Can anyone report on the accuracy and usefulness of the dead reckoning capability in the built-in nav system? In a big city, for example, where the GPS signal will often be partly or completely blocked, is the dead reckoning sufficiently accurate to be helpful? Thanks.
While not necessarily needed, I find it very nice to use the dead reckoning with my Navi when I am in underground garages in the middle of the city. It seems to accurately sense the direction that I am headed no matter how many levels underground. What surprises me more is that my XM works pretty well underground as well. This may be due to a ground repeater that is used to broadcast when there is not direct line of site, but I know that the Sirius radio that I had until I got the Prius would lose signal the instant I went through the door to the garage. Now, I am able to listen to it uninterrupted until I parked, sometimes 3 to 5 stories underground. Someone else complained about poor XM reception recently, so the only thing I can think of for them is a combination of no line of site to the satellite, combined with a lack of ground repeaters.
Yes, it's quite helpful. As long as you intermittently get GPS signal so the system can recalibrate it will keep you very close on track. You need to be in some pretty dense tall buildings to completely loose the signal though.
There must be something like that going on, because I've lost reception just by driving close to high rock formations. I just assumed I was out of the line-of-site of the appropriate satellite(s), so I can't imagine it would work underground without some type of "help" in the city.
