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re-recording existing cameras

 
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divadiow
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Joined: Jun 14, 2005
Posts: 30

PostPosted: Mon Jul 10, 2006 11:59 am    Post subject: re-recording existing cameras Reply with quote

some cameras arent located in quite the right positions around me, will the databse be amended if I stand underneath them and get them 100%?
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JockTamsonsBairn
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Joined: Jan 10, 2004
Posts: 2777
Location: Bonnie Scotland (West Central)

PostPosted: Mon Jul 10, 2006 12:19 pm    Post subject: Re: re-recording existing cameras Reply with quote

divadiow wrote:
some cameras arent located in quite the right positions around me, will the databse be amended if I stand underneath them and get them 100%?
Eventually. The positions are, as I understand it, averaged. I think it would be best to send the file with a comment explaining that you have made these captures while stationary.
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TomTom Go 940 LIVE (9.510, Europe v915.5074 on SD & 8.371, WCE v875.3613 on board)
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neil01
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Joined: May 06, 2005
Posts: 902
Location: Leeds

PostPosted: Mon Jul 10, 2006 1:18 pm    Post subject: Reply with quote

Just remember that even standing next to the camera (or more correctly at the side of the road nearest the camera) is not in itself 100% accurate due to the implementation of the GPS technology.

As an example, I have an external antenna in a window which I use when setting up/testing, and my reported position still varies by up to 30 feet.

Even what you believe to be 100% correct, unfortunately may not be - and will still need to be verified/corrected, possibly by transposing the position to a map and taking the co-ordinates from there.

Admittedly, it isn't always 30 feet out, and even 30 feet feet on a country road may make little difference in practice, but in a built up area, this level of error could actually put a camera on the wrong road or junction.

I mentioned about the position nearest the road being more important than its true position, because sometimes (often?) if the camera position is recorded exactly, it will not be reported by some applications. I think that I even read of a situation where a camera in the database had to be moved to the carriageway of the main road, because its (true) position at the side of a filter lane resulted in it not being reported by an application.
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mcwarre
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Joined: Mar 25, 2004
Posts: 157

PostPosted: Wed Jul 12, 2006 3:26 pm    Post subject: Reply with quote

neil01 wrote:
Just remember that even standing next to the camera (or more correctly at the side of the road nearest the camera) is not in itself 100% accurate due to the implementation of the GPS technology.



This is more an implementation problem rather than a GPS one. To fix your point there are four unknowns; lat, long, alt & time. Full GPS systems (such as aircraft) use expensive receivers which solve the four unknowns with five simultaneous equations (hence need to see 5 sats). In sat nav (cars etc) they have 3 unkowns (not worried about alt); they 'cheat' and use 3 sats which means that their receivers don't have to be as good and are, therefore, cheaper. This 'fudge' brings in the larger error. Mil equipment is much more accurate
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neil01
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Joined: May 06, 2005
Posts: 902
Location: Leeds

PostPosted: Wed Jul 12, 2006 8:45 pm    Post subject: Reply with quote

mcwarre wrote:
neil01 wrote:
Just remember that even standing next to the camera (or more correctly at the side of the road nearest the camera) is not in itself 100% accurate due to the implementation of the GPS technology.



This is more an implementation problem rather than a GPS one....


But that was exactly what I wrote - you even quoted it!

I understand your reasoning, but while I can get a fix with three satellites, it does, as you say not have enough information for altitude, however this is shown once there is a fix on four or more satellites.

I regularly have fix on 5 or more satellites, a fix of 9 being the maximum I have ever seen, with an additional 2 registering, but being of insufficient strenght to gain a fix. And I certainly wouldn't describe my MIO as top-end; far from it.

I won't go into detail here, but a good explaination on GPS can be found here:
http://www.montana.edu/places/gps/understd.html
for anyone who wants detailed information.
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