3. What is the minimal number of cameras needed to reconstruct the 3D coordinate

Question

3. What is the minimal number of cameras needed to reconstruct the 3D coordinates of a reflective marker? Why it would be advantageous to have additional cameras? Three cameras located at 10 degrees from each other along a large circle on the floor looking toward the center will be able to more/less (circle one) accurately reproduce the location of a marker in 3D space than the same three cameras set at 30 degrees from one another. 4. True or False: Soft tissue artifact is a large source of error for determining the movement of bone during motion capture 5. List two reasons why you would consider using a passive reflective marker system in place of an active LED marker system for motion capture. 6. 7. True or False: Force plates measure pressure distribution of the foot on the ground. True or False: In its current state, markerless motion capture can accurately measure axial rotation movements of the legs. 8. 9. Properly order the following terms that describe the gait cycle, starting and ending with right foot heel strike: Right foot heel strike, Left foot heel strike, Right foot toe-off, Left foot toe-off, Right foot heel strike 10. Properly order the following terms describing the gait cycle of the right leg, starting with right heel strike: Right foot heel strike, right leg swing phase, right leg stance phase, right foot toe-off, right foot heel strike

Explanation / Answer

Answers:

3. There will be minimum two or more cameras needed to reconstruct 3D coordinator of the reflective marker. The additional cameras are required to link the information provided by two cameras to reconstruct a 3D space. It became easy to relate image point to object point when the additional camera is used. It also provides silhouette (a two-dimensional representation of the outline of an object) is viewed from different angles. More accuracy it provides. Maximum angle can be cover.

4. Camera placed with 10 degree angle facing toward the center of the circle will produce more accurate location of the marker in 3D as the viewing angle is less and accuracy will be more instead of 30 degree angle. Magnification and view will be more accurate in less angle.

5. True, Soft tissue artifacts are commonly considered the most troublesome source of error in measurements of human motion. It is due to the reduced subject specificity of the soft tissue artifacts model and due to the relative motion between the markers and bone.

6. Passive markers have retro-reflective balls instead of LEDs. Passive markers allow the actor more freedom and range of movement. Markers need to be placed where the skin is closest to the bone and near joints in order to reproduce accurate movement.

7. True (although not completely true ): force plate measure pressure distribution of foot on the ground floor. That can be done through marker-based capture system which includes markerless tracking device known as “kinect (Microsoft)” or through the sensor. The reaction forces, moments and joint moments acting on the athletes’ moving joints can be determined through the link-segment model.

8. Yes, it is true. Markerless motion system can accurately measure axial rotation movements of the legs. It is widely used in biomedical field with greater accuracy and estimates the location of movements.

9. Correct order: right foot heel strike, left foot toe off, left foot heel strike, right foot toe off, right foot heel strike

10. Correct order: right foot heel strike, right leg stance phase, right foot toe off, right leg swing phase, right foot heel strike.

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