1. Field of the Invention
The present invention relates to a rigidity checking method and apparatus for effectively checking the rigidity of an object perceived by a automated robot of vehicle, or of an object indruding into the sensing field of monitor camera.
2. Description of the Prior Art
The distance between two arbitrary points on a rigid body remains unchanged even when the rigid body takes a force or moves. This property of the rigid body permits a decision to be made from an image sequence including a target body as to whether the target body is a rigid body or not.
A rigidity checking technique is described in detail by S. Ullman and R. Basri, Object Recognition by Liner Combination of the Model, IEEE Trans. PAMI (Pattern Analysis and Machine Intelligence). In this technique, assuming three pairs of coordinates of a feature point of the target object in three pictures taken at different times to be (X.sub.1, Y.sub.1), (X.sub.2, Y.sub.2) and (X.sub.3, Y.sub.3), tests are made to see to what extent the coordinates (X.sub.1, Y.sub.1), (X.sub.2, Y.sub.2) and (X.sub.3, Y.sub.3) satisfy the following linear constraint equations: EQU .alpha..sub.1.sup.1 S.sub.1 +.beta..sub.1.sup.1 Y.sub.1 +.gamma..sub.1.sup.1 X.sub.2 +.omega..sub.1.sup.1 X.sub.3 =0, (1) EQU .alpha..sub.1.sup.2 X.sub.1 +.beta..sub.1.sup.2 Y.sub.1 +.gamma..sub.1.sup.2 Y.sub.2 +.omega..sub.1.sup.2 Y.sub.3 =0, (2) EQU .alpha..sub.2.sup.1 X.sub.1 +.beta..sub.2.sup.1 X.sub.2 +.gamma..sub.2.sup.1 Y.sub.2 +.omega..sub.2.sup.1 X.sub.3 =0, (3) EQU .alpha..sub.2.sup.2 X.sub.1 +.beta..sub.2.sup.2 X.sub.2 +.gamma..sub.2.sup.2 Y.sub.2 +.omega..sub.2.sup.2 X.sub.3 =0, (4) EQU .alpha..sub.3.sup.1 X.sub.1 +.beta..sub.3.sup.1 X.sub.2 +.gamma..sub.3.sup.1 Y.sub.3 +.omega..sub.3.sup.1 X.sub.3 =0, and (5) EQU .alpha..sub.3.sup.2 X.sub.1 +.beta..sub.3.sup.2 X.sub.2 +.gamma..sub.3.sup.2 Y.sub.3 +.omega..sub.3.sup.2 X.sub.3 =0, (6)
where .alpha..sub.i.sup.j, .beta..sub.i.sup.j, .gamma..sub.i.sup.j and .kappa..sub.i.sup.j are appropriate coefficients. Since a rigid body satisfies these constraint equations, the rigidity of the target object can be estimated by the extent to which the three pairs of coordinates satisfies the above constraint equations, that is, a satisfaction degree of the constraint equation.
In order to estimate the satisfaction degree, the optimum values are conventionally found for the coefficients of the constraint equations by means of least square error estimate by using a sufficient number of feature points. Then, the residue of each constraint equation is calculated as a satisfaction degree. It is determined that the smaller the residues or the satisfaction degrees are, the more rigidity the target object has.
However, the values of the constraint equations changes with a change in the resolutions of the three pictures. Since the resolutions of the pictures which have essentially nothing to do with the rigidity of the target object have effects on a judgement of the rigidity of the target object, the conventional rigid checking technique is not suitable for a general purpose tool.
Further, the conventional rigid checking technique requires calculations of the coefficients of the constraint equations which have no direct relationships with the rigidity of the target object, and accordingly is not effective.