Re: what's your 2005 Accord V6 MPG?

Sparky Spartacus <Sparky@xxxxxxxxxxxxxxxxxxxx> wrote:
> See signature for email address wrote:
> > harry <harry_liuNOSPAM@xxxxxxx> wrote:
> >
> >>Also I found the Navi
> >>screen shows less miles driven compared to the counter under the
> >>speedometer. I found around 10 miles difference from 300 miles of driving.
> >>Navi screen tends to have less miles displayed. Which one is more accurate
> >>to use for MPG calculation?
> >
> >
> > GPS, as I understand, can measure distance travelled in horizontal plane
> > fairly accurately but not so accurately in vertical plane. So I would
> > expect GPS distance to be quite accurate on very flat roads, provided it
> > maintains a good satellite lock, but if there is elevation change on the
> > road, accuracy of distance travelled may be questionable.

> 4 or more satellites give a 3D fix - it was fun when I first used my GPS
> unit to watch the speed, direction & altitude change as I motored around
> at 2 AM (on & off an Interstate gives some nice altitude changes).

Yes, 4 or more satellites will give a 3D fix but margin of error in
vertical plane is lot more than horizontal plane. I can stop at a red
light with 8 satellites locked with WAAS and watch my altitude drift on
Garmin SP2610 while staying still.

I do not understand solid geometry well enough to explain this but there
have been a few explanations on the GPS newsgroups on why GPS has a hard
time calculating vertical distances accurately. Here are some links with
some answers:

<http://www.gpsinformation.net/main/altitude.htm>
<http://www.gpsinformation.net/articles/tripdistanceerror.htm>

====================================================================
Khalid

khalid AT gonehiking DOT org
.

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