System Analysis & Modelling In Structured Light Systems
System Analysis & Modelling In Structured Light Optical Non-Contact Measuring Systems:
The need for non-contacting measurement of surface topography is very important in many applications. My research is mainly concerned with non-contact measurement using structured light techniques. The aim is to put forward a generic approach to model the relationship between fringe phase and surface height taking into account a wide range of parameters that are sufficient to describe a general behaviour of the system.
Generally speaking, Structured Light optical non-contact measuring systems (or SL systems, for short) are concerned with performing 3-D non-contact measurements by using structured light techniques. They employ the use of various devices and systems like: projectors, cameras, fibres, and computer hardware & software … etc., to project, capture, and analyse the information in the captured patterns.
Optical patterns play a vital role in SL systems. They interact with objects and can encode the surface profile information (e.g., height, texture, colour, and other physical/optical properties). Furthermore, patterns also interact with the system and can give us information about the measuring system itself. Therefore, understanding the role of these patterns will allow us to extract information not only about the object but also about the system.
Basically, the principle behind non-contacting measurement is that when patterns are projected on objects they tend to be modified (e.g., phase modulated) in a way related to the object properties. Therefore, in order to measure the object we need to extract (demodulate) the object effects embedded in the modified patterns and then use the set-up geometry to relate these effects to the object properties we wish to measure.
Although the aforementioned principle is simple, however, the process is rather complex. We actually do not have a complete understanding of the pattern-object interaction, and pattern-system interaction. We only have a baseline understanding of such issues. However, although our understanding is not complete, and perhaps will never be, we did have, somehow, a fair understanding of various aspects and principles.
Researchers have developed and improved the theory of SL systems in order to better understand the problem at hand and to put-forward suitable techniques for solving existing limitations. It was mentioned before that we do have an accurate understanding of various aspects of SL systems and that we only have a baseline understanding. This is because of various complexities and non-linearities inherent in SL systems; therefore, various approaches employ numerous assumptions and simplifications to reduce the system complexity. Examples for such assumptions and simplifications are:
-
Assuming simple objects with continuous low frequency height profiles
-
Assuming simple baseline camera and projector models, using simple pattern models.
-
Using simple 2-D geometry to derive the object height treating the projection and viewing systems as a whole system. This will be valid for limited arrangements.
As a result, such approaches provide us limited information about the accurate system behaviour and a large number of inaccuracies will be introduced (usually, such inaccuracies were compensated by using some sort of calibration algorithms).
Bashar Rajoub bashar@ieee.org
