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I am new to working with raster data and I am trying to teach myself a few things. I have what I think is a simple problem but I can't seem to figure this one out after a few hours of searching Arc Help etc.

I have raster with ground elevations to which I want to add tree heights. I have a Forest Cover polygon vector layer which has tree heights for my study area. I would like to add the heights of trees to the elevation data.

My first guess was to convert the Forest Cover polygon to a raster based on the tree height field and then Merge/Combine the two rasters?

I have esri's 3d Analyst so I think I would have all the available tools? I am using ArcMap 10.0

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Could you please supply more details such as what the purpose of the analysis is? Is this for cartographic or analytic purposes? –  Aaron Mar 28 at 18:54
Hi Aaron. I am just doing some basic visual analysis using the Line of Sight tool. I am wondering if a certain study area is visible from a few specific viewpoints, however I would like to add tree heights to my raster data to make it slightly more accurate –  ChrisA Mar 28 at 18:59
I'm new to this too but thinking of this logically: you'd have a forest raster. On that raster you would have a point that represents a tree. That tree would have 3 values: x,y would be the lat/long of the tree and z would be the tree height. Now the how to in setting all that is far beyond me. –  SASS_Shooter Mar 28 at 19:02
If I've created a raster which cells are based off of tree heights, and the cells of my two data sets are the same size... is it as easy as adding the two rasters together using the Raster Calculator tool? –  ChrisA Mar 28 at 19:34

1 Answer 1

up vote 4 down vote accepted

you can do this with the raster calculator, but probably not as easy as a sum because you probably have NoData values where there is no forest . In this case, here is a more robust method :

Con(IsNull("converted_polygon"), "DEM", "DEM" + "converted_polygon" )
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+1 nice approach –  Barbarossa Mar 28 at 20:14
Thanks Radouxju. I believe this has worked for me. –  ChrisA Mar 28 at 20:19
Another Approach: Reproject Forest Cover polygons to the same projection as the DEM. Run the reprojected Forest Cover Polygon feature class using the Polygon to Raster tool with the height field and set the cell size to the same as the DEM and set the Environmental Settings in the Polygon to Raster tool - Processing Extent - Snap Raster to your current DEM. Use the Spatial Analyst Plus Tool (Spatial Analyst - Math - Plus) to add the DEM and the Forest Cover Raster together. –  ChrisA Apr 11 at 21:29
@ChrisA be careful that you will have no data where there is no forest, so if you use the plus tool, something + NoData will yield NoData –  radouxju Apr 13 at 9:28
Good point, radouxju. –  ChrisA Apr 25 at 16:35

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