FLCC> [Fwd: Today's 46 mi ride - MapMyRide.com]
Bill Goffe
goffe at oswego.edu
Mon Apr 7 11:19:58 EDT 2008
To add my own $0.02 worth, I've long used an Ciclosport CM 414 (now
discontinued), which records not only altitude, but also both climb and
descent. It seems to have a very sensitive sensor -- I can see a change in
altitude if I hold it near my feet and then hold it overhead.
As Mike points out, changes in air pressure due to storms can indeed
affect them, but in practice I rarely see that. For the typical ride, it
measures total climb and total descent to 1-2% of each other. As climbs
and descents are measured at different times and in different places, it
give me some confidence that it is "correct." It generally finds less
climbing than what you get with TopoZone.
I tend to think that any climb "matters" as after all you have to move
you and your bike uphill.
Data from topo maps isn't as accurate as you might guess; I'm pretty sure
that TopoZone and all the on-line services use the same dataset from the
U.S. Geological Services (I would think that the military uses maps from
National Geospatial-Intelligence Agency (NGA) http://www.nga.mil/ .) USGS
maps aren't as accurate as you'd think:
http://erg.usgs.gov/isb/pubs/factsheets/fs17199.html .
One would think that measuring total climbing on a ride would be really
straightforward...
- Bill
Mike said:
> I should probably let Shan the GPS guru answer this one, but I think it
> is an interesting question from an engineering standpoint, so I'll put
> in my $0.02.
>
> Most "inexpensive" altimeters use (only) a pressure sensor to determine
> altitude. This is because pressure drops about 1" of Hg (mercury) for
> every 1000 ft gained. The problem, of course, is that pressure also
> fluctuates with weather conditions. I suppose if you started a ride on
> your trainer on a beautiful day where the barometer reads 31" Hg and
> ended it during a thunderstorm when the barometer reads 28" Hg, you
> might have "climbed" 3000 ft.
>
> GPS units typically still use pressure sensors, but they use the
> not-so-accurate vertical GPS position to remove the effect of changing
> atmospheric pressure.
>
> The best way to get the "right answer" is probably using software (like
> DeLorme) that uses digital terrain elevation data (DTED) maps. These
> are the very maps that told our beloved cruise missles how to fly
> through canyons to bring democracy to the Iraqis. ;-) The civilian
> versions of these maps probably have 1m accuracy (I really have no
> idea).
>
> The trick, as Andrejs point out, is following a particular set of rules.
> I personally like the thought that every time my bike hits a 1mm bump in
> the road that it is added to my climb total. Perhaps that's the only
> way I can start getting in some real "climbs" here in Indiana. I look
> pretty silly doing repeats over the highway overpass.
>
> Best,
>
> Mike Moorhead
>
>
> -----Original Message-----
> From: flcc-bounces at icycle.org [mailto:flcc-bounces at icycle.org] On Behalf
> Of Andrejs Ozolins
> Sent: Monday, April 07, 2008 10:11 AM
> To: Ruth E. Sherman
> Cc: flcc at icycle.org
> Subject: Re: FLCC> [Fwd: Today's 46 mi ride - MapMyRide.com]
>
> I can add another climbing number to those: DeLorme's Topo software says
>
> you climbed 2,763 feet. It's interesting that your GPS is closer to
> that number than the MapMyRide because GPS units are not particularly
> good at measuring vertical movement. But, behind the disagreement is the
>
> fact that your measurement of climbing depends on how you define
> climbing. If you count every single inch of vertical movement as a
> climb, then you'll come up with astronomical figures for a whole ride.
> In practice, the rules can be be defined to give a range of results --
> at what minimum rise to start measuring; what increments to measure,
> etc. Anyway, my impression is that the Topo figure of 2,700 is probably
> closest -- over the years, seeing elevation figures from watches and
> bike computers as well as other people's reports, the DeLorme estimate
> has always been pretty much in the ballpark.
>
> Andrejs
>
> Ruth E. Sherman wrote:
> > Also, there is a big discrepancy between my GPS and MapMyRide's
> estimate
> > of our total ascent - the GPS said we climbed 2321' whereas MapMyRide
> says
> > we climbed 1363'. I prefer to believe the former.
> >
> > ---------------------------- Original Message
> ----------------------------
> > Subject: FLCC> Today's 46 mi ride - MapMyRide.com
> > From: "Ruth E. Sherman" <res6 at cornell.edu>
> > Date: Sun, April 6, 2008 10:42 pm
> > To: flcc at icycle.org
> >
> ------------------------------------------------------------------------
> --
> >
> > After much trial and error and a lot of googling, I was able to
> download
> > today's route from my GPS into a mapping program (most of these
> mapping
> > programs are not well supported for us Mac users). You can access the
> > route at the site below:
> >
> > Ruth Sherman thinks that you should check out the workout he/she
> just
> > plotted online:
> > http://www.mapmyride.com/ride/united-states/ny/ithaca/639350988
> >
> > You can also search for other cycling routes in Ithaca, New
> York:
> > http://www.mapmyride.com/find-ride/united-states/ny/ithaca
> >
> >
>
>
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