How does my car’s GPS navigation system know what direction the car is pointing in when I first turn on the car, before I move it. Does it simply store the last calculated direction from when I turned off the car?
I know it knows because it shows a little arrow pointing to in the direction my car is pointing, and it properly orients the map. I could probably test some of this by driving around backwards, but I’m nowhere near my car right now.
My WAG is that you’re correct, or it’s possible the GPS has a compass in it. That would probably require some kind of calibration though. At any rate, I don’t know for sure, so consider this just a bump. 
Cars have had electronic compasses for years. Doesn’t seem unreasonable that it’d be linked in.
My portable GPS has an annoying feature whereby when I stop – such as at a red light – it forgets which direction I was going in, and the whole map rotates towards the default. PITA.
Yeah, I’ve got GPS on my handheld and it clearly derives your heading based on the direction of motion. So if I stop moving it sometimes goes wonky. Likewise if I first turn it on, it doesn’t orient itself correctly until I start moving.
No wag about it, the ones in the cars I teach on have a compass.
The GPS does not care what direction the car is going. Only the direction the GPS is going. When it boots up, it gets information from the sats and goes from there.
The GPS does not care about the car.
If you where to turn your car off while pointing east and have ten friends slide the car till it’s pointing south. When you start the car, it will say that you are pointing south. It has very little to do whith the car.
WTF?
since the GPS unit is bolted into the car, the direction of the car and the direction of the GPS are one and the same.
Now if you had said that unbolting the GPS unit and turning it 90 degrees would cause the display to rotate 90 degrees I would agree. But as long as the unit remains bolted in place, it does know the direction of the car.
Also it does not need sat info to give you a direction. There are times and places where it may not have sat coverage for several miles. In this case it uses dead reckoning, the compass, the gyro, and the on board maps to display your location and direction.
My handheld Garmin can do better than that.
The direction that the car is pointing is coming from the GPS. It’s attached to the car. That the GPS is attached to a car or a hiker makes no differece. Not the other way around.
Yes, the direction of the car is very important. The OP thought (I think) that if the car was pointed south, the GPS may think it’s pointing east. The GPS determains the position and direction. Nothing is coming from the ‘car’. Direction and position is cominig from the GPS.
The whole system is separate.
We are talking across each other at this point.
Read the OP
Car’s, not hand held.
I stand by my comments.
And I, as a GIS professional that builds the data that the new GPS systems use stand by mine. I don’t want to argue with you Rick. As I said, I think we are talking across each other. It does not mater if it’s in a car or in a hand held.
Data is data.
Enipla, your posts are confusing me.
“Going” implies movement. How can a GPS in a car be moving in a direction different from the car’s?
All it can get from the satellites is position and time information. When moving, it can report the direction of movement by looking at the change in position with time - but not when stationary.
This seems wrong for any GPS receiver that does not also contain some sort of method for measuring heading (the most common being a magnetic sensor of some sort). Only a limited number of GPS receivers have this.
Some of them have compasses - but a gyro? For inertial navigation?
Depends a lot on what kind of base map or street database that the system is using. A good GPS will follow the base map underneath it. Correct you when it can and get you to your destination based on pre loaded steet data. It’s not just lat and long. It follows the best route that it has.
GPS only tells you your position and velocity. If the vehicle is moving, GPS does tell you which direction of movement. But if the vehicle is stationary, a GPS receiver will not tell you which way the vehicle is pointed.
I think most GPS car navigation systems have magnetic field sensors (electronic compasses) for this reason. High-end handheld GPS receivers have this feature as well.
In addition, many car navigation systems use wheel sensor signals, accelerometers and/or gyroscopes to supplement the GPS signal. Otherwise you’d lose your position every time the GPS signal is interrupted by buildings, trees, tunnel, etc.
enipla, I think you’re misunderstanding. In OEM-equipped GPS units, as soon as you start the car prior to movement, the indicator and map orientation are correct. The GPS unit alone requires motion to determine direction (remember, direction means “direction of motion” – no motion, no direction). Your Garmin has no idea of your heading until you start moving. Car GPS units somehow already know the heading prior to initiating motion. Rick’s explanation, then, is entirely correct. I recognize what you’re saying, though. But consumer expectations for cheap handhelds and expensive OEM units are different. Cars GPS units do require external information when the satellite clocks can’t provide it. Compass bearing is a good one; it’ll point you the right way without requiring movement; dead-reckoning, as Rick says, is essential for higher-end units when the timing signal isn’t available from the sats.
But the question is what it knows about your heading when you aren’t moving. I don’t see how that has anything to do with the receiver’s maps or database.
I did some googling and there are indeed units that contain “gyros” for dead-reckoning navigation. I put the word in quotes because in all the examples I found these were solid-state inertial sensors (piezoelectric or fiber-optic);
What’s the declination where you live. It’s about 7.5 degrees here.
No need for a magnetic north on a GPS (though mine has it). Thats why its a GPS.
No Gyro. No need for internal navigation for the car.
It’s a GPS.
Hmmm… How to explain.
I was talking to a buddy a year ago and he said that that his 15’ fishing boat was going about 30 miles per hour. I asked if he had a speedohmeter on the thing, and he said no. I just used the GPS. Oh, of course. My little Garmin will do that.
It’s two different systems.
The ‘map’ is ‘dumb’ it’s data. Good or bad it is what it is. It knows that 4th and
This seems wrong for any GPS receiver that does not also contain some sort of method for measuring heading (the most common being a magnetic sensor of some sort). Only a limited number of GPS receivers have this.
Main is at such and such Lat and Long. It can find the Starbucks on the corner because somebody put in that data.
Where your car really is, is relayed to a satellite and the information is crunched by the receiver in your car.
The connection to the satellite tells the receiver what your Lat and Long is. It then uses the ‘dumb’ data in your receiver to get you as close as it can.
Routing algorithms are something else. Fasest time? Highways or local streets?
Most of that is crunched in your receiver, based on local maps that are pre-loaded.
In the reviews of new GPSs I’ve read, the gyro is for when you lose a signal, such as going in a tunnel. They gyro allows the GPS to do inertial navigation, and thus not get confused.