RSC 40 (top)
Repeated Measurements
Differences from mean value
lil dx max C dx min B dy max El dy min
Repeated Measurements
Differences from mean value
RSC 41 (center)
I
SM RO
SR LV
lll dx max C dx min & dy max & dy min
Repeated Measurements
Differences from mean value
RSC 42 (bottom)
variations
lll dx max Ni dx min B dy max Ei dy min
Fig. 6. Repeated measurements: image coordinates
NM: no sensor movement; SM: with sensor movement; RO: with
rotary movement; SR: sensor and rotary movement; LV: light
3.2 Distance Measurements
In this part of the investigation the system accuracy for
distance measurements shall be verified. For this
purpose different distances (approximately 700mm and
1400mm) have been positioned at various locations
within the measuring volume, oriented in different spatial
directions. The nominal distances were measured using
a first-order coordinate measurement machine (CMM).
The distance bars are made of aluminium and cylindrical,
retro-reflective targets are used for measurement.
The measurements are performed using a sub-pixel
algorithm for the precise detection of ellipse-shaped
targets [Zhou 1986]. The measured image coordinates
are processed by an spatial intersection program which
determines the 3D coordinates of the target.
The distance points have been measured in different
configurations:
NR measurements with different cameras, without
rotations
WR measurements with one camera and various
rotations
CO measurements with combinations of cameras
and rotations
20bs | measurements with 2 images
3obs measurements with 3 images
> 3 obs measurements with more than 3 images
The number of observations per point varies between 2
and 9 images. Fig. 7 shows a few results from different
points of view. The first three clusters show the
dependency of accuracy on the number of observations.
The last three clusters show the results of different
configurations. In each cluster the mean deviation is
displayed, as well as the minimum and maximum
deviations. Deviations are computed from the calculated
distance between measured points and the nominal
value measured by the CMM.
Distance Measurements
Differences from nominal distance
mm
0.20
0.15 -—B -
0.05 HN E -
0.00 IN ES Ed ] | WS l N. |
NR WR 2 obs 3 obs
MM ds_min LS mean Bl ds max
Fig. 7. Distance measurements
NR: different cameras, no rotation; WR: one camera and rotations;
CO: camera/rotary combinations; 2 obs: two images per point; 3
obs: three images per point; >3 obs: more than three images
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