Abstract
Single circular targets are widely used as calibration objects during line-structured light three-dimensional (3D) measurements because they are versatile and easy to manufacture. This paper proposes a new calibration method for line-structured light 3D measurements based on a single circular target. First, the target is placed in several positions and illuminated by a light beam emitted from a laser projector. A camera captures the resulting images and extracts an elliptic fitting profile of the target and the laser stripe. Second, an elliptical cone equation defined by the elliptic fitting profile and optical center of the camera is established based on the projective geometry. By combining the obtained elliptical cone and the known diameter of the circular target, two possible positions and orientations of the circular target are determined and two groups of 3D intersection points between the light plane and the circular target are identified. Finally, the correct group of 3D intersection points is filtered and the light plane is progressively fitted. The accuracy and effectiveness of the proposed method are verified both theoretically and experimentally. The obtained results indicate that a calibration accuracy of 0.05 mm can be achieved for an 80 mm × 80 mm planar target.
Highlights
The light plane is calibrated with a single circular target by performing the following steps: (1) An elliptic fitting profile of the circular target is obtained by the proposed “revisited arc-support line segment (RALS) method”, and sub-pixel points of the light stripe are extracted by another technique based on the Hesse matrix
A novel calibration method for line-structured light 3D measurements based on a single circular target is proposed
The RALS method is used for extracting the elliptic fitting profile because of its high accuracy and robustness
Summary
Measurement is a process of obtaining quantifiable information that requires a very high accuracy [1]. Huynh [11], Xu [12], and Dewar [13] introduced a 3D target to define the light plane calibration points using the cross-ratio invariability principle (CRIP) All these three methods were very complex and possessed a low calibration accuracy. A new method for the on-site calibration of a line-structured light 3D measurement process based on a single circular target is proposed. The light plane is calibrated with a single circular target by performing the following steps: (1) An elliptic fitting profile of the circular target is obtained by the proposed “revisited arc-support line segment (RALS) method”, and sub-pixel points of the light stripe are extracted by another technique based on the Hesse matrix.
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