But this system property is not ideal for the spection of tubes,pipes,and hollow spaces,i.e.,for systems such as sewer pipe inspection robots and endoscopes,where there are almost no obiects directly in front of the inspection heads and where wide-angle objective lenses are used to inspect the walls of the hollow space while the system moves through it. For these applications a modification of the structured light measurement principle was developed at the Fraunhofer-Institut fur informations-und Datenverarbeitung. in this modification the illumination and the objective lens are located(virtually) on the same optical axis, and thw triangulation baseline (the distance between the object -side principal plane of the lens and the source of the illumination) is located on this common optical axis. After sketching the measurement principle and comparing it with a standard strucured light system, we show that this modification has significant advantages for wide-angle measurement problems:
The measurement accuracy is not affected by the distance between illumination and camera perpendicular to the line of sight.
These systems are ideal for applications in which a minimal diameter of the inspection system is necessary.
They measure with higher accuracy in the wideangle region.
They provide rotationally symmetric measurements and measurement accuracies perpendicular to the optical axis.
when this symmetry is used, coordinate calculation is simplified.
These advantages show that the measurement principle is ideal for wide-angle inspection problem, i.e., endoscopic measurement systems and tube and hole inspection systems. Shown further in the sequel is the application of this measurement principle in an optical system for sewer pipe inspection.
2.Basic Principle of Structured Light Projection Techniques
Figure 1 illustrates the principle of optical 3D measurements by structured light projection: Point P, the center of lens L(focal length f), and a laser determine the trangle for the measurement of P. Angle w and the distance of the laser to the optical axis are system parameters(determined by calibration of the system). The angle of the central ray from the object through the lens is calculated from image point B. Thus the triangle laser-lens-P is completely determined.
From the basic equations of image formation follows
The second equation for determining object coordinates is given by the condition of illumination; i.e., point P is illuminated by the laser beam, whose ray is described by
An alternative point of view, that of this measurement principle ,is also shown in Fig.1 Equivalent to regarding the baseline b as the reference for the calculation is the use of the intersection of the laser beam with the optical axis at a . The laser beam is then described by
The object coordinates are calculated by
respectively. By the projection of a light pattern corresponding to that of the sketched laser,rotated around the potical axis, a completely rotationally symmetric measurement system is derived:a system for optical 3D measurements by a tadially symmetric structured light projection.
The measurement accuracy is not affected by the distance between illumination and camera perpendicular to the line of sight.
These systems are ideal for applications in which a minimal diameter of the inspection system is necessary.
They measure with higher accuracy in the wideangle region.
They provide rotationally symmetric measurements and measurement accuracies perpendicular to the optical axis.
when this symmetry is used, coordinate calculation is simplified.
These advantages show that the measurement principle is ideal for wide-angle inspection problem, i.e., endoscopic measurement systems and tube and hole inspection systems. Shown further in the sequel is the application of this measurement principle in an optical system for sewer pipe inspection.
2.Basic Principle of Structured Light Projection Techniques
Figure 1 illustrates the principle of optical 3D measurements by structured light projection: Point P, the center of lens L(focal length f), and a laser determine the trangle for the measurement of P. Angle w and the distance of the laser to the optical axis are system parameters(determined by calibration of the system). The angle of the central ray from the object through the lens is calculated from image point B. Thus the triangle laser-lens-P is completely determined.
From the basic equations of image formation follows
The second equation for determining object coordinates is given by the condition of illumination; i.e., point P is illuminated by the laser beam, whose ray is described by
An alternative point of view, that of this measurement principle ,is also shown in Fig.1 Equivalent to regarding the baseline b as the reference for the calculation is the use of the intersection of the laser beam with the optical axis at a . The laser beam is then described by
The object coordinates are calculated by
respectively. By the projection of a light pattern corresponding to that of the sketched laser,rotated around the potical axis, a completely rotationally symmetric measurement system is derived:a system for optical 3D measurements by a tadially symmetric structured light projection.
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