[Towertalk] Terrain Analysis the computer way (NS4T)

[mwdink@eskimo.com]

>There is a fairly easy way to generate terrain profile maps 
>for your QTH.  It uses free USGS DEM maps and a free 
>program called MicroDEM written by  Peter Guth of the 
>U.S. Naval Academy.  I've written an article on how to 
>do this and the ARRL is publishing it in the next Antenna 
>Compendium scheduled for publication this fall.   Dean 
>Straw (N6BV, author of YT and ARRL editor) and I are 
>working on the final editorial revisions now.  Pete Smith, 
>N4ZR, has also been involved in the review efforts.  This 
>enhances everyone's ability to use Pete's method of 
>"Scoring" antenna's since multiple terrain profiles can 
>easily be made. 
>
>Using MicroDEM you can generate a terrain profile from 
>any location at 1 degree increments for 10 foot intervals 
>of in less than 10 minutes from sitting down at your 
>computer.  Of course that's after you've done a few 
>things like installing the software, combined the DEM 
>maps and learned the program a bit. 
>
>With very little work MicroDEM can also tell you things like 
>line-of-sight coverage for UHF/VHF communications, distance 
>between stations, true north for any location in the world, height 
>for antenna's to have line of sight between to fixed points, and 
>projected flood plane levels for those of you involved in emergency 
>communications. 
>
>MicroDEM can also merge DEM files for multiple area's so if you 
>find you live next to an edge of a USGS map you can still use it 
>to get accurate terrain profiles.  Dean did find that in some locations 
>this feature doesn't work correctly and is working with the USGS and 
>Professor Guth on why not. 
>
>Unfortunately the free maps available seem to be pretty much limited 
>to the U.S.  That's probably because they're put out by the U.S. 
>government. 
>
>If you want to use it, do a web search for MicroDEM and download it. 
>It's pretty big -- around 30 mB.  Read the help file about how to use 
>the program.  Pay particular attention to inputting your latitude and 
>longitude, calculating "offset", and how to make a "stream profile". 
>What I did was selected my location on the map and then calculated 
>an offset distance (say 10,000 feet) and a bearing (say 40 degrees). 
>Then followed the directions  to show a "stream profile" for that offset 
>by using the starting and ending points of the offset.  You'll be given 
>a graphical representation of the "stream profile" but MicroDeM allows 
>you to download the data used to generate it.  That data can be 
>converted manually into an ASCII file for input to YT or TA.  I used 
>Excel originally, but Dean wrote a short program to do it automatically. 
>
>If you don't want to figure it out using the above information again, the 
>article should be published this fall.   Since the ARRL has publishing 
>rights to the article I'll check with them and find out if I can give more 
>information or not.  This should at least give some of you a good start 
>and save you a lot of work! 
>
>You can get the DEM files for your area from the USGS website at 
><http://www.gisdatadepot.com/dem/demdownload.html>http://www.gisdatadepot.com/dem/demdownload.html 
>
>Kevan Nason 
>NS4T 
>knason@ e m e r a l d i s . c o m