Passive ranging based on virtual circle from three matched points

It is critical to extract the linear rotational invariant of an imaged target in passive ranging from the images, and it' s more difficult to extract the parameters from a general non-cooperative than from a cooperative ones. A method was presented to construct a virtual circle as the inherent rotation invariance of a circular target. The proposed virtual circle was the circumcircle of equilateral by triangles extended from three matched points in adjacent frames in the image sequence. It is demonstrated by the simulations that the probability density function curve of the proposed virtual circle has tighter error distribution than that of a few other methods, and further studies indicate that the diameter of this virtual circle is also a preferable depth-related line segment feature. The line segment feature is used for the target distance estimation and it displays superior performance. It is characterized by its simple for the distance estimation using line segment features, and the concept of virtual circle increases the flexibility in practice. Because as few as three matched points are the least points in target tracking based image feature, so it is attractive for passive ranging to non-cooperative targets. The method is valid under the condition of the inclination angle of target relative to camera increased or decreased from -10 degree to 10 degree between adjacent sampling times.