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TOPIC: GPS systems
http://groups.google.com/group/entstrees/t/9160cf56c198a744?hl=en
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== 1 of 1 ==
Date: Sun, Nov 23 2008 1:18 pm
From: treedunn@gmail.com


Im looking to purchase a new gps with a better pinpoint accuracy that
will work in areas of dense canopies. I would like to be able to
better document sites. I currently have a Garmin Etrex Legend that
doesnt work so well. Any thoughts?

Michael B. Dunn

== 2 of 4 ==
Date: Mon, Nov 24 2008 6:53 am
From: MyCamel


no matter which GPS you have or purchase, in my experience, none will
work with dense canopy. they MUST 'see' the satellites. canopy will
reflect the satellite signal.

there is however, an option. you can use a laser rangefinder and
compass, connect to a GPS with offset capabilities (the GPS would need
to be set up in a clear area). the laser and compass will feed offset
information to the GPS.

Good Luck!

Michael A. Hammel
Opti-Logic Corporation

== 3 of 4 ==
Date: Mon, Nov 24 2008 8:34 am
From: Frank Broughton

Look at a Garmin GPSmap60CSx works in heavy coverage pretty good!

Frank

== 4 of 4 ==
Date: Mon, Nov 24 2008 8:34 am
From: "Hugh Irwin"


The Garmin 60 CSX works great under a canopy. It is rare - even in a
forested canyon with rhodo - to lose the signal. Accuracy is usually in the
30 feet or better range. For finding landmarks like big trees, this usually
gets you close enough to spot easily. All of the Garmins with "X" on the end
should have good reception. The X denotes an improved - more sensitive
receiver that in my experience works great.

The high end (and very expensive) GPS units like Trimble will be more
accurate if they can get a signal. But these units actually filter out the
lower grade signals to achieve higher accuracy. I haven't compared them head
to head but in talking with a lot of people about this, including Trimble
reps, the consensus seemed to be that the Trimble units had the definite
edge in accuracy, but the Garmin "X" units would maintain a signal in
thicker forest.

The sensitivity of both can be boosted by an external antenna. But these can
be very awkward in the field. I tore up many units in the field with my old
garmin that didn't have the "X" receiver.

If you can stand an accuracy of 30 feet or so, I would go with a Garmin with
the "X" receiver.

Hugh Irwin
Conservation Planner
Southern Appalachian Forest Coalition
46 Haywood Street
Suite 323
Asheville, NC 28801
email: hugh@safc.org
(828) 252-9223 FAX (828) 252-9074
http://www.safc.org   

==============================================================================
TOPIC: GPS for tree location
http://groups.google.com/group/entstrees/t/8d07ee34a8e9ac39?hl=en
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== 1 of 2 ==
Date: Mon, Nov 24 2008 9:08 pm
From: Gary Reif

I purchased a Garmin GPSMap60CSX a couple years ago to map hiking
trails. It has a much better chipset than the Etrex and I have used it
without loosing signal on days when most say I should have trouble (in
the hills, cloudy, rainy, many wet leaves overhead).

The GPSMap60CX is similar without compass and barometer
(the compass is kind of a pain (wants to be very level), but the
barometer measures small height changes (~1 foot) in addition to the
height satellite signals, so height profiles are much better.

The x in the PN is what indicates the high sensitivity chipset, so the
GPS60 and GPSMAP60 are not in the class of the X models.

If you get one, the default is WAAS turned off- so turn it on to get
improved accuracy.
Also note that when you mark waypoints, you want to use the average
feature and get at least 10 points.
GR

== 2 of 2 ==
Date: Tues, Nov 25 2008 11:23 am
From: "Gary A. Beluzo"

Michael,

My experience has been that none of the GPS systems under $2000 work
very well under tree canopies. However, there are a few things to
maximize the reception.

I tend to do tree location after leaf off, from November to April.
That alone will provide better reception under deciduous canopies. If
you are trying to do work in a hemlock forest, not good.

Also, I back away from the tree until I get a good signal, sometimes
up to 30m or more, then I spiral in towards the tree until I am
standing at the stem. I find that once the GPS locks in usually I can
slowly spiral to the stem and I will continue to get readings. Also
if you are spiraling and doing averaging you don't need to make it to
the stem.

Gary