A lumbar spine specimen from L1 to L3 is tested under a flexion moment with L3 fixed and L1 and L2 free to move. Three IREDs are attached to each vertebra and the 3-D location of each marker is known in two positions. Using the values given below calculate rotation about and translation along a helical axis for L1 and L2. All coordinates are given in the fixed reference frame.
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Position 1
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Position 2
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reference LEDs
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reference LEDs
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x
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y
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z
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x
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y
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z
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1
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242.2
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183.4
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56
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1
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242.3
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183.7
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55.7
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2
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39.3
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186.5
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58
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2
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39.3
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186.8
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58.1
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3
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138.4
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82
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57.6
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3
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138.5
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82.2
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57.6
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L1 LEDs
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L1 LEDs
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x
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y
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z
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x
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y
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z
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1
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261
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212.7
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111.5
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1
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260.3
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222.4
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127.4
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2
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43.1
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196.3
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116.4
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2
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42.2
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205.8
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129.5
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3
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130.5
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96.7
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104
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3
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129.6
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106.6
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136.8
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L2 LEDs
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L2 LEDs
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x
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y
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z
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x
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y
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z
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1
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242.2
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214.5
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164.8
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1
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240.1
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240.5
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184.5
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2
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31.6
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204.1
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144.7
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2
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30.1
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224.6
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163.1
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3
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149.7
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119.1
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152.8
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3
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148
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145.2
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197.4
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