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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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