[Az-Geocaching] EasyGPS and coordinates being off

[Scott Nicol]

Karl,

It is possible (although, I dont think too likely) that the coordinates 
could be off if your GPS is set to a different coordinate grid. To be 
compatible with the coords used in Geocaching, you need your GPS set to 
DD.MM.MMM (not degree, min, sec. as I think GPS's usually are set to when 
you start them up if you havent specified any other grid).

I use two different coordinate grids with my GPS's. I use the metric grid in 
my aviation operations (hot air ballooning competitions). That is NAD27 
/UTM. When I am out geocaching, of course, we use the WGS84 / DD.MM.MMM.

I usually use different GPS's for each operation, but, I did take my 
aviation unit out geocaching one day and forgot to switch over the 
coordinate system and arrived at my destination many feet off. Never saw it 
over 300' off though. It was, however, sometimes over 50' off. That day I 
had simply uploaded a couple of caches into my aviation unit (the one set to 
NAD27/UTM) and, of course, they ended up being in the UTM coordinate grid. 
This was the only time I ever did that, so, don't know if they coords would 
typically be off like that or not. Myabe the cache coords were off 
originally. Something someone else might try one day.

I use a Garmin 3+ pilot for ballooning and a Garmin Etrex Legend for 
geocaching. (I also have a Magellan 300 and a magellan Blazer 12 I would 
like to sell if anyone is interested).

I dont see why a GPS would put the same location at different spots 
dependant upon which coordinate grid you are using. But, I have seen this 
before. Food for thought.

In other words, if you punch in a geocache coordinate utilizing the 
DD.MM.MMM grid and then switch your GPS over to NAD27/UTM, would it be off 
when you arrived at the given spot? Has anyone else ever tried this and had 
this happen?

I have thought about trying this to find a geocache in perhaps a very remote 
spot: I would punch in the coordinates (as geocaching.com gives them in 
DD.MM.MMM) and then switch the GPS over to NAD27/UTM. Now that I have done 
that, I can easily locate those coordinates on the 7.5' topo. The 7.5' topo 
utilizes the UTM 1000 meter grid. I 'grid' all my 7.5' topo maps to show 
1000x1000 meter boxes. I then, break those boxes down into .10th using an 
overlaid grid on a clear film paper. This allows me to almost precisely find 
out where a cache is and thus, helping to plan my route into the cache 
location (something I didnt do on our first cache, Junk Drawer Junkie and 
ended up at the bottom of the canyon when there was a MUCH easier approach! 
Yep!). I utilize this type of planning in our hot air balloon competitions 
to find a target (and thus being able to plan our launch point to the 
target). We have never tried it caching, as we have always been able to just 
go at it by the GPS map. But, for those really remote caches, sometimes 
pre-planning an approach can make the hike to a cache alot easier. By 
placing the cache on the 7.5' topo, we can visually set up a route from the 
vehicle to the cache (thus potentially minimizing having to climb over a 
mountain when it would have been easier to go around, etc).

Anyways, just some food for thought. Wondering if anyone else has arrived 
many feet off by switching the coordinate system in their GPS?

Scott Nicol
arizcowboy@hotmail.com

Scotts Adventure Flying Web Page
http://www.geocities.com/safwp



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