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Mt. Rainier Challenge: Superior Overlays using 3DEM

Supplied by John Childs, August 27, 2001 (Printer Friendly Version)

The author uses this opportunity to discuss how amateurs can come close to the pros using inexpensive software tools (3DEM in this case) and free USGS DEM data available from gisdatadepot.com.
A section of a webpage at www.terrainmap.com outlines 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 http://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 small 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 have to do was 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 , , . 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 <3D View>.

Normally at this point we would select and under the 'Terrain' window, select the Mt. Rainier topo map file and click 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 you 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 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 often less than 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 (albeit necessarily large) topo to overlay on my DEM.

Another trick 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 a crisper. Another problem is lighting. The contour lines on the slopes toward the light source can get washed if the light is too bright. Also, a little post- processing in Paintshop 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 from gisdatadepot.com.


About The Author

John Childs (digital_terrain@yahoo.com) maintains a not-for-profit website at www.terrainmap.com where he offers a series of dem file translation utilities that he has developed have available for free download.

Entire Article Copyright 2001 John Childs, all rights reserved. Reproduction or redistribution in whole or in part without contacting the author and The Geocommunity is strictly prohbited.
How are you working with 3D data? We want to hear about a project you've worked on. Please send details to Glenn at editor@geocomm.com

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