[Openstreetmap] Inner city accuracy

Christian van den Bosch cjb at cjb.ie
Wed Jan 25 21:39:41 GMT 2006


Lars Aronsson wrote:

> Are some GPS units better than others?

Apparently, recent GPS units based on the "Sirf Star III" chipset are 
far better than the previous generation at detecting and locking onto 
low-strength signals - I read one review where such a unit sitting in 
the cup holder in a car stayed locked onto 8 satellites and gave 
something like 4-metre accuracy. With my old Garmin eTrex Vista, I 
consider myself lucky to get a fix like that out in the open holding my 
unit up to the sky! In a car, I have to put the GPS on the dashboard to 
get any worthwhile signal at all. I haven't had a chance to play with 
one of these Sirf-based units myself yet though. Soon, my precious...!

> Or should we wait for WAAS or Galileo to give us better accuracy, 
> before we can do useful maps of inner cities?

I gather Galileo won't hit showtime till 2008 at least, so I wouldn't 
hold my breath on that front. WAAS is slowly becoming more available, 
both in terms of regions, and units that support it. DGPS has been 
somewhat revived by DGPS-over-IP, but I don't think it'll ever really be 
mainstream.

In the meantime, I think all we can do is go down the same streets lots 
of times to amass a statistically significant sample set to base our map 
drawing on...

Christian / cjb

http://www.cjb.ie/




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