Wireless on recumbents (RANS Stratus)

"Cletus D. Lee" wrote in message
T...
In article k.net,
says...

"Cletus Lee" wrote in message
Another choice, a Garmin Geko. uses GPS for speed and distance. No
wheel
magnet. It does under report speed by about 1.5% over a well calibrated
wired computer.

My Garmin Geko doesn't under report speed--it's right on.

I am sorry, You are correct about the speed. Mine is accurate to the
0.10 mph. Except for the time it registered 888 mph in downtown Houston
while I was stopped at a traffic light. It is distance that is under
reported by ~1.5%. The reason the distance is off is because the Geko
measures distance from point to point. A route with a lot of turns will
be in error. Also I have found that false signals are causing route
track errors in city canyons.

--
Cletus D. Lee
Bacchetta Giro
Lightning Voyager
http://www.clee.org
- Bellaire, TX USA -

Some of that tracking error may be avoidable, one problem is they are always
off by a few feet anyway and if I select power saver mode on my emap it
checks position every 2 or 3 seconds instead of 1, small difference but
still a difference. Even then both gps and computer are pretty spot on in
the end.

Odd thing is mine always shows me at least 100 feet off in my home town,
anywhere else is fine

"brian hughes" wrote in message
hlink.net...


Well, I'm not so sure about the trip distance being under-reported. When
I
first bought it, just for an experimentation I brought it along and
watched
it update while my wife was driving down the freeway. Assuming the survey
mile markers were correct, I didn't see any noticeable error at all. I
also
used it when I rode a century (actually a 108 mile ride), every rest stop
was exact on my Garmin, as was the final distance when compared to the
cheat-sheet. It was not 1.5 miles off, it wasn't even .15 miles off. But
heck, I guess you could also argue that they probably used some kind of
GPS
to calculate and make the cheat sheet to start with.

Maybe you know for sure, but I theorize the Garmin does not simply
triangulate between points (thus cutting corners as you indicate). I
believe the Garmin somehow integrates velocity, and thus doesn't
necessarily
cut off corners. The reason I believe this is I've seen the Garmin
continue
to update trip distance for a several seconds (at least) after the GPS
signal is lost.

Brian

My only gripe about Garmin is they are wayyyyy too slow updating maps, I
often ride on roads I know have been around for at least 10 years that still
don't show up on the gps.

"brian hughes" wrote in message
link.net...

"bentcruiser" wrote in message
om...
Rvc wrote:
I've just purchased a Stratus and wonder if any improvements have
been
made in the wireless computer world ?



If you are talking distance trouble, try putting the computer on the
derailleur tube.

That's what I did on my RANS Tailwind, it works just fine on the derailler
tube. Except last Tuesday when the weather was quite cold for these parts
(about 15 deg F) on my morning commute. My wireless only reported about
1/2 the distance I really traveled--kept jumping between my actual speed
and
zero. The rest of the week the temp was in the mid 20's and it worked
fine--I guess I could try a new battery but this one isn't that old.
Seems
like under 20 deg F it doesn't work dependably.

I don't think poor cold weather performance is a wireless thing. On my
V-Rex and my DFs I have wired computers and they don't work well either
when
it gets well below freezing. Anyone know of a computer that works well in
the bitter cold?

Some of that may be atmospheric conditions instead of the temperature

In article k.net,
says...

"Cletus D. Lee" wrote in message
T...
In article k.net,
says...

"Cletus Lee" wrote in message
Another choice, a Garmin Geko. uses GPS for speed and distance. No
wheel
magnet. It does under report speed by about 1.5% over a well calibrated
wired computer.

My Garmin Geko doesn't under report speed--it's right on.

I am sorry, You are correct about the speed. Mine is accurate to the
0.10 mph. Except for the time it registered 888 mph in downtown Houston
while I was stopped at a traffic light. It is distance that is under
reported by ~1.5%. The reason the distance is off is because the Geko
measures distance from point to point. A route with a lot of turns will
be in error. Also I have found that false signals are causing route
track errors in city canyons.

--
Cletus D. Lee
Bacchetta Giro
Lightning Voyager
http://www.clee.org
- Bellaire, TX USA -

Well, I'm not so sure about the trip distance being under-reported. When I
first bought it, just for an experimentation I brought it along and watched
it update while my wife was driving down the freeway. Assuming the survey
mile markers were correct, I didn't see any noticeable error at all. I also
used it when I rode a century (actually a 108 mile ride), every rest stop
was exact on my Garmin, as was the final distance when compared to the
cheat-sheet. It was not 1.5 miles off, it wasn't even .15 miles off. But
heck, I guess you could also argue that they probably used some kind of GPS
to calculate and make the cheat sheet to start with.

Maybe you know for sure, but I theorize the Garmin does not simply
triangulate between points (thus cutting corners as you indicate). I
believe the Garmin somehow integrates velocity, and thus doesn't necessarily
cut off corners. The reason I believe this is I've seen the Garmin continue
to update trip distance for a several seconds (at least) after the GPS
signal is lost.

What I know is from observation. Take a look at the track produced by
your Garmin. Compare on a map against the roads actually taken. I
think you will find the route is a series of chords. The distance along
those chords is the distance measured and reported by the GPS. The
Chord is always (by definition) shorted than the curve that it spans.
This is the error that I refer to. It is not much but it accumulates.
More accurate on straight roads, less so on routes with lots of turns.

As for your 108 mile Century, if the sponsors did anything other than
actually chain off the actual distance, then it is an approximation.

If you want to really see how accurate your Garmin really is at
distance, take it to a High School track. At cycle speeds, do several
miles of a known distance (caution the track may be metric). See how
that compares to the known distance.

I did this with my Magellan once and was lucky to get three points per
lap. I would have sampled more often if I had been walking.


--
Cletus D. Lee
Bacchetta Giro
Lightning Voyager
http://www.clee.org
- Bellaire, TX USA -

I agree with Cletus about chords being shorter than arcs. I would try his
method of testing the distance of a GPS unit at a High School track.

My Garmin GPS III+ takes readings when I change speed or direction. The
following excerpt from one of my journeys (this was in an uphill portion of
the route) shows how frequently it will mark a point on a track. When I
change direction or speed it stores a "Trackpoint", provides the latitude
and longitude of the point, shows the time it created the point, then shows
the distance, elapsed time, speed, and heading to the next "Trackpoint"
Trackpoint N47 48 39.4 W122 00 44.8 3/15/03 9:10:33 AM 36 ft 00:00:02 12.2
mph 278° true
Trackpoint N47 48 39.4 W122 00 45.1 3/15/03 9:10:34 AM 17 ft 00:00:01 11.7
mph 270° true
Trackpoint N47 48 39.0 W122 00 46.2 3/15/03 9:10:39 AM 88 ft 00:00:05 12.0
mph 242° true
Trackpoint N47 48 38.8 W122 00 46.6 3/15/03 9:10:41 AM 39 ft 00:00:02 13.2
mph 227° true
Trackpoint N47 48 38.6 W122 00 46.8 3/15/03 9:10:42 AM 20 ft 00:00:01 14.0
mph 220° true

The following excerpt shows the frequency when I am in flat and straight
sections of a ride
Trackpoint N47 50 18.4 W122 04 25.5 3/15/03 9:24:04 AM 570 ft 00:00:18
21.6 mph 326° true
Trackpoint N47 50 21.2 W122 04 30.4 3/15/03 9:24:17 AM 438 ft 00:00:13
23.0 mph 310° true
Trackpoint N47 50 23.9 W122 04 36.1 3/15/03 9:24:32 AM 476 ft 00:00:15
21.7 mph 306° true
Trackpoint N47 50 26.2 W122 04 39.6 3/15/03 9:24:41 AM 332 ft 00:00:09
25.1 mph 313° true
Trackpoint N47 50 26.7 W122 04 41.0 3/15/03 9:24:44 AM 113 ft 00:00:03
25.6 mph 300° true
Trackpoint N47 50 29.8 W122 04 47.1 3/15/03 9:24:58 AM 520 ft 00:00:14
25.3 mph 307° true
Trackpoint N47 50 30.8 W122 04 49.4 3/15/03 9:25:04 AM 188 ft 00:00:06
21.3 mph 302° true

As you can see it does a fairly good job of reporting the changes in
direction and speed. If my direction and speed remain constant, the
frequency of reporting get stretched out. Most roads have a fairly large
radius curves. If you have an 11.5 degree arc with a 500 foot radius the
difference between the arc length and the chord length is about 0.16 feet.
This is in a nominal 100 section of road. Most roads that I work with and
ride on have a radius that is usually measured in the thousands of feet. In
cases like that the difference becomes even less.

Having said something about the theoretical side I would advise a person to
use the approach suggested by Cletus. That should give you a good reference
for the accuracy of the unit you use.

William Higley, Sr.
Vision R-50
RANS Rocket


"Cletus D. Lee" wrote in message
T...
In article k.net,
says...

"Cletus D. Lee" wrote in message
T...
In article k.net,
says...

"Cletus Lee" wrote in message
Another choice, a Garmin Geko. uses GPS for speed and distance.
No
wheel
magnet. It does under report speed by about 1.5% over a well
calibrated
wired computer.

My Garmin Geko doesn't under report speed--it's right on.

I am sorry, You are correct about the speed. Mine is accurate to the
0.10 mph. Except for the time it registered 888 mph in downtown
Houston
while I was stopped at a traffic light. It is distance that is under
reported by ~1.5%. The reason the distance is off is because the Geko
measures distance from point to point. A route with a lot of turns
will
be in error. Also I have found that false signals are causing route
track errors in city canyons.

--
Cletus D. Lee
Bacchetta Giro
Lightning Voyager
http://www.clee.org
- Bellaire, TX USA -

Well, I'm not so sure about the trip distance being under-reported.
When I
first bought it, just for an experimentation I brought it along and
watched
it update while my wife was driving down the freeway. Assuming the
survey
mile markers were correct, I didn't see any noticeable error at all. I
also
used it when I rode a century (actually a 108 mile ride), every rest
stop
was exact on my Garmin, as was the final distance when compared to the
cheat-sheet. It was not 1.5 miles off, it wasn't even .15 miles off.
But
heck, I guess you could also argue that they probably used some kind of
GPS
to calculate and make the cheat sheet to start with.

Maybe you know for sure, but I theorize the Garmin does not simply
triangulate between points (thus cutting corners as you indicate). I
believe the Garmin somehow integrates velocity, and thus doesn't
necessarily
cut off corners. The reason I believe this is I've seen the Garmin
continue
to update trip distance for a several seconds (at least) after the GPS
signal is lost.

What I know is from observation. Take a look at the track produced by
your Garmin. Compare on a map against the roads actually taken. I
think you will find the route is a series of chords. The distance along
those chords is the distance measured and reported by the GPS. The
Chord is always (by definition) shorted than the curve that it spans.
This is the error that I refer to. It is not much but it accumulates.
More accurate on straight roads, less so on routes with lots of turns.

As for your 108 mile Century, if the sponsors did anything other than
actually chain off the actual distance, then it is an approximation.

If you want to really see how accurate your Garmin really is at
distance, take it to a High School track. At cycle speeds, do several
miles of a known distance (caution the track may be metric). See how
that compares to the known distance.

I did this with my Magellan once and was lucky to get three points per
lap. I would have sampled more often if I had been walking.


--
Cletus D. Lee
Bacchetta Giro
Lightning Voyager
http://www.clee.org
- Bellaire, TX USA -

"William Higley, Sr." wrote in
:

I agree with Cletus about chords being shorter than arcs. I would try
his method of testing the distance of a GPS unit at a High School
track.

My Garmin GPS III+ takes readings when I change speed or direction.
The following excerpt from one of my journeys (this was in an uphill
portion of the route) shows how frequently it will mark a point on a
track. When I change direction or speed it stores a "Trackpoint",
provides the latitude and longitude of the point, shows the time it
created the point, then shows the distance, elapsed time, speed, and
heading to the next "Trackpoint" Trackpoint N47 48 39.4 W122 00 44.8
3/15/03 9:10:33 AM 36 ft 00:00:02 12.2 mph 278° true
Trackpoint N47 48 39.4 W122 00 45.1 3/15/03 9:10:34 AM 17 ft
00:00:01 11.7 mph 270° true
edit for brevity
00:00:06 21.3 mph 302° true

As you can see it does a fairly good job of reporting the changes in
direction and speed. If my direction and speed remain constant, the
frequency of reporting get stretched out. Most roads have a fairly
large radius curves. If you have an 11.5 degree arc with a 500 foot
radius the difference between the arc length and the chord length is
about 0.16 feet. This is in a nominal 100 section of road. Most roads
that I work with and ride on have a radius that is usually measured in
the thousands of feet. In cases like that the difference becomes even
less.



A couple of observations if I may.

Altitude is bizarre in GPS speak. For giggles google geoid. Beyond
that, the earth model used by a particular GPS can have an impact on
accuracy, particularly given your surface route is in 3 dimensions.

Further be aware of the distinction between "taking a reading" and
"storing a datum." While there is an entire newsgroup dedicated to GPS,
here are some basics.

Garmin supports two families of near real time reporting protocols, one
proprietary and one per the not-as-tight-as-it-could-be NMEA standard.
Per NMEA, it will report each "sentence" every 2 seconds. I don't
remember the frequency of the proprietary messages, but it's something
similar (not a useful improvement for most applications. Its chief
advantage seems to be in a more tightly written spec). Given the RAM
inside the device is finite, if you were saving vectors it would stand to
reason to skip any successive vectors where the data (excluding
timestamp) were the same, and let the plotting software figure it out.
Think of it as a finely detailed cue sheet - the changes you don't make
aren't recorded. In any event, you'll have no saved updates closer
together than some arbitrary minimum time which is quite likely some
multiple of the actual calculation frame. Anything less than 500ms would
surprise me on a low-cost unit, with 1 sec being a more expected delta
time. My hunch is that they use the same "engine" on most of their GPS
receivers, but dumb 'em down for non time critical applications (read non
aviation, non-NASA, and non-military). I'd suspect the device is running
through the position calculations every 20-1000ms; that's just a hunch
though.


"guess where you are now!"
Howard

bitshift blah blah.

In my property description, there is a description of a rail road right
of way. It starts 1/2 miles south of my house, 1/4 mile west, going
east, and 2 degree turn to the north until some station number, and
somehow comes across my property. The only way that makes send is if it
is about 1/4 radius turn.

"William Higley, Sr." wrote:
snip
Most roads have a fairly large
radius curves. If you have an 11.5 degree arc with a 500 foot radius the
difference between the arc length and the chord length is about 0.16 feet.
This is in a nominal 100 section of road. Most roads that I work with and
ride on have a radius that is usually measured in the thousands of feet. In
cases like that the difference becomes even less.
snip
William Higley, Sr.
Vision R-50
RANS Rocket

Railroad curves are treated a bit differently than road curves. A 2 degree
railroad curve will have a radius of approximately 2865'. The 2 degrees
refers to the interior angle that well be subtended by a 100' chord. Most
modern highway curves use a 100' arc length definition. The older highways
used the railroad definition because at the time, most Engineers with route
layout experience came from the railroads.

I may have caused confusion in my original statement when I spoke of an 11.5
degree arc. More properly stated it should have read "a curve with a 500'
radius and a central angle of 11.5 degrees." This would provide an arc
length of approximately 100'.

William Higley, Sr., P.L.S.
Vision R-50
RANS Rocket
"Mike Schwab" wrote in message
...
In my property description, there is a description of a rail road right
of way. It starts 1/2 miles south of my house, 1/4 mile west, going
east, and 2 degree turn to the north until some station number, and
somehow comes across my property. The only way that makes send is if it
is about 1/4 radius turn.

"William Higley, Sr." wrote:
snip
Most roads have a fairly large
radius curves. If you have an 11.5 degree arc with a 500 foot radius the
difference between the arc length and the chord length is about 0.16
feet.
This is in a nominal 100 section of road. Most roads that I work with
and
ride on have a radius that is usually measured in the thousands of feet.
In
cases like that the difference becomes even less.
snip
William Higley, Sr.
Vision R-50
RANS Rocket

"William Higley, Sr." wrote:

Railroad curves are treated a bit differently than road curves. A 2 degree
railroad curve will have a radius of approximately 2865'. The 2 degrees
refers to the interior angle that well be subtended by a 100' chord. Most
modern highway curves use a 100' arc length definition. The older highways
used the railroad definition because at the time, most Engineers with route
layout experience came from the railroads.

I may have caused confusion in my original statement when I spoke of an 11.5
degree arc. More properly stated it should have read "a curve with a 500'
radius and a central angle of 11.5 degrees." This would provide an arc
length of approximately 100'.



Hmm, two radii of 2865' with outer ends 100' apart = two degrees of
subtended arc, right?

Now, two radii of 500 foot length and included angle of 11.5 degrees has
100' arc length?

Scribble, scribble, erase, erase, scribble...

Tune in next year for response, if I can find my way back!

Dean Arthur wrote:

"William Higley, Sr." wrote:

Railroad curves are treated a bit differently than road curves. A 2 degree
railroad curve will have a radius of approximately 2865'. The 2 degrees
refers to the interior angle that well be subtended by a 100' chord. Most
modern highway curves use a 100' arc length definition. The older highways
used the railroad definition because at the time, most Engineers with route
layout experience came from the railroads.

I may have caused confusion in my original statement when I spoke of an 11.5
degree arc. More properly stated it should have read "a curve with a 500'
radius and a central angle of 11.5 degrees." This would provide an arc
length of approximately 100'.


Hmm, two radii of 2865' with outer ends 100' apart = two degrees of
subtended arc, right?

No. At 100 feet distance from starting point, the curve is 2 degrees to
one side of the straight ahead line. Repeart 45 times for 4500 feet
along the circumference, you will have turned 90 degrees. 90 times for
9000 feet 180 degrees, 180 times 18000 feet 360 degrees. C = 2 PI r
18000 /2 = 9000, 9000 /3.1415926 = 2864.789 feet radius. That distance
makes sense for this railroad to touch my property.

Now, two radii of 500 foot length and included angle of 11.5 degrees has
100' arc length?
At 100 feet, the curve is 11.5 degrees to one side of the straight ahead
line. Reapeat for 15.65 times for 1565 feet for 180 degrees divide by
PI 3.1415926 = 498.15 feet.