Common Global Coordinate System Research Articles

Characterisation of a multi-view fringe projection system based on the stereo matching of rectified phase maps

Multi-view fringe projection systems can be effective solutions to address the limitations imposed by the limited field of view, line-of-sight issues and occlusions when measuring the geometry of complex objects, associated with single camera–projector systems. However, characterisation of a multi-view system is challenging since it requires the cameras and projectors to be in a common global coordinate system. We present a method for characterising a multi-view fringe projection system which does not require the characterisation of the projector. The novelty of the method lies in determining the correspondences in the phase domain using the rectified unwrapped phase maps and triangulating the matched phase values to reconstruct the three-dimensional shape of the object. A benefit of the method is that it does not require registration of the point clouds acquired from multiple perspectives. The proposed method is validated by experiment and comparison with a conventional system and a contact coordinate measuring machine.

Arbitrary pattern formation on infinite grid by asynchronous oblivious robots

The Arbitrary Pattern Formation problem asks to design a distributed algorithm that allows a set of autonomous mobile robots to form any specific but arbitrary geometric pattern given as input. The problem has been extensively studied in the literature in continuous domains. This paper investigates a discrete version of the problem where the robots are operating on a two dimensional infinite grid. The robots are assumed to be autonomous, identical, anonymous and oblivious. They operate in Look-Compute-Move cycles under a fully asynchronous scheduler. The robots do not have access to any common global coordinate system. However, the grid allows the robots to have a partial agreement on coordinate system as they can align the axes of their local coordinate systems along the grid lines. In this setting, we have shown that a set of robots can form any pattern, if their starting configuration is asymmetric.

Large-scale shape measurement by a combined method based on three instruments

The accuracy of optical three-dimensional metrology scanning decreases as the size of the parts for inspection increase to several tens of meters because of accumulated errors. A combined method that includes coordinate and surface metrology is proposed. The method features the use of a laser tracker, photogrammetric system, and a hand-held scanner that identifies fiducials. Each instrument provides a distinct measurement density of point data and ranges which are complementary to each other. The laser tracker is used to position and orient the scanner within a large volume, thus, to ensure accurate measurement, the data captured in the respective sensors' coordinate system is aligned to a common global coordinate system. Close-range photogrammetry is used to improve the speed with which fiducials are measured. The measurements obtained, using the photogrammetric system and laser tracker, are combined to produce highly accurate measurements of part surfaces. The performance, of the combined measurement systems, is verified by measuring calibrated lengths. Results show that the proposed technique enables quick measurement and yields submillimeter accuracy in measuring the absolute distance up to the laser tracker range. Error accumulation is therefore avoided.