[Openstreetmap] Inner city accuracy

[Zebedee Mason]

Christian van den Bosch wrote:

> 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...!
>
Christian

I've just had a Garmin Edge 305 for a week, the GPS MAP CSx and Cx's 
aren't out for a few months according to the people on the Garmin stand 
at the London Boat Show. (The eTrex Cx's are only expandable and so 
don't come with the Sirf chip, shame).

With my old Vista I had problems getting a reproducable signal 
especially around buildings, ravines and trees. The new one is finally 
allowing me to map the city centre - well I've done the test of the 
crescent near work (4 storey houses) and of the local valley road 
through the trees. I get beautiful results compared to the junk I used 
to get out of the Vista for both these cases. One thing I've noticed 
thus far is that there seems to be a difference of 100m between tracks 
from the Vista and the Edge. Loading the data into Tracklogs 
(www.tracklogs.co.uk) I see that the two sets are on opposing sides of 
the OS 1:50,000 roads and that the new tracks are much closer to the OS 
maps.

I was once shocked to get a signal from my Vista while it was sat on the 
passenger seat of my car. Seemed to be reasonably accurate compared to 
the proper way of recording tracks. i.e. from the handlebars of one of 
my bicycles.

Zeb


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