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Hi!
I have a problem using viewshed. Im doing analysis of where tower is visible and where not. I have done viewshed analysis of my data (DEM, towerpoints), I have calculated OFFSETA, OFFSETB, RADIUS...) I have also a shapefile, that consists of forest area. My problem is, how I can insert forest elevation to my viewshed analysis? In this analysis average height of forest should be 15m, so I have to add that information to viewshed, because that take effect in visibility analysis.
So, how i can merge (or do i have to merge) DEM and forest shapefile into one and run that new file in viewshed?
Is there some other way, that I can add that information (forest area 15m height) in my analysis?
Tomas,
There a number of forums that discuss this, but I can outline it for you. First, I will assume your forest polygons have an attribute field for height. Given this, when you convert the polygons to raster you need to specify the height field to use as the value field during the conversion. You need to set the extent of output to be equal to your DEM, and at the same resolution. This will result in a raster that covers the entire DEM area, and is made up of data (where you had polygons) and nodata pixels (no polygon data). Next you want to add the tree height raster to the DEM, and where you have no tree height data you want to return the original DEM value. You do this will map algebra. This syntax is old (pre 10) because I copied it from another forum where I posted in but the concept is here for you.
[newsurface] = CON(ISNULL([treeheight]),[dem],[dem] + [treeheight])
Once you have the surface that incorporates the tree's you will have to rerun Viewshed.
Regards,
Eric
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You do this will map algebra. This syntax is old (pre 10) because I copied it from another forum where I posted in but the concept is here for you.
[newsurface] = CON(ISNULL([treeheight]),[dem],[dem] + [treeheight])
Once you have the surface that incorporates the tree's you will have to rerun Viewshed.
Regards,
Eric
The treeraster in this example is created from polygons that have an attribute of height (such as 15 m) and have been converted to raster using that attribute for the value field. This would result in a raster that has pixels with a value of 15 underneath the polygon, but NoData where you have no polygons.
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