Buckinghamshire CC ANPR cameras

John Wilson tugwilson at gmail.com
Sat Jan 7 12:06:58 GMT 2012

On 7 January 2012 09:27, Roland Perry <lists at internetpolicyagency.com> wrote:
> In article <AFD1C8AA-C7DC-4F81-A66F-C32CA7ED0B2A at sourcetagged.ian.co.uk>,
> Ian Mason <ukcrypto at sourcetagged.ian.co.uk> writes
>>>> Is there a standard "depersonalisation" algorithm? If so anybody know
>>>> what it is?
>>> No. Indeed, in general, it is not possible to "depersonalise" and
>>> retain any usefulness in the data.
>>> So step 1 is probably to find out WTF they're actually doing.
>> It depends. If they are strictly monitoring traffic flows and journey
>> times then all they have to do is assign a unique journey number to a set of
>> records for a vehicle and drop/delete the registration number when the
>> journey seems complete. Each time the vehicle starts a journey it gets
>> assigned a new unique journey number so that there's no link with previous
>> journeys for the same vehicle and no record of the registration number at
>> all once a journey has completed.
> aiui the Trafficmaster system (blue cameras) works a lot like this.
>> Obviously  there's detail to work through such as: a vehicle enters the
>> area, is  seen by ANPR on entry, then parks up for several days and isn't
>> seen  by a second ANPR camera; at what point do you delete the partial
>>  journey record that will, of necessity, still contain a registration
>>  number.
> About an hour after last seeing the plate would be plenty if you are looking
> at the "flow" of traffic.

That's quite true but it seems clear from the Council documents that
they intend to hold the camera even data for some time. There are
perfectly legitimate reasons for this. They can, no doubt, get useful
information from the bulk data which would help in planning traffic

I've found the schema for the data packet sent by ANPR cameras which
conform to the UTMC standard it has information like the direction of
travel and the carriage used. It also has optional fields for vehicle
speed and classification (presumably things like, car, motocycle, van,
etc). Even if the cameras don't provide this extra information now you
would want to build a database to hold it as and when the capabilities
become available.

John Wilson

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