Television – Special applications – Observation of or from a specific location
Reexamination Certificate
1998-11-20
2003-07-29
Kelley, Chris (Department: 2613)
Television
Special applications
Observation of or from a specific location
C382S154000
Reexamination Certificate
active
06600509
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The problem of building security is an important issue currently being addressed by developing technology. Automatic counting mechanisms for determining and/or controlling the number or identity of people passing through a particular entrance or exit have been around for some time. They vary from the simple automatic turnstile to swipe card access and radio-frequency tagging systems. A principal disadvantage of all these previous techniques is the low access speed. An automatic turnstile is particularly obstructive in requiring considerable effort to be made by moving personnel. None of the systems can be operated with a default unlocked door making a locking/unlocking mechanism unavoidable. In swipe card systems such door mechanisms are prone to failure. Radio-frequency tagging doesn't detect untagged intruders and so cannot be used to maintain a default unlocked system.
There is a perceived need for a detection system capable of monitoring personnel movement which provides for a faster throughput of traffic.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a detection system capable of providing non-intrusive monitoring of personnel movement through default unlocked entry and exit points.
The present invention provides a detection system including a light source arranged to project light onto an obstructing surface and imaging means arranged to selectively image the intersection of the projected light with the obstructing surface characterised in that the imaging means comprises at least one camera sensitive to light emitted from said light source and the imaging means and light source are mutually arranged such that the orientation of imaging means optical axis and direction of light projection from said source are parallel or intersect at a position on the opposite side of the obstructing surface to the imaging means and source of projected light.
The invention provides the advantage of non-intrusive detection. It exploits the effects of perspective on objects when viewed from a particular direction: an object interrupting such projected light can be readily detected as an outward movement of an imaged intersection in the field of view. It thus allows for the detection of object movement through the system without obstruction of the traffic flow.
The system is preferably arranged to monitor the presence or absence of bodies on a bounding surface intersecting the projected light. In this regard, the bounding surface forms the obstructing surface in the absence of a body; and the surface of the body forms the obstructing surface in the presence of a body. The imaged intersection then has different positions according to whether it arises from the bounding surface or the surface of the body and these positions are relatively displaced in accordance with the body surface's remoteness from the bounding surface. This provides the advantage of simplicity in application of the invention to numerous situations. The intersection of the projected light with a surface can be imaged and that image monitored continuously. Movement of the image can be ascribed to an object on the surface passing through the projected light. The necessary movement may be provided by the object itself, motion of a level surface supporting the object or by movement of the light sheets and imaging means across a stationary surface and objects. Moreover, the objects need not be physically separable from the surface the invention can be used to map the structure of the surface itself.
The projected light is preferably in the form of a substantially planar sheet of light and the imaging means is arranged such that its optical axis is substantially parallel to and offset from the plane of the light sheet. This improves the detection capability of the system. The intersection with a level surface will thus be a bright line which will form a well defined image. Any object crossing this bright line anywhere along its length will cause a deflection in the image. Furthermore the narrowness of the line improves the capability of the system in its provision of accurate information regarding the height of an interrupting object.
The projected light may be in the form of two substantially parallel planar sheets of light disposed about the imaging means and the imaging means arranged such that its optical axis is substantially parallel to the planes of the light sheets. This provides the capability for determining direction of travel through the system by means of observing the sequence of light sheet disturbance.
The imaging means may be arranged to form an image of an intersection of the obstructing surface and a light sheet wherein the intersection is detectable as a line in the image. The system may be arranged to respond to a deflection of such an image line. This provides an improvement to utility. The system is capable of responding to the data received and the need for manual interpretation is reduced.
The system may be arranged to monitor the profile of bodies on a bounding surface intersecting a projected light sheet. In the presence of a body, the surface of the body forms the obstructing surface and the image line defines a deflection pattern characteristic of the profile of the body. This increases the information available to the detection system and renders it capable of more sophisticated responses.
The deflection pattern may comprise perpendicular displacements of image line components from their original positions in the line. The displacements (d
shift1
) measured at the image plane of the imaging means are described by the equation
d
shift
⊥
=
fd
⊥
h
body
h
c
(
h
c
-
h
body
)
where d
1
is the perpendicular distance from the imaging means to the light sheet responsible for the line in the image, f is the focal length of the imaging means
1
h
c
is the distance between the imaging means and the bounding surface and h
body
is a parameter describing the body height at each point that it intersects the light sheet. This provides a straightforward means of deriving the profile of an interrupting object from the deflection pattern observed as the object passes through a light sheet.
The projected light may be directed transversely of a longitudinally extending transit zone, and projected from a bounding region in which the imaging means is located. This provides for complete coverage across the transit zone and the system is therefore capable of detecting any object moving along it. In one embodiment the transit zone may be a corridor, the obstructing surface is the corridor floor or the surface of a body and the bounding region is the corridor ceiling. This provides a detection system which is capable of monitoring personnel movement into and out of a designated room or area of a building.
The imaging means may be a single camera or a one-dimensional array of at least two cameras, the array alignment being substantially perpendicular to the component cameras' optical axes and substantially parallel to the plane of the projected light. A single camera provides the advantage of cost reduction but an array will allow imaging along the length of the light sheets without demanding an extensive single camera field of view. Furthermore the array also provides an improvement in accurate counting. A single camera could find its view of one body obscured by a second, nearer body. This is particularly likely to occur if the second body is taller than the first. The effects of such obscuration are largely overcome by the use of a number of cameras as any one body will be imaged in at least one camera.
The light source may be at least one strip source extending longitudinally along one side of each light sheet. Alternatively, it may comprise an array of point sources for each sheet such that the array is located along one side of each light sheet and arranged to project light to the opposite side of the respective light sheet. Each point source may be associated with a cylindrical lens and thereby arranged
Kent Philip J.
O'Connor John T.
Radford Charles J.
Savage John T.
Smith Robert W M
Kelley Chris
Parsons Charles
Qinetiq Limited
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