I would like to readout the altitude. Any GPS has all three coordinates (latitude, longitude, altitude). But I've found no way to do this in the Prius. Ideas? PLEASE?
We can only guess, but one such guess is that the GPS is used solely by the Nav system to remain calibrated (it used gyros and wheel rotatin sensors for most of it's tracking); since altitude is not required for navigation, they didn't "bother" to add it to the display. Altitude on commercial GPS units is only accurate to about 100 feet or so anyway, but it sure wouldn't have taken them much effort to make that aviailable in the coordinate display mode.
I am one of the previous askers of this questions too. One of the big disappointments for me when I got my Nav Prius, was the lack of altitude readout, as I'd become spoiled by the hand-held Garmin unit I kept on a dash bracket in my previous car. I've googled my way all around the net on this issue, and found no solution. I'm fairly certain the data is there, but it appears that reaching and displaying it would call for some pretty serious hacking. The altitude solution on my Garmin is way better than 100' accuracy. By all appearances, it's as good in elevation as it is in lat/long. I live near sealevel, and I get consistent, repeated accurate reads at well several points of well-known elevation. My unit, btw, is WAAS enabled, but as far as I know, virtually all current consumer models are.
And why not use the GPS for time and speed? At least make this information available for casual viewing. Tom
There have been a few threads on GPS vertical accuracy over the past couple of years (here and on POL), so I'll leave the details for the search function. But to summarize, due to sat (triangulation) geometry (even with all 12 are in view), altitude will never be as accurate as lat/long, and this is true for military as well as civilian units. D-GPS can augment GPS data with surveyed data and can attain better accuracy, but the Prius does not use this method. Also, many mistake the displayed "elevation error" on many handheld units to be the actual total elevation error (natural enough given the name), but this metric is misnamed; it only refers to the additional error due to less than ideal sat geometry. The basic triangulation uncertainties are usually greater than this calculated value. Even though 100' accuracy isn't good enough to use the Nav system to improve the charge/discharge algorithms, it is still useful and interesting, so I don't know why it was omitted, if not simply for cost reasons. The Nav system can "nav" fine without it, so it may not even be calculated from the raw sat data. Here is a link that discusses unaided GPS altitude accuracy: gps altitude Here is a plot of accuracy (y-axis) as a function of averaging time (x-axis) for various coordinates (E-W, N-S, altitude). You can see that altitude is accurate to about 35 meters or more without averaging, and is always worse than either east-west or north-south accuracy.
