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Main
Date: 17 Sep 2007 12:11:33
From: Colin Campbell
Subject: Bicycle Computer Altimeter Accuracy
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Yesterday, I did one of Southern California's classic mountain rides -
Glendora Mountain Road. According to my bike computer, I did 1298
meters of climbing, and 1541 meters of descending (ending up exactly
where I started).
Is there any way of guessing which of these numbers might be more accurate?
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Date: 20 Sep 2007 18:07:25
From: Robert Chung
Subject: Re: Bicycle Computer Altimeter Accuracy
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On Sep 20, 4:35 pm, Ron Hardin <rhhar...@mindspring.com > wrote:
> rechungREMOVET...@gmail.com wrote:
>
> > On Sep 20, 11:03 am, Ron Hardin <rhhar...@mindspring.com> wrote:
>
> > > Yet you gain thousands of feet over the ride, which is indistinguishable
> > > effort-wise from an everywhere-level ride.
>
> > Those two rides are distinguishable.
>
> Actually not.
Actually, yes.
http://anonymous.coward.free.fr/wattage/cda/indirect-cda.pdf
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Date: 20 Sep 2007 19:35:21
From: Ron Hardin
Subject: Re: Bicycle Computer Altimeter Accuracy
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rechungREMOVETHIS@gmail.com wrote:
>
> On Sep 20, 11:03 am, Ron Hardin <rhhar...@mindspring.com> wrote:
>
> > Yet you gain thousands of feet over the ride, which is indistinguishable
> > effort-wise from an everywhere-level ride.
>
> Those two rides are distinguishable.
Actually not. Your speed drops less for a given rise the higher your speed.
dE = V dV
or
dV = dE / V
where dE is the energy from the rise. dV the change in speed is less the
faster you're going.
You notice this at the bottom of a valley when you think you're going to
make it way, way up the next hill because you're not slowing down much,
an opinion you change when you've climbed about 20 feet, but not before.
At normal bicycle speeds, you'd never notice a half foot ``road wave.''
--
rhhardin@mindspring.com
On the internet, nobody knows you're a jerk.
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Date: 20 Sep 2007 20:43:48
From:
Subject: Re: Bicycle Computer Altimeter Accuracy
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On Sep 20, 11:03 am, Ron Hardin <rhhar...@mindspring.com > wrote:
> Yet you gain thousands of feet over the ride, which is indistinguishable
> effort-wise from an everywhere-level ride.
Those two rides are distinguishable.
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Date: 20 Sep 2007 14:03:11
From: Ron Hardin
Subject: Re: Bicycle Computer Altimeter Accuracy
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> > Right, but the reason why most of us want to know the elevation gain
> > is because elevation gain has come to be a proxy measure for effort.
It's not true, though.
Imagine that the road is a series of half foot hills, a wavy surface but
smoothly spaced, so you just ride over them.
There's almost no reduction in speed at the tops, and your average speed
is pretty exactly the same as without them.
Yet you gain thousands of feet over the ride, which is indistinguishable
effort-wise from an everywhere-level ride.
The energy you put into kinetic energy serves as a buffer that gives out
and takes back the energy of the height changes without any intervention
by you, except the normal keeping-up against level air resistance.
--
rhhardin@mindspring.com
On the internet, nobody knows you're a jerk.
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Date: 20 Sep 2007 05:52:56
From:
Subject: Re: Bicycle Computer Altimeter Accuracy
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On Sep 18, 10:25 pm, rechungREMOVET...@gmail.com wrote:
> On Sep 17, 11:30 pm, "b...@mambo.ucolick.org" <b...@mambo.ucolick.org>
> wrote:
>
> > > In certain circumstances, a bicycle power meter has greater resolution
> > > in measuring elevation change than either the consumer level
> > > altimeters or GPS receivers that one finds on bicycles.
>
> > Yesbut, resolution is not the same as accuracy, as you
> > know. It may be accurate under certain circumstances,
> > but in the mountains, there is often a wind blowing.
>
> Right, but the reason why most of us want to know the elevation gain
> is because elevation gain has come to be a proxy measure for effort.
>
> FWIW, take a look at this:http://anonymous.coward.free.fr/wattage/cda/indirect-cda.pdf
Hey, this is really cool! Have you tried publishing this in a sports
related journal?
> It's an old version and I've done a bit more with it since then, but
> notice that I picked out a drainage grate on the edge of a "flat"
> road. I'd appreciate your comments.
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Date: 18 Sep 2007 21:23:00
From: Arthur Shapiro
Subject: Re: Bicycle Computer Altimeter Accuracy
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In article <46eed159$0$9534$4c368faf@roadrunner.com >, Colin Campbell <cmcampb@adelphia.net> wrote:
>Yesterday, I did one of Southern California's classic mountain rides -
>Glendora Mountain Road. According to my bike computer, I did 1298
>meters of climbing, and 1541 meters of descending (ending up exactly
>where I started).
For what it's worth, when I do GMR starting at Boulder Springs Road (the one
stop light, a convenient place to park), my Cateye ranges between 4860 and
5240 feet of climbing for the ordinary back-and-forth to Mt. Baldy Village. I
wish the results were more consistent.
Art
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Date: 18 Sep 2007 17:46:05
From: Colin Campbell
Subject: Re: Bicycle Computer Altimeter Accuracy
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Arthur Shapiro wrote:
> In article <46eed159$0$9534$4c368faf@roadrunner.com>, Colin Campbell <cmcampb@adelphia.net> wrote:
>> Yesterday, I did one of Southern California's classic mountain rides -
>> Glendora Mountain Road. According to my bike computer, I did 1298
>> meters of climbing, and 1541 meters of descending (ending up exactly
>> where I started).
>
> For what it's worth, when I do GMR starting at Boulder Springs Road (the one
> stop light, a convenient place to park), my Cateye ranges between 4860 and
> 5240 feet of climbing for the ordinary back-and-forth to Mt. Baldy Village. I
> wish the results were more consistent.
>
> Art
>
Art,
I don't find a Boulder Springs Road using Google Maps. Where is that?
I usually start from the 210 Freeway & Grand in Glendora. North on
Grand to Sierra Madre, east on Sierra Madre to GMR. Occasionally, we'll
start from Costco (W Foothill & Todd in Azusa). This past Sunday, we
started from a fellow club member's place in La Verne (I was mostly lost
at the start).
Colin
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Date: 18 Sep 2007 20:33:30
From:
Subject: Re: Bicycle Computer Altimeter Accuracy
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On Tue, 18 Sep 2007 17:46:05 -0700, Colin Campbell
<cmcampb@adelphia.net > wrote:
>Arthur Shapiro wrote:
>> In article <46eed159$0$9534$4c368faf@roadrunner.com>, Colin Campbell <cmcampb@adelphia.net> wrote:
>>> Yesterday, I did one of Southern California's classic mountain rides -
>>> Glendora Mountain Road. According to my bike computer, I did 1298
>>> meters of climbing, and 1541 meters of descending (ending up exactly
>>> where I started).
>>
>> For what it's worth, when I do GMR starting at Boulder Springs Road (the one
>> stop light, a convenient place to park), my Cateye ranges between 4860 and
>> 5240 feet of climbing for the ordinary back-and-forth to Mt. Baldy Village. I
>> wish the results were more consistent.
>>
>> Art
>>
>Art,
>I don't find a Boulder Springs Road using Google Maps. Where is that?
>
>I usually start from the 210 Freeway & Grand in Glendora. North on
>Grand to Sierra Madre, east on Sierra Madre to GMR. Occasionally, we'll
>start from Costco (W Foothill & Todd in Azusa). This past Sunday, we
>started from a fellow club member's place in La Verne (I was mostly lost
>at the start).
>Colin
Dear Colin,
http://yellowpages.superpages.com/directions.jsp?SRC=411loc1&URI=&UI=2004&var1=&var2=&var9=&var10=&STYPE=&OCC=&DCC=&ORPIM=1&DRPIM=1&OPNAME=1&SP_LABEL_ORIGIN=&SP_LABEL1_ORIGIN=&SP_ADDR_ORIGIN=&SP_CITY_ORIGIN=&SP_STATE_ORIGIN=&SP_GEOCODE_ORIGIN=false&SP_LONG_ORIGIN=&SP_LAT_ORIGIN=&SP_LABEL_DESTINATION=&SP_LABEL1_DESTINATION=&SP_ADDR_DESTINATION=&SP_CITY_DESTINATION=&SP_STATE_DESTINATION=&SP_GEOCODE_DESTINATION=false&SP_LONG_DESTINATION=&SP_LAT_DESTINATION=&LANG=en-US&ADDR_ORIGIN=&CITY_ORIGIN=glendora&STATE_ORIGIN=CA&ZIP_ORIGIN=%28optional%29&ADDR_DESTINATION=boulder+springs+drive&CITY_DESTINATION=glendora&STATE_DESTINATION=CA&ZIP_DESTINATION=%28optional%29&results_display_mode=map&route_type=fastest&ROUTE_UNITS=2
Cheers,
Carl Fogel
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Date: 18 Sep 2007 19:58:14
From: Colin Campbell
Subject: Re: Bicycle Computer Altimeter Accuracy
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carlfogel@comcast.net wrote:
> On Tue, 18 Sep 2007 17:46:05 -0700, Colin Campbell
> <cmcampb@adelphia.net> wrote:
>
>> Arthur Shapiro wrote:
>>> In article <46eed159$0$9534$4c368faf@roadrunner.com>, Colin Campbell <cmcampb@adelphia.net> wrote:
>>>> Yesterday, I did one of Southern California's classic mountain rides -
>>>> Glendora Mountain Road. According to my bike computer, I did 1298
>>>> meters of climbing, and 1541 meters of descending (ending up exactly
>>>> where I started).
>>> For what it's worth, when I do GMR starting at Boulder Springs Road (the one
>>> stop light, a convenient place to park), my Cateye ranges between 4860 and
>>> 5240 feet of climbing for the ordinary back-and-forth to Mt. Baldy Village. I
>>> wish the results were more consistent.
>>>
>>> Art
>>>
>> Art,
>> I don't find a Boulder Springs Road using Google Maps. Where is that?
>>
>> I usually start from the 210 Freeway & Grand in Glendora. North on
>> Grand to Sierra Madre, east on Sierra Madre to GMR. Occasionally, we'll
>> start from Costco (W Foothill & Todd in Azusa). This past Sunday, we
>> started from a fellow club member's place in La Verne (I was mostly lost
>> at the start).
>> Colin
>
> Dear Colin,
>
> http://yellowpages.superpages.com/directions.jsp?SRC=411loc1&URI=&UI=2004&var1=&var2=&var9=&var10=&STYPE=&OCC=&DCC=&ORPIM=1&DRPIM=1&OPNAME=1&SP_LABEL_ORIGIN=&SP_LABEL1_ORIGIN=&SP_ADDR_ORIGIN=&SP_CITY_ORIGIN=&SP_STATE_ORIGIN=&SP_GEOCODE_ORIGIN=false&SP_LONG_ORIGIN=&SP_LAT_ORIGIN=&SP_LABEL_DESTINATION=&SP_LABEL1_DESTINATION=&SP_ADDR_DESTINATION=&SP_CITY_DESTINATION=&SP_STATE_DESTINATION=&SP_GEOCODE_DESTINATION=false&SP_LONG_DESTINATION=&SP_LAT_DESTINATION=&LANG=en-US&ADDR_ORIGIN=&CITY_ORIGIN=glendora&STATE_ORIGIN=CA&ZIP_ORIGIN=%28optional%29&ADDR_DESTINATION=boulder+springs+drive&CITY_DESTINATION=glendora&STATE_DESTINATION=CA&ZIP_DESTINATION=%28optional%29&results_display_mode=map&route_type=fastest&ROUTE_UNITS=2
>
> Cheers,
>
> Carl Fogel
Thanks, Carl. When are you coming to ride it?
Now I know that Art is short-cutting the route by starting at the very
base of the climb! Maybe I'll see his car next time I go.
It's funny that Google Maps wouldn't try to show me more "Boulder
Springs" choices when I had the "Road" part wrong. But now I know to
try other "types", like Avenue, Drive, Boulevard, etc. Also, when I
tried "Boulder Springs", Google Maps gave me a useless location in the
middle of the desert. I had to add "Glendora, CA" to get the right place.
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Date: 18 Sep 2007 21:09:01
From:
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Tue, 18 Sep 2007 19:58:14 -0700, Colin Campbell
<cmcampb@adelphia.net > wrote:
>carlfogel@comcast.net wrote:
>> On Tue, 18 Sep 2007 17:46:05 -0700, Colin Campbell
>> <cmcampb@adelphia.net> wrote:
>>
>>> Arthur Shapiro wrote:
>>>> In article <46eed159$0$9534$4c368faf@roadrunner.com>, Colin Campbell <cmcampb@adelphia.net> wrote:
>>>>> Yesterday, I did one of Southern California's classic mountain rides -
>>>>> Glendora Mountain Road. According to my bike computer, I did 1298
>>>>> meters of climbing, and 1541 meters of descending (ending up exactly
>>>>> where I started).
>>>> For what it's worth, when I do GMR starting at Boulder Springs Road (the one
>>>> stop light, a convenient place to park), my Cateye ranges between 4860 and
>>>> 5240 feet of climbing for the ordinary back-and-forth to Mt. Baldy Village. I
>>>> wish the results were more consistent.
>>>>
>>>> Art
>>>>
>>> Art,
>>> I don't find a Boulder Springs Road using Google Maps. Where is that?
>>>
>>> I usually start from the 210 Freeway & Grand in Glendora. North on
>>> Grand to Sierra Madre, east on Sierra Madre to GMR. Occasionally, we'll
>>> start from Costco (W Foothill & Todd in Azusa). This past Sunday, we
>>> started from a fellow club member's place in La Verne (I was mostly lost
>>> at the start).
>>> Colin
>>
>> Dear Colin,
>>
>> http://yellowpages.superpages.com/directions.jsp?SRC=411loc1&URI=&UI=2004&var1=&var2=&var9=&var10=&STYPE=&OCC=&DCC=&ORPIM=1&DRPIM=1&OPNAME=1&SP_LABEL_ORIGIN=&SP_LABEL1_ORIGIN=&SP_ADDR_ORIGIN=&SP_CITY_ORIGIN=&SP_STATE_ORIGIN=&SP_GEOCODE_ORIGIN=false&SP_LONG_ORIGIN=&SP_LAT_ORIGIN=&SP_LABEL_DESTINATION=&SP_LABEL1_DESTINATION=&SP_ADDR_DESTINATION=&SP_CITY_DESTINATION=&SP_STATE_DESTINATION=&SP_GEOCODE_DESTINATION=false&SP_LONG_DESTINATION=&SP_LAT_DESTINATION=&LANG=en-US&ADDR_ORIGIN=&CITY_ORIGIN=glendora&STATE_ORIGIN=CA&ZIP_ORIGIN=%28optional%29&ADDR_DESTINATION=boulder+springs+drive&CITY_DESTINATION=glendora&STATE_DESTINATION=CA&ZIP_DESTINATION=%28optional%29&results_display_mode=map&route_type=fastest&ROUTE_UNITS=2
>>
>> Cheers,
>>
>> Carl Fogel
>Thanks, Carl. When are you coming to ride it?
>
>Now I know that Art is short-cutting the route by starting at the very
>base of the climb! Maybe I'll see his car next time I go.
>
>It's funny that Google Maps wouldn't try to show me more "Boulder
>Springs" choices when I had the "Road" part wrong. But now I know to
>try other "types", like Avenue, Drive, Boulevard, etc. Also, when I
>tried "Boulder Springs", Google Maps gave me a useless location in the
>middle of the desert. I had to add "Glendora, CA" to get the right place.
Dear Colin,
Alas, too many roads, not enough time. But thanks for the invitation.
Let's not say that Art is short-cutting. Rather, he is honoring the
tradition of the early Tour de France riders, who sometimes abridged
the tedious official route with taxis and trains:
"Lifts: in the early years, riders would regularly grab a lift in
supporters' cars or else cling to them. In 1928, two riders jumped in
a taxi after the truck they were travelling in crashed into a ditch."
"Short cuts: in 1906, three riders caught the train to Dijon, but were
caught by Tour officials; three-time Tour winner Philippe Thys once
asked a shepherd for a short cut over the Col de Peyresourde, but got
lost on the track."
http://sport.independent.co.uk/general/article2740529.ece
At least he isn't chopping down trees to block the road:
"Trees: in 1904, fans blocked the road with felled trees to prevent
rival riders getting past."
Cheers,
Carl Fogel
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Date: 19 Sep 2007 04:28:42
From: Arthur Shapiro
Subject: Re: Bicycle Computer Altimeter Accuracy
|
>Let's not say that Art is short-cutting. Rather, he is honoring the
>tradition of the early Tour de France riders, who sometimes abridged
>the tedious official route with taxis and trains:
Hey, guys. I start there simply because that's the way my club has always
"advertised" the ride, with Boulder Springs being a nice neighborhood with
ample parking. There's no intent to cheat, although I realize it's a few
blocks up up from Sierra Whatchamacallit. If I have to ride down and back at
the end of the ride to be "pure", just tell me - I'm not scared of climbs.
Hell, I did the ski lifts three times in July, and threw in Little GMR down
and back one of those times for an 8340' day. The ski lifts in a 39x25 hurts,
Big Time. And I did GMR the day before Labor Day, and it was 109 degrees when
I got back to the car. So give me a break!
Art (grumble, grumble)
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Date: 19 Sep 2007 10:46:12
From: Colin Campbell
Subject: Re: Bicycle Computer Altimeter Accuracy
|
Arthur Shapiro wrote:
>> Let's not say that Art is short-cutting. Rather, he is honoring the
>> tradition of the early Tour de France riders, who sometimes abridged
>> the tedious official route with taxis and trains:
>
>
> Hey, guys. I start there simply because that's the way my club has always
> "advertised" the ride, with Boulder Springs being a nice neighborhood with
> ample parking. There's no intent to cheat, although I realize it's a few
> blocks up up from Sierra Whatchamacallit. If I have to ride down and back at
> the end of the ride to be "pure", just tell me - I'm not scared of climbs.
>
> Hell, I did the ski lifts three times in July, and threw in Little GMR down
> and back one of those times for an 8340' day. The ski lifts in a 39x25 hurts,
> Big Time. And I did GMR the day before Labor Day, and it was 109 degrees when
> I got back to the car. So give me a break!
>
> Art (grumble, grumble)
OK, Art, I'll give you the benefit of the doubt. I think I'm probably
already "slogging" when I get to that intersection, and that's why I
never noticed the street name. And I've sure never gone to the ski
lifts - people who CAN climb tell me it's darned tough, so kudos to you!
I did a beach loop on Labor Day (and it only got to 108F in Fullerton,
and 90F inside my house) - took me two days to recover from that. I
can't imagine what GMR would have done to me!
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Date: 18 Sep 2007 23:24:09
From:
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Wed, 19 Sep 2007 04:28:42 GMT, arthur-temp-3@cox.net (Arthur
Shapiro) wrote:
>
>>Let's not say that Art is short-cutting. Rather, he is honoring the
>>tradition of the early Tour de France riders, who sometimes abridged
>>the tedious official route with taxis and trains:
>
>
>Hey, guys. I start there simply because that's the way my club has always
>"advertised" the ride, with Boulder Springs being a nice neighborhood with
>ample parking. There's no intent to cheat, although I realize it's a few
>blocks up up from Sierra Whatchamacallit. If I have to ride down and back at
>the end of the ride to be "pure", just tell me - I'm not scared of climbs.
>
>Hell, I did the ski lifts three times in July, and threw in Little GMR down
>and back one of those times for an 8340' day. The ski lifts in a 39x25 hurts,
>Big Time. And I did GMR the day before Labor Day, and it was 109 degrees when
>I got back to the car. So give me a break!
>
>Art (grumble, grumble)
Dear Art,
Sorry, just kidding!
I do understand that many posters on RBT aren't lucky enough to have a
nice ride starting from their driveway (like mine, though I dislike
that lone stoplight) and that driving to where your friends meet you
for a good ride makes sense.
With luck, Colin will show up at Boulder Springs some day and keep you
hon--
Er, company.
Hope your weather is more bearable with fall approaching.
Cheers,
Carl Fogel
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Date: 20 Sep 2007 15:18:14
From: Dorfus Dippintush
Subject: Re: Bicycle Computer Altimeter Accuracy
|
carlfogel@comcast.net wrote:
> On Wed, 19 Sep 2007 04:28:42 GMT, arthur-temp-3@cox.net (Arthur
> Shapiro) wrote:
>
>>> Let's not say that Art is short-cutting. Rather, he is honoring the
>>> tradition of the early Tour de France riders, who sometimes abridged
>>> the tedious official route with taxis and trains:
>>
>> Hey, guys. I start there simply because that's the way my club has always
>> "advertised" the ride, with Boulder Springs being a nice neighborhood with
>> ample parking. There's no intent to cheat, although I realize it's a few
>> blocks up up from Sierra Whatchamacallit. If I have to ride down and back at
>> the end of the ride to be "pure", just tell me - I'm not scared of climbs.
>>
>> Hell, I did the ski lifts three times in July, and threw in Little GMR down
>> and back one of those times for an 8340' day. The ski lifts in a 39x25 hurts,
>> Big Time. And I did GMR the day before Labor Day, and it was 109 degrees when
>> I got back to the car. So give me a break!
>>
>> Art (grumble, grumble)
>
> Dear Art,
>
> Sorry, just kidding!
>
> I do understand that many posters on RBT aren't lucky enough to have a
> nice ride starting from their driveway (like mine, though I dislike
> that lone stoplight) and that driving to where your friends meet you
> for a good ride makes sense.
>
> With luck, Colin will show up at Boulder Springs some day and keep you
> hon--
>
> Er, company.
>
> Hope your weather is more bearable with fall approaching.
>
> Cheers,
>
> Carl Fogel
Our town has one stop light. We don't mind it because it gives visitors
the impression our town is busy.
Dorfus
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Date: 18 Sep 2007 13:31:19
From:
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Sep 18, 12:04 pm, bbe...@telemark.slac.stanford.edu (Booker Bense)
wrote:
> Doc O'Leary <droleary.use...@3q2007.subsume.com> wrote:
> >Flip a coin if you want to guess. If you want to *know*, go an online
> >map (and/or Google Earth) and measure the route.
>
> Most topo programs provide even less accurate results that even
> the worst bike altimeter.
IMO, topo maps provide very accurate measurements of
start and finish altitudes, but topo programs that compute
cumulative elevation gain are quite unreliable. This is
likely because they model both the road and the elevation
contours as a bunch of line segments and introduce noise
into the elevation profile. When I look at a profile from one
of these programs, it's often much jaggier than any real
road would be.
Ben
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Date: 18 Sep 2007 20:25:27
From:
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Sep 17, 11:30 pm, "b...@mambo.ucolick.org" <b...@mambo.ucolick.org >
wrote:
> > In certain circumstances, a bicycle power meter has greater resolution
> > in measuring elevation change than either the consumer level
> > altimeters or GPS receivers that one finds on bicycles.
>
> Yesbut, resolution is not the same as accuracy, as you
> know. It may be accurate under certain circumstances,
> but in the mountains, there is often a wind blowing.
Right, but the reason why most of us want to know the elevation gain
is because elevation gain has come to be a proxy measure for effort.
FWIW, take a look at this:
http://anonymous.coward.free.fr/wattage/cda/indirect-cda.pdf
It's an old version and I've done a bit more with it since then, but
notice that I picked out a drainage grate on the edge of a "flat"
road. I'd appreciate your comments.
|
| | |
Date: 18 Sep 2007 23:55:45
From:
Subject: Re: Bicycle Computer Altimeter Accuracy
|
someone writes:
>>> In certain circumstances, a bicycle power meter has greater
>>> resolution in measuring elevation change than either the consumer
>>> level altimeters or GPS receivers that one finds on bicycles.
>> Yesbut, resolution is not the same as accuracy, as you know. It
>> may be accurate under certain circumstances, but in the mountains,
>> there is often a wind blowing.
> Right, but the reason why most of us want to know the elevation gain
> is because elevation gain has come to be a proxy measure for effort.
> FWIW, take a look at this:
http://anonymous.coward.free.fr/wattage/cda/indirect-cda.pdf
> It's an old version and I've done a bit more with it since then, but
> notice that I picked out a drainage grate on the edge of a "flat"
> road. I'd appreciate your comments.
One of the most important features in recording altitude gain is
hysteresis in the accumulator. That is to say, if a bicycle is ridden
on a country road that undulates +- up to ten feet in long waves, an
instrument with no hysteresis would accumulate great climbs even
though the rider didn't notice any or gain any elevation.
Realizing this, I submitted a patent on the instrument on which I
worked for Avocet. Besides ignoring atmospheric pressure undulations,
I also wanted RR underpasses to not appear as altitude gains, gains
for which the average bicyclist does not shift into lower gears as one
does to climb mountain roads.
Jobst Brandt
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Date: 18 Sep 2007 13:47:19
From: Doc O'Leary
Subject: Re: Bicycle Computer Altimeter Accuracy
|
In article <46eed159$0$9534$4c368faf@roadrunner.com >,
Colin Campbell <cmcampb@adelphia.net > wrote:
> Yesterday, I did one of Southern California's classic mountain rides -
> Glendora Mountain Road. According to my bike computer, I did 1298
> meters of climbing, and 1541 meters of descending (ending up exactly
> where I started).
>
> Is there any way of guessing which of these numbers might be more accurate?
Flip a coin if you want to guess. If you want to *know*, go an online
map (and/or Google Earth) and measure the route.
--
My personal UDP list: 127.0.0.1, 4ax.com, buzzardnews.com, googlegroups.com,
heapnode.com, localhost, teranews.com, x-privat.org
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Date: 18 Sep 2007 19:04:13
From: Booker Bense
Subject: Re: Bicycle Computer Altimeter Accuracy
|
In article <droleary.usenet-BAC011.13471918092007@sn-ip.vsrv-sjc.supernews.net >,
Doc O'Leary <droleary.usenet@3q2007.subsume.com > wrote:
>In article <46eed159$0$9534$4c368faf@roadrunner.com>,
> Colin Campbell <cmcampb@adelphia.net> wrote:
>
>> Yesterday, I did one of Southern California's classic mountain rides -
>> Glendora Mountain Road. According to my bike computer, I did 1298
>> meters of climbing, and 1541 meters of descending (ending up exactly
>> where I started).
>>
>> Is there any way of guessing which of these numbers might be more accurate?
>
>Flip a coin if you want to guess. If you want to *know*, go an online
>map (and/or Google Earth) and measure the route.
>
Most topo programs provide even less accurate results that even
the worst bike altimeter.
_ Booker C. Bense
|
| | | |
Date: 19 Sep 2007 14:16:17
From: Doc O'Leary
Subject: Re: Bicycle Computer Altimeter Accuracy
|
In article <fcp7fc$7ce$1@news.Stanford.EDU >,
bbense@telemark.slac.stanford.edu (Booker Bense) wrote:
> In article
> <droleary.usenet-BAC011.13471918092007@sn-ip.vsrv-sjc.supernews.net>,
> Doc O'Leary <droleary.usenet@3q2007.subsume.com> wrote:
> >In article <46eed159$0$9534$4c368faf@roadrunner.com>,
> > Colin Campbell <cmcampb@adelphia.net> wrote:
> >
> >> Yesterday, I did one of Southern California's classic mountain rides -
> >> Glendora Mountain Road. According to my bike computer, I did 1298
> >> meters of climbing, and 1541 meters of descending (ending up exactly
> >> where I started).
> >>
> >> Is there any way of guessing which of these numbers might be more
> >> accurate?
> >
> >Flip a coin if you want to guess. If you want to *know*, go an online
> >map (and/or Google Earth) and measure the route.
> >
>
> Most topo programs provide even less accurate results that even
> the worst bike altimeter.
I'd like something more than your baseless claim to go on.
--
My personal UDP list: 127.0.0.1, 4ax.com, buzzardnews.com, googlegroups.com,
heapnode.com, localhost, teranews.com, x-privat.org
|
| | | | |
Date: 19 Sep 2007 21:09:19
From: Booker Bense
Subject: Re: Bicycle Computer Altimeter Accuracy
|
In article <droleary.usenet-B2807C.14161719092007@sn-ip.vsrv-sjc.supernews.net >,
Doc O'Leary <droleary.usenet@3q2007.subsume.com > wrote:
>In article <fcp7fc$7ce$1@news.Stanford.EDU>,
> bbense@telemark.slac.stanford.edu (Booker Bense) wrote:
>
>> Most topo programs provide even less accurate results that even
>> the worst bike altimeter.
>
>I'd like something more than your baseless claim to go on.
>
Old La Honda road in Woodside california. It goes up never down
and is 1300ft of climbing. I have yet see a topo program that
comes within 30% of the well know result.
Nearby is the well known Alpine-Portola Valley-Sandhill loop.
Every topo program I've tried ( except Klimb which cheats... )
gets the total climbing on that loop off by 50% or more.
_ Booker C. Bense
|
| | | | | |
Date: 20 Sep 2007 14:06:16
From: Doc O'Leary
Subject: Re: Bicycle Computer Altimeter Accuracy
|
In article <fcs35v$e60$1@news.Stanford.EDU >,
bbense@telemark.slac.stanford.edu (Booker Bense) wrote:
> In article
> <droleary.usenet-B2807C.14161719092007@sn-ip.vsrv-sjc.supernews.net>,
> Doc O'Leary <droleary.usenet@3q2007.subsume.com> wrote:
> >In article <fcp7fc$7ce$1@news.Stanford.EDU>,
> > bbense@telemark.slac.stanford.edu (Booker Bense) wrote:
> >
>
> >> Most topo programs provide even less accurate results that even
> >> the worst bike altimeter.
> >
> >I'd like something more than your baseless claim to go on.
> >
>
> Old La Honda road in Woodside california. It goes up never down
> and is 1300ft of climbing. I have yet see a topo program that
> comes within 30% of the well know result.
So you're essentially saying you haven't bothered to try Google Earth or
Google Maps. Both give results that seem to be in the range you expect.
You're going to have to be much more specific on what the error is if
you want to be taken seriously.
> Nearby is the well known Alpine-Portola Valley-Sandhill loop.
> Every topo program I've tried ( except Klimb which cheats... )
> gets the total climbing on that loop off by 50% or more.
Compared to *what*? Please cite the "well know[n] results" you are so
certain are correct in the first place. And, for goodness sake, give
GPS coordinates (or a link) so that everyone who isn't "nearby" can more
easily figure out where the hell you're talking about.
--
My personal UDP list: 127.0.0.1, 4ax.com, buzzardnews.com, googlegroups.com,
heapnode.com, localhost, teranews.com, x-privat.org
|
| |
Date: 18 Sep 2007 06:23:42
From: Ron Hardin
Subject: Re: Bicycle Computer Altimeter Accuracy
|
Barometric is subject to wind effects ; if you open the window of a light
airplane, the altimeter jumps a hundred feet.
The same thing happens without you noticing on the ground - whether you're
in the shelter of the mountain and so out of the wind (but therefore at
a lower than natural atmospheric pressure) or on the upwind side and
therefore in the wind, the wind produces local highs and lows as it goes
around natural obstructions, large and small.
If there's no wind at all, you can think of the entire atmospheric systems
as the same effect, except you get a correction to set for those, over the
radio or something. But wind is what creates and sustains pressure changes,
be they continential-large or tree trunk small.
--
rhhardin@mindspring.com
On the internet, nobody knows you're a jerk.
|
| | |
Date: 19 Sep 2007 12:10:03
From: Artoi
Subject: Re: Bicycle Computer Altimeter Accuracy
|
In article <46EFA72E.1D32@mindspring.com >,
Ron Hardin <rhhardin@mindspring.com > wrote:
> Barometric is subject to wind effects ; if you open the window of a light
> airplane, the altimeter jumps a hundred feet.
There's truth in this. AIUI, iBike power meter uses this feature.
However, a well designed altimeter built for bikes should be immune to
this issue.
--
|
| | |
Date: 18 Sep 2007 21:32:13
From: Dorfus Dippintush
Subject: Re: Bicycle Computer Altimeter Accuracy
|
Ron Hardin wrote:
> Barometric is subject to wind effects ; if you open the window of a light
> airplane, the altimeter jumps a hundred feet.
>
> The same thing happens without you noticing on the ground - whether you're
> in the shelter of the mountain and so out of the wind (but therefore at
> a lower than natural atmospheric pressure) or on the upwind side and
> therefore in the wind, the wind produces local highs and lows as it goes
> around natural obstructions, large and small.
>
> If there's no wind at all, you can think of the entire atmospheric systems
> as the same effect, except you get a correction to set for those, over the
> radio or something. But wind is what creates and sustains pressure changes,
> be they continential-large or tree trunk small.
On a bike it doesn't make much difference but it does if I'm moving in
my car. Winding down the window of my car makes a change to my GPS
indicated altitude, by a few metres.
Dorfus
|
| |
Date: 18 Sep 2007 06:30:01
From: bjw@mambo.ucolick.org
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Sep 17, 10:40 pm, rechungREMOVET...@gmail.com wrote:
> On Sep 17, 3:41 pm, "b...@mambo.ucolick.org" <b...@mambo.ucolick.org>
> wrote:
>
> > In the OP's case, the readings might be different if e.g. the weather
> > changed, or he started off very early in the morning when it was
> > cold at the base, or something like that. It's easy to check a
> > single climb against a topo map, but harder if the computer's
> > number is "total climbing" from cumulating all the small ups and
> > downs.
>
> In certain circumstances, a bicycle power meter has greater resolution
> in measuring elevation change than either the consumer level
> altimeters or GPS receivers that one finds on bicycles.
Yesbut, resolution is not the same as accuracy, as you
know. It may be accurate under certain circumstances,
but in the mountains, there is often a wind blowing.
For real accuracy, any metrology should be calibrated
against a standard. Topo maps are pretty good for this
application.
Ben
measure once, publish twice
|
| | |
Date: 18 Sep 2007 12:28:39
From: Clive George
Subject: Re: Bicycle Computer Altimeter Accuracy
|
<bjw@mambo.ucolick.org > wrote in message
news:1190097001.537681.95490@o80g2000hse.googlegroups.com...
> For real accuracy, any metrology should be calibrated
> against a standard. Topo maps are pretty good for this
> application.
Heh - which reminds me of of the bemusement I had when I first heard the
phrase "Topo map" used. Having been brought up with OS maps, I thought all
sensible maps would have contours. Little did I know how spoilt I was...
cheers,
clive
|
| |
Date: 18 Sep 2007 05:40:16
From:
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Sep 17, 3:41 pm, "b...@mambo.ucolick.org" <b...@mambo.ucolick.org >
wrote:
> In the OP's case, the readings might be different if e.g. the weather
> changed, or he started off very early in the morning when it was
> cold at the base, or something like that. It's easy to check a
> single climb against a topo map, but harder if the computer's
> number is "total climbing" from cumulating all the small ups and
> downs.
In certain circumstances, a bicycle power meter has greater resolution
in measuring elevation change than either the consumer level
altimeters or GPS receivers that one finds on bicycles.
|
| |
Date: 17 Sep 2007 20:46:20
From: KF
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Sep 17, 9:25 pm, mitosis <mitosis.2x3...@no-
mx.forums.cyclingforums.com > wrote:
> KF Wrote:
> > .... in fact the GPS is about
> > the only way to conveniently reset a baromeric altimeter after unknown
> > changes in elevation/barometric pressure.
>
> > DR
>
> Barometric altimeters in aircraft are set according to local
> pressures.
> :)
Yes, and typically at *known* field elevations, but not "after unknown
changes in elevation/barometric pressure"
DR
|
| |
Date: 17 Sep 2007 20:10:54
From: KF
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Sep 17, 3:01 pm, "Clive George" <cl...@xxxx-x.fsnet.co.uk > wrote:
> T'other way round - the barometric is more accurate. At a guess, a plane
> doesn't really care that much about a 10m altitude difference, until it gets
> close enough to the ground that the pilot can work that bit out. (fx: reads
> Garmin website. It appears they don't use GPS for altitude unless the main
> barometric one has died).
Not necessarily so, but let's at least define what we mean by
"accurate."
Take a GPS altimeter reading. With a decent "view" of the sky, it's
almost always within 20 feet or so of the correct altitude and NEVER
varies as the barometer fluctuates. So if you don't know where you are
and don't know what the barometric trend has been, the GPS
gives far more reliable elevation information.
On the other hand if you have just calibrated your barometric
altimeter and you climb a small hill (say, 200 feet high) the
barometric altimeter wil be able to tell you quite accurately how high
the top of the hill is, and even without calibration, can tell you how
much you have gained (the difference in elevation), probably to within
a few feet (although not all have that kind of fine resolution). But
try to measure the top of the hill again tomorrow without
recalibrating and you could easily be off by a couple hundred feet
just due to normal atmospheric changes. The GPS will always be
subject to the +/- 20 feet at any one location but will very rarely be
off more than that. So while the barometric altimeter under ideal
conditions may tell you that the hill is 200 +/- 5 feet high, under
unknown barometric changes it may really only tell you that the hill
is 200 +/- 200 feet high.
And if we change the hill to 2000 feet and still use the same +/-
figures, suddenly the +/-20 feet of the GPS starts to look VERY
accurate.
My experience from a number of years of use of both types of
instruments is that I'll take the overall consistency/accuracy of the
GPS over the barometric altimeter any day, in fact the GPS is about
the only way to conveniently reset a baromeric altimeter after unknown
changes in elevation/barometric pressure.
DR
|
| | |
Date: 17 Sep 2007 21:46:29
From: Mark
Subject: Re: Bicycle Computer Altimeter Accuracy
|
KF wrote:
> On Sep 17, 3:01 pm, "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
>> T'other way round - the barometric is more accurate. At a guess, a plane
>> doesn't really care that much about a 10m altitude difference, until it gets
>> close enough to the ground that the pilot can work that bit out. (fx: reads
>> Garmin website. It appears they don't use GPS for altitude unless the main
>> barometric one has died).
>
> Not necessarily so, but let's at least define what we mean by
> "accurate."
> Take a GPS altimeter reading. With a decent "view" of the sky, it's
> almost always within 20 feet or so of the correct altitude and NEVER
> varies as the barometer fluctuates. So if you don't know where you are
> and don't know what the barometric trend has been, the GPS
> gives far more reliable elevation information.
>
> On the other hand if you have just calibrated your barometric
> altimeter and you climb a small hill (say, 200 feet high) the
> barometric altimeter wil be able to tell you quite accurately how high
> the top of the hill is, and even without calibration, can tell you how
> much you have gained (the difference in elevation), probably to within
> a few feet (although not all have that kind of fine resolution). But
> try to measure the top of the hill again tomorrow without
> recalibrating and you could easily be off by a couple hundred feet
> just due to normal atmospheric changes. The GPS will always be
> subject to the +/- 20 feet at any one location but will very rarely be
> off more than that. So while the barometric altimeter under ideal
> conditions may tell you that the hill is 200 +/- 5 feet high, under
> unknown barometric changes it may really only tell you that the hill
> is 200 +/- 200 feet high.
> And if we change the hill to 2000 feet and still use the same +/-
> figures, suddenly the +/-20 feet of the GPS starts to look VERY
> accurate.
>
> My experience from a number of years of use of both types of
> instruments is that I'll take the overall consistency/accuracy of the
> GPS over the barometric altimeter any day, in fact the GPS is about
> the only way to conveniently reset a baromeric altimeter after unknown
> changes in elevation/barometric pressure.
Heh, heh, my barometric altimeter watch is a really cheap one. I'm
almost certain I see abrupt changes in the reported altitude due to the
pressure wave of passing trucks. It's still a fun toy, considering it
was cheap, and it's usually not off by too much over the course of a day.
Mark J.
|
| | |
Date: 18 Sep 2007 13:25:17
From: mitosis
Subject: Re: Bicycle Computer Altimeter Accuracy
|
KF Wrote:
> On Sep 17, 3:01 pm, "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
> > T'other way round - the barometric is more accurate. At a guess,
> plane
> > doesn't really care that much about a 10m altitude difference, unti
> it gets
> > close enough to the ground that the pilot can work that bit out. (fx
> reads
> > Garmin website. It appears they don't use GPS for altitude unless th
> main
> > barometric one has died).
>
> Not necessarily so, but let's at least define what we mean by
> "accurate."
> Take a GPS altimeter reading. With a decent "view" of the sky, it's
> almost always within 20 feet or so of the correct altitude and NEVER
> varies as the barometer fluctuates. So if you don't know where you are
> and don't know what the barometric trend has been, the GPS
> gives far more reliable elevation information.
>
> On the other hand if you have just calibrated your barometric
> altimeter and you climb a small hill (say, 200 feet high) the
> barometric altimeter wil be able to tell you quite accurately how high
> the top of the hill is, and even without calibration, can tell you how
> much you have gained (the difference in elevation), probably to within
> a few feet (although not all have that kind of fine resolution). But
> try to measure the top of the hill again tomorrow without
> recalibrating and you could easily be off by a couple hundred feet
> just due to normal atmospheric changes. The GPS will always be
> subject to the +/- 20 feet at any one location but will very rarely be
> off more than that. So while the barometric altimeter under ideal
> conditions may tell you that the hill is 200 +/- 5 feet high, under
> unknown barometric changes it may really only tell you that the hill
> is 200 +/- 200 feet high.
> And if we change the hill to 2000 feet and still use the same +/-
> figures, suddenly the +/-20 feet of the GPS starts to look VERY
> accurate.
>
> My experience from a number of years of use of both types of
> instruments is that I'll take the overall consistency/accuracy of the
> GPS over the barometric altimeter any day, in fact the GPS is about
> the only way to conveniently reset a baromeric altimeter after unknown
> changes in elevation/barometric pressure.
>
> DR
Barometric altimeters in aircraft are set according to loca
pressures.
:
--
mitosis
|
| |
Date: 18 Sep 2007 02:36:28
From: !Jones
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Mon, 17 Sep 2007 12:11:33 -0700, in rec.bicycles.tech Colin
Campbell <cmcampb@adelphia.net > wrote:
>Yesterday, I did one of Southern California's classic mountain rides -
>Glendora Mountain Road. According to my bike computer, I did 1298
>meters of climbing, and 1541 meters of descending (ending up exactly
>where I started).
>
>Is there any way of guessing which of these numbers might be more accurate?
Yeah, the issue is that your front wheel is probably a 700 and your
rear is 27". Take the ratio and that's what you *would* have done.
Jones
|
| |
Date: 17 Sep 2007 22:41:10
From: bjw@mambo.ucolick.org
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Sep 17, 12:52 pm, Ted Bennett <tedbenn...@earthlink.net > wrote:
> Colin Campbell <cmca...@adelphia.net> wrote:
> > Yesterday, I did one of Southern California's classic mountain rides -
> > Glendora Mountain Road. According to my bike computer, I did 1298
> > meters of climbing, and 1541 meters of descending (ending up exactly
> > where I started).
>
> > Is there any way of guessing which of these numbers might be more accur=
ate?
>
> Your starting point has apparently dropped by 243 meters. Happens in
> Southern California all the time=ADit's those pesky subduction zones.
>
> In my experience those altimeters are fairly useless. Since they figure
> altitude by measuring air pressure fluctuations, which changes according
> to temperature as well as altitude, there is built-in inaccuracy. Add
> to that the cheapness of the instrument and you're bound to get the sort
> of "measurements" you did.
>
I don't have such a computer, but I have a watch with a barometric
altimeter, which is very likely similar. It uses some kind of lookup
table that relies on an average run of temperature and pressure
with altitude (possibly the International standard atmosphere).
In general it is quite accurate in a _differential_ sense
but the zeropoint will be off. For example, when I hike up an
Arizona mountain in summer, it's systematically off because the
temperature at 10,000 feet is higher than the watch is expecting.
However, the differential between bottom and top is fairly
stable as long as the weather doesn't change.
The other effect is the weather. It's a barometer, so of course
the readings at a fixed point will be different if a front blows
thrpugh
and the pressure changes.
In the OP's case, the readings might be different if e.g. the weather
changed, or he started off very early in the morning when it was
cold at the base, or something like that. It's easy to check a
single climb against a topo map, but harder if the computer's
number is "total climbing" from cumulating all the small ups and
downs.
Ben
|
| |
Date: 17 Sep 2007 22:25:29
From: Lou Holtman
Subject: Re: Bicycle Computer Altimeter Accuracy
|
Colin Campbell wrote:
> Yesterday, I did one of Southern California's classic mountain rides -
> Glendora Mountain Road. According to my bike computer, I did 1298
> meters of climbing, and 1541 meters of descending (ending up exactly
> where I started).
>
> Is there any way of guessing which of these numbers might be more accurate?
(1541 + 1298)/2 = 1420 m, is your best bet.
Lou
--
Posted by news://news.nb.nu (http://www.nb.nu)
|
| | |
Date: 17 Sep 2007 18:22:03
From: Colin Campbell
Subject: Re: Bicycle Computer Altimeter Accuracy
|
Lou Holtman wrote:
> Colin Campbell wrote:
>> Yesterday, I did one of Southern California's classic mountain rides -
>> Glendora Mountain Road. According to my bike computer, I did 1298
>> meters of climbing, and 1541 meters of descending (ending up exactly
>> where I started).
>>
>> Is there any way of guessing which of these numbers might be more
>> accurate?
>
> (1541 + 1298)/2 = 1420 m, is your best bet.
>
> Lou
Yes, I'll take it. I'll tell the metrically challenged (nearly
everybody!) that I did about 4,500 feet.
|
| | | |
Date: 18 Sep 2007 02:58:10
From: Clive George
Subject: Re: Bicycle Computer Altimeter Accuracy
|
"Colin Campbell" <cmcampb@adelphia.net > wrote in message
news:46ef282e$0$18936$4c368faf@roadrunner.com...
> Yes, I'll take it. I'll tell the metrically challenged (nearly
> everybody!) that I did about 4,500 feet.
Ah, the joy of mixing one's units. I prefer distance in miles but height in
metres - and annoyingly my ciclosport won't let me choose that :-(
cheers,
clive
|
| |
Date: 17 Sep 2007 12:52:05
From: Ted Bennett
Subject: Re: Bicycle Computer Altimeter Accuracy
|
Colin Campbell <cmcampb@adelphia.net > wrote:
> Yesterday, I did one of Southern California's classic mountain rides -
> Glendora Mountain Road. According to my bike computer, I did 1298
> meters of climbing, and 1541 meters of descending (ending up exactly
> where I started).
>
> Is there any way of guessing which of these numbers might be more accurate?
Your starting point has apparently dropped by 243 meters. Happens in
Southern California all the timeit's those pesky subduction zones.
In my experience those altimeters are fairly useless. Since they figure
altitude by measuring air pressure fluctuations, which changes according
to temperature as well as altitude, there is built-in inaccuracy. Add
to that the cheapness of the instrument and you're bound to get the sort
of "measurements" you did.
If you want more accuracy, get a GPS which measures your altitude by
triangulation from satellites rather than air pressure. Usually within
one meter.
--
Ted Bennett
|
| | |
Date: 18 Sep 2007 11:10:21
From: _
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Mon, 17 Sep 2007 12:52:05 -0700, Ted Bennett wrote:
>
> In my experience those altimeters are fairly useless. Since they figure
> altitude by measuring air pressure fluctuations, which changes according
> to temperature as well as altitude, there is built-in inaccuracy. Add
> to that the cheapness of the instrument and you're bound to get the sort
> of "measurements" you did.
>
I seem to remember JB (the one who bikes, not the one who blusters) posting
about the now-defunct Avocet gadget that had an altimiter in it; the units
were designed with a one-time programmable adjustment so that they could be
tweaked for accuracy after manufacture.
|
| | |
Date: 18 Sep 2007 04:01:34
From: Artoi
Subject: Re: Bicycle Computer Altimeter Accuracy
|
In article
<tedbennett-F2FCF5.12520517092007@earthlink.vsrv-sjc.supernews.net >,
Ted Bennett <tedbennett@earthlink.net > wrote:
> In my experience those altimeters are fairly useless. Since they figure
> altitude by measuring air pressure fluctuations, which changes according
> to temperature as well as altitude, there is built-in inaccuracy. Add
> to that the cheapness of the instrument and you're bound to get the sort
> of "measurements" you did.
>
> If you want more accuracy, get a GPS which measures your altitude by
> triangulation from satellites rather than air pressure. Usually within
> one meter.
The truth is that the barometric altimeters are more sensitive and is
good for small and rapid changes in elevation. While GPS is good for the
X/Y coordinate but less precise in the vertical plane. Those Garmin
units eg. Edge 305, uses the barometric meter for their altitude data
but they constantly get calibrated by the data stream from the GPS
system. In other words, the GPS data significantly reduces the inherent
errors in a barometric unit.
--
|
| | |
Date: 18 Sep 2007 13:22:10
From: mitosis
Subject: Re: Bicycle Computer Altimeter Accuracy
|
Ted Bennett Wrote:
> Colin Campbell <cmcampb@adelphia.net> wrote:
>
> > Yesterday, I did one of Southern California's classic mountain ride
> -
> > Glendora Mountain Road. According to my bike computer, I did 1298
> > meters of climbing, and 1541 meters of descending (ending up exactly
> > where I started).
> >
> > Is there any way of guessing which of these numbers might be mor
> accurate?
>
> Your starting point has apparently dropped by 243 meters. Happens in
> Southern California all the time*it's those pesky subduction zones.
>
> In my experience those altimeters are fairly useless. Since the
> figure
> altitude by measuring air pressure fluctuations, which change
> according
> to temperature as well as altitude, there is built-in inaccuracy. Add
> to that the cheapness of the instrument and you're bound to get th
> sort
> of "measurements" you did.
>
> If you want more accuracy, get a GPS which measures your altitude by
> triangulation from satellites rather than air pressure. Usuall
> within
> one meter.
>
> --
> Ted Bennett
I think you will find altitude by air pressure is more accurate than b
GPS. The better GPS devices that also measure altitude defer to ai
pressure changes rather than satellite triangulation. Aircraft use ai
pressure changes for their altimeters, correcting them with pressur
readings collected by radio enroute
--
mitosis
|
| | |
Date: 17 Sep 2007 21:15:03
From: Clive George
Subject: Re: Bicycle Computer Altimeter Accuracy
|
"Ted Bennett" <tedbennett@earthlink.net > wrote in message
news:tedbennett-F2FCF5.12520517092007@earthlink.vsrv-sjc.supernews.net...
> In my experience those altimeters are fairly useless. Since they figure
> altitude by measuring air pressure fluctuations, which changes according
> to temperature as well as altitude, there is built-in inaccuracy.
They do measure temperature as well - well, the Ciclosport ones do anyway. I
agree one which didn't wouldn't be very useful.
> Add
> to that the cheapness of the instrument and you're bound to get the sort
> of "measurements" you did.
>
> If you want more accuracy, get a GPS which measures your altitude by
> triangulation from satellites rather than air pressure. Usually within
> one meter.
That would be why the GPSs which record height have a barometric altimeter
on them as well?
cheers,
clive
|
| | | |
Date: 17 Sep 2007 16:29:21
From: David L. Johnson
Subject: Re: Bicycle Computer Altimeter Accuracy
|
Clive George wrote:
> "Ted Bennett" <tedbennett@earthlink.net> wrote in message
>> If you want more accuracy, get a GPS which measures your altitude by
>> triangulation from satellites rather than air pressure. Usually within
>> one meter.
>
> That would be why the GPSs which record height have a barometric
> altimeter on them as well?
A GPS uses the barometer primarily, with the satellites used as a
periodic check, since the satellite data is not all that accurate for
altitude, but the barometer is subject to drift due to atmospheric
conditions.
--
David L. Johnson
Some people used to claim that, if enough monkeys sat in front of
enough typewriters and typed long enough, eventually one of them would
reproduce the collected works of Shakespeare. The internet has
proven this not to be the case.
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Date: 18 Sep 2007 06:27:37
From: Michael Press
Subject: Re: Bicycle Computer Altimeter Accuracy
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In article <862dnZThZ-IYfnPbnZ2dnUVZ_hadnZ2d@ptd.net >,
"David L. Johnson" <david.johnson@lehigh.edu > wrote:
> Clive George wrote:
> > "Ted Bennett" <tedbennett@earthlink.net> wrote in message
>
> >> If you want more accuracy, get a GPS which measures your altitude by
> >> triangulation from satellites rather than air pressure. Usually within
> >> one meter.
> >
> > That would be why the GPSs which record height have a barometric
> > altimeter on them as well?
>
> A GPS uses the barometer primarily, with the satellites used as a
> periodic check, since the satellite data is not all that accurate for
> altitude, but the barometer is subject to drift due to atmospheric
> conditions.
Strictly speaking, drift in a measuring instrument is a
change in its ability to make the primary measurement
caused by changes in the instrument itself. With
barometric altimeters it is interpretation of the
measurement that is the problem, not drift in their
measurement of ambient air pressure.
--
Michael Press
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Date: 17 Sep 2007 14:07:50
From: Ted Bennett
Subject: Re: Bicycle Computer Altimeter Accuracy
|
"David L. Johnson" <david.johnson@lehigh.edu > wrote:
> Clive George wrote:
> > "Ted Bennett" <tedbennett@earthlink.net> wrote in message
>
> >> If you want more accuracy, get a GPS which measures your altitude by
> >> triangulation from satellites rather than air pressure. Usually within
> >> one meter.
> >
> > That would be why the GPSs which record height have a barometric
> > altimeter on them as well?
>
> A GPS uses the barometer primarily, with the satellites used as a
> periodic check, since the satellite data is not all that accurate for
> altitude, but the barometer is subject to drift due to atmospheric
> conditions.
Hmm. That differs from my understanding, which results from my
conversations with pilots. But I'm willing to be corrected, as pilots
are likely not to be GPS experts. Can anyone else who is knowledgeable
chime in?
--
Ted Bennett
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Date: 17 Sep 2007 19:47:41
From: David L. Johnson
Subject: Re: Bicycle Computer Altimeter Accuracy
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Ted Bennett wrote:
> "David L. Johnson" <david.johnson@lehigh.edu> wrote:
>> A GPS uses the barometer primarily, with the satellites used as a
>> periodic check, since the satellite data is not all that accurate for
>> altitude, but the barometer is subject to drift due to atmospheric
>> conditions.
>
> Hmm. That differs from my understanding, which results from my
> conversations with pilots. But I'm willing to be corrected, as pilots
> are likely not to be GPS experts. Can anyone else who is knowledgeable
> chime in?
>
I got this from Garmin, IIRC.
--
David L. Johnson
"What am I on? I'm on my bike, six hours a day, busting my ass.
What are you on?"
--Lance Armstrong
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Date: 18 Sep 2007 15:09:59
From: Booker Bense
Subject: Re: Bicycle Computer Altimeter Accuracy
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In article <7IOdnQQ-AbNijHLbnZ2dnUVZ_s3inZ2d@ptd.net >,
David L. Johnson <david.johnson@lehigh.edu > wrote:
>Ted Bennett wrote:
>> "David L. Johnson" <david.johnson@lehigh.edu> wrote:
>
>>> A GPS uses the barometer primarily, with the satellites used as a
>>> periodic check, since the satellite data is not all that accurate for
>>> altitude, but the barometer is subject to drift due to atmospheric
>>> conditions.
>>
>> Hmm. That differs from my understanding, which results from my
>> conversations with pilots. But I'm willing to be corrected, as pilots
>> are likely not to be GPS experts. Can anyone else who is knowledgeable
>> chime in?
>>
>I got this from Garmin, IIRC.
>
The garmin units definite use a barometer for relative altitude
and use the GPS to calibrate. Same with the etrex summit, I think
there is a big difference between GPS in a plane where you pretty
much have clear signal all the time and GPS 4 feet from the
ground were the signal can be blocked and lost quite often.
This leads to a lot of jitter in the signal and makes GPS
attitude cumlative measurements less accurate. Basically the
combo of the two improves the accuracy of both.
The Garmin Edge also uses a traditional bike speedo for cadence
and speed/distance correction for exactly the same reason.
I have noticed that the altitude measurement gets more accurate
and consistant as the software of the unit gets upgraded.
_ Booker C. Bense
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Date: 17 Sep 2007 13:26:17
From: Ted Bennett
Subject: Re: Bicycle Computer Altimeter Accuracy
|
"Clive George" wrote:
> "Ted Bennett" wrote
> > If you want more accuracy, get a GPS which measures your altitude by
> > triangulation from satellites rather than air pressure. Usually within
> > one meter.
>
> That would be why the GPSs which record height have a barometric altimeter
> on them as well?
Some do it by barometric pressure measurement, actually most do.
However units used in aviation use the satellites for better accuracy.
Hardly practical for bicycle use, I would agree.
--
Ted Bennett
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Date: 17 Sep 2007 22:01:59
From: Clive George
Subject: Re: Bicycle Computer Altimeter Accuracy
|
"Ted Bennett" <tedbennett@earthlink.net > wrote in message
news:tedbennett-429A10.13261717092007@earthlink.vsrv-sjc.supernews.net...
>> That would be why the GPSs which record height have a barometric
>> altimeter
>> on them as well?
>
> Some do it by barometric pressure measurement, actually most do.
> However units used in aviation use the satellites for better accuracy.
> Hardly practical for bicycle use, I would agree.
T'other way round - the barometric is more accurate. At a guess, a plane
doesn't really care that much about a 10m altitude difference, until it gets
close enough to the ground that the pilot can work that bit out. (fx: reads
Garmin website. It appears they don't use GPS for altitude unless the main
barometric one has died).
cheers,
clive
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Date: 17 Sep 2007 14:21:15
From: Ted Bennett
Subject: Re: Bicycle Computer Altimeter Accuracy
|
"Clive George" <clive@xxxx-x.fsnet.co.uk > wrote:
> "Ted Bennett" <tedbennett@earthlink.net> wrote
>
> >> That would be why the GPSs which record height have a barometric
> >> altimeter on them as well?
> >
> > Some do it by barometric pressure measurement, actually most do.
> > However units used in aviation use the satellites for better accuracy.
> > Hardly practical for bicycle use, I would agree.
>
> T'other way round - the barometric is more accurate. At a guess, a plane
> doesn't really care that much about a 10m altitude difference, until it gets
> close enough to the ground that the pilot can work that bit out. (fx: reads
> Garmin website. It appears they don't use GPS for altitude unless the main
> barometric one has died).
>
> cheers,
> clive
This may be nearly unheard of on this group: I was wrong.
Shows where repeating hearsay can lead one astray. Thanks.
Ted
--
Ted Bennett
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Date: 18 Sep 2007 17:41:18
From: Lou Holtman
Subject: Re: Bicycle Computer Altimeter Accuracy
|
Ted Bennett wrote:
> "Clive George" <clive@xxxx-x.fsnet.co.uk> wrote:
>
>> "Ted Bennett" <tedbennett@earthlink.net> wrote
>>
>>>> That would be why the GPSs which record height have a barometric
>>>> altimeter on them as well?
>>> Some do it by barometric pressure measurement, actually most do.
>>> However units used in aviation use the satellites for better accuracy.
>>> Hardly practical for bicycle use, I would agree.
>> T'other way round - the barometric is more accurate. At a guess, a plane
>> doesn't really care that much about a 10m altitude difference, until it gets
>> close enough to the ground that the pilot can work that bit out. (fx: reads
>> Garmin website. It appears they don't use GPS for altitude unless the main
>> barometric one has died).
>>
>> cheers,
>> clive
>
> This may be nearly unheard of on this group: I was wrong.
>
> Shows where repeating hearsay can lead one astray. Thanks.
>
> Ted
>
Anyone who recorded and displayed an altitude graph using a GPS in a
fast and curvy descent could tell you.
Lou
--
Posted by news://news.nb.nu (http://www.nb.nu)
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Date: 17 Sep 2007 15:34:42
From: Ron Hardin
Subject: Re: Bicycle Computer Altimeter Accuracy
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Colin Campbell wrote:
>
> Yesterday, I did one of Southern California's classic mountain rides -
> Glendora Mountain Road. According to my bike computer, I did 1298
> meters of climbing, and 1541 meters of descending (ending up exactly
> where I started).
>
> Is there any way of guessing which of these numbers might be more accurate?
There's actually no correct number, for the answer depends on how much rise or fall
actually counts.
If you're riding on a random surface with wheel diameter D, the total vertical
excursion rises like 1 / sqrt(D), going to infinity as the diameter goes to zero.
The real world would just notice that things count that you don't want to count,
as the height wobbles get smaller ; yet they contribute the most to the total.
You'd like the up and down totals to agree, though.
--
rhhardin@mindspring.com
On the internet, nobody knows you're a jerk.
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Date: 18 Sep 2007 02:37:58
From: !Jones
Subject: Re: Bicycle Computer Altimeter Accuracy
|
On Mon, 17 Sep 2007 15:34:42 -0400, in rec.bicycles.tech Ron Hardin
<rhhardin@mindspring.com > wrote:
>You'd like the up and down totals to agree, though.
Personally, I prefer the downhill... I'm not into deferred
gratification.
Jones
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Date: 18 Sep 2007 06:18:19
From: Ron Hardin
Subject: Re: Bicycle Computer Altimeter Accuracy
|
!Jones wrote:
>
> On Mon, 17 Sep 2007 15:34:42 -0400, in rec.bicycles.tech Ron Hardin
> <rhhardin@mindspring.com> wrote:
>
> >You'd like the up and down totals to agree, though.
>
> Personally, I prefer the downhill... I'm not into deferred
> gratification.
>
> Jones
Actually I prefer uphills. That's the change that 10 speed gearing brought
years ago.
From a strict physics point of view, you waste the least energy on uphills;
any work you do winds up saved as potential energy.
Then you fritter it all away on air turbulence on downhills, which are the most
wasteful of energy.
--
rhhardin@mindspring.com
On the internet, nobody knows you're a jerk.
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