Week 04 - Kinematic motion analysis 1

Question 1

Define Kinematics

Answer 1

Describes HOW somethings moving (not why)

Question 2

• List examples of kinematic measurement methods other than visual measurement techniques.

Answer 2

• goniometers
  
  • accelerometers
  • timing gates
  • radar guns
  • laser guns
  • GPS

Question 3

• Explain the function a shutter has on camera motion capture.

Answer 3

• Open and closes to allow light in, the faster it is, sharper image it but darker image is, and vice versa

Question 4

• Define “depth of field” and “aperture” and explain the relationship between them.

Answer 4

• Depth of field is the distance between nearest and furthest element in frame that are ‘sharp’, aperture refers to amount of light a lens can transmit (The smaller the aperture opening, the greater the depth of field)

Question 5

Explain the relationship between shutter speed, aperture and exposure.

Answer 5

Exposure selects correct amount of light to enter, while shutter speed determines how much light can get into the lens, aperture is the amount of light the lens cans transmit. High f number = smaller aperture, less light. High shutter speed = quicker capture, less light. High ISO = brighter, but more noise

Question 6

Define the term “Frame rate” and explain its importance when capturing motion for biomechanical analysis.

Answer 6

How quickly a number of frames appears within a second (FPS). High frame rate = many more points can be captured and slowed down

Question 7

Cinematography has largely been superseded by video. However, there still remain some advantages of using this method for motion analysis. List the advantages and disadvantages of cinematography over video.

Answer 7

• Clarity of image (more co-ordinate points when digitizing)
• Higher shutter speeds
• More frames

Question 8

What is the difference between analogue video (VHS & SVHS) and digital video?

Answer 8

Super VHS has x2 dots per line (double = higher resolution)

Question 9

List the advantages and disadvantages of video over cinematography.

Answer 9

Advantages:
- inexpensive
- less knowledge of photographic principles required
- immediate result
- accurate time scaling
- immediate feedback

Early disadvantages:
- decreased clarity of image (resolution)
- inflexible adaptations
- interchangeable lenses (distortion)
- gen-locking for 3D analysis
- often have non-manual settings

Question 10

List the advantages and disadvantages of digital video over analogue video.

Answer 10

Digital Video Advantages:
- No loss in picture quality importing to PC and can copy without losing quality
- storage
- Higher resolutions (HD, 4k)
- Compact (cameras, tapes, discs, other)

Digital Video Disadvantages:
- Large file sizes (storage issues??)

Question 11

• Several problems and sources of error in 2D recording were presented to you in class. List and explain each of these issues.

Answer 11

• Perspective error
• Parallax error
• lens distortion
• location of landmarks
• accuracy of sampling rate
• image quality
• calibration

Question 12

List and explain further problems and sources of error when performing 3D recording.

Answer 12

• Calibration: clearly viewed points by all cameras, good accuracy, min of 6 controls for direct linear transformation
• Camera placement: Position must related to the algorithm chosen for reconstruction of the movement space co-ordinates