Master Thesis - Fachbereich Informatik

102 CHAPTER 5. RESULTS AND EVALUATION
Figure 5.1: Measuring slide used for acquiring ground truth measurements by hand.
with ltotal(i), lgt(i) andN as defined before. A small root mean square error indicates the
measurements are close to the ground truth data.
5.1.3. Ground Truth Measurements
The acquisition of ground truth data is important for evaluating the vision-based inspection
system with respect to human measurements. For this purpose a special digital
measuring slide as can be seen in Figure 5.1 has been used. The precision of this device
is up to 1/100mm.
However, there is a significant deviation in human measurements, since heat shrink
tubes are flexible. Depending on the force the human operator applies to the measuring
slide, the measured length gets smaller or larger. This variation has been investigated
empirically.
12 sample tubes of different diameter (6, 8 and 12) are selected as test set (see Table
5.3). One half of the samples are black, the other half transparent tubes. For each
combination of color and diameter, one tube has a length of approximately 50mm and one
was manipulated, i.e. slightly larger or shorter than the tolerance allows for.
No. color diameter mean length
1 Transparent 8 49.95
2 Transparent 6 49.77
3 Transparent 12 49.82
4 Transparent 8 48.19
5 Transparent 6 51.33
6 Transparent 12 51.88
7 Black 8 50.98
8 Black 6 50.19
9 Black 12 50.00
10 Black 6 50.84
11 Black 8 49.66
12 Black 12 51.56
Table 5.3: Test set used to determine the human variance in measuring.
The results are shown in Figure 5.2. In a first experiment, the variance of a single
person is investigated denoted as intra human variance. Each tube in the test set has
been measured 10 times by the same person with the goal to be as precise as possible.