Even before moving, how doe the NAV system know the heading of the vehicle (RL)?
In otherwords, how does it figure where to point the arrow where the front of the car is pointed?

 

im thinkin the gyro and the gps...

 

it may just store the last time it was booted which direction it was pointing and the direction changes depending on the gps cordinates....

 

thats what the gyro units and speed sensors are for.
Take a browse thru the nav ops book, amazing stuff in there

 

Triangulation with the distances between satellites..

 

here is your answer right here... the navi brain has a front and back that needs to be mounted the correct way... that way it knows which direction you are traveling and which way is always front...

on my carputer for my 98 TL, my GPS mouse does not have a defined forward and back, so many times when i am sitting at a complete stop at a light, you will see the arrow start to spin trying to figure out which way i am headed... its annoying because sometimes it thinks im going another way, and recalculate my route...

not the case with OEM Navis because of the defined directions that are embedded into the units... hope that helps...

 

Have you tried to drive in reverse for like a block and see if the arrow changes direction... I bet it will, and will now need to try it as a result.

FWIW - the GPS simply gets a new location reading (point A to point B), the CPU deciphers this into the picture you see on the screen, very simple really... But there's some added usability features where they've tried to make the system appear seamless... For example, the vehicle's speed sensor is integrated to account for errors and roadway placements. I can see this using my handheld Garmin that isn't linked to the vehicle, the car actually travels "alongside" the road... This makes sense if you consider the fact that chartography and Longitude/Latitude values don't always agree or these values are set to a single point... Think of the following crudeness as being a GPS road map, were the dots represent the stationary points identifying the road and the equal signs represent a two lane hiway... Traveling in either lane, you're technically missing the path and creating your own...

=.===.===.===.===.===

The CPU flattens this out for us and likely does the same for the direction indicator, where I bet traveling in reverse long enough will get the arrow to swap ends.

 

he's right. just like my avic the brain has to be mounted a certain way so that the unit is parallel with the car. one time i accidently had the brain moved around and put it in a awkward direction and my navigation started going crazy had me travelling in weird directions my screen showed me in philly while i was in boston. the navi unit reads the brain to see wat direction it is pointed in and relays it back to the screen thus showing you wat direction u are pointed in.

 

I think most of you are confusing two different things.

The nav simply remembers which way it was pointed when it was turned off. So does my pocket GPS.

The nav must be installed in a specific orientation in the vehicle because it uses a combination of gyros and a tap into the speedometer sensor as an inertial navigation system to update your location while satellites are out of view, such as when you're in a tunnel.

 

how about a compass? My 97 Ford Explorer knows which way I am pointing as soon as I turn the key on, it just doesn't have a clue WHERE I am.

 

All this info is in the 3G Garage....

 

Yeah... I'm gonna go with the compass suggestion. The car could easily know its current position / direction over short distances without the satellites using a compass and measuring wheel speed.

 

Does the NAV TL have a built in compass? Does it work in a covered parking space where GPS signals would not penetrate ?

 

The navi uses a combination of GPS and gyros (yaw and pitch sensors).

Navi does not know your heading unless you are moving so that it can plot a course from point A (where you used to be a few minutes ago) to point B (where you are now). Obviously, that takes time and is not instantaneous. Also, it only works if you're moving.

However, as you go around a corner, the heading red pointer will turn with you in real time. That is due to the gyros that are real time. The gyros are always corrected by the GPS calculations to confirm heading.

When you boot up, the navi remembers your heading when you shut down last.

 

I can't speak to how, but the fact that it works (and is right) is simply amazing to me. I park in an underground garage. The second I go under the door I lose all GPS guidance. 5 windy floors down it is still correctly showing my heading. When I go to leave at night, it's the exact same story. It is dead on the entire way out of the ramp.