I would'nt be surprised if they are incorporating accelerometer readings into their extrapolation algorithm.
On Monday, August 6, 2012 9:47:41 AM UTC-4, Jef De Busser wrote: > I can see how extrapolating would yield good results if you have a small > delay between reported position & real position, e.g. the 1s update rate of > most GPS receivers. > What I can't see however, is how you could make that work with larger > delays, especially for large accelerations. > > Say for example you drive on a straight road at 3m/s, accelerate with > 2m/s2, and we exampime multiple delays. > We can extrapolate from the last known location at constant speed over > that delay and compare position to where we really are. > > 1s delay: > const speed: 3m > reality: 4m > error: 33% > > 2s delay > const speed: 6m > reality: 10m > error: 66% > > 4s delay: > const speed: 12m > reality: 28m > error: 133% > > I've measured delays varying from 1 to 4 seconds several times, and yet > Google Nav manages to position the car at the exact location. > It can't use map data to correct its position, since we're on a straight > road. > > So that must mean that it uses sensor data, right? Or am I missing > something? > > > > On 08/03/2012 08:47 PM, Nadeem Hasan wrote: > > That would be extrapolation. And that is actually the exact reason why the > GPS lags on exits if they are off-route because it has extrapolated your > position based on your route till the next actual GPS location update > arrives. I have seen this behaviour with my Garmin device too when I decide > not to follow the route. > > On Friday, August 3, 2012 11:46:45 AM UTC-4, Nobu Games wrote: > >> I'd go for interpolation and take the current average speed and the >> "structure" of the streets into account. That of course only works when you >> have something like a graph / vector representation of the streets and know >> how they are connected and what orientation they have. >> >> It is also pretty common that even Google Navigation is off, especially >> on highways with exits. Sometimes the navigation draws the car following >> the highway even though you are already leaving on an exit. >> >> >> On Wednesday, August 1, 2012 9:18:33 AM UTC-5, bushido wrote: >>> >>> Hi all, >>> >>> I'm writing an application for android for which I need good position >>> accuracy, I use a Galaxy Nexus as test device. >>> >>> My test application subscribes to location updates and draws a car >>> symbol in a map, the map is centered to the location of the car & >>> rotates according to the bearing of the location (exactly like google >>> maps on android does). I noticed that when up to speed, the positions >>> don't match with reality, they lag behind considerably. >>> When I cross a street at 90km/h for example, it will take a few >>> seconds before the car on the map is also crossing that street. It >>> isn't an error in the map data, because when I'm standing still, the >>> car gets drawn on the correct location. Google maps for android shows >>> exactly the same behavior. >>> >>> The position of the car in Google Navigate on the other hand matches >>> reality rather closely. I've noticed that the position updates are a >>> lot smoother as well. (10Hz rather than the 1Hz updates which you get >>> from GPS) >>> >>> My question is: how do they do it? What I can think of is: >>> - using the phone's sensors (gyro & accelero) together with a kalman >>> filter or similar. But I can't see how you could make that work for >>> every phone, since not all phones have these sensors. >>> - interpolating, but in that case I would expect overshooting when >>> there is a sudden stop or a sharp corner >>> >>> Thanks in advance. >>> Bushido >>> >> > -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
