Accord GPS "time to destination" error

A good friend has a new Accord with the GPS navigation system. For
whatever reason, while it perfectly pinpoints his location, the estimated
time to destination is off a good 30%. It's as if the system is reading
the car's MPH with a 30% error on the slow side. However, the car's
speedometer is accurate, as is the GPS position location. We've confirmed
that other similar models (of the same year) do NOT have this problem.

Basically, the dealer is clueless as to what to fix, as they've never seen
the problem and don't know what to do. So, they refuse to do anything.
The car's GPS system has this problem consistently. It's not
intermittent. You can put in a destination 60 miles away (for example),
proceed to drive 60 miles an hour, and it'll tell you that you're 1:18
away (instead of 1 hour).

Do any of you experts out there have a clue? TIA. Neall

 

I don't have the built-in navigation system, but I use a GPS on the dash with a laptop computer. My system determines car speed and location strictly from the satellites, it has no connection with the car's components. I would expect the Accord to do the same, so I would look to upgrade the DVD software for a possible fix. On the other hand, if this error is so predictable, you have one of the easiest issues to overcome... Al
A good friend has a new Accord with the GPS navigation system. For
whatever reason, while it perfectly pinpoints his location, the estimated
time to destination is off a good 30%. It's as if the system is reading
the car's MPH with a 30% error on the slow side. However, the car's
speedometer is accurate, as is the GPS position location. We've confirmed
that other similar models (of the same year) do NOT have this problem.

Basically, the dealer is clueless as to what to fix, as they've never seen
the problem and don't know what to do. So, they refuse to do anything.
The car's GPS system has this problem consistently. It's not
intermittent. You can put in a destination 60 miles away (for example),
proceed to drive 60 miles an hour, and it'll tell you that you're 1:18
away (instead of 1 hour).

Do any of you experts out there have a clue? TIA. Neall

 

Maybe it discounts speed for traffic lights and such.

I wonder if (please excuse me) there's anything about this in the
owner's manual?

J.

 

I don't have the built-in navigation system, but I use a GPS on the dash with a laptop

The built-in navigation systems use the signal from the vehicle speed
sensor in addition to GPS. Most of them also use a gyroscope. This
provides for more robust navigation in areas where satellite view may be
spotty, like in tunnels, parking garages, and when you are surrounded by
tall buildings.

Newsgroups are ASCII only forums, so please turn off your HTML or "Rich
Text" (or whatever you are using) when posting to newsgroups.

 

Hmmm... don't buy that, the only way the navigation system knows where you
are, and how far you are from where you are going is with satellites.
Perhaps the Accord navi uses the vehicle speed connection, but that is not
more accurate than the speed determined from satellites, nor does it help
when satellites are not available because of obstructions... Al

BTW, thanks for reminding me about using ASCII for posts

 

Honda's manual does describe the navi system in the Odyssey as also
utilizing some sort of inertial guidence system, a small gyro.

 

And as an additional point, when I am descending down a multi story,
enclosed, concrete parking lot the system know exactly which way I am going
and accurately tracks my travel. I don't think satellite reception is all
that good. My Garmin handheld, for example, does not work in that same
environment.

 

I don't have a clue, but I will say that my Accord's estimated times
are right on, and even corrects itself while driving if going slower
or faster than normal. However, my dad's Toyota Prius seems to be off
in this regard. Turns out that, on his car, it simply uses three
different default speeds for all highway, surface street, etc. routes
(or something like that), and you can go in somewhere and adjust those
speeds to your liking and to match present-day driving realities. You
might have your friend dig into the NAV manual to see if that
adjustment is possible on Hondas as well.

Rob

 

Navigation systems can be made entirely without GPS (or other satellite
or terrestrial based navigation network). Etak (now TeleAtlas,
http://www.teleatlas.com) did this back in the mid 80's. One version
relied only on speed sensors at the wheels, distance traveled was
calculated based on average of left and right sensor, changes in
direction were calculated based on the difference between left and
right. The path traveled was matched with an electronic map; the system
would assume you were traveling on actual roads and find the best match
of known roads the the measured travel path.

Upon initial installation of the system, a calibration run had to be
made to allow the system to know the characteristics of the wheel
sensors and suspension geometry. An initial absolute location would have
to be entered as well. As tires wore down etc. the system would
recalibrate itself. The system worked well, except for in larger cities
with streets in a regular grid pattern. Here, the system would
occasionally get confused as to what street you were turning onto. E.g.
if you were driving down 2nd ave. for miles, and then made a right turn,
the system would not be accurate enough to know if you were turing on
56th street or 57th street. The system had menu selections for "Skip one
street ahead" and "skip one street back" to overcome this. If you got
wheel spin (e.g. while driving in snow and ice) the system would get
confused as to what direction you were traveling in. On early systems,
the electronic maps were stored on cassette tapes. Later gyroscopes were
added, and the maps were put on CDs.

Gyroscopes were added later (I have one of the early gyroscopes sitting
on my shelf) and experiments were done with using a compass also (turned
out the compass confused the system more than it helped it due to local
variations in the magnetic field etc.).

Navigation without the help of GPS (or similar systems) is called dead
reckoning, and most of the navigation systems that are permanently
installed in cars have some form of dead reckoning in addition to GPS.
If you know where you are (based on GPS data) and then loose the GPS
signal, dead reckoning will give a very accurate estimate of where you
go until you receive a GPS sugnal again.

 

Thanks Randolph for sharing your knowledge here... Al

 

You are more than welcome. A few years back I had the pleasure of
working with one of the founders of Etak. He was happy to discuss the
details of the navigation system, and also showed me one of the very
early ones that he had installed in his car.