topic Viewshed function does not seem to use vertices from polyline as documented in ArcGIS Spatial Analyst Questions

Viewshed function does not seem to use vertices from polyline as documented

WillemTims — Sun, 27 Apr 2014 16:43:21 GMT

I'm having some problems with the viewshed function in ArcGIS 10.1 and 10.2. According to the tool description and help file, it uses both nodes and vertices as observer points: http://resources.arcgis.com/en/help/main/10.1/index.html#//009z000000v8000000

In the output I got, I have the strong feeling only nodes are being used as observer points. To illustrate this I attached the result that I got (the viewshed was run for the selected polyline). Am I misunderstanding the help, am I not using the correct settings, or is this a bug in the software?

Thanks already for your kind help!

[ATTACH=CONFIG]33392[/ATTACH]

Re: Viewshed function does not seem to use vertices from polyline as documented

WillemTims — Mon, 28 Apr 2014 13:20:39 GMT

Hi all,

As a test I took the same polyline, and densified it with nodes at every 500 meter using the densify tool. The result looks much more like what I expected. I attached an image of the result. The question remains however why the viewshed tool does not use vertices as observer points like documented. Is the documentation wrong (already since version 9.1), or am I not using the correct settings or input data?

I hope someone can shed a view on this :cool:

[ATTACH=CONFIG]33414[/ATTACH]

Re: Viewshed function does not seem to use vertices from polyline as documented

XuguangWang — Mon, 28 Apr 2014 16:23:35 GMT

The nodes and vertices are all used in viewshed computation. This is illustrated in your second test case above. When you densify the line, you inserted more vertices and changed the viewshed output. This means that the vertices are used.

Re: Viewshed function does not seem to use vertices from polyline as documented

WillemTims — Mon, 28 Apr 2014 16:40:36 GMT

You are absolutely right, I mixed up terminology 😞

So densifying a polyline that contains very few vertices is probably the best solution to improve the viewshed?

Re: Viewshed function does not seem to use vertices from polyline as documented

XuguangWang — Mon, 28 Apr 2014 18:01:18 GMT

I would say it depends on your application or goal of the viewshed analysis. Densification inserts more vertices / observers to your analysis at a regular distance.