Police, Camera, Action.

How do they do it?

A stationary police car a hundred yards down a side road apparently
instantly recorded the speed of a vehicle on the main road, passing the
turning.
Anyone else see it? Any idea how they do it?

(Do I need to mention the usual hypocrisy and bullshit from the narrator?)

 

Eiron emerged from their own little world to say

The old fashioned way of timing a vehicle between two markers.

 

In uk.rec.motorcycles, Eiron amazed us all with this pearl of wisdom:

Blame the script writers unless you know the narrator regularly speeds.

Not seen it btw ;-)

 

a) No. b) One way: Take a CCD camera with a known lens a known
distance from the road. Do a 2D FFT of frames a known time apart.
Perform a correlation on the two FFTs to get the distance objects moved
between the two frames. Do the simple calculation required to transform
this to a speed.

--
Ivan Reid, Electronic & Computer Engineering, ___ CMS Collaboration,
Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN
GSX600F, RG250WD "You Porsche. Me pass!" DoD #484 JKLO#003, 005
WP7# 3000 LC Unit #2368 (tinlc) UKMC#00009 BOTAFOT#16 UKRMMA#7 (Hon)
KotPT -- "for stupidity above and beyond the call of duty".