When you look closely at a Topo road you can see it is made
up of straight line segments. If you are familiar with the
road you know it curves. Line segments are not always good
approximations for curves, so you have inaccuracies. This
kind of inaccuracy is largest on winding mountainous roads.
Topo just isn't made to give us hill climbers the detailed
data we would like.
Using stragiht line segment approximations enables Topo to
get its database on 5
CDs. Doubling the accuracy requires 25 CDs because lines
are one dimensional but areas (maps) are two
dimensional.
psycholist wrote:
> "Roger Zoul" <
[email protected]> wrote in message
>
news:[email protected]...
> > Ken wrote:
> > :: "Bestest Handsander" <
[email protected]> wrote in
news:5O-
> > ::
[email protected]:
> > ::: I just picked up DeLorme Topo from eBay for $7
> > ::: bucks. This thing is cool. Mark a route, view it in
> > ::: 3d, and then check the profile. The interface isn't
> > ::: the best, but it's been fun finding all the grades
> > ::: and elevation gains of all my favorite rides.
> > ::
> > :: I've found the grades and elevation gains in the
> > :: program to be wildly inaccurate. Elevations at
> > :: particular points aren't too bad, but the road
> > :: vectors in their database do not follow the real
> > :: world roads very closely.
> >
> > Can you explain how you know this? I mean, have you
> > actually measured
> "road
> > vectors" while following a map from it's database?
> >
>
> Well, I just got DeLorme Topo 5.0 and I profiled the last
> section of the Brasstown Bald climb which Lance and all
> the pros rode a week or so ago. According to Topo 5.0, it
> has stretches of 47% grade. I don't think so.
>
> I've checked out some climbs I do regularly and know well.
> It seems to be pretty good at giving an average gradient
> for a climb. But some of the individual slopes along the
> route it does exaggerate quite wildly.
>
> Bob C.