Recently I've been helping some colleagues in my department convert some historical maps into contour lines. They are at the stage of using ArcScan to convert old scanned topographic maps into contour lines. Interestingly, ArcScan doesn't make use of multi-band image files, but rather single-band grayscale images. When trying to pull out contour lines as distinct from other types of lines this became problematic. Using a simple band thresholding method browns and grays tended to get confused.
The solution? I used the
Marine Geospatial Ecology Tools to perform a random forest classification to separate brown lines from all other colored lines. The results were really impressive. Pretty much all of the gray lines were removed. See the picture below for an illustration of the result.
Original scanned topographic map with contour lines in brown and other lines in black/gray.
The result when using a simple band thresholding approach. Black lines represent cells that will be used in the vectorization process.
The result from the random forest classification plus a small amount of speckle removal using the regiongroup tool in ArcGIS.
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