SiRF III: is sensitivity better than accuracy?

Larry G wrote:

Most handheld receivers generate a position every second. As time passes,
the position calculated will vary. If you keep recording the position
over a long period of time, you will get a curve something like a "bell
curve". This is the probability distribution that has been talked about.
The width of the distribution is what the "accuracy" is all about.
The wider the distribution curve, the lower the accuracy.

In case you don't know... You set the the track logging parameters to
"Distance", "Time", or "Auto". If "Time" is chosen the interval is
listed and is user settable.

--
Dan
(email change 2001 to 2004)
(www.gpsmap.net)

very helpful... explanations... thank you

I noticed the options for auto, time, and distance... and my
inclination was to leave it alone... not knowing what effect the time
or distance setting would have on it's operations in the field.

Larry G wrote:

I've not done anything where I wanted to collect data points on a timed
basis. Whichever method you use, you can always see both the time and
distance values when you look at the track later, That applies to the
*.gpx file tracks, *not* the Saved Tracks. With the saved tracks some
points may be lost to the 700 point maximum. And you don't get the date
and time data on Saved Tracks, just the lat/long and elevation.

With a 10,000 point track memory you can collect points for a 100 mile
journey at the .01 mile setting. That is where mine is set most of the
time. With the Overwrite when full option on and the Log Track to Data
Card box checked, if you go more than 100 miles the GPS will start over
writing the oldest points but all points collected will still be in that
day's *.gpx file on the microSD card.

When the track log is full and overwriting, the percentage used just
stays at 99% until you clear it. I'm not sure but I think if you set it
to stop writing when full (to preserve the track in track memory for
example), it still continues to record points to the *.gpx file.

I seldom need 100 points per mile for anything but the next setting (.1
miles) will only give you 10 points per mile and that is a little
coarser than I like for some things.

I love tracks, the 76Cx has about as good a track recording capability
as you can get. It is almost as good as the Meridian Color that it
replaced.

Jack

--
Jack Erbes in Ellsworth, Maine, USA - jackerbes at adelphia dot net
(also receiving email at jacker at midmaine.com)

Although WAAS is desirable, it isn't very useful unless you are in
open sky environment. It requires downloading of ionosphere
corrrection data for it to be effective, which takes several minutes.
WAAS won't be useful if you are driving in urban area, where signal is
constantly being interrupted; the ionosphere correction data most
likely will not be able to be completely collected for WAAS signal to
be used for correction.

So don't worry too much about not having WAAS unless you are using
your receiver on sea, air, or out in open fields where signal won't be
blocked, it makes no difference in most land navigation applications
with or without WAAS.

I don't know what your experience is, but I have used WAAS many times
in "urban canyons". My Magellan Meridian indicates very clearly when
WAAS is being used and it is pretty much always available. I think
the real issue is whether it actually makes much of a difference. The
corrections applied seem to be on the order of 1-2 meters. My basic
accuracy seems to be on the order of 5 or more meters. So I don't
think I would see an additional 1-2 meters of fuzz on top of that.

I made the initial post when I was having trouble getting WAAS to work
with my Holux 240 receiver that uses the SiRF III chip set. I have
gotten that to work and do not see much of a difference either way.
So I am not really concerned with using WAAS at all now.