4.4 Transformation into Object Space
Figure 10 illustrates the complete measurement process.
A given set of control points (adjusted for a reference
plane) is detected and measured in the image. Under
consideration of the interior orientation parameters the
projective transformation (1) is calculated. The 8
transformation parameters are used to transform the CAD
data into image space in order to support edge detection.
The results of edge measurement will then be
transformed back into object space by inverse projective
transformation and can be compared to the given nominal
values of the CAD model.
control point
detection
|
precise point
measurement
|
» projective
transformation
|
edge detection
|
2D CAD inverse projective
data transformation
|
quality check
nominal control
point coordinates
Interior orientation
Figure 10: Measurement process
5 FIRST PRACTICAL RESULTS
A protoype system has been installed in the factory
environment. First series measurements of manufactured
parts have demonstrated that the objects show deviations
in the order of 20 to 50mm (max. 100mm) according to
the nominal CAD data. The main influence for production
deviation is the way how the shuttering for the concrete of
wet consistency has been mounted on the production
platform. Figure 11 shows an example of real
measurement results.
246
Figure 11: Measurement check
Due to these results this part of the process will change in
order to ensure a higher geometric quality. A new
shuttering system also serves for a better contrast and
edge definition for the automatic edge measurement.
Further investigations will be carried out regarding a
modified calibration method and a different system setup
using cameras of higher resolution.
6 REFERENCES
Beyer, H. (1992): Geometric and radiometric analysis of a
CCD-camera based photogrammetric close-range
system. Mitteilungen Nr. 51, Institute for Geodesy and
Photogrammetry, ETH Zurich.
Fryer, J.G. (1996): Camera Calibration. In Atkinson (ed.):
Close Range Photogrammetry and Machine
Vision.Whittles Publishing, Caithness, UK, pp. 156-179.
Godding, R. (1995): Ein photogrammetrisches Verfahren
zur Überprüfung und Kalibrierung digitaler
Bildaufnahmesysteme. Zeitschrift für Photogrammetrie
und Fernerkundung, pp. 82-90, 2/93.
Godding, R. (1995) Neue Lösungen in der
Nahbereichsphotogrammetrie durch die Kombination
digitaler Systeme und moderner Auswerteverfahren.
Publikationen der DGPF, Band 4, Hannover, pp. 261-269.
Luhmann, T. (1986): Automatic Point Determination in a
Reseau-Scanning System. ISPRS Symposium, Comm. V,
Ottawa.
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