LPR · ANPR · License plate reader
Put a license plate camera on the plan, give the car its speed and open the camera's preview. CCTVplanner simulates the plate under the camera's own infrared, the smear of its shutter and the glare, and tells you whether the plate can be read, and if not, what stops it.
Four checks
A number plate is retroreflective: under the camera's own infrared it returns hundreds of times more light than the road. An ordinary camera exposed for the scene burns it into a white patch; a plate camera exposes for the sheeting and reads it on a black frame. The preview works out how far past full scale the plate lands for the camera you placed, at its distance and angle, and draws that.
Give the car a speed and the preview smears it by the shutter the camera chose. Axis's rule is that the plate may move no more than about 14 mm across the picture while the shutter is open. At 100 km/h the ordinary camera smears it by 29 mm; the plate camera, at 1/1000 s, by 12 mm.
Both cameras on a 4 m pole over the kerb, aimed 18 m up the street at the oncoming lane, with the 3D roads on so the preview fills them with traffic driving on dipped beams. Every passing car is lit, shaded and smeared in every frame and the verdict follows the best plate in view. Axis puts the floor at 75 pixels across the plate and most reading software asks for 100 to 150, so the ordinary camera's wide view fails on pixels before anything else, and the plate camera's narrow one does not.
In daylight the sun lights the plate and the road alike, so nothing is overexposed: both cameras read the plate, and the plate camera simply gives a monochrome picture. The simulation changes only what physics changes.
What it is built on
The 3D view and the camera preview are in the Pro plan. See the plans
Because the plate is retroreflective and sends the camera's own infrared straight back, hundreds of times brighter than the road. A camera exposed for the dark scene clips it, and the light the lens scatters covers the characters. A plate camera exposes for the plate instead.
One made for it: a short shutter, its own infrared and an exposure set for the plate. In CCTVplanner, filter the catalogue for plate-reading cameras and check the plate in the preview at your site's distance and speed.
Short enough that the plate moves no more than about 14 mm across the picture during the exposure: at 50 km/h and 20° to the lane that is about 1/340 s, and shorter for faster traffic or a wider angle.
As far as its lens keeps 100 to 150 pixels across the plate and, at night, its infrared reaches. The preview counts the pixels for the camera and lens you placed.
Place the camera, set the car's speed and read the verdict in the preview, by day and at night.
