GPS users.

Vince · Posted: Mon Oct 27, 2008 6:54 pm Post subject: Re: GPS users.

Dimitri wrote:

gelandangan wrote:

could you do a small write up of this technique?

I am not Vince but I am sure he wont mind. Dimitri

Thanks mate...no problems at all 'Mitri....the most important thing is that the message gets across mate.

I don't know exactly what nomenclature everyone uses to identify things in all parts of the world, soooooo....where it mentions azimuth you can substitute the word bearing. You obviously read your bearing or azimuth, in either degrees or Mils, straight off your compass.

I have a similar book to the one 'Mitri mentions, although the one I have was put together by the Aussie Army. If anyone has any problems following the instructions 'Mitri has posted then feel free to ask either of us how its done. There are a couple of very minor details missing, but they relate to the magnetic variation and age of your map.

Cheers, Vince

Dimitri · Super Member Joined: Nov 25, 2005 Posts: 5944

Vince wrote:

There are a couple of very minor details missing, but they relate to the magnetic variation and age of your map.

I always figured that was more related to general map reading then a specific use ?? Confused

Dimitri

Vince · Posted: Mon Oct 27, 2008 8:15 pm Post subject: Re: GPS users.

Dimitri wrote:

Vince wrote:

There are a couple of very minor details missing, but they relate to the magnetic variation and age of your map.

I always figured that was more related to general map reading then a specific use ?? Confused

Dimitri

No mate. When you take a bearing (azimuth) from a map to use on your compass, or you take a bearing (azimuth) with your compass to plot onto your map then you must take into account the magnetic variation. This variation is recorded on the map. If you do not take into account the magnetic variation, then you can be many hundreds of metres out over a not so long walk.

When converting a bearing from Grid (the Map) to Magnetic (the Compass) for use on your Compass as a bearing to follow, then you must SUBTRACT the magnetic variation. Whereas if you are converting a Magnetic (the Compass) bearing to plot on your map, then to convert it to a Grid (the Map) bearing your must ADD the magnetic variation.

We had two little ditties to remember this by....but I won't tell them here because they are a bit raunchy. Make up your own that means something to you...Grid to Magnetic you Subtract (GMS) and Magnetic to Grid you Add (MGA).

Cheers, Vince

Dimitri · Super Member Joined: Nov 25, 2005 Posts: 5944

Vince,

I meant going from your magnetic North (or South) to your map grids True North (or South) was a general map reading skill set, not necessarily something specific to triangulating your position on a map.

So it's "assumed" you'd do the conversion without referring specifically to it.

Dimitri

Vince · Posted: Mon Oct 27, 2008 8:26 pm Post subject: Re: GPS users.

You still must take into consideration the Magnetic Variation of the map mate. The magnetic variation varies each year and if you are using a very old map, then a magnetic bearing could well be very different to a bearing plotted on your map.

It doesn't matter what you are doing with your map or compass...if you are going to plot a bearing with one and use that bearing with the other, then you MUST apply the Magnetic Variation.

Remember...doing a resection involves "shooting" a bearing with your compass, then plotting that bearing onto your map...Magnetic to Grid you MUST add the Magnetic Variation.

'Mitri' wrote:

So it's "assumed" you'd do the conversion without referring specifically to it.

Not everybody knows about the Magnetic Variation...even so-called experienced navigators.

It's something that you need to be aware of.

Cheers, Vince

Wicky · Posted: Mon Oct 27, 2008 8:42 pm Post subject: Re: GPS users.

I use a garmin 12xl for most of my bush stuff and have just got a garmin 76csx which has the toppo maps of Australia on it. Shonkymaps.com.au has the maps for Australia for free!.

I carry a compass as a backup and was trying to find a bushwalkig/rogaining book that has very good instructions in it but I think the wife has put it away!! When I find it I'll post the details.

A good book for Aussies - if you are that way inclined is Dick Smiths GPS guide. It has heaps of waypoints for a lot of touristy places and most towns.

Oh, and for my GPS i put in brand new batteries right before I go out and carry two sets of spares in my day pack - haven't had a failure or got lost yet.

Wicky · Posted: Tue Oct 28, 2008 12:58 am Post subject: Re: GPS users.

Found that book - Cross Country Navigation by Phillips/Phillips/Foley.
It really is a wealth of good info for compass users - not taking anything away from Vince and Dimitri 'cause that is good stuff as well.

Addendum - the web address I gave you all was a lie, my apologies here is the right one: Sad

shonkylogic.net/shonkymaps/

I was close - Not. Thanks to Vince for pointing out I blew it Very Happy

gelandangan · Posted: Tue Oct 28, 2008 3:25 pm Post subject: Re: GPS users.

@Wicky..
Mate Thanks for the heads up..
I have used an eTrex Legend for 6 years, purchased from the USA, it doesnt have any Oz maps in it.
With your link, hopefully I can put in some much needed data.

I have been carrying a small solar recharger sewn up on top of my backpack for the last few years, in it there is a couple of AA rechargable ready to be deployed onto whichever equipment that needed it.
I reckon everybody have their own safety measure taken care of which is good considering the type of hobby we all share, ie. remote area, far away from immediate help and often alone or in very small group.

English Mike · Posted: Sun Nov 02, 2008 10:07 pm Post subject: Re: GPS users.

Maps 'n compasses aren't much use when you're deep in the woods unless you're VERY observant as to contours & how far you've travelled.
GPS isn't any use at all if you don't trust it.
I saw two examples of the latter happening a couple of weeks back, despite the sun being visible to point out the obvious error.

Before next year's hunt I'll be getting a Garmin GPSMAP 60 CSX or whatever replaces it - if I don't blow ALL my "fun money" on a Montana Rifleman 22-250 & Nightforce scope....... Very Happy