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ZTV Module

ZTV is a multi-target visibility analysing program that assesses the impact of visual barriers within the landscape. It produces a colour map in plan view where the target object(s) can be seen from within a given radius, for example, 10 km from the targets.

Zones of Theoretical Visibility (ZTV)

The number of Environmental Consultants and Landscape Practices using ZTV has grown considerably in recent years as the need to produce evidence regarding the locating of structures and developments has increased. Having been at the forefront of ZTV software development for many years the KeyTERRA-FIRMA 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.

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 in an easy-to-understand format. The simplest form is to have a background colour overlaid on areas where an observer would be able to see the development. Better presentations might show different shades of colour depending on the extent of the development visible from various viewpoints. Sometimes the result may need to show the areas of invisibility with the depth of the shadow the observer is under at a given location.

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

Over or under the horizon?

In instances where the target of the ZTV is a tall structure, it may be necessary to know how its 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 may partially blend into the background. The ZTV module has tools to interrogate those conditions. As part of the Vertical Field of View analysis, ZTV can produce a model highlighting whether the structure is above or below the horizon from the observer’s point of or what the vertical viewing angle is between the top of the structure to the horizon. The output is a gradient colour map.

Horizontal field of view highlights how much the visible ZTV target obscures the observer’s view. This is measured as an angle between the leftmost visible target point to the rightmost visible target point and is presented in degrees. Vertical field of view analyses produce a similar output in a vertical plane, calculating the angle between the lowest and highest visible target points

Shadow flicker

With ZTV you can quickly produce a colour map showing the annual exposure to shadow flicker and produce a detailed report based on any number of locations. 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.


If you’d like to see any of our software in action, you can request a personalised demo or try it for yourself with a 30-day trial.

Our experts are on hand to answer any of your queries so feel free to get in touch, we’re here for you.

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