We first provide an overview of 3-D shape measurement us- ing various optical methods. Then we focus on structured light tech- niques where various optical configurations, image acquisition tech- niques, data postprocessing and analysis methods and advantages and limitations are presented. Several industrial application examples are presented. Important areas requiring further R&D are discussed. Finally, a comprehensive bibliography on 3-D shape measurement is included, although it is not intended to be exhaustive. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00101-X)

Overview of three-dimensional shape measurement using optical methods

We report the basic concepts and experimental arrange- ments of self-calibrating 3-D measurement systems using structured- light illumination (fringe projection), which ensure a high number of ob- ject points, rapid data acquisition, and a simultaneous determination of coordinates and system parameters (self-calibration), making the system completely insensitive to environmental changes. Furthermore, it is un- necessary to have any marker on the object surface and a subsequent matching of the single views is not required to obtain a full-body mea- surement. For this purpose, the test object is successively illuminated with two grating sequences perpendicular to each other from at least two different directions, resulting in surplus phase values for each measure- ment point. Based on these phase values one can calculate the orienta- tion parameters as well as the 3-D coordinates simultaneously. Different measurement setups that have the ability to measure the entire surface (full-body measurement) are reported. Results are presented showing the power of this concept, for example, by measuring of the complete 3-D shape of specular technical surfaces, whereas the object volumes can differ strongly. Theoretical estimations proven by first measurements show a coordinate measurement accuracy of up to 10 25 of the measure- ment field size. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)01801-8)

Theory and arrangements of self-calibrating whole-body 3-D-measurement systems using fringe projection technique

Microscopic fringe projection profilometry: A review

We present a system for 3-D shape measurement in large volumes based on combined digital-fringe-Gray-code projection. With the help of a new calibration procedure, the system provides accurate results despite its crossed-axis configuration and unknown aberrations of the digital light projector and CCD camera. Also, the separate clouds of points captured from different directions are automatically merged into the main cloud. The system delivers results in the form of (x,y,z) coordinates of the object points with additional (R,G,B) color information about their texture. Applicability of the system is proven by presenting sample results of measurements performed on complex objects. The uncertainty of the system was estimated at 10 4 of the measurement volume.

Digital fringe projection system for large-volume 360-deg shape measurement

Advances in image sensors and evolution of digital computation is a strong stimulus for development and implementation of sophisticated methods for capturing, processing and analysis of 3D data from dynamic scenes. Research on perspective time-varying 3D scene capture technologies is important for the upcoming 3DTV displays. Methods such as shape-from-texture, shape-from-shading, shape-from-focus, and shape-from-motion extraction can restore 3D shape information from a single camera data. The existing techniques for 3D extraction from single-camera video sequences are especially useful for conversion of the already available vast mono-view content to the 3DTV systems. Scene-oriented single-camera methods such as human face reconstruction and facial motion analysis, body modeling and body motion tracking, and motion recognition solve efficiently a variety of tasks. 3D multicamera dynamic acquisition and reconstruction, their hardware specifics including calibration and synchronization and software demands form another area of intensive research. Different classes of multiview stereo algorithms such as those based on cost function computing and optimization, fusing of multiple views, and feature-point reconstruction are possible candidates for dynamic 3D reconstruction. High-resolution digital holography and pattern projection techniques such as coded light or fringe projection for real-time extraction of 3D object positions and color information could manifest themselves as an alternative to traditional camera-based methods. Apart from all of these approaches, there also are some active imaging devices capable of 3D extraction such as the 3D time-of-flight camera, which provides 3D image data of its environment by means of a modulated infrared light source.

3-D Time-Varying Scene Capture Technologies—A Survey

The described 3-D measurement system with fringe projec- tion applies the principle of uniform scale representation by the exclusive use of phase measurement values for the coordinates of each point. The test object is successively illuminated with a grating structure from at least three different directions with a telecentric system, where gray code is combined with five 90-deg phase shifts. A CCD camera records the intensity distribution of the fringes that appear as intersection lines on the surface of the object. This provides the linearly independent absolute phase values that are necessary for the calculation of the coordinates. Note that all coordinates (x,y,z) are determined with the same accuracy. To compensate the influence of specular reflections or shadowed areas up to 15 light projection directions can be used. Moreover, the object can be rotated around a second axis, yielding other views of the object. Thus we acquire different patches of the object that are transformed into a global coordinate system without any interactive user help. During this procedure, correlation methods or special points are not necessary. The calibration of the 3-D orientation of the second axis is realized with a special calibration body. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)01701-3) Subject terms: adaptive optical three-dimensional measurement system; struc- tured light; gray code; uniform scale representation; phase measurement; calibra- tion method development.

Adaptive optical 3-D-measurement with structured light

The appliance consists of a light source (1) illuminating a lens system (2) for generating a light pattern (6) on the surface of the object. A camera generates images of the object form which an evaluator determines the distances and/or spatial coordinates by triangulation. For generating the light pattern the lens system has at least one arrangement (3) made up of several mirrors (4). These can be adjusted individually into at least two predetermined positions of tilt. In this way the incident light falling on the mirrors can be reflected in a predetermined direction

Distances and-or spatial coordinates measuring device for moving objects

Es wird ein Verfahren zur Bestimmung der raumlichen Koordinaten eines Gegenstandes vorgeschlagen, bei dem der Gegenstand mit einer Projektionsvorrichtung aus mindestens zwei Richtungen mit Lichtmustern beleuchtet wird. Eine Kalibrierkamera und mindestens eine Messkamera zeichnen die projizierten Lichtmuster auf den Gegenstand zumindest teilweise auf, wobei die Kalibrierkamera in Bezug auf den Gegenstand ortsfest ist. Mittels mindestens vier Phasenmesswerten wird die Kalibrierung der Projektionsvorrichtung vorgenommen, anschliesend wird unter Verwendung von mindestens zwei Phasenmesswerten die Messkamera kalibriert und schlieslich werden unter Verwendung von mindestens einem Phasenmesswert die dreidimensionalen Koordinaten des Gegenstandes berechnet. Die Projektionsvorrichtung und die Messkamera werden dabei zusammen in die gewunschten Positionen umgesetzt.

Verfahren zur Bestimmung der räumlichen Koordinaten eines Gegenstandes

The measurement of three-dimensional object shapes plays an important role in machine vision, solid modeling and other industrial applications. Well known optical methods for 3D- shape inspection are moire-techniques and contouring. Unfortunately, as a rule they are lacking because they measure only one coordinate, i.e., the height above a reference surface. The other coordinates in the reference plane have to be determined using the pixel distance of the observing CCD-camera or by other means. Here, we demonstrate a real 3D-coordinate measuring system using fringe projection techniques where the scale of coordinates is given by the illumination-structures. This method has the advantage that the aberration of the observing system and the depth-dependent imaging scale have no influence on the measuring accuracy. Moreover, the measurements are independent of the position of the camera with respect to the object under test.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Three-coordinate measuring system with structured light

The paper is aimed at the description of an optical shape measuring technique based on a consistent principle using fringe projection technique. We demonstrate a real 3D- coordinate measuring system where the sale of coordinates is given only by the illumination-structures. This method has the advantages that the aberration of the observing system and the depth-dependent imaging scale have no influence on the measuring accuracy and, moreover, the measurements are independent of the position of the camera with respect to the object under test. Furthermore, it is shown that the influence of specular effects of the surface on the measuring result can be eliminated. Moreover, we developed a very simple algorithm to calibrate the measuring system. The measuring examples show that a measuring accuracy of 10-4 (i.e. 10 micrometers ) within an object volume of 100 X 100 X 70 mm3 is achievable. Furthermore, it is demonstrated that the set of coordinate values can be processed in CNC- and CAD-systems.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Peter Kuehmstedt

Papers

Adaptive optical 3-D-measurement with structured light

Distances and-or spatial coordinates measuring device for moving objects

Verfahren zur Bestimmung der räumlichen Koordinaten eines Gegenstandes

Three-coordinate measuring system with structured light

Optical 3D-coordinate measuring system using structured light