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I am new to GIS and I want to run several view shed analysis operations for wind turbines located in the North of England

I have installed QGIS and have the GRASS r.los plug in installed for line of sight analysis.

Is this the best way of running view shed analysis?

Also, I am unsure about what terrain data to use for this operation?

Thanks in advance for any insight

Note: I am using a Mac with OS X Mavericks

  • you should look for dem data or otherwise vector contour data depending on the size of your project area. – Brad Nesom Aug 8 '14 at 22:37
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You can use QGIS for this analysis but do not confuse line of sight calculations with viewshed analysis. They are related but r.los returns a raster whose values are null for not-visible or the vertical angle required by the view to see the location. The module r.viewshed on the other hand returns a raster that simply marks a cell as visible or not (1 or 0). The advantage of r.viewshed is that, if you have multiple turbines, you can calculate the visibility for each turbine and then simply add all your rasters together and that will give you the number of turbine tips (or hubs depending on the 'observer' height you use) that can be seen at any given location.

BUT be careful! Remember that you are effectively doing things backwards if your 'observer' point is a turbine location. So you must set the target elevation to a normal viewer height (1.75m is a good value, though a value of 2m is often applied). The observer height is then set to the turbine tip height.

You need a decent DEM and I would recommend a resolution of 50m or better (50m is the minimum resolution permissible in the UK - you don't sday where you are based but if it is the UK then I reccomend the OS Terrain50 data set). SRTM is really not good enough away from the equator for serious viewshed analysis of planning-application quality (and therefore credibility).

If you have more than a couple of turbines, using GRASS will quickly become tedious due to all the additional steps, unless you script a solution to add them altogether afterwards. Fortunately there are a number of Windfarm packages out there designed to do just this and OpenWind is a free one which is easy to use. See this thread and this one for more discussion on using GRASS with multiple turbines. Also, here is a thread on how to use OpenWind.

  • Thank you for your answer. I am using a mac and open wind is not supported so I will have to stick with QGIS and Grass. I tried downloading OS Terrain 50 but the data was split into numerous folders and I could not work out how to unzip them all and merge them all into one file for QGIS, do you know how I can do this? I only need a DEM for the North West of England. – lilmawi Aug 9 '14 at 12:10
  • You need to recursively unzip the folders and then merge the data. I can tell you how to do it but it is probably better asked as a separate question according to board rules (namely that it is a very different issue). – MappaGnosis Aug 9 '14 at 13:03
  • Ok, i'll create a separate question. Thanks for your answers, they are really helpful! – lilmawi Aug 9 '14 at 17:58
  • Hi @MappaGnosis. As discussed in this question: gis.stackexchange.com/questions/110115/… I am having problems with r.viewshed. As an alternative, I have found this plugin: plugins.qgis.org/plugins/ViewshedAnalysis Do you have any experience with this plug in and do you know if it will offer a good alternative to r.viewshed? Thanks – lilmawi Aug 14 '14 at 13:54

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