight may be computed from a single point to multiple destinations at regular angular intervals, providing a simplified picture of overall visibility from an observation point. However, for a more detailed picture complete viewsheds should be computed.

Using the example provided in Figure 6‑19A (OS TQ81NE tile) can might examine the line of sight from the proposed mobile phone mast in Figure 6‑19B to a sample point on the coast. The result is illustrated in Figure 6‑22, where the source point has an offset of 10m. Locations highlighted in red are not visible from the source or target along this line. Again, as discussed in Section 6.3.1, with telecommunications modeling specific line-of-sight profile analysis tools are required. These include the ability to insert surface clutter such as trees, water areas and buildings, and to observe the effect of these on the signal strength and the Fresnel zones.

Figure 6‑22 Line of sight analysis

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Some modeling packages, such as MATLab, provide a number of functions for line of sight and viewshed computation that can be combined in a variety of ways and displayed as 3D visualizations. This approach has the advantage of flexibility of both display and access to the computational details and results. An example is illustrated in Figure 6‑23, where visible areas are shown in dark blue visible lines of sight in yellow (white) and invisible line profiles in dotted red. The computations are based on an offset from the surface of 20 meters.

Figure 6‑23 Viewsheds and lines of sight on a synthetic (Gaussian) surface

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