GPS Newbie Questions
I'm having trouble understanding how I can use my gps to indicate my position on a paper map. I tried to set the user grid as suggested on this site but none of my waypoints give a reading; just USR_________
Help! (please)
22 comments
I think John is talking about grid lines, probably has to draw them in on the photocopy they are too faint. If you are connecting the latitude and longitude markings in the margin (do they have them on the new maps?) the lines will not be parallel to the grid lines or the edges of the maps. You would also be asking for trouble doing this because lats and longs are about 300m different between WGS84 and Geodatum49.
Ah, okay. That makes sense then.
pmcke, yes I just checked and the new Topo50 maps do still have lat/long scales down the edges, but there are no grid lines of any sort for lat/long and I expect it's only for rough guidance. It's exactly the same presentation as the old maps in this respect, except that the map grid has changed and the geodetic datum that's the basis of the latitude and longitude positions has changed.
I remember the first time I saw a GPS on a tramping trip. It was an old Trimble Scout with a two line digital display. The guy who had it brought it out from the depths of his pack and had it wrapped in about 5 layers of cloth to protect it from damage. We stood around in awe as he took about 10 mins to get a fix and then we strung dental floss across the map to join the lat long lines to get a fix.
Haha, we didn't know anything in those days. I imagine we were 300m out but remember that "selective availability" was in place in those days so the GPS signal was dithered by 100m. We probably thought it was pretty good that the GPS showed us to be in the valley we were in.
I do remember the first time I discovered the 300m error. I was running a GPS training exercise for SAR people. We had to bludge GPS units from everywhere and some had NZMG and some didn't. So I converted the instructions to lats and longs and had both NZMG and lats and longs.
It wasn't a problem until I saw that half the group were doing the exercise in one place and the other half were doing it somewhere else.
The only points I was trying to make are 1) Use an enhanced map that you can read easily when you are totally buggered and the weather is extreme 2) Practice using the GPS so you can quickly pin-point your position on that map (which you have orientated) 3) Put your compass on the map, edge against the grid line and then set the pointer to where you want to go 4)Tramp on that bearing 5)Take another GPS reading after a few hundred metres, relate that reading to the map and confirm you heading in the right direction. This is the technique I use in white-out conditions on the tops in the Tararuas. It has never failed me.
Hi John. Have you ever had battery or other electrical problems? That's a major reason why I'm reluctant to rely on a GPS as a navigation aid except as a backup for when I'm having more problems than I anticipated.
The first means of navigation should always be your eyes and your brains. I have a mapping GPS so don't bother with a compass now a days. When I did use a compass and a GPS together the only problem I had was when one day I was getting confusing readings from the compass. Then I realised I was holding the compass and GPS side by side and the compass was pointing at the GPS.. Duh!
As for electrical problems, that is an issue and I always carry a map and compass as well. I did dunk one GPS in a river which killed it, consequently I don't trust the waterproof ratings for the GPS and keep it in a transparent dry bag in wet weather.
When GPS was first available it was emphasised that it was a navigation aid and knowledge of the use of map and compass was integral.
I've often since wished that the compass was the more recent invention and marketed on the basis it is reliable, lighter, smaller and not dependant on batteries and a system of satellites.
I marvel at the idea that learning how to use map and compass is any more complicated than understanding the nuances of GPS.
Reading a map and judging the topography, position of the sun etc rarely even calls for the use of the compass.
So much for self reliance.
Yes, that's true. I didn't find the concept of compass use hard to pick up. Learning about how to put it on a map, then get the needle in the right place for the real world is straightforward whichever method you use.
For me though, experience and learning from other people has had lots of influence in shaping how I actually use it and think about navigation overall. I'm still always learning, too.
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| Forum | The campfire |
|---|---|
| Started by | neilpendo |
| On | 18 April 2010 |
| Replies | 21 |
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