The previous section outlined how to make overlays of topographical maps over DEMS.  To show you just how impressive these maps can be, take a look at the Avenza map contest page at www.avenza.com. Charles Kitterman’s overlay DEM of Mt. Rainer, winner of "Best of Show at the American Congress of Surveying and Mapping 2000" is featured. This map is a fine effort completely worthy of the prize. A smaller rendering of his large jpeg is shown to the right.  Let’s try to emulate his work using our humble tools and the free USGS mapping database

The first thing we must do is to find out where Mt. Rainier is.  It is in the state of Washington, of course but I had to consult my Gousha Road Atlas to determine that it was in Pierce County.  It was then an easy matter to log on to www.gisdatadepot.com and query the database until I located the 1:24,000 Mt. Rainer topo.  Second problem: two topos are offered: Mt Rainier East and West. I took a chance and downloaded the West topo first, which turned out to be the correct one containing the peak.  After downloading and unzipping the topo I downloaded and unzipped the corresponding 1:24,000 Mt. Rainier DEM.

I opened 3DEM and clicked  <File>, <Digital Model>, <Terrain Model>.  I made sure that 'USGS SDTS DEM' was selected and loaded the DEM file into 3DEM.  When I saw the familiar color depth DEM image I knew that it had loaded correctly.  It is important at this point to create the 3D image and get everything set up as far as viewing perspective, lighting, etc. before you apply the overlay because the image takes less time to manipulate before you apply the overlay.  This is done by selecting <Operation> <3D View>.

Normally at this point we would select <Operation> and <Apply Overlays> under the 'Terrain' window, select the Mt. Rainier topo map file and click <Load> to load it.  When you do this 3DEM will automatically do the following things: (1) Convert the USGS TIFF file to a BMP file;  (2) thin the raster down to a much smaller file size;  (3) rotate the file so that the map border aligns straight up and down.  At this point we would go into the overlay with 3DEM’s cropping tool and cut off the white borders, which is easy because the file has been rotated by 3DEM to align (well-enough) with the cropping window.  When you have the map cropped, you would select <Accept> and 3DEM will overlay your image onto the DEM.

In order to create a superior image, however, we need to apply a few tricks.  The main problem is that 3DEM thins the topo to such an extent that it loses too much image quality.  Another problem is that the alignment rotation is sometimes not exactly perfect. So instead of letting 3DEM have its way, I imported the TIFF image into Paint Shop Pro.  I carefully cropped it, rotated it, and saved it as an un-thinned BMP.  (The less processing of the image, the better.)  I then imported the un-thinned image into 3DEM as above.  Now I had a much better topo to overlay on my DEM.

Another tip is to view the image from directly above. A perspective view tends to muddy up the contour lines of the map but a straight overhead view keeps them crisper.  The lighting is also important in keeping the countour lines from washing out on the "sunny" slope of the mountain. A little post-processing in Paintshop also helps an already pretty-good image look its best.

Our result is shown in the second figure below. Mr. Kitterman's is undoubtedly the better map. A map of this type is only as good as the overlay topo, and Mr. Kitterman did his homework here. However, our brief effort shows that we amateurs can come close to the pros using inexpensive software tools and free USGS data.

Note: This article was originally published in June, 2001 when gisdatadepot.com offered USGS topos for free. Unfortunately, this is no longer the case and this site now charges for topos. For free topo maps, check the following links: www.nb.net and www.topowest.com.