-c p define el coeficiente eólico o de presión depende de la forma y orientación de la
3.3.4. OTRAS MEJORAS
It was only about a decade ago that a few researchers started to exploit one of the most exciting capabilities offered by modern silicon-based semiconductor technology, the monolithic integration of photosensi- tive, analog and digital circuits. Some of the results of these efforts are described in this work, representing just a small fraction of the many applications already demonstrated. They all support the main asser- tion of this chapter, that today’s image sensors are no longer restricted to the acquisition of optical scenes. Image sensors can be supplied with custom integrated functionality, making them key components, application-specific for many types of optical measurement problems. It was argued that it is not always optimal to add the desired custom functionality in the form of highly-complex smart pixels, because an in- crease in functionality is often coupled with a larger fraction of a pixel’s area being used for electronic circuit, at the cost of reduced light sen- sitivity. For this reason, each new optical measurement problem has
5.10 References 149
to be inspected carefully, taking into account technical and economical issues. For optimum system solutions, not only smart pixels have to be considered. Functionality could also be provided by separate on-chip or off-chip circuits, perhaps by using commercially available electronic components.
Machine vision system architects can no longer ignore the freedom and functionality offered by smart image sensors, while being well aware of the shortcomings of semiconductor photosensing. It may be true that the seeing chips continue to be elusive for quite some time. The smart photosensor toolbox for custom imagers is a reality today, and a multitude of applications in optical metrology, machine vision, and electronic photography can profit from the exciting developments in this area. “Active vision,” “integrated machine vision,” “electronic eyes,” and “artificial retinae” are quickly becoming more than concepts: the technology for their realization is finally here now!
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6 Geometric Calibration of Digital
Imaging Systems
Robert Godding
AICON GmbH,Braunschweig,Germany 6.1 Introduction . . . 153 6.2 Calibration terminology . . . 154 6.2.1 Camera calibration. . . 154 6.2.2 Camera orientation . . . 154 6.2.3 System calibration . . . 155 6.3 Parameters influencing geometrical performance . . . 155 6.3.1 Interior effects . . . 155 6.3.2 Exterior effects . . . 157 6.4 Optical systems model of image formation . . . 157 6.5 Camera models . . . 158 6.5.1 Calibrated focal length and principal-point location . 159 6.5.2 Distortion and affinity . . . 159 6.6 Calibration and orientation techniques. . . 163 6.6.1 In the laboratory . . . 163 6.6.2 Bundle adjustment . . . 163 6.6.3 Other techniques. . . 168 6.7 Photogrammetric applications . . . 170 6.7.1 Applications with simultaneous calibration. . . 170 6.7.2 Applications with precalibrated camera . . . 171 6.8 Summary . . . 173 6.9 References . . . 1736.1 Introduction
The use of digital imaging systems for metrology purposes implies the necessity to calibrate or check these systems. While simultaneous cali- bration of cameras during the measurement is possible for many types of photogrammetric work, separate calibration is particularly useful in the following cases:
153
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• when information is desired about the attainable accuracy of the measurement system and thus about the measurement accuracy at the object;
• when simultaneous calibration of the measurement system is im- possible during the measurement for systemic reasons so that some or all other system parameters have to be predetermined;
• when complete imaging systems or components are to be tested by the manufacturer for quality-control purposes; and
• when digital images free from the effects of the imaging system are to be generated in preparation of further processing steps (such as rectification).
In addition, when setting up measurement systems it will be neces- sary to determine the positions of cameras or other sensors in relation to a higher-order world coordinate system to allow 3-D determination of objects within these systems.
The following chapters describe methods of calibration and orienta- tion of imaging systems, focusing primarily on photogrammetric tech- niques as these permit homologous and highly accurate determination of the parameters required.