View Full Version : Another ? for Dick Blust

10-10-2004, 09:41 PM

I have the National Geographic Topo program and just got the Brunton Combi compass you mentioned.

Two questions. I am a military pilot and am quite familiar with UTMs as the guys we are protecting on the ground use them extensively for targeting. A much superior and quicker system than Lat/Longs. We use WGS84 vs NAD27 though as long as your GPS and map are in the same coordinate reference, everything will work out okay. Correct?

Second question. I printed out a map using your system (7.5" - 1:24,000 at 48%)and got a much bigger UTM grid than the 1:50,000 scale on the compass. To get the UTM scale to work I had to reduce the map to 31% and then the detail is so small it is hard to work with. What am I doing wrong??

Excellent essay and waiting expectantly for part 2!! Thanks, Skeeter

10-10-2004, 10:06 PM
I have the same TOPO! program and 30% seemed to fit the 1:50,000 scale better for me. Yes, the detail is very small but it worked ok this weekend while I was hunting a new area. I worked with the map on the standard size on my computer to create my waypoints, routes and glassing locations and then reduced it.


Dick Blust
10-11-2004, 05:43 AM

First question first: You're correct, the Map Datum setting for your GPS must always match the Map Datum used for your maps. The "store-bought" USGS topos are virtually all NAD 27 (I've never seen one that wasn't), thus, if you're using these, your GPS must be set for NAD 27. (Some GPSs, especially the Garmins, offer options within NAD 27 - with one of these, if you're in the lower 48, use NAD 27 CONUS; if in Alaska, use NAD 27 ALASKA) I don't know offhand which datum the National Geographic program uses; I'd strongly suggest a quick email to them to find out; the program itself may allow you to choose between the two. If so, once again, match everything up.

This is a particularly important issue in Canada, where more and more of the issued topos use WGS 84. As always, the Map Datum setting on the GPS must match the Map Datum for the particular map itself.

Second question: The printout at the 48% rate applies to maps generated by MapTech's Terrain Navigator program; the National Geographic program apparently does things differently. (Your information seems to match ggaff's; it looks like you must print at the 30% to 31% rate to get a 1:50,000 scale.) Bottom line: you're not doing anything wrong - it's the difference between the two mapping programs. One thing you might try: experiment with printing out at a rate of 60% to 62% to get a scale of 1:25,000. You won't be covering nearly as large an area, but check it against the precise area you plan to hunt - you may find this approach workable and will permit you to use the 1:25,000 scale on the Brunton Combi. Otherwise, consider switching to Terrain Navigator at some point. The free download demo at their website, <a href="http://www.maptech.com," target="_blank">http://www.maptech.com (http://www.maptech.com,),</a> will give you a better hands-on feel for its features.

You're going to love your Brunton Combi. In the direction-finding essay on compasses that the Kifaru staff is now preparing for posting and the compass position plotting essay that's nearly finished, I provide step-by-step instructions in its use

Hope this helps,

10-11-2004, 01:23 PM
I currently have National Geographic and it will let you select many different datums. I print my maps out at the 50% rate which allows for a fairly large area for viewing. Select the UTM grid option, it will only grid in 1000 meter increments and you can choose what color you would like them to be. For more accuracy make your own corner scale by marking off the ticks on the printed scale at the bottom of the printed map. This will get you to within 100 meter accuracy which should be plenty good enough for most hunting situations.

10-11-2004, 03:57 PM
Wyoelk - National Geo will let you pick the grid increments - you can grid to 100 meters, or whatever you want. Go to the <View> drop down menu, then click <grid...> and you will get to make the changes you desire.


10-12-2004, 06:35 AM
I will try that out later tonight. Whenever I select grid it just does it at 1000 meters. I will look to see if it will do it at 100. That would be nice. Thanks Mike.

10-12-2004, 07:45 PM

After printing out the map in best quality, I believe it will be workable in the 1:50,000 scale (as long as I have a magnifing glass!).

Once again, excellent info and waiting on more info in your second writing!


Dick Blust
10-13-2004, 05:55 AM

Thanks for the comments; the next section of the essay should be up soon.

Take it easy,