Structured light projection is one of the most accurate non-contact methods for scanning surface topologies. The field of view of such a scan may range from millimeters to several meters. One of the most precise and robust methods of structured light is Phase Measuring Profilometry. This method utilizes a sinusoidal pattern that is laterally shifted across a surface. An image is captured at uniform intervals and the "phase" is recovered for each pixel position by correlating across the shifted patterns. In general, the more pattern shifts and the higher the spatial frequency, the more accurate the depth measurement becomes, at each pixel location. However, with a high frequency, ambiguity errors can occur, so a dual frequency approach is commonly used where a low frequency pattern is used for non-ambiguous depth, followed by high frequency pattern. The low frequency result is used to unwrap the high frequency to yield a nonambiguous and precise phase. If the high frequency is too high, then ambiguity errors will occur. The solution is a multi-frequency method. We present experimental results for several variations of the multi-frequency approach yielding accuracies of 0.127mm standard deviation in depth with 0.92 mm pixel spacing. With consumer camera mega pixel technology this equates to a 0.127mm deviation over a field of view of 2 to 3 meters. To achieve this level of accuracy also requires calibration for radial and perspective distortions. Applications for this technology include noncontact surface measurement and robotic and computer vision.

No abstract

No abstract

No abstract

A Phase-only spatial light modulator can provide active spot pattern projection with high signal-to-noise ratio and form near-arbitrary phase modulation surfaces. As a result they can diffract laser beams into a near-arbitrary pattern of laser spots. Depending on the sequence of phase images loaded onto the SLM, the spots can be scanned on independent and continuous two-dimensional trajectories. We refer to this flexible beamsteering system as the real-time adaptive multispot laser beamsteering system (RAMS-LBS). This paper presents work under progress, in developing 2D and 3D calibration algorithms for a spot pattern projection system. In the 2D calibration process, spot grids are projected with successively more spot locations. After each projection, a higher order model is determined for camera to projector coordinate transforms. The accuracies of different model orders are measured. In the 3D calibration process, grids of spots are projected onto non-coplanar target grid to construct the transformation matrix between different coordinates. Perspective distortions are included in the transformation vectors after the calibration. Therefore, 3D information of the target can be obtained in the calibrated system. Applications such as 3D target surface topology measurement and target detection using 2D and 3D information are described in this paper.