I keep reading about GPS for boats and how innacurate it can be.

Why is the same not innacurate in cars?

My car GPS is so accurate it tells me I am on the white line at a
traffic signal stop light or in my driveway.

Why not the same for boats?

Try this for an experiment:

Cover up your windshield and drive entirely by trying to follow the line
on you car's GPS system. That's what you doing on a boat in the fog.

Also, consider that the streets have been well mapped in the last few
years by survey companies that drive around in cars and mark each
intersection. Many nautical charts are based on century old data. Much
of the issue is the map/chart quality, not the accuracy of the GPS itself.

Actually, the boat gps is just as accurate, perhaps even better since
there is no shielding from high buildings. Its just that on a boat you
may be relying 100% on the GPS as the primary, and perhaps only, source
of position. In a car, you glance occasionally at the map plotter and
would never notice if the GPS sometimes said you were on someone's front
lawn.

One can easily imagine a situation on a boat where failure of the GPS
would cause you to drop anchor and wait until the weather clears; I
doubt you would do the same in a car!


BTW, my wife got a new car with a nav system just last night. It
currently in the driveway reporting two different street addresses
(depending on how you ask), both wrong. Both are actually nonexistent
addresses - one of them would be a hundred yards past the other end of a
dead end street. The actually position on the map is well reported,
however.


anchorlt wrote:
I keep reading about GPS for boats and how innacurate it can be.

Why is the same not innacurate in cars?

My car GPS is so accurate it tells me I am on the white line at a
traffic signal stop light or in my driveway.

Why not the same for boats?

anchorlt,
I have a hand held Garmin. When I first got it, and had tracking
enabled, I piloted a course that took me under a draw bridge. The tracking
showed that I was about a 1/4 mile inland, most disconcerting. I called Boat
U.S. where I had bought it and was advised to "reset" the unit by depressing
a button with a paper clip. After this it reported my track to be exactly
right. My experience has been very positive to accuracy.
Paul

"anchorlt" wrote in message
om...
I keep reading about GPS for boats and how innacurate it can be.

Why is the same not innacurate in cars?

My car GPS is so accurate it tells me I am on the white line at a
traffic signal stop light or in my driveway.

Why not the same for boats?

(anchorlt) wrote:

I keep reading about GPS for boats and how innacurate it can be.

Why is the same not innacurate in cars?

My car GPS is so accurate it tells me I am on the white line at a
traffic signal stop light or in my driveway.

Why not the same for boats?

There are two parameters here - the accuracy of the GPS and the
accuracy of the chart or map that it is being tracked on.

When I have the tracking on the car GPS it sometimes has me parallel
to the road but off it by a considerable amount. Most of the time the
tracking on the boat is very good. If there is a discrepancy it is
often because the chart or map is off.


grandma Rosalie

On 23 Nov 2004 11:01:16 -0800, (anchorlt)
wrote:

I keep reading about GPS for boats and how innacurate it can be.

Why is the same not innacurate in cars?

My car GPS is so accurate it tells me I am on the white line at a
traffic signal stop light or in my driveway.

Why not the same for boats?

GPS receivers that are intended for road use often have a "lock to
road" feature, that will lock your displayed position to the nearest
road that the GPS knows about, regardless of your true position.

This sort of function is definitely not desirable for marine use.


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

Try this for an experiment:

Cover up your windshield and drive entirely by trying to follow the line
on you car's GPS system. That's what you doing on a boat in the fog.

This thread is interesting!

alot of things I never thought about.

Tim

On 23 Nov 2004 11:01:16 -0800, (anchorlt)
wrote:

I keep reading about GPS for boats and how innacurate it can be.

Why is the same not innacurate in cars?

My car GPS is so accurate it tells me I am on the white line at a
traffic signal stop light or in my driveway.

Why not the same for boats?

Actually it works better in boats, because the sky is clearer. It can
tell you which side of the finger pier your slip is on, and whether
you backed in.

However, if you have only one GPS receiver, and no other way of
telling where you are, you are stuck if it fails. If course, they are
so cheap now that nobody would have only one if matters.

If the satellites all quit, you have far more serious things to worry
about than where you are. Or, you have no worries at all.



Rodney Myrvaagnes Opionated old geezer

Faith-based economics: It's deja voodoo all over again

anchorlt wrote in message
om...
I keep reading about GPS for boats and how innacurate it can be.

Why is the same not innacurate in cars?

My car GPS is so accurate it tells me I am on the white line at a
traffic signal stop light or in my driveway.

Why not the same for boats?

I have been told that factory GPS and most high-end retrofit systems for
cars also use a speed sensor input from the car transmission that is
separate from the GPS signal. It is used primarily to keep position
calculations going when the satellite signal is lost (tunnel) but it also
helps improve the accuracy of the position readings.

Eisboch

Eisboch wrote:

I have been told that factory GPS and most high-end retrofit systems for
cars also use a speed sensor input from the car transmission that is
separate from the GPS signal. It is used primarily to keep position
calculations going when the satellite signal is lost (tunnel) but it also
helps improve the accuracy of the position readings.


That is the claim for my wife's Toyota nav.

I don't think ours uses a "lock to road" feature - watching the marker
as we drive we were frequently 10 to 20 feet on either side of the road.
Also, it seems to take us "off road" 50 feet going down the driveway.

Jeff Morris wrote:
Eisboch wrote:


I have been told that factory GPS and most high-end retrofit systems for
cars also use a speed sensor input from the car transmission that is
separate from the GPS signal. It is used primarily to keep position
calculations going when the satellite signal is lost (tunnel) but it also
helps improve the accuracy of the position readings.


That is the claim for my wife's Toyota nav.

I don't think ours uses a "lock to road" feature - watching the marker
as we drive we were frequently 10 to 20 feet on either side of the road.
Also, it seems to take us "off road" 50 feet going down the driveway.



This is a similar problem on marine chart plotters when doing close-in work.
Aside from the typical "lag" time, you will frequently find yourself not
exactly where you want to be and/or are. G Gonna be awhile before GPS
takes over completely, but as processors get faster......

otn