FLCC> [Fwd: Today's 46 mi ride - MapMyRide.com]

[Moorhead, Michael S]

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
>
>  


_______________________________________________
FLCC mailing list
FLCC at icycle.org
http://icycle.org/mailman/listinfo/flcc_icycle.org