ArcGis--how to lower a DEM's Z value along a line

I'm a raw newbie, so please excuse the ignorance.

I'm trying to do the following in ArcGis 10: reduce the Z value of a DEM along a line. My goal is to "etch" a very shallow line into the DEM surface, so I can then hillshade it and see the etched track in 3d. I've been messing around with the Interpolate Shape and Add Surface Information (and other) tools, but can't get the right result.

As I see it, the necessary steps probably include these:

1. Transfer Z information from raster DEM to line. (use Interpolate Shape or Add Surface Info for this?)


2. Subtract from the line's Z value to effect the etching or depression. (Adjust 3D Z for this?)


3. Subtract the difference between DEM raster and line Z-values from the DEM raster. This is, I think, where I'm getting stuck. Not sure which tools are appropriate: Raster Calculator, Raster Math (Minus), Intersect, etc.?


4. Now with "etched" DEM (where Z values have been subtracted along the line), hillshade it.

So basically I'm trying to define a shallow (around 1 meterx1 meter) 3d line and subtract it from the DEM. I'm sure I'm not going about this the right way--any help would be much appreciated. Thanks.

Answer

It would be easier to convert your line directly to raster, and then use spatial analyst tools to modify the DEM

1. Add an attribute to your line shapefiles that defines how mucch elevation should be reduced.



2. Convert the line to raster, using your new attribute as the value. In the Environment Settings set extent, and snap raster to match your DTM. Set the resolution to match your DTM.


3. Use Reclassify Raster to set the NoData value of your line raster to 0.


4. Use the minus tool with the DTM and Lines rasters an input, This will reduce the height of the DTM.