Re: [gpsd-dev] Errors, questions, and FAQ notes

[Ed W]

On 31/03/2013 12:37, Ed W wrote:

Hi

I plan on buying a total of four receivers and try to do something like this article (which I can not read because it is behind a paywall)

http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6166295

https://docs.google.com/viewer?a=v&q=cache:PN1D_wI1GRAJ:sysconf10.ieeesystemscouncil.org/sites/default/files/uploads/1569519559.pdf+&hl=en&gl=us&pid=bl&srcid=ADGEESjZ7-NiAWOFy_BdaQt3k6uDWpUcQB7z54PrLnoFcDCRYQX8e9GGmkll2kgkhV7wjaMBKxf_K8ak5cZoQ7zyMmULHgfwWjPscjUFiBiWI8mt9H8gdLnrsWxbIzO-ja_0NWyEdOAq&sig=AHIEtbQfv7hMOK-mKMIEjpnu-D5pAxtjVg

Hint: Google is a very useful tool?

Hmm, After a quick scan of his results I'm unconvinced.  I think the author has a misunderstanding of gaussian noise?

He notes that after 1 min all the receivers exhibit some kind of random walk around the known position, but the average position is closer with 2 GPS inputs than 1.  Then he compares over 4 mins and gets the same shape of results, but all shifted down in accuracy. It seems to me therefore that he is simply sampling the random walk more frequently by using X GPS units rather than a single GPS input, hence he converges on the centre faster (probably at a rate of 1/sqrt(samples) )

10Hz GPS units are available, I shouldn't be surprised if these don't exhibit a random walk over 60 seconds which is roughly like having 10x 1Hz GPS units over the same period?

I think a more promising area of research is to look at integrating the veolocity vector from the GPS with the change in position? It's not clear to me if this is already used in a standard Kalman filter that the GPS uses, hence whether this is already done?  The velocity vector seems to be often quite accurate (at non stationary speeds), coupled with knowledge of the change in position vector (and better yet some vehicle inertial nav), and you might be able to integrate the information more accurately

It's on my todo list to play with some of the Kalman filtering variants which incorporate significant lookback history

Good luck

Ed W