Using GIS to Determine Horizon Belts[2]

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The main tasks of the methodology are listed and annotated as follows: Create a triangulated irregular network (TIN) model and viewshed ridgeline data DEMs are a type of raster data representing terrain as a series of discrete steps, 10 meters squared. TIN models can be derived from DEMs, and are a more realistic representation of terrain with a surface of continuous elevation change. The ArcView 3D Analyst Extension was used to generate a TIN for the town of Kent. Lakes are features of constant elevation and were used as breaklines for refining the TIN model, assigning those areas of the model a constant elevation. Viewshed ridgelines were derived from the boundaries delineated in the subbasins data, after eliminating subbasin boundaries that do not correspond with topographically distinct ridges. Some topographically distinct ridges not corresponding to a subbasin boundary were manually added. Create the road viewpoints file The road viewpoints were obtained from public roads in the town of Kent. Viewpoints were chosen that corresponded to intersections of these road segments with other roads, the town boundary, subbasin boundaries (an indicator of high points along the road), or known vistas (Figure 1). The viewpoints were converted to a 3D file, with the elevation derived from the TIN model, and a target offset (OffsetB) value of 35 feet was assigned as an attribute to each viewpoint.
Figure 1: Viewshed analysis for Carter Road, Kent, Connecticut. A. Carter Road viewpoints were chose from intersections with other roads, basin boundaries, or known vistas. B. Ridge viewpoints were chosen from along the edge of the viewshed analysis, and corresponded with high points along the edge, or at viewshed junctions. A digital elevation model (DEM) is used for the display. Run a road viewshed analysis The target offset value of 35 feet corresponds to current zoning regulations for the town of Kent. The viewshed analysis used the TIN model to calculate the areas of the landscape where a 35 foot structure would be visible to at least one of the selected viewpoints. The output of a viewshed analysis is a raster grid, with each discrete cell of the grid given the value of how many viewpoints are visible to that cell. The grid was reclassified to indicate whether a cell was visible to any (value = 1) or none (value = 0) of the viewpoints (Figure 1).
Page 1 and 2: USING GIS TO DELINEATE HORIZON BELT
Page 3: The challenge to be met by the new
Page 7 and 8: Figure 2: Horizon belt northwest of
Page 9 and 10: Results All the public roads in the
Page 11 and 12: Concave ridges pose a problem for t
Page 13 and 14: or slope gradient requirements for
Page 15: ewarding view, while hidden or camo

Using GIS to Determine Horizon Belts[2]

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