Interceptor said:
What does the 3D do anyway?
Having used various GPS navigation for a long time now (the better part of a decade), normally "3D" navigation is when the GPS is able to get a fix on enough satelites to generate a three dimensional location fix for the X,Y, and Z axis. Using this, it can more accurately determine your position on the map because not only does it have a 2D X,Y triangulation, but also the 3D axis that gives it "Altitude". So in this case, using that altitude attribute, it can make the map more accurate and display more information.
Now, that being said, I'm not sure the AVIC-Z1 manual describes it this way, because they do also have accelerometers that provide a “dead reckoning” ability to the navigation unit. However, I’ve noticed quite a few technical and other inconsistencies in the manual, so I’m left wondering if the person(s) who wrote it fully understand the technology they were describing. As ducatiboy described the use of the accelerometers, the Z1 uses them to make approximate determinations of direction, movement and speed if everything is working correctly, but they can be confused by steep terrain or excessive vibration. That is why the speed sensor is so vitally important.
My interpretation in this case would be that 3D hybrid mode simply means the unit has a good GPS fix for 3D navigation (in the traditional X,Y,Z sense), and it is also taking measurements from the internal accelerometers and speed sensor into account when it plots vehicle location on the map.