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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