viewshed problems

2008
3
08-16-2012 03:45 PM
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by Anonymous User
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Original User: schuster_sara

Hello-

I am trying to figure out what is visible to an animal at a given point. Using a handful of points, I used the viewshed function. Everything seemed normal. (shown below on "viewshed jpg" with light green as the visible areas) I am only interested in a 500m radius around the point though, so I created a  buffer around the point.  I tried using the Clip Raster by Polygons feature under Hawth's tools. During this operation, 16 small rasters were created of varying colors. Not quite sure why they are different colors, but I will go with it. Here is the weird part: some of the rasters have bands in the middle of the circle, making it appear to have an error. The missing bands are of different sizes, and don't seem to have a rhyme or reason. I attached a jpg of that too.

Any thoughts/suggestions are welcome. Thanks!
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3 Replies
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by Anonymous User
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Original User: jbswain

I am not sure if Hawth's tools created the issue or not, but since it is not present in the original that would be my guess.  In terms of moving forward, if you are only interested in the 500 meters around the point, why not limit the viewshed to that radius for each point using the RADIUS2 field in your point file?  I think that may get you to the desired output. Also I would consider the Clip tool from ArcMap, not the equivalent in Hawth's, if you want to use Spatial Analyst then there is the Extract by Mask tool.
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New Contributor
Thank you so much for the advice! It worked beautifully. I do have another question though, since we have 800+ points per animal is it possible to run the viewshed function once and get accurate results? Does it calculate line by line? We are worried that by running all the points together there will be overlapping results, making it look like animal A and animal B can see the same areas, even though they really could not. However picking out 10 points at a time would be very time consuming.

Thanks for your help!
sara
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by Anonymous User
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Original User: ad_giles@hotmail.com

Sara,

If you run all points at the same time your results would be confusing as you would get areas that are seen by either none, one, two, three.... observers but you don't know which observer can necessarily see what areas.

You are better off using the iterate tool in model builder to run through your feature class and create individual viewsheds for each point, have a look at this thread:

http://forums.arcgis.com/threads/33707-Multiple-Single-Observer-Viewsheds

Regards

Anthony
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