DEM Reader will create a Macintosh color or grayscale pict image from a USGS DEM file. It comes in both Power Macintosh and 68K versions. It can create an elevation map, relief map or a composite of both from 7.5 minute and 1 degree DEMs.
Note: If you will be saving color picts from 1 deg DEMs set DEM Reader's prefered memory (in the get info box) to 6000k.
Version 1.5 adds contours and a legend. You can now copy the map or legend to the clipboard as well a saving them as PICTs. There are some internal changes to DEM Reader's offscreen g-worlds. If you are adding your own color tables see section E.
B. About Digital Elevation Models (DEMs)
1. A DEM is a file containing geographic elevation data. The format was developed by the U.S. Geological Survey (USGS). The most common are 7.5 minute and 1 degree. They correspond to 1:24,000 and to 1:250,000 scale USGS maps. Data points for 7.5 min. DEMs are 30 meters apart. 1 deg. DEM data point are 3 seconds of latitude and longitude apart.
2. For more information on Digital Elevation Models check the USGS WEB page :
Standard DEM file are in text format making for large files. A typical 7.5 min. DEM is ~1MB. While 1 deg. maps are over 9MB! The USGS stores DEMs in .gz format. So you’ll need MacGzip to expand them. The file must be expanded as a text file or DEM Reader will not see it. The image may be reduced to fit on screen.
C. How to use DEM Reader.
1. The file menu:
Draw map... This opens a file. A dialog box will follow for setting options:
Minimum and maximum elevation: This is useful if you are tiling multiple maps in an image editing program such as Adobe Photoshop. You can set all maps to a common minimum and maximum elevation.
Zero Elevation: If this is checked DEM Reader will draw areas with zero elevation as light gray or blue. You will want to turn this off for areas below sea level.
Relief: If this is checked DEM Reader will draw the map in relief form. If color is checked the relief will be superimposed on it.
Color: Display elevations as color. If you select this a menu will appear giving you the option of choosing different color tables. (If you are familiar with using a Macintosh resouce editor such as Resedit, you can add your own 'clut's).
Projection: (1 deg. DEMs only) this gives a better visual representation of the DEM.
Contours: DEM Reader will draw contours at intervals set by the user.
Redraw map... Allows you redraw the currently loaded map.
Save as... This converts the file to DEM Reader’s own binary format. It is 3x smaller than the text file and loads much faster. You cannot overwrite the original text file. This is only available when reading text files.
Save pict... This saves the image at full resolution to a pict file. This can be up to 1.4MB for a 1deg. DEM in grayscale or color without relief, 2.8MB for color with relief.
Close.
Quit.
2. The edit menu.
You can copy either the map or the legend to the clip board depending on which window is in front.
3. The window menu.
Info. Display the DEM info window.
Map. Brings the map window to the front.
Display 1:1. If the map is reduced to fit the screen (as shown in the window title) this will display it at full size.
4. The info window.
This shows the DEM's header information. It also displays the position of the cursor while it's in the map window. It will give latitude and longitude for 1 deg. DEMs and Lambert coordinates (in meters) for 7.5 min. DEMs.
D. Future versions and comments.
Plans for future version include: displaying of user defined contours, a legend for elevations and support for exporting Quickdraw 3D 3DMF files. A Photoshop plug-in is also planned. Future versions will be posted to my DEM Reader web page as they become available. Comments, suggestions and bug reports are welcome. Please send them to:
I've changed the way DEM Reader uses color. It now uses 'clut' resources instead of 'pltt's. If you would like to add your own color tables you can do so with a resource editor like ResEdit. You should be familiar with ResEdit before you try this.
F. Shareware fee & copyright stuff.
DEM Reader is copyright of Brian Wagner. This version is shareware. If you find this program useful please send in the $20.00 shareware fee to the address below. This is incentive for me to keep upgrades coming. This fee will include the next two upgrades of DEM Reader.
DEM Reader cannot be sold or distributed with any commercial package without my permission.
To register DEM Reader please send a check for $20.00 payable to Brian Wagner to:
Brian Wagner
607 Fern Glen
La Jolla, CA 92037
Include an e-mail address if you'd like to be on the mailing list to receive upgrade information.
