The MulticamDIC system is a combined, stereo-rig DIC system consisting of 4 or more (up to 16), USB3, or GigE Cameras. In this DIC configuration, multiple cameras are used in synchronization to acquire images and perform the measurement of large, double-sided, and/or complex surface geometries, that would otherwise not be possible to measure using a single stereo-rig DIC system.
One of the key benefits of using a MulticamDIC system is that the Field-of-View (FoV) can be expanded to multiple m2 (up to ca. 25-30 m2), using the added view provided by multiple cameras. This allows for complete measurement visualization of entire components, objects, and structures.
For example, the FoV area of using a (16-camera) MulticamDIC system can be enlarged by up to 8x (with the same spatial accuracy), compared to the FoV provided by a single, stereo-rig DIC system.
Cameras may be arranged in a planar or circular setup, measuring only one (continuous) face of a (single-sided) surface, or alternatively, from both (adjacent) faces of a (double-sided) surface. Double-sided measurements have the advantage that the thickness of a sample can be accurately measured using a double-sided calibration target.
This is advantageous specifically for the determination of the true stress (as opposed to only the engineering stress) via measurement of the real, cross-section thickness throughout a test.
A MulticamDIC system uses the bundle-adjustment algorithm for calibration of the projection within one coordinate system. This approach uses one calibration target whereby the identified grid intersections of the target are identified in (at least) a pair of cameras and each additional camera that can identify the same grid intersections then contributes to the generation of the volumetric (calibrated) space.
Effectively, this approach relinquishes the inaccurate approach of stitching multiple datasets together via performing a coordinate system transformation based on the identification of common fiducial points from individual stereo-rigs. A key issue with this approach is that the data between two independent stereo rigs are smoothed-out (and not actually measured) as a result of the stitching process. Using the bundle-adjustment algorithm the projected space is calibrated accurately, with one accurate target in one combined, measurement setup configuration.
Multicamera Subset Reference Tracking (MSURET) is a feature in Istra4D V4.10. for MulticamDIC systems that allows a subset/facet to be continually tracked throughout the complete multicamera setup, even if the subset is no longer visible in the reference camera pair. As such, a subset can be tracked wherever it goes throughout a test, provided it can be seen. MSURET is an important feature, especially for large, full-scale tests of motion analysis, impact, ballistic, torsion, and fatigue testing.
Every camera in a MulticamDIC system that views a common FoV with another camera contributes to the improvement of the measurement accuracy via the reduction in contour measurement error. This advantage is significant, particularly for measurements of corners or edges with small radii.
Another advantage of the MulticamDIC system is that the presence of shadows from protruding objects is omitted from the measurement since multiple perspectives are acquired around the object and resolved within the Istra4D software.
Measurement Principle
Digital Image Correlation (DIC) is a full-field image analysis method, based on grey value digital images, that can determine the contour and the displacements of an object under load in three dimensions.
