Fully Reversed Engineering: streamlining 3D component digitization, modification, and reproduction

The availability of rapid prototyping enhances a designer’s creativity and speed, enabling quicker development of new products. However, because this process relies heavily on CAD models it can often be time costly and inefficient when a component is needed urgently in the field. This paper proposes a method to seamlessly integrate the digitization of existing objects with the rapid prototyping process. Our technique makes use of multiple structured-light techniques in conjunction with photogrammetry to build a more efficient means of product development. This combination of methods allows our developed application to rapidly scan an entire object using inexpensive hardware

A Practical Approach to 3D Scanning in the Presence of Interreflections, Subsurface Scattering and Defocus

Global or indirect illumination effects such as interreflections and subsurface scattering severely degrade the performance of structured light-based 3D scanning. In this paper, we analyze the errors in structured light, caused by both long-range (interreflections) and short-range (subsurface scattering) indirect illumination. The errors depend on the frequency of the projected patterns, and the nature of indirect illumination. In particular, we show that long-range effects cause decoding errors for low-frequency patterns, whereas short-range effects affect high-frequency patterns. Based on this analysis, we present a practical 3D scanning system which works in the presence of a broad range of indirect illumination. First, we design binary structured light patterns that are resilient to individual indirect illumination effects using simple logical operations and tools from combinatorial mathematics. Scenes exhibiting multiple phenomena are handled by combining results from a small ensemble of such patterns. This combination also allows detecting any residual errors that are corrected by acquiring a few additional images. Our methods can be readily incorporated into existing scanning systems without significant overhead in terms of capture time or hardware. We show results for several scenes with complex shape and material properties

Spatial Augmented Reality Using Structured Light Illumination

Spatial augmented reality is a particular kind of augmented reality technique that uses projector to blend the real objects with virtual contents. Coincidentally, as a means of 3D shape measurement, structured light illumination makes use of projector as part of its system as well. It uses the projector to generate important clues to establish the correspondence between the 2D image coordinate system and the 3D world coordinate system. So it is appealing to build a system that can carry out the functionalities of both spatial augmented reality and structured light illumination. In this dissertation, we present all the hardware platforms we developed and their related applications in spatial augmented reality and structured light illumination. Firstly, it is a dual-projector structured light 3D scanning system that has two synchronized projectors operate simultaneously, consequently it outperforms the traditional structured light 3D scanning system which only include one projector in terms of the quality of 3D reconstructions. Secondly, we introduce a modified dual-projector structured light 3D scanning system aiming at detecting and solving the multi-path interference. Thirdly, we propose an augmented reality face paint system which detects human face in a scene and paints the face with any favorite colors by projection. Additionally, the system incorporates a second camera to realize the 3D space position tracking by exploiting the principle of structured light illumination. At last, a structured light 3D scanning system with its own built-in machine vision camera is presented as the future work. So far the standalone camera has been completed from the a bare CMOS sensor. With this customized camera, we can achieve high dynamic range imaging and better synchronization between the camera and projector. But the full-blown system that includes HDMI transmitter, structured light pattern generator and synchronization logic has yet to be done due to the lack of a well designed high speed PCB

Adaptive Fringe Projection and Error-Compensated Calibration for Compact 3D Shape-Measurement Systems

Measurement of the three-dimensional (3-D) shape of an object is needed for both industrial and consumer applications. In industrial applications, compact measurement systems are needed to accomplish certain tasks such as measuring an interior surface in a confined space. In consumer applications, compact measurement systems are also needed for common consumers to conveniently get access to 3D data for a wide range of everyday uses. Fringe-projection techniques have been increasingly used for 3D shape measurement due to the advantage of dense full-field measurement. For a camera-projector measurement system, system geometry (the relative camera-projector position and angle) determine the system compactness. Analysis of the relation of system geometry to measurement accuracy is challenging owing to the effect of the various factors that vary with system geometry on measurement accuracy. It is thus necessary to experimentally determine how measurement accuracy varies with system geometry, in order to determine the most compact design that satisfies a desired measurement accuracy. This has been achieved in a compactness study, in which the measurement accuracy is evaluated at different relative camera-projector positions and angles. Measurement results in the compactness study have shown that there is a tradeoff in loss of accuracy for increased compactness and loss of compactness for increased accuracy. The smallest camera-projector angle (for an industrial system) or the smallest physical distance between the camera and projector (for a consumer system) that satisfies the desired accuracy would provide the most compact design. Several new methods including 1) an improved heterodyne phase-unwrapping method, 2) an adaptive fringe-pattern projection (AFPP) method for surfaces of high variation in reflectivity and illumination, and 3) a pixel-wise adaptive fringe-pattern projection (PWAFPP) method for such surfaces, have been developed in this research to improve measurement accuracy, thus contributing to enable a more compact system design to achieve a desired measurement accuracy. First, the new improved heterodyne phase-unwrapping method detects and compensates for the spike-like errors in absolute phase maps. The method has demonstrated improved projector calibration accuracy from 18.2 to 0.2 pixels, thus ensuring usable camera-projector stereovision system calibration for 3D measurement. Second, the new AFPP method adapts the projector maximum input gray levels (MIGLs) to local surface reflectivity using only two prior fringe-pattern projection and image-capture rounds. The method demonstrated greatly improved 3D measurement accuracy by avoiding image saturation in highly-reflective surface regions while maintaining high intensity modulation of captured fringe patterns across the entire surface with large range in reflectivity. Third, the new PWAFPP method projects a MIGL adapted to the surface reflectivity and illuminance for each pixel. The method has demonstrated a 34% root-mean-square (RMS) error reduction in 3D measurement for pixels that remained saturated after applying the AFPP method. The new method can thus be used to measure surfaces with more complex variation in surface reflectivity

Three-dimensional geometry characterization using structured light fields

Tese de doutoramento. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 200

Fringe Projection Profilometry in Production Metrology: A Multi-Scale Comparison in Sheet-Bulk Metal Forming

Fringe projection profilometry in combination with other optical measuring technologies has established itself over the last decades as an essential complement to conventional, tactile measuring devices. The non-contact, holistic reconstruction of complex geometries within fractions of a second in conjunction with the lightweight and transportable sensor design open up many fields of application in production metrology. Furthermore, triangulation-based measuring principles feature good scalability, which has led to 3D scanners for various scale ranges. Innovative and modern production processes, such as sheet-bulk metal forming, thus, utilize fringe projection profilometry in many respects to monitor the process, quantify possible wear and improve production technology. Therefore, it is essential to identify the appropriate 3D scanner for each application and to properly evaluate the acquired data. Through precise knowledge of the measurement volume and the relative uncertainty with respect to the specimen and scanner position, adapted measurement strategies and integrated production concepts can be realized. Although there are extensive industrial standards and guidelines for the quantification of sensor performance, evaluation and tolerancing is mainly global and can, therefore, neither provide assistance in the correct, application-specific positioning and alignment of the sensor nor reflect the local characteristics within the measuring volume. Therefore, this article compares fringe projection systems across various scale ranges by positioning and scanning a calibrated sphere in a high resolution grid

Toward a compact underwater structured light 3-D imaging system

Thesis (S.B.)--Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 53-54).A compact underwater 3-D imaging system based on the principles of structured light was created for classroom demonstration and laboratory research purposes. The 3-D scanner design was based on research by the Hackengineer team at Rice University. The system is comprised of a low-power, open-source hardware single-board computer running a modified Linux distribution with OpenCV libraries, a DLP pico projector, camera board, and battery module with advanced power management. The system was designed to be low-cost, compact, and portable, while satisfying requirements for watertightness. Future development and applications may involve navigation systems for an autonomous underwater vehicle (AUV). An initial study of 3-D imaging methods is presented, and the strengths and drawbacks of each type are discussed. The structured light method was selected for further study for its ability to produce high-resolution 3-D images for a reasonable cost. The build of the 3-D imaging system was documented for reproducibility, and subsequent testing demonstrated its functions and ability to produce 3-D images. An instruction guide for operation of the device is provided for future classroom and laboratory use. The 3-D imaging system serves as a proof-of-concept for utilizing structured light methods to produce 3-D images underwater. Image resolution was limited by the output resolution of the pico projector and camera module. Further exploration in obtaining ultra high-resolution 3-D images may include use of a more powerful projector and a higher resolution camera board module with autofocus. Satisfactory 3-D scanning validated the performance of structured light scanning above water. However, contaminants in the water hindered accurate rendering by the system while submerged due to light scattering. Future development of a on-the-fly mapmaking system for AUV navigation should include algorithms for filtering light scattering, and hardware should based on an instantaneous structured light system utilizing the Kinect 2-D pattern method. Autofocus and increased projector brightness would also be worthwhile additions.by Geoffrey E. Dawson.S.B