SPECS questions Approved: wibble

On Tue, 4 Oct 2005 10:34:26 +0100, Tim Downie was popularly supposed to have said:

I don't know for certain how the units work, but a best guess is as follows:

In each unit, you have a clock synchronised to a GPS clock somewhere using NTP to ensure the system clocks are accurate to a few tenths of a second.

Then each unit logs each registration number as it pbuttes, and logs this with the time it pbutted the unit and the unit ID number. All logs are sent to a central point.

At the central point a computer goes through the logs and works out vehicle speed over each leg between the detection units.

At this point you can do one of two things:

a) buttume all vehicles are cars and only pursue vehicles exceeding the car limit, then sort out if they are HGVs etc afterwards at the NIP-issuing stage.

b) Look up registrations against the central database and apply speed limits based on vehicle type at this time.

Option b) requires a net link to the central DVLA computerdatabase, but since the registrations won't alter much over time, you could get away with making a local mirror of that database and updating the mirror intelligently every night between when you are processing the camera data.

The lookup stuff is not, BTW, what I would term rocket science. You'd have to think a bit to get the databases set up properly, and the IT kit would need to work correctly most ofthe time, but it isn't hard to work all this out, and lookups are certainly not hard to do once the data is in plaintext format.

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