From: Alan R. Hamm (ahamm@alanhamm.com)
Date: Fri Jul 19 2002 - 07:35:20 CDT
I find this thread fascinating, I guess because I started it, but it is
likely to bore a lot of people.
For the record, my datum was set to WGS84. If you can find a different
setting on a Philmont map, I would love to see it. I looked several times.
I was very surprised there was no reference to a datum on the maps.
Also, while my GPS does not have the newer WAAS technology, I have found it
to be very accurate in marine use. As for satellites, 80% of the time I had
strong signals from 6 to 8 satellites in almost all cases (top of Phillips,
11 of 12). My GPS has an estimated position error (EPE), which generally
was within 25 feet. Also, these units give altitude. It takes a minimum of
3 satellites (see triangulation) to give an altitude setting, of course.
With each satellite locked, this number becomes more accurate. My altitudes
were almost always very close, maybe more accurate than the various ones
posted throughout the ranch.
As for accuracy due to tree canopy and not having a strong signal, sure, I
did not have a perfect signal for the entire trek. But again, my unit shows
a breadcrumb trail with dots that it leaves every 82'. These were not
jumping around all over the place (except during switchbacks) which would
be the case if I was having intermittent signals. If I could extract all of
these points into my pc and plot them (I am not sure I can as I think it
will summarize the points to a maximum of 250) you would see a very accurate
track of our trek. Yes there are some gaps (mostly mental to forget to turn
the darn thing on) and a few lost signals, but it is very accurate.
Here is the point. Coming down the Tooth of Time and down the ridge there
are no trees. There were no clouds. I had very strong coverage the whole
way. I know where I walked. I would love it if anyone can show me a me a
map that resembles that route. I planned it based on the latest map of the
South region available (South and Central both show it) but it was still a
good ways off. In fact, when I plotted the point where the trail ends at
base camp from UTM coordinates on the map, that waypoint showed up on the
other side of the main road, according to the built in map in the GPS.
Guess what, that point was way on the other side of the road although I did
not walk to it as I had had enough hiking that day.
The difference may be Datums for the plotting of waypoints accurately.
WGS84 vs. NAD27 maybe. I tried to find a datum on the maps to no avail.
Again, the camps, roads and streams located in the software (Garmin's
Mapsource) were very close. Enter a waypoint for the intersection of 2
steams from the maps UTM coordinates, not close. Generally 1/4 mile south.
I guess the answer to the original question is........Nobody really wants or
can trust this data........right?
Alan Hamm
702-F1
----- Original Message -----
From: "Paul Lamson" <plamson@twcny.rr.com>
To: "Multiple recipients of list philmont" <philmont@troop47.com>
Sent: Friday, July 19, 2002 6:26 AM
Subject: [Philmont]: GPS Data
> One of the most important things to keep in mind when using a GPS is the
> number of satellites that you are able to track on. If you are in a place
> that you only get two tracking, your readings will not be that accurate.
> three is bare minimum to get a seasonably accurate fix. four or more
should
> put you right on the money when you take a fix. There is also the
> possibility of difference's due to the type of unit and lots of other
things
> that affect GPS usage. Even the expensive ones that we use in the
military
> can be off if the conditions are not ideal for tracking in the satellites.
>
>
>
> Paul Lamson
>
>
>
>
>
>
>
> -------------------------------------------------------
> Scouting E-mail Discussion Lists @ usscouts.org
> Subscribe/Unsubscribe at http://usscouts.org/lists/
> Listserv Commands at http://usscouts.org/lists/lc.asp
> -------------------------------------------------------
> Send listserv commands to: listserv@troop47.com
> Send postings to: philmont@troop47.com
> List FAQ found at: http://usscouts.org/lists/faq.asp
> List Administrator: philmont_owner@troop47.com
> -------------------------------------------------------
> As you gather around this virtual campfire with fellow
> Scouts and Scouters, do your best to be trustworthy,
> loyal, helpful, friendly, courteous, kind, obedient,
> cheerful, thrifty, brave, clean and reverent.
> -------------------------------------------------------
>
>
>
>
>
>
>
-------------------------------------------------------
Scouting E-mail Discussion Lists @ usscouts.org
Subscribe/Unsubscribe at http://usscouts.org/lists/
Listserv Commands at http://usscouts.org/lists/lc.asp
-------------------------------------------------------
Send listserv commands to: listserv@troop47.com
Send postings to: philmont@troop47.com
List FAQ found at: http://usscouts.org/lists/faq.asp
List Administrator: philmont_owner@troop47.com
-------------------------------------------------------
As you gather around this virtual campfire with fellow
Scouts and Scouters, do your best to be trustworthy,
loyal, helpful, friendly, courteous, kind, obedient,
cheerful, thrifty, brave, clean and reverent.
-------------------------------------------------------
This archive was generated by hypermail 2.1.7 : Thu Mar 13 2003 - 10:38:05 CST