| Inaccurate coordinates can be a real pain when searching
for a cache, so when I place my caches I want to have the coordinates as
accurate as practical. In an attempt to do this I take several
readings in a session, waiting as long between readings as
practical. After giving the unit about five minutes (more is
probably better) to settle, I move it around a little so it will start a
new average. Then I let it average for about two and a half minutes without moving it. I watch the last digits for the final
30 seconds to see if they're changing. If they're changing I wait another
30 seconds -- still changing another 30. I don't average for more
than 3.5 minutes. I capture my first pair this way, then walk a hundred or so feet
away, return, do the average again and capture another pair. Then go off in a
yet different direction
and repeat. I try to take three sets this way, but even if I don't have time to do the full averaging between readings I take
at least three with the walking away between readings. The next time I'm at the cache location I do it all again. If
possible I come at a different time on a different day.
The GPS satellites are always moving, and their different locations can
give better or worse results. A different time is more important
than a different day, so three times a few hours apart on the same day is better than the same time on
three different
days.
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Sidebar
If your unit does not average while
remaining stationary, you'll have to take more readings to get good
results. I've never used a unit that didn't average, but if I
were using one this would be my procedure:
I would take at least 9 reading on each of
3 visits to the cache location. I would use the above procedure
but instead of waiting 2-3 minutes for each reading, I would take a
reading, and without moving take another after about 15 seconds, and
repeat for a third. Then I would do the walk away and return,
and repeat the three readings. I'd do this 3 times for the 9
readings total. |
A recent topic on the geocaching.com forums made me
realize I need to add another point to this that I forgot to mention in
earlier versions of this article. I make
a mental note of the EPE values when taking these readings. I should
jot them down, but usually I just remember them. If my EPE values
are high, say 30 feet or greater, I come back at another time. If
possible I try to only take readings when the EPE is 20 feet or less,
preferably 13 feet. I don't normally get an EPE less than 13 when
placing a cache. In the few caches I have placed I've
never had to use readings when EPE values were as great a 30 and
rarely greater than 20. If I ever have to I will mention it in the
cache description. A decent EPE is important. A single reading at EPE 10 is likely to be better
than the average of 3-5 readings at EPE 50.
Here's my article on EPE.
My SproTrak Pro must be held vertical to get the best
signal. I got tired of holding it, so I made this
hook. It's surprising how many things it will hang on. The large end of the hook
probably looks familiar:
I needed a way to combine all my readings into a single set of coordinates. That's what this program
does. It works with coordinates in the
typical geocaching format of degrees minutes and decimal minutes, like
this:
N 29° 35.715'
W 95° 05.051
Typically I only enter the decimal part of the minutes.
In this example I would enter 715 and 051. In the very unusual case
that you're near the minute change point and some values have different
minutes you would have to enter 4 digits. For example, if the
minutes value above had been 35.999 and another 36.000 I would enter 5999
and 6000. You can enter the entire number if you want, but do not
include the decimal and you must include 3 numbers after the decimal
even if they're zeros -- e.g., 35999 and 36000.
When you click Plot you get this display. |
