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InnoWare Best Practices…a guide into LPR in practice

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Cam

era

Choic

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How to position my camera

for LPR and why?

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Rele

vance This comes down - completely and solely - to capturing a

good image of the license plate.

For LPR purposes, the camera should be positioned in such a way that it can repetitively capture good images of the license plates of the objects passing by or approaching.

Because of the influence of the speed of the passing objects, we must make a difference between access control and free flow applications.

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Acc

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Contr

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• The theoretical principle is simple: the camera is best positioned straight in front of the approaching object.

• In practice this is of course generally not possible, as a camera cannot be placed in the middle of a driving lane, and as there would likely be disturbance from oncoming headlights.

• Thus, the camera will be placed aside, and somewhat higher.

• In other words, we create a horizontal and vertical angle between the camera and the object to be detected, c.q. plate to be read.

Theoretical limitations are as follows: InnoVis LPR algorithm allow an access control LPR camera should be positioned in such a way that the horizontal angle (turning angle) of the camera does not exceed 45° and the vertical angle (tilting angle) does not exceed 60°.

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• In practice it is advised to limit the horizontal or turning angle to 15° and the vertical or tilting angle to 25°

• What does this mean in practice for the vertical positioning of the camera:

<25°

• What does this mean in practice for the horizontal positioning of the camera:

<15°

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• Note: whilst these drawings show a car, InnoWare can detect on most any moving object: car, truck, trailer, motorcycle, container,...

• Considerations: always keep queue effect and motion blur effects in mind.• Place your camera in such a way that, for the given

circumstances, it can capture the plate of every object, even when they are queuing.

• Choose your camera’s shutter speed in such a way that, for the given circumstances, multiple consecutive images of the objects are equally sharp, even when moving.

• It should always be noted that the above angles are theoretical maxima. In practice it is advisable to put an access control LPR camera as close to the lane as possible at a height of around two meter.

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Concl

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on

• For access control LPR cameras, InnoWare recommends the following:

• Place your camera at about 1m aside of the lane

• Place your camera at about 2m height

• Place your camera at about 6m from the detection zone

• Chose a camera + lens combination that provides between 20 and 50 pixels plate height in the image

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Free F

low • In free flow environments objects move at (much) higher speeds,

making the influence of speed on detection much bigger.

• Why is the speed effect much bigger here?

• Because for proper, reliable LPR, we still need three to five sharp frames of the object, with sufficient character height (preferably +22 pixels plate height).

• In theory, the same limits apply as for access control applications: a theoretical maximum horizontal angle of 45° and a maximum vertical angle of 60°.

• Because of object speed however, this imposes such high demands on camera specification, that it becomes unrealistic.

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Free F

low • In practice it is advised to – where possible – position the camera

directly above the lane, or – where not possible – as close to the side of the lane as possible.

• For the vertical position of the camera, the influence of queue effects and multiple sharp frame capture coincide:

• The camera should be positioned in such an angle that it can capture the plates of every object,

• Whilst also being able to capture multiple (preferably at least five) consecutive sharp frames of each object,

• Each frame showing a sufficiently high character size (preferably about 22 pixels).

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Concl

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• For free flow LPR cameras, InnoWare recommends the following:

• When positioned above the lane:• Place your camera at about 5m height• Place your camera at about 15m to 20mfrom

the detection zone• Place your camera at an angle of about 15° to

20°• Chose a camera + lens combination that

provides between 20 and 50 pixels plate height in the image

• Chose a camera + lens combination with the appropriate depth of view (about 12m to capture 5 frames of an object moving at +200kph with a 25fps camera)

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• For free flow LPR cameras, InnoWare recommends the following:

• When positioned alongside of the lane:• Place your camera at about 3m height• Place your camera at about 1m aside of the

lane• Place your camera at about 15m to 20m from

the detection zone• Place your camera at an angle of about 5° to

10°• Chose a camera + lens combination that

provides between 20 and 50 pixels plate height in the image

• Chose a camera + lens combination with the appropriate depth of view (about 12m to capture 5 frames of an object moving at +200kph with a 25fps camera)

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CO

NTA

CT U

S

BELGIUM

M +32 499 73 09 84Skype miguel..sabbe

ITALY

M + 39 335 83 24 950Skype

giovanni_marianiinfo@innoware-tech.com www.innoware-tech.com

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