Does the mirror have a backup camera?

Is there a compass in the rear view mirror or anywhere on the dash?

 

Any one got a picture of that rear view mirror with screen?

 

And it's not a real compass, but a compass display of GPS heading. For those that don't understand the difference, a real compass tells you which direction the car is pointing. The GPS compass tells you which direction the car has moved. If you don't move a little ways, the GPS has no idea what direction you are pointing. For example, if you are driving north and the GPS shows you pointing north, and you stop and have a bunch of strong guys pick up your Prius and turn it around so that it points south, the GPS will still say that you are pointing north. GPS only knows where you are and where you were. Everything else is calculated from that.

Here is another, more dramatic example. Let's say you take your Prius and load it onto a railroad flatcar. On this flatcar you have a giant lazy susan, so you can freely rotate the Prius. With the Prius pointing to the front of the train, the train pulls out of the station and heads due north. The GPS display in the Prius shows that you are pointing north. Now you rotate the Prius 90° so that it is pointing east. The GPS still shows the Prius pointing north. You rotate the Prius south. It still shows north. Finally you give the Prius a big spin so that it goes round and round. The GPS still shows that you are pointing north. GPS has no idea what direction you are pointing. GPS knows where you are, and knows that a second ago you were a little farther south than you are now, so you must be going north. If you are going north, you must be pointing north. It's all assumptions.

Most of the time it doesn't make any difference, but there are some gotchas. The most common is making a tight turn in a parking lot and then looking at the GPS for directional information. The GPS thinks you are pointing one direction but you are actually pointing somewhere else. It can be confusing if you don't understand it.

Tom

 

FWIW, my '08 Prius has some dead reckoning capability that allows it to estimate where it's facing and where it is even when there is no GPS reception (in an underground parking structure, for example). It's not perfect but it doesn't just stop at the entrance to the garage like my Garmin does.

 

With all the high-tech doo-dahs, I'm surprised Toyota didn't think to add a compass to the homelink rearview mirror.

Had we not purchased our 07 with the package that already included the homelink mirror, I would have bought the aftermarket version mirror with a compass in it.

I'm a man, damnit! I need my compass!

 

Here is one picture of it.
Mazda shares lots of part sources with Toyota.
I think there is a version with a digital compass at the top right corner.

http://mazdagear.com/images/view.as...mages/cx9/Mazda_CX9_RearCameraSystemlarge.jpg

The compass direction is based on magnetic field of earth, which slightly varies depending on which states you are in. The direction of GPS is the true north (map north), which is more in-line with what people expect as far as direction is concerned.

 

All of the Prius with Nav have dead reckoning. It uses the odometer and steering inputs to estimate course and location. It is better than nothing, but gets lost very quickly, especially in tight, slow turns.

Tom

 

OE NAVI also takes speed sensor input (pulse counts per sec) in addition to the steering angle to "dead reckon" where you are in the event of insufficient GPS signals. On open roads, the NAVI system can see 6-8 GPS satellites. In a covered garage, it can see 0. NAVI needs 4 GPS to pin point your exact location. (1-> sphere. 2-> a circle. 3-> 2 points. 4-> 1 point)

The projection error accumulates as it dead-reckons for longer period of time.

 

The obvious lesson here is that we need lower flying satellites to get inside the parking garage: "Watch out! Here comes another one..."

Tom