lo 26 3o
value % value % value %
CIC I 0.0182 67 0.0364 88 | 0.0547 99
CLC 2 0.0167 70 0.0335 97 | 0.0503 100
CEC3 0.0198 28 0.0397 67.|. 0.0393 84
Table 5: Percentage of LME within expected deviation
The extended model for camera calibration achieves significant
improvements of accuracy as finally pointed out by results of
the same data sets with conventional bundle-invariant camera
model (Table 6). An improvement up to 25um in object space
could be achieved including image-variant parameters.
Oo [um] RMS xyz) Relative
precision
CLC] 0.553 0.0655 1:41000
CLCO 0.506 0.0611 1:44000
CLE3 0.609 0.0747 1:36000
Table 6: results by conventional camera model
4. CONCLUSIONS
Because of nowadays mostly used high-quality cameras —
partial-metric cameras - new mathematical approaches are
necessary to model all instabilities and camera based influences
sufficiently. With the implementation of image-variant principal
distance, image-variant principal point and an additional
correction grid to model remaining sensor and lens based
influences these instabilities can be considered. In general the
adjustment results, especially the variation in image-variant
parameters, are highly dependent on imaging direction. The
variation in y-direction points peaks up to 33um to the mean
value. Using an invariant interior orientation the effects of
image-variant part are smeared to other parameters. The
smearing effects cause probably wrong results. Data sets with
high instable interior orientation might not be computable by
conventional approaches. The mentioned data set of the DCS
Pro Back 645M proofs this assumption. The CCD-array is
mounted to the camera body and relocatable in x-direction. An
offset of about 100um during image acquisition with the DCS
645M was only computable with the described image-variant
mathematical model. Significant improvements in accuracy
with respect to a modelling with bundle-invariant interior
orientation have been achieved.
The presented bundles do not figure optimal configuration
because of almost exclusively fulfilling images and influences
by the image measurements of the object point with small
ellipses caused by point diameter of only Smm in object space.
Improvements of image acquisition configuration need to be
required. The 3-D testfield for verification of the bundle results
needs closer research. At least one additional measurement of
the reference points is necessary to eliminate the remaining
length-dependent part in the length measurement errors. The
overbalancing part of LME in the range of +40um under
consideration of instable parts and with careful handling of the
camera point high-accuracy 3-D results.
5. FURTHER INVESTIGATIONS
For further project work a major research will be addressed to
the improvement of imaging acquisition configuration. The
optimal number of images and images per imaging direction,
camera stations by optimal efficiency need to be verified. This
investigation depends on the 3-D testfield, the reference
coordinates and the knowledge of the testfield’s behaviour with
respect to different exterior influences.
Beyond analyses concerning accuracy of three-dimensional
objects and verification based on the German guideline
VDI/VDE 2634 will be done.
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