Joined: 10 Jun 2007 Posts: 87 Location: DC Metro Area
"Where Am I" elevation keeps changing Wed May 28, 2008 4:37 pm
I really like the new Where Am I feature on the 760 but there's a couple of things that are really puzzling. First, each time I select it, while I am parked in the same location (i.e., at home), it gives me a different closest address. Sometimes, even the street is not correct. I can understand the house number being off, but not the street itself! Second, the elevation keeps changing! Now, I tried this when I was on a trip over the weekend. I was standing still inside the hotel lobby and selected Where Am I. The hourglass kept churning and the elevation reading kept going up and down -- it varied by over 200 feet! Now, I know I wasn't on a rollercoaster or riding an elevator. Why would it do this? Since I started noticing this phenomenum, it happens allthe time. The hourglass never stops, even though I haven't moved, and the elevation reading goes up and down.
When you say it shows you on a street that you are not on... is it at least on a nearby street?
The GPS system itself is accurate (horizontally) to about 10 meters. The mapping database isn't nearly that accurate in most cases. And the vertical accuracy of GPS is even less accurate than horizontally, so swings of a couple hundred feet isn't completely out of the ordinary.
Joined: 10 Jun 2007 Posts: 87 Location: DC Metro Area
Wed May 28, 2008 7:13 pm
It shows either my street or one of the adjacent streets. My street is short and my house is near the middle, but I'm sure I'm quite a bit further than 10 meters from any other street.
Regarding the elevation reading -- I understand that you are saying that the GPS isn't very accurate vertically -- but why would it keep moving up and down? Is it unable to get a "fix" on the vertical location?
If you are more than 10 meters from any other street then what will happen (and what it does anyway) is to figure out what the closest street is (according to the street database) to your calculated position. Where I live the street database is off by a couple hundred feet which makes it think I'm on an entirely different road than I'm actually on when I'm driving to or from my house.
As for the vertical accuracy, itt keeps moving up and down as new calculations are made, some satellites start to appear in view, and others disappear, just like it does horizontally, but more exaggerated.
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