Date: Fri, 4 Aug 2006 11:42:43 -0500
Reply-To: Ken Lake <ken.lake@ALEREON.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Ken Lake <ken.lake@ALEREON.COM>
Subject: Re: Reasonable cruising speed?
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Ok, I admit to having studied this several years ago, and my personal
handheld GPS does operate this way. It would certainly be possible to
sum up the distances between plotted points and get true distance of
travel. Mine does not have the memory or computing power for that.
The distance reported is accurate. It is within about 50 feet, closer
if allowed to average for a while. Mine operates in the mode where it
will tell me the distance from any set point (like HOME) to where I am
at. Or between any two set points, but it is always straight line, not
track. It does store track information but does not use it for
distance. Now that you can get 4GB of memory in an Ipod Nano, it would
certainly be possible for some one to build that in. The laptop could
be programmed to add up incremental distances reported by the GPS over
time and I am sure this program exists somewhere. I have a lower budget
than that.
GPS uses a very accurate time system, and can calculate the position to
within 50 ft (or less) and so the speed is very accurate. Total
distance is very accurate since the error tends to average out, but mine
does not do track distance. Newer one's may. I probably should not
have generalized quite so much. There is a larger error in elevation
(less than 200 ft)since it is very hard to triangulate elevation from
the satellites.
Ken
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of Loren Busch
Sent: Friday, August 04, 2006 11:00 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Reasonable cruising speed?
Interesting point and one that was discussed quite a bit a couple of
years
ago. Assuming you are correct then that would say that GPS indicated
speed
is only correct when traveling a straight road. And what does that say
about the ground track trace most, even older GPS units, store? And
what of
the newer GPS units , especially those designed for use in vehicle? Do
they
provide more accurate data, or, like my older hand held unit (Magellan
4000)
give bad info on the odometer function?
BTW, not trying to get an argument going here, just really curious about
other peoples real world experience with hand helds vs. GPS units sold
for
use in vehicles vs. laptop software/GPS combinations.
Guess I'll have to set up both the handheld and the laptop and run them
together for a hundred miles or so and then compare.
On 8/4/06, Ken Lake <ken.lake@alereon.com> wrote:
>
> RE: GPS distance.
>
> This is because the GPS calculates the straight line distance between
> the starting and ending points. Although it calculates its exact
> location several times a second and uses that to determine its speed,
it
> does not store the incremental distances between locations, which it
> would need to calculate total distance. Hence it can plot your trip,
> give you the speed, current location, but distance from starting is
> always wrong (compared to how you got there)
>
>
>
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