Single View Metrology: A Practical Example

In machine vision applications it is often desirable to make metric measurements with a single camera. However, operational constraints can limit the use of off-line calibration methods and the lack of reference planes can prevent the use of current single-view metrology techniques. In this paper, we describe the design, implementation, and validation of a visual inspection system for the measurement of angles from a single, uncalibrated camera. We provide a step-by-step, single-view metrology approach which we demonstrate in an operational setting. We first assess the imaging conditions present using hypothesis testing based on a norm-induced metric between possible world to image mappings. Our metric provides a measure of localization error derived from physical measures in the world. The hypothesis testing demonstrates that affine viewing conditions are present in our setting and we show how the affine approximation can be used to make measurements of points off the plane of interest. We employ our algorithm in a manufacturing plant to make blade angle measurements of variable stator vanes in jet engines.