SiRF III: is sensitivity better than accuracy?

Larry G wrote:

I've not used the NG software. But with GPS Utility I can open the USGS
topo *.tif (tiff?) images and display my tracks and waypoints over them.
The USGS topos are a free download and are the same maps you have in
the NG package I think. They may add some features to the NG package
but I think the detail is the same. GPSU even comes with some sample
files and a good tutorial for calibrating maps. I don't remember that
the map images can be edited from GPSU though.

I bought GPSU and have found it meets all my needs for looking at data
and moving it around and I've received a great number of upgrades with
no additional fees. The developer, Alan Murphy, is an occasional
visitor here and very interactive with users. He seems to have the goal
of keeping GPSU as compatible and up to date with as possible. The
trial version is worth looking at.

Ozi Explorer is another good bet for those that want to work on their
own map editing. I think it has quite a bit of versatility as far as
editing the map image files. I did not ever actually use Ozi Explorer
to do that though, I was just looking at tracks and data as temporary
overlays, not as edited into the map. I did buy Ozi Explorer-CE and use
it on a iPAQ PDA for marine and topo navigation until I got my Magellan
Meridians equipped with marine and topo mapping.

I am still waiting for a good rugged waterproof handheld (like my 76Cx)
that has an open architecture for mapping.

Jack

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

Interesting you mention that. I have been giving consideration to the
idea of an open source GPS receiver. Of all the issues involved, I
think the mechanicals are the hardest for an open source project.
Software is perfect for such a project. I have even seen open source
hardware designed. But the packaging is a whole 'nother ball of wax
that would be very hard to produce. I have this on my list of things
to explore. There may be some sort of case that can be bought off the
shelf for inserting your own electronics into.

Otherwise, I have a couple of people interested in working on an open
source software effort using PDAs. I think this would be the best
first step. PDAs may not be as rugged as off the shelf GPS devices,
but they can be obtained cheaper by using older technology and can be
made rugged using an Otterbox or similar. The real advantage is that
the flexibility is unlimited!

If you are interested, I will keep you informed as things progress.

nemo wrote:

Magellan was on the fringes of attracting me at one point in time.
Their MobileMapper models in the Thales/Magellan professional products
line seemed to be really nice. Except for their pricing of course.

The pages for those are still around but I'm not sure how viable or well
supported they are under the new ownership:

http://pro.magellangps.com/en/products/product.asp?PRODID=1021

I was using both Magellan Meridians and PDAs at the time and that model
see seemed to combine the best of all of it. And that was supported by a
free for the downloading MobileMapper Office software suite that opened
the mapping it could use to a lot of things that are in the GIS world.

http://pro.magellangps.com/en/products/product.asp?PRODID=984

I'm not sure what the status of all that Magellan stuff is now. But
that is the kind of device I envisioned myself as wanting. In the
meantime I've moved away from wanting to do some of those for myself.
But the interest in being able to use the free down loadable USGS and
NOAA maps and charts on a device like that still lingers in the back of
my mind.


I agree, I had a lot of fun messing with iPAQ and Palm devices. I
starting doing some boat deliveries that necessitated (and paid for) my
move to good rugged waterproof off the shelf stuff and it is hard to
move back to trying to do it with that nest of bits and pieces, cables,
and the general fragility of it all.


Please do. And I think it is always of some interest to these
newsgroups too.

Jack

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

Larry G wrote:


That "walking" is the distance accumulated from one track to the next.
It is a rare (if ever) occurrence to have two consecutive trackpoints
with the same location so they are always going to be some distance apart.


It generates a track point in track memory. And if you have that option
turned on it will save all track points collected to a *.gpx file on the
microSD card. There are user settings for the collection rate and you
can collect trackpoints either on time intervals or on distances.


Is that the blue (cyan?) circle seen around the location marker? If so,
that represents the EPE (Estimated Position Error, the value can be seen
on the Satellite page) as a circular area. In theory, you could be
anywhere within that circle. You'll notice that the size of the circle
changes with the EPE value. It is particularly noticeable when the GPS
is first started up because the in initial fix will be a large number
and it will decrease pretty rapidly.


It is normal. The 60/76 Cx/CSx (and all the "x" series models that have
microSD cards) are really very capable as far as track recording. If
you have the Log Track To Data Card check box checked, every single
track point collected by the unit will be saved to a *.gpx file on the
microSD card. There is one file for each the GPS is turned on and there
will be separate track segments for each no fix to fix transition or
each time the GPS is turned on.

The *.gpx files cannot be seen from the GPS. You can to download them
to your hard drive (from the GPS in the USB Mass Storage Mode or from
the microSD card in a reader) and open them with MapSource or with any
of a number of third party applications that will read *.gpx files.

I really like the fact that I can set a high trackpoint collection rate
and, let the GPS overwrite the 10,000 trackpoint memory capacity when it
is full, and still recover all track data from the *.gpx file. And as
long as there is space on the data card, I can go for long periods of
time without having to download tracks. The *.gpx files contain the
location, date and time, and elevation for each track point.


I don't know of any consumer grade GPSRs that are calibrated by the
users. In the pure sense of the word "calibrate", there are no options
for the user to collect or study the GPS data and made any changes to
the receiver to improve or change performance based on their
observations. The fix locations are derived from the satellite data and
the routines in the software, what you see is what you get at any given
moment. There are some calibration requirements and options for the
models with internal compasses and barometers but not for the GPS function.

Jack

Jack Erbes wrote:
[snip]

The "walking" is simply the unit generating different position values
as time passes. Larry has the receiver sitting on a desk that's
not moving.

The recorded trackpoints will usually be some distance apart
only if track logging is set to "Auto" or "Distance". If
track logging is set to "Time" and the receiver is stationary,
then successive same locations may be common (somewhat
dependent on time interval).

For some data I've collected recording locations at a one
second rate and a fairly good view of the sky:

Of 54,805 trackpoints,
92% were the same as the previous location
7% changed one of the two horizontal coordinates from
the previous location
< 1% changed both horizontal coordinates
from the previous location

For some data I've collected recording locations at a one
second rate and a poor view of the sky:

Of 75,874 points,
71% were the same as the previous location
23% changed one of the two horizontal coordinates from
the previous location
6% changed both horizontal coordinates
from the previous location

The standard deviation of the above points is 19 feet.

Number of Times Coordinates Changed:
Easting Northing 2d Distance
Count Percent Count Percent Count Percent
Less than 1: 63332 83.5 83 61870 81.5 82 53959 71.1 71

By 1 meter: 10477 13.8 97 11336 14.9 96 17966 23.7 95

By 2 meters: 1568 2.1 99 1549 2.0 99 2544 3.4 98

By 3 meters: 108 0.1 99 625 0.8 99 713 0.9 99

By 4 meters: 68 0.1 100 79 0.1 99 197 0.3 99

By 5 meters: 40 0.1 100 82 0.1 100 66 0.1 99

By 6 meters: 32 0.0 100 25 0.0 100 51 0.1 100

By 7 meters: 18 0.0 100 43 0.1 100 31 0.0 100

By 8 meters: 17 0.0 100 18 0.0 100 29 0.0 100

By 9 meters: 19 0.0 100 22 0.0 100 32 0.0 100

10 or more: 194 0.3 100 224 0.3 100 285 0.4 100


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