95.8 degrees

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95.8 degrees

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95.8 degrees
50 cm


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Measuring a known angle between 3 markers

This test measured the angle between the markers on the rotating plate.  The known angle between the plate markers was 95.8 degrees. These results are presented in Table 3.

This measurement is very sensitive to errors since 3 markers are involved.  Any movement in any of the individual marker will significantly affect the angle. In addition, these 3 markers were obscured from any camera at least 50 percent of the time.  This means that the implementation of the DLT was measured to see how systems can cope with this effect.

APAS uses a DLT algorithm with a PPT algorithm, which represent linear and non-linear Direct Linear Transformation. Not surprisingly, APAS was the top performer for this test.  Note as well, that the RMS and the maximum errors recorded were the lowest for APAS.

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Slide 15. Angle measurement from Top Plate Markers.

  Measured Rank RMS Error Rank Max Error Rank Total Rank Sub-Total
  [deg] Score [deg] Score [deg] Score Error Score Score
Ariel 95.104 4 1.215 5 2.919 5 4.134 5 19
Motion 95.912 5 1.778 3 7.010 3 8.788 3 14
Peak 96.500 3 3.772 2 12.666 2 16.438 2 9
Qualisys 94.389 1 4.498 1 19.256 1 23.754 1 4
Vicon 94.543 2 1.421 4 4.632 4 6.053 4 14

   Table 3. 95.8 Degrees test from the top plate markers.

Slide 16 illustrates the average measured angle between the plate markers.  The Motion Analysis system measured the average the closest. APAS recorded the second closest score.  However, when measuring the maximum error in estimating the angle, APAS scored the highest with an RMS error of 1.2 degrees.  Although the Motion Analysis system had the best average with 95.1 degrees, the maximum error amounted to more than 7 degrees.  The APAS' calculated average with 95.1 degrees had as it's maximum error only 2.9 degrees. When combining the average error with the RMS error, APAS scored the best with 4.1 degrees total error with the next equipment being Vicon with 6 degrees.

The largest error recorded was from Qualisys with 23.7 degrees and Peak with a 16.4 degree error.  If consideration is given to the switching point problem previously mentioned, this error would increase by an order of magnitude and raise questions among researchers as to the appropriateness of these equipment choices for serious research.

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Slide 16. Average Measured Angle between Plate Markers.

APAS performed well on this test although this situation would never occur in normal human movement. But APAS was very accurate in determining the angle.  Other systems produced as much as 23 degree errors. Of particular interest was the poor performances by the Peak, Qualisys, and Vicon systems.

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Slide 17. RMS Error from Plate Angle Measures.

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Slide 18. Maximum Error from Plate Angle Measures.

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