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From: John Navas on 10 Jun 2010 22:16
On Thu, 10 Jun 2010 18:02:18 +0100, in
<0qydnah-CPAHh4zRnZ2dnUVZ8lmdnZ2d(a)bt.com>, Bob <bob(a)invalid.invalid>
wrote:

>On 10/06/2010 16:57, Char Jackson wrote:

>> I've only seen the camera cars twice, once on my street and once again
>> in another residential part of my city. Both times they were moving
>> with the speed of traffic, about 25-30 MPH. If they were stopping
>> every time they saw an open network, they wouldn't get very far.
>>
>I haven't seen them as yet as I was on holiday when they did my town.
>Given the accuracy of GPS and if they were moving all of the time I
>can't see that wifi location will be all that accurate. ...

FYI, business grade GPS is quite accurate even while moving, on the
order of a few feet. Even my new wrist GPS can manage that.

--
Best regards, FAQ for Wireless Internet: <http://wireless.navas.us>
John FAQ for Wi-Fi: <http://wireless.navas.us/wiki/Wi-Fi>
Wi-Fi How To: <http://wireless.navas.us/wiki/Wi-Fi_HowTo>
Fixes to Wi-Fi Problems: <http://wireless.navas.us/wiki/Wi-Fi_Fixes>
From: Bob on 11 Jun 2010 03:26
On 11/06/2010 02:42, Brad Allen wrote:
>> Where I live over 50% oh households turn off their routers when they are
>> not at home and at present I am staying at relatives, about 200 miles
>> north of where I live, and that figure has increased to about 80%. I
>> would also say that with people changing their ISP options and
>> consequently their SSID's, most people never change their ISP's unique
>> SSID's but everytime the router or ISP is changed the SSID changes,
>> that their has been a 40% change in the last 18 months and I doubt
>> Google are going to renew their database that frequently so I am not
>> convinced about using consumer wifi as a location device in the UK. It
>> would probably work with wifi hotspots which tend not to change and are
>> near to your "fish and chip shops" but I see no reason for them to be
>> recording wifi networks on housing estates which are a couple of miles
>> away from anything.
>
> You'd have to think like a programmer to realize these things, but:
>
> 1. MAC addresses (Bob Metcalfe et al& Std Bodies) are used, not SSIDs.
As I pointed out the router is being changed and hence the MAC address
is changed.
From: Bob on 11 Jun 2010 03:33
On 11/06/2010 03:16, John Navas wrote:

> FYI, business grade GPS is quite accurate even while moving, on the
> order of a few feet. Even my new wrist GPS can manage that.
>
And how do you know? Have you actually gone to known reference point and
taken several readings or do you assume the adverts are correct?
"The declaration of the accuracy by Garmin GPS receivers often leads to
confusion. What does it mean if the receiver states an accuracy of 4 m?
This readout refers to the so-called 50 % CEP (Circular Error Probable).
This means that 50 % of all measurements are within a radius of 4 m. On
the other hand, 50 % of all measured positions are outside of this
radius. Furthermore, 95 % of all measured positions are within a circle
of twice this radius and 98.9 % of all positions are within a circle of
2.55 the radius. In the given example, nearly all positions are within
circle with a radius of 10 m. The determined position is in the worst
case accurate to 10 m."
<http://www.kowoma.de/en/gps/accuracy.htm>

From: John Navas on 11 Jun 2010 12:13
On Fri, 11 Jun 2010 08:33:35 +0100, in
<rcWdndNTXqZNe4zRnZ2dnUVZ8oqdnZ2d(a)bt.com>, Bob <bob(a)invalid.invalid>
wrote:

>On 11/06/2010 03:16, John Navas wrote:
>
>> FYI, business grade GPS is quite accurate even while moving, on the
>> order of a few feet. Even my new wrist GPS can manage that.
>>
>And how do you know?
>Have you actually gone to known reference point and
>taken several readings or do you assume the adverts are correct?
>...

I do repeatability testing against fixed objects. Quite important when
you want (as I do) to be able to navigate a boat in close quarters
without good visuals (e.g., in dense fog).

--
Best regards,
John

Navas' Sailing and Racing in the San Francisco Bay Area
http://sail.navas.us
From: John Higdon on 11 Jun 2010 18:43
In article <rcWdndNTXqZNe4zRnZ2dnUVZ8oqdnZ2d(a)bt.com>,
Bob <bob(a)invalid.invalid> wrote:

> And how do you know? Have you actually gone to known reference point and
> taken several readings or do you assume the adverts are correct?
> "The declaration of the accuracy by Garmin GPS receivers often leads to
> confusion.

Their maps aren't very good, either. I got rid of mine when right after
a map download update, my stick-on Garmin GPS showed me flying across
the bay rather than riding on the north-bound span of the Benicia
bridge. The update wasn't free, and I considered that an egregious
error, even for freeware.

I quit using it as not dependable.

--
John Higdon
+1 408 ANdrews 6-4400
AT&T-Free At Last
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