A practical evaluation of sequential estimation for vision metrology

Parameter estimation in photogrammetry is generally accomplished by means o f a simultaneous least-squares adjustment in which all observational data m ust be at hand prior to solution. It follows that, despite the rapid turnar ound provided by digital imagery and current measurement technology, the si multaneous adjustment cannot offer an indication of quality until acquisiti on and measurement are complete. On-line quality control of single-sensor v ision metrology (VM) can be implemented effectively through on-line triangu lation (OLT) with sequential estimation. In combination with established ne twork design principles, sequential estimation can have a significant posit ive influence on economy and productivity in the industrial environment. Wh ile enhancing the efficiency of the triangulation procedure, the risks of c ollecting either insufficient or surplus imagery are also diminished. Furth ermore, localised weaknesses within the overall network can be isolated and corrected. Sequential estimation is applicable to a variety of VM tasks. H ere, in addition to quality control for single-sensor VM, the calibration o f real-time, multi-sensor systems is addressed. This paper presents an over view of sequential estimation for VM consisting of a description of the gen eral sequential problem followed by the necessary mathematical derivations. Significant implementational aspects are discussed and evaluations of prac tical testing are given. Promising experimental results clearly demonstrate that OLT can be an effective and valuable tool in industrial VM. (C) 1998 Elsevier Science B.V. All rights reserved.