*It depends on what website you use. My understanding is that each
interpolates the same topo data base in its own way. Also, my impression is
that each website keeps tuning their algorithms in the hope of greater
accuracy. What's not clear is whether any of these sites get access to side
information or secondary databases *
*
*
*My own experience is with the Garmin 705 (which has a barometric altimeter)
and a VDO MC1.0+ which also has a barometric altimeter but no GPS. I've
found that the two tend to report results within about 10% of each other.
The VDO which has doesn't have GPS, tends to do more averaging of the
barometer readings. *
*
*
*As for websites, I've been using bikeroutetoaster.com and ridewithgps.com.
My experience was that a bikeroutetoaster often underestimated the vertical
feet in a route by 10-20%. On the other hand, ridewithgps tended to be
closer, and occasionally overestimate a little. It seems possible to me that
ridewithgps may well have added a correction factor to account for small ups
and downs? *
*
*
*In any case, both have been much better than my experiences with mapmyride.
However, I stopped using mapmyride 2 years ago, and it is very possible they
have changed their algorithms in the meantime.
*
...Roy
On Mon, Feb 15, 2010 at 4:10 PM, Eric Norris campyonly...@me.com wrote:
Can't compare web to GPS, but I've found over the years that both calculate
more climbing than is shown by an altimeter watch or bike computer. The
altimeter typically shows about 30% less altitude gain, probably because the
mapped versions add up every little up while most altimeters ignore small
gains.
— Eric Norris
www.campyonly.com
www.wheelsnorth.com
[image: Blog] http://campyonlyguy.blogspot.com[image:
Flickr]http://www.flickr.com/photos/35176...@n03[image:
Web] http://www.campyonly.com[image: Web]
http://www.wheelsnorth.org[image:
Web] http://www.groovyboy.org[image: Email] campyonly...@me.com
On Feb 15, 2010, at 12:59 PM, doug peterson dougpn...@cox.net wrote:
In mapping out routes, I've noticed big differences in both distance
and elevation gain between GPS and plotting the same route on web
based mapping services. Distances can be off by 5%-10% and elevation
by double. The web based systems are always higher than GPS. Has
anyone else encountered this? It's entirely possible I'm doing
something wrong on the web based systems.
dougP
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