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Viewshed Analysis along Route

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Jason JB

Jason JB


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Hi there,

I'm currently working on a potential railway route and would like to do a viewshed analysis along the rail route.
Has anyone had any experience on how to do this? I have not done this type of analysis before so any ideas on how
I could come up with a useful output for Visual Impact Assessment would be really helpful. I am using ArcGIS and
I know of the viewshed tool.




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Do you want a viewshed analysis or some fly through over the route? A fly through would give you an overview of the route or you can generate an overview as you go along the route. There are free tools like 3DEM which can generate crude fly throughs. If you want to improve upon that then you may need Leica Photosuite or similar Photogrammetry software to generate realistic fly bys.




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I have done visual impact assessments for planned high voltage power lines using the viewshed tool. basically it will calculate the viewshed for every point if you have a point feature layer or every node if you have a polyline feature layer. a couple of attributes can be given in the attribute table (like point offset from DEM and observer offset from DEM).
if you have n points/nodes you get a grid with values from 0 to n. this gives you the number of visible point/nodes for every grid cell.One major backdraw is that no partial visibility is used. even if only the top inch of your point would be visible, the grid cell says "yeah, i can see that point". i am implementing partial visibility using GRASS as we speak but it's going slow as there are more urgent projects.

For the power line we calculated single viewsheds for every point (using ArcObjects to iterate over each point) and multiplied them with a (weighted) distance grid for the point. this was a nice approach which i hope to refine once i have partial visibility.

So all (well, most of) the tools are available in ArcGIS, but depending on what you want to do, some scripting in ArcObjects is needed.

Crischan Wygoda

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