Data Processing

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Lecture 4

• Data Processing

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Body Segment Parameters

• Inertial properties of the body segments
• Mass (mass ratio) m
• CM location (CM ratio) k
• 3 Principal moments of inertia (radii of
  gyration) Ixx, Iyy Izz

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CM of a Segment

• Use CM ratios

(Px, Py, Pz)
(CMx, CMy, CMz)
(Dx, Dy, Dz)
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Whole Body CM

• Use ms and segmental CMs

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Angles
A P1 - V (Ax, Ay, Az)
B P2 - V (Bx, By, Bz)
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Time Derivation

• Average velocity

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Time Derivation (cont.)

• Instantaneous velocity

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Velocity Computation
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Velocity Computation (cont.)
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Acceleration Computation
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Data Filtering

• Experimental errors
• Digitizing errors
• Video resolution
• Random human error
• Random in nature
• High frequency

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Data Filtering (cont.)
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Data Filtering (cont.)
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Data Filtering (cont.)

• Filtering
• Elimination of the random error
• Digital filters or spline functions
• Butterworth low-pass filter
• Cubic (3rd-order) or quintic (5th-order) splines

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Butterworth LP Filter

• 2nd-order filter

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Butterworth LP Filter (cont.)

• Filter coefficients
• Function of freq ratio
• F ratio Fs / Fc
• Phase-lag problem
• Phase delay
• 4th-order zero phase-lag filter
• Double pass forward (2nd-order) backward
  (2nd-order)
• Fc(4th) Fc(2nd) / 0.082