NavList:

   

Reply

On Sun, 03 Dec 2006 19:26:32 -0700, Bill  wrote:

> 1. When a GPS unit converts between true and magnetic or vice versa,  
> does it
> use up-to-date variation values downloaded form a satellite or is it  
> using a
> lookup table imbedded in its firmware?
>
I would suspect a lookup table, but I don't know.  A place like  
etrex@yahoogroups.com would be one place to find out; or might be able to  
direct you to an answer.

Or, from :
=======quote=======
     Most GPS receivers have internal data and an algorithm to compute the  
declination after the position is established. For example, the Garmin  
GPS-45 displays the value on the Navigation Setup page, Heading: "Auto  
Mag," and uses it to supply magnetic bearings. However; this data cannot  
be updated from satellite transmission, therefore it is subject to become  
outdated.

When asked about this issue for the 12XL, Garmin responded:

"The magnetic variation model used within our products is a series of  
tables derived from the NOAA IGRF '90 model, which accounts for the  
movement of the magnetic poles over time."
=======end quote=======

> 2. Is a geocache hunt really an exercise in navigation (except for being
> able to find your way through a road-map maze to a known point) or is it
> more being clever enough to find a toy soldier etc. hidden in a  
> hollowed-out
> fence post when you are <20 feet from it?
>
If you have a map of some sort, so you don't end up on the wrong side of a  
ravine, it's more being able to find the container without calling undue  
attention to yourself.  But mostly, I think it is an excuse to get some  
exercise for your body and mind, at your own pace.

The first two part I tried needed first to find a small, dogbone shaped  
rock.  Now this seemed to be somewhere on a ridge, and the readings were  
different depending on which direction you approached the peak.  Turns out  
I climbed the wrong side first (200 feet), got a better bearing from the  
top, slid down into a little hollow where the readings were terrible, and  
finally got a match on my cheap little eTrex.  There, just off the deer  
path, was that one little rock.  On the underside was written another set  
of coordinates about two hundred yards in the next valley to the south.   
This time I wandered in a criss/cross pattern until I thought I had a fix,  
which was fairly easy to find once within five feet or so.  This was a  
slump area of very hummocky ground, had lots of little bushes and deer  
beds; but still close to a walking trail.  It was a beautiful area close  
to home that I never would have found on my own.

I think it best to have a small compass with you, so you can read the  
distance (say a good thirty yards) and bearing to the cache on your GPS;  
and mentally plot a small house sized elliptical area on the ground in the  
right direction.  Continue on an easy path for another fifty yards and  
check again.  Turn a right angle at a convenient location and make a third  
check.  A good place to start looking *without* the GPS is in the centre  
of the overlap area of those three house sized ellipses.  If you have tree  
cover or hills blocking the southern sky (as I did on that two part I  
mentioned) the position readings can even stop updating; so you have to  
stand away further.

-- 
Richard . . .
Using Opera's e-mail client since Dialog, "the Dog", died.

--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com

To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply