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Proportion of View

06-11-2013 03:32 PM
New Contributor II
Hi all,

Ive come across a problem thats left me scratching my head. Im conducting some analysis which looks at the amount of forested areas that can be seen from hundreds of observer points. In the first instance I ran viewsheds through arcpy and got the total land area of visible forested areas. Cool. But now I need to calculate a measure of the proportion of view that is forested areas. In other words I want to be able to represent (through a value) what someone would be seeing if they were standing at the observer point. It is different to the viewshed as the angle of the visible target relative to the observer needs to be known. For example a forest growing on a cliff side (extreme example I know) would take up a higher proportion of the total viewing angle than forest on a slight slope. 

In the example below (assuming all visible areas were forested) the observer would have ~100 degrees of visible forest. If only the larger hill was forested they would only have ~30 degrees of visible forest.


Keep in mind that this sketch is 2D. The viewer can also see 360 degrees laterally and 360 degrees vertically (could be standing on the top of a hill.)

Does anyone know of any tools that would be able to calculate this?
Sorry if this explanation is a bit rough, let me know if you have any questions. I am comfortable with arcpy and python with access to arcpy 10 and 10.1.

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Regular Contributor II
You might use the Viewshed output to Extract by Mask the visable parts of the landcover raster.
You may want to set the 0 values in the Viewshed output to Null first,
so only the visable parts of the extracted landcover raster have data.
Then the propotions are pretty easy to find.
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