# How to calculate the Zone of Impact using OpenWind

After downloading OpenWind, I am trying to calculate the ZVI for a single Turbine. There is no documention regarding this from the developers.

At this point I just want to compare the output of the visibilty analysis i.e the Viewshed.

I have loaded my DGM and defined it as my Elevation layer with Properties>Interpretation>Terrain Elevation.

I have a point shapefile which contains a single location for a turbine. And this is where I get lost. How do I define the turbine specifications and let the software know that the point is the turbine location?

Thanks for any pointers,

yours,

Robert

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For the benefit of less familiar readers: ZVI = Zones of Visual Influence. The term ZTV (Zones of Theoretical Visibility) is becoming more common. In either case it refers to a map of the areas from which something (wind turbines in this case) can be seen. The basic calculation uses a 'bald earth' DEM, but is often supplemented by calculations accounting for obstacles such as trees and buildings in particular. –  MappaGnosis May 14 '12 at 9:09

The turbine specifications are controlled by the turbine types dialog box. If you want to preserve the existing turbines, create a new one (Settings->Turbine Types->New). Use the dialog box that pops up here to set your rotor and hub height.

You can add turbines to your layout in a couple of ways:

1. Manually - add a layer by right-clicking in the TOC pane and selecting 'New Layer->Turbine Layout'. Make the layer editable by selecting your new layerr and clicking on the Edit button (squiggly line + arrow icon to the right of the info button). The point and click in the main main window to add turbines.
2. Using an existing point shapefile: File->Open Vector Layer and then right click on the point layer in TOC and choose to 'Turbine Layout' in the pop up menu. This will make a Site Layout layer (in addition to your original point layer, but it uses the point layer to create the turbine locations.

In either case, once you have the locations, double click on your Site Layout layer and you can then either set all the turbines in one go (using the Set All Turbines button on the Site tab) or set turbine specifications individually (using the Turbines tab and iterating over them).

To calculate the ZVI (ZTV), right click on your DEM layer and select Properties. Go to the 'Interpretation' tab and select 'Terrain Elevation' from the 'To be Interpreted As' drop down dialog and check the units are correct. Now make the Site Layout a child of the Terrain (drag and drop it on top). Next go to Operations->Calculate ZVI. If the Site layout is not parented to the DEM your ZVI will show all turbines visible everywhere.

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Thanks. I have done as you explained, but it produces a layer containing one colour with the attribute "1". I set the Turbine tyle in the site layer to Evercon 44 to test. (as this is the shortest Turbine). Under Environmental parameters there is the "site Altitude". Usually this is read from the Elevation model...I have also entered a base height here...but the results are the same...a raster layer with only one attribute - "1". What could I be doing wrong? –  Robert Buckley May 14 '12 at 9:35
I think I figured this out...the site layer needs to be a child of the elevation layer. Now I am getting a better visual result! –  Robert Buckley May 14 '12 at 9:40
I edited my reply above. Note the last paragraph. Parenting the site layer to the DEM is crucial. –  MappaGnosis May 14 '12 at 9:49