3-D shape measurement of complex objects by combining photogrammetry and fringe projection

Abstract

A new concept for 3-D shape measurement of complex objects is proposed, which is based on photogrammetry and fringe projection. The shape of a partial view is determined by a combination of the phase-shift method for fringe evaluation and a photogrammetric triangulation to calculate the 3-D coordinates related to the sensor coordinate system. For the measurement of complex objects, partial views are taken from different sensor positions. The problem of matching the partial views into each other is solved by transforming each sensor position and the relating point cloud of the shape in a global coordinate system by photogrammetric matching of reference targets.

Determining Exact Point Correspondences in 3D Measurement Systems Using Fringe Projection – Concepts, Algorithms and Accuracy Determination

“…The classical approach of fringe projection is described e.g. by Schreiber and Notni (Schreiber & Notni, 2000), which has been extended depending on several applications (Reich et al, 2000;Chen & Brown, 2000). The principle should be briefly explained as follows.…”

“…A fringe projection unit projects one or two perpendicular, well defined fringe sequences onto the object, which is observed by one or more cameras. These sequences may consist of a binary code sequence as the Gray code (Sansoni et al, 1999;Thesing, 2000) and a sequence of up to 16 sinusoidal fringe patterns. The so called rough phase value (Schreiber & Notni, 2000), and in combination with the Gray code the unique unwrapped phase value (Sansoni et al, 1999) is obtained using the sequence of sinusoidal patterns.…”

“…In this work the various methods to obtain unique point correspondences are not described in detail, but rather the second aspect (precision) should be dealt with. Uniqueness of point correspondences is obtained by phase unwrapping (Sansoni et al, 1999;Reich et al, 2000). This can be realized e.g.…”

“…The third one called VR mode (virtual raster) uses a virtual projection grid and finds the phase values of the grid points in the two camera images. This method corresponds to the technique described by Reich (Reich et al, 2000).…”

“…Arising methods are based on triangulation (Luhmann et al, 2006) between two or bundle adjustment between more than two viewpoints (sensor positions), or between two camera positions within one sensor position. The most common triangulation procedure to obtain 3D measurement data in fringe projection systems is between two cameras or one camera and one projector (Schreiber & Notni, 2000;Reich, 2000).…”