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Smoothing hillshades that contain lots of details

August 19 2008 | 1 comment
Categories: Data Modeling, Map Data, Symbology

How do you smooth hillshades that contain a lot of details (see attached image)? I’ve followed the instructions given on the Mapping Center to smooth hillshades, but it didn’t seem to work for me. I still get a lot of lines/noises on lower elevation surfaces. How can I get that smooth surface without all the details so that I can use it as a backdrop for my map? Thanks a lot for your help!

Mapping Center Answer:

This looks like a case of using DEM data that is in geographic coordinates but the elevation values are in meters or feet. In these situations, you need to use the Z factor option to essentially make the elevations values the same as your x and y coordinates (which would be in degrees). There is a blog entry called "Setting the Z Factor Parameter Correctly" that will help you.

Filter your DTM posted by Thanos Doganis on Sep 7 2008 12:56PM
Filter your DTM using Low pass filter
In Arc prompt issue the command
Filter LOW 3
If you need even smoother try more itterations of have a custom convolution matrix (the filter file). If I remember well the default is a 3X3 matrix with aces. If you use 5X5 or even 7x7 you get smoother results. Then calculate Hillshade effects using the filtered DTM.

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