Triangulation-Based Approaches to Three-Dimensional Scene Reconstruction - 3D Computer Vision: Efficient Methods and Applications - page 30

Fig. 1.5 Left : The calibration rig proposed by Bouguet ( 2007 ). Right : The non-ambiguous cali-
bration rig proposed by Krüger et al. ( 2004 )
reflection is detected as a point feature in one image, it will be associated with a dif-
ferent physical surface point in an image acquired from another viewpoint, leading
to inaccuracies or even gross errors in the measured image coordinates of the cor-
responding points. Under unfavourable circumstances, the determination of point
correspondences may become impossible, since the specular object surface may
look completely different from different viewpoints (the problem of stereo image
analysis in the presence of specularly reflecting surfaces and the physically correct
determination of point correspondences is regarded in detail in Sect. 5.4 ).
This section therefore describes the semi-automatic camera calibration approach
by Krüger et al. ( 2004 ) which is employed in the application scenarios described
in Chaps. 6 and 7 . The presentation is adopted from Krüger et al. ( 2004 ). In con-
trast to self-calibration techniques relying on point features extracted from a scene
of unknown geometry, this method requires a calibration rig with accurately known
control points, but no user interaction is necessary since the control points are au-
tomatically extracted from the calibration images. A camera calibration is then per-
formed which is similar to the methods of Heikkilä and Silvén ( 1997 ) and Zhang
( 1999a ) for determination of the intrinsic and extrinsic camera parameters.
1.4.7.1 The Calibration Rig
The calibration rig as proposed by Bouguet ( 2007 ) consists of a planar chequerboard
pattern, e.g. as generated by a laser printer. The parts of this rig will be named as
follows: The term 'square' denotes the black or white fields of the rig, which do not
need to be square but may be rectangular. A 'corner' is a point where four squares
touch, while a 'rig corner' denotes the outermost four corners where one large and
three small squares touch. This calibration rig is very simple to generate but does
not provide an orientation, which is required for camera systems where the cam-
eras are not arranged in standard geometry. With a slight modification consisting of
acentrical marks without sharp edges, an orientation can be obtained even if only a
part of the rig is visible. Figure 1.5 illustrates the original calibration rig by Bouguet
( 2007 ) and the calibration rig proposed by Krüger et al. ( 2004 ).