Zones of Theoretical Visibility

The number of Environmental Consultants and Landscape Practices using KeyTERRA-FIRMA for Zones of Visual Impact Analysis has grown considerably in recent years as the need to produce evidence regarding the locating of environmentally sensitive structures and developments has increased. Having been at the forefront of ZTV software development for many years the KTF ZTV module now includes Field of View output to illustrate the impact on the receptor's field of view (e.g. the angle within the view containing targets from left to right hand extents) and Shadow Flicker analysis for individual wind turbines.

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    • Environmental Impact Assessment (EIA)

      The UK and European EIA directives and environmental regulations state that the impact of a development on the visual aspects of a landscape should be assessed. Part of this assessment is to present an OS map base with zones on the map showing visual impact as easy to understand manner. Simplest form would be to have a background colour overlaid on areas where an observer can see the development. Better presentations might show different shades of colour depending on the extent of the development visible on the areas. Sometimes the result may need to show the areas of invisibility with the depth of the shadow the observer is under at locations.

      More advanced outputs might include Field of View to the development from surrounding area, either horizonally, vertically or both. And in some occations where wind turbines are constructed near buildings a Shadow Flicker assessment may be needed.

    • KTF ZTV module

      KTF's ZTV is a multi-target visibility analysing program that recognizes visual barriers within surrounding landscape. It produces a colour map showing in plan view where the target object(s) can be seen from within a given radius, say, 10 km from the targets. It also can compute the shadow areas, field of view and shadow flicker assessments.

      We started developing this module back in 1998 with much appriciated assistance from David Watson, a chartered landscape architect with extensive experience in landscape and visual impact assessment.

      Image on right shows the areas where a stucture is visible (purple) and invisible (green) to an observer. Hovering a mouse over the image exposes further details and you see in lighter shades of purple where only part of the target is visible and in darker greens where observer would need to "jump higher" in order to see the structure.

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    • Over or under the horizon?

      Especially when the target of the ZTV is a tall structure it might be interesting to know how it's visibility relates to the horizon. Seeing a structure against a clear blue sky can make it more visible compared to when the structure can be seen but it is fully below the horizon and hence it may partially blend into the background. KTF ZTV has tools to expose those conditions. As part of the Vertical Field of View analysis KTF can produce a model telling not only if the structure is above or below the horizon from the observer's point of view but also what is the vertical viewing angle between the top of the structure to the horizon enabling to produce a gradient colour map of this effect (see images on right).

      Horizontal field of view tells how much the visible ZTV targets cover the observer's view. This is measured as an angle between the leftmost visible target point to the rightmost visible target point and it is presented in degrees. Vertical field of view analyses similar angle but vertically, telling the angle between the lowest and highest visible target points - note that this is slightly different from the over/under the horizon result depicted above.

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    • Shadow flicker

      Shadow flickering effect is caused when rotating wind turbine blades periodically cast shadows over neighbouring properties as they turn, through constrained openings such as windows. This can cause discomfort to people living or working in building nearby a wind turbine. The effect are measured by hours per one calendar year and minutes per one day.

      With KTF you can produce a colour map showing the annual exposure to this effect (see image on right) and a detailed report of any number of locations can also be generated. The report summarises the annual and daily maximum minutes with an optional schedule of dates and times when the shadow flicker is expected to occur at each location.

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KeyTERRA-FIRMA Ltd., Henley-in-Arden, Warwickshire, England 01978 225497