Browse Publications Technical Papers 2001-01-1473
2001-04-30

Measuring a Geometry by Photogrammetry: Evaluation of the Approach in View of Experimental Modal Analysis on Automotive Structures 2001-01-1473

The very first step when starting an experimental modal analysis project is the definition of the geometry used for visualization of the resulting mode shapes. This geometry includes measurement points with a label and corresponding coordinates, and usually also connections and surfaces to allow a good visualization of the measured mode. This step, even if it sounds straightforward, can be quite time consuming and is often done in a rather approximate way. Photogrammetry is a technique that extracts 2D or 3D information through the process of analyzing and interpreting photographs. It is widely used for the creation of topographic maps or city maps, and more and more for quick modeling of civil engineering structures or accident reconstruction.
The purpose of this paper is to evaluate the use of this technique in the context of modal testing of automotive structures. After a short description of the method, the approach will be evaluated with regard to several criteria: accuracy, convenience, cost, required time. Two cases will be shown: the measurement of an exhaust, on which the measurements will be compared with a classical coordinate measurement machine and the measurement of a body in white, for which the measured points will be correlated with points of an FE model.
The study will show that photogrammetry is indeed an interesting approach to measure the geometry. The main benefits are the increased accuracy compared to manual measurements, short immobilization time of the object, simplicity, enhanced visualization and low cost.

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