Reduce Z values from DEM along a line

10-25-2013 07:58 AM
New Contributor
Hi--extreme newbie here, so please pardon the ignorance.

I'm trying to subtract from Z values from a DEM along a line.  The idea is to "etch" a line of depression into the DEM layer, so that I can then hillshade it and see the depressed line in 3d.  I've used the Interpolate Shape tool to capture the Z values of the DEM along the line.  But I just don't know enough to see how to subtract a certain depth and width along that line from the original DEM.  I'd like to depress the DEM along the line by a very small amount, less than a meter if possible, and by maybe a meter wide, just to leave the trace of the track.

Of course I may be going about it entirely wrongly!  Any help would be much appreciated.
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Esri Contributor

For this you would need the Spatial Analyst extension. What you do is convert your line to raster with the Polyline to raster tool, set the same cellsize and extent as your DEM. Then use the Raster Calculator tool and enter an expression like this:

Con("line"==1, "DEM" - 1, "DEM")

The '-1' part is where you set how much you want to depress your DEM, expressed in the unit of you coordinate system. If you want a wider depression the easiest way would be to buffer your line first.
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