Master Thesis - Fachbereich Informatik

106 CHAPTER 5. RESULTS AND EVALUATION
up to 55m/min are tested. For all velocities > 30m/min,thetubeshavetobeplacedonto
the conveyor using the supply tube.
Again the inspected tube size is about 50mm in length within the allowed tolerance and
a diameter of 8mm both for black and transparent tubes. The spacing in between the tubes
must be large enough following the results of the minimum tube spacing experiments.
In this scenario, all evaluation criteria introduced in Section 5.1.2 are considered including
a comparison to ground truth measurements. The evaluation is performed offline.
Tube Diameter If the distance between camera and conveyor belt does not change,
the diameter of a tube influences the distance between the measuring plane ΠM (see
Section 4.2) and the image plane. Tubes with a smaller diameter are further away and
appear smaller in the image, while tubes with a larger diameter are magnified in the image.
Thus, the calibration factor that relates a pixel length to a real world length in mm has
to be adapted.
The test data includes transparent and black tubes with a diameter of 6, 8 and 12mm
and a length of 50mm that meet the allowed tolerances. The conveyor velocity is constant
at 30m/min. Again all evaluation criteria are considered and the evaluation is performed
offline.
Repeatability In this scenario, a tube of known size is measured many times in a row
at a constant velocity of 30m/min. Theoretically, the system should measure the same
length each time, since one can assume the length of the tube does not change throughout
the experiments. As mentioned before there are several parameters that can influence the
repeatability in practice like a varying background.
In the same experiment one can not only determine the repeatability, i.e. the precision
of the system, but also the accuracy if one does not use a heat shrink tube, but an ideal
tube gage. Such a gage can be made from metal with much higher precision overcoming
the human variance in measuring deformable heat shrink tubes. For comparable results,
the gage should have the same shape and dimension of a heat shrink tube. Since it does
not transmit light, a metallic gage can simulate black tubes only.
The real world length of the gage is known very accurate and precise. Thus, the RMSE
of the measuring results gets almost independent of errors in the ground truth data.
The measurements can be best performed online, i.e. in real-time, due to the amount
of accumulating data. The resulting lengths are stored in a file for later evaluation.
Outlier Detection Until now, all experiments are based on test data that is known to
meet the given tolerances. In this scenario, tubes of approximately 50mm length are mixed
with tubes that are too long or too short, i.e. differ from the target length for more than
0.7mm.Thepositionandthenumberoftheoutliersinasequenceisknown.Thesystem
must be able to detect the outliers correctly. Thus, the false positive and false negative
rate are the main criteria of interest in this scenario.
The evaluation can be performed both offline or online.
Tube Length As mentioned before, the focus in this thesis is set to tubes of 50mm length.
In addition it is shown that the system is able to measure also tubes of different length
exemplary for tubes of 30 and 70mm length.