Mounted search and rescue

["Robert Eversole at Turtletop Farm" <robert@turtletopfarm.com>]

New Years Greetings from a lurker,

Lat / Long positional drift is a combination of many factors including:
1) Receiver accuracy - Recreational models like the eTrex have a general
accuracy of plus or minus 10 meters. 
2) Receiver Configuration - Internal antennas are less accurate than
external.
3) Canopy - Vegetative cover can play havoc with your reading's accuracy.

These and other factors, all fold into why your GPS thinks it's moving when
it's clearly not. These units capture data continuously and with each
capture errors are introduced. As long as the drift you're experiencing is
within an area of about 60 feet (the sum of expected variations) your unit
is most likely working fine. 

Hopefully, the realities of GPS accuracy will not shatter your expectations
of recreational GPS receivers and applications. A GPS's ability to
accurately give location is an amazing feat of technology.

For general and S&R usage I use a Garmin GPSmap 60CSx. (For work I use a
Trimble that's accurate to under 1 meter). The Garmin's external antenna
helps with accuracy and canopy issues. 

As far as the design goes, my Garmin unit also has external buttons. To keep
them from being accidentally depressed, and to keep the receiver in better
view of the satellites, I've glued Velcro to both it and the shoulder straps
of my camelback. Works well for me although conditioning the horse to the
noise of the Velcro was interesting.

Happy mapping!

Turtletop Farm
Robert & Celeste Eversole
Email - robert@turtletopfarm.com


-----Original Message-----
From: msar-riders-bounces@lists.ibiblio.org
[mailto:msar-riders-bounces@lists.ibiblio.org] On Behalf Of Pennbo's
Sent: Tuesday, January 01, 2008 3:50 PM
To: Mounted search and rescue
Subject: [MSAR] GPS issue

Hi all, I got a nice new Garmin eTrex Vista HCx.  Nice unit in general. 
Expandable memory card that includes topo's for the US and street maps 
for the US and Europe. Color screen, scrolling, zoom, altimeter... 
excellent satellite connection even from inside. Seems perfect. However 
it has a serious flaw for our kind of work- and Garmin is aware of it. I 
thought I'd let you all know in case anyone is considering a purchase. 
Garmin will be putting out a firmware fix- sometime soon but they 
couldn't say when.

Here's the problem- the cursor 'drifts' when on track record mode and 
while sitting still. Which means that when you stop to check maps, talk 
with people, etc the cursor continues to drift and lay track. This could 
be a serious nightmare if you download your tracks at the command post! 
How on earth could anyone decipher where you went? The alternative- 
turning the unit off when stopped, is not really practical. They really 
should be warning folks of this issue instead of waiting for folks like 
me to contact them!!

Another potential issue in the design of the unit- there is a nice 
little raised button on the front of hte unit that is used for 'enter' 
and to scroll in all directions. Problem is you can't LOCK IT. Which 
means that in a holster you can accidentally engage it. Garmin is NOW 
aware of it and will be working on a firmware fix for this as well. I'm 
trying to design a little locking cap so it doesn't happen.

In general I like this unit but if anyone knows of another unit wiht 
similar features and price that does not have these issues- I'm 
listening. It wouldn't break my heart to return and exchange this unit.

thanks,
Chris Pennington


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