Kinematic Motion 1 Flashcards
Define kinematics.
Describes the motion of human bodies (how something is moving)
List examples of kinematic measurement methods other than visual measurement techniques
Goniometers
- Electrical potentiometer that can be attached to measure a joint angle
- 2 or 3 dimensions
Accelerometers (Inertial Measurement Units)
- Measures acceleration of a moving body part
- Force transducer (Inertial sensor) measures reaction to acceleration but no guarantee that the acceleration vector will act at right angles
- 1 or 3 directions
GPS
Timing Gates
Explain the function a shutter has on camera motion capture
- The shutter is an open & close section that moves in the focal plane (directly adjacent to the film / light recording panel)
- The shutter allows you to adjust how much light enters and hits the film / sensor
Define “depth of field” and “aperture” and explain the relationship between them
Depth of Field - When an image is at its sharpest only in a single plane but the eye is able to accept as sharp points that vary in diameter
Aperture - This refers to the amount of light a lens can transmit
Depth of field is increased by using smaller lens aperture (high f stop #) but if too high a f stop # is used the small hole causes diffraction rings
Explain the relationship between shutter speed, aperture and exposure.
Shutter speed - The time it takes for the shutter to open and close
Aperture - This refers to the amount of light a lens can transmit (pupil)
Exposure - This refers to the selection of correct amount of light to fall on film
- For a given film / sensor sensitivity the exposure depends on the shutter speed and the f-stop number (size aperture or “hole”)
- Shutter speed and aperture are inversely proportional to one another.
- This means that both shutter speed and aperture must be balanced in order to your images to have ideal exposure.
Define the term “Frame rate” and explain its importance when capturing motion for biomechanical
analysis.
Frame rate - Measurement of how quickly a number of frames appears within a second (frames per second - FPS)
- More frames per second allows for very precise analysis of motion and slower playback analysis
- Allows for better analysis of movement as it reduces the chance of not capturing an important point of movement during a video
Cinematography has largely been superseded by video.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.
Early advantages
- More clarity of images
- More co-ordinate points when digitizing
- Higher shutter speed - 1/48000 sec
- Freeze bullet
- Freeze gold ball
- More frames/sec - easily up to 500 per sec
Disadvantages
- Lack of immediacy in result
- Manual digitizing
- Expensive
- Poor time scale
What is the difference between analogue video (VHS & SVHS) and digital video?
Analogue video
- Picture made up of dots on screen (Resolution)
- 625 lines per screen (limits sharpness)
- Expensive
Digital video
- Images recorded digitally(AVI, Mp4, Mov, & other file formats)
- Cameras work using many of the same principles of photography
Analog is a continuous waveform (or record) whereas a digital recording is composed of discrete bits of data, usually represented as ones and zeroes.
List the advantages and disadvantages of video over cinematography
Analogue Video Advantages - Relatively inexpensive - Less knowledge of photographic principles required - Immediate result - Accurate time scaling - Immediate Feedback
Early Disadvantage
- Decreased clarity of image (resolution)
- Inflexible adaptations
- Interchangeable lenses (distortion)
- Gen-locking for 3D analysis
- Often have non-manual settings
Digital Video
Advantages
- No loss in picture quality importing to PC or repeated copying
- Storage
- Higher resolutions (HD, 4k video)
- Compact (cameras, tapes, discs, & other)
Disadvantages:
- Large File size (storage issues)??
List the advantages and disadvantages of digital video over analogue video
Advantages
- No loss in picture quality importing to PC or repeated copying
- Storage
- Higher resolutions (HD, 4k video)
- Compact (cameras, tapes, discs, & other)
Disadvantages
- Large File size (storage issues)??
Several problems and sources of error in 2D recording were presented to you in class. List and
explain each of these issues.
- Three dimensionality of movement requires care to be taken in set-up due to non-coincidence of the plane of motion and the plane perpendicular to the optical axis
- Perspective error - must operate at right angles to where the camera is positioned
- Parallax error
- Lens distortions
- Location of landmarks
- Identification of anatomical features
- Measurement estimates based on skin markers (problem - skin can move)
- Joint obstruction from view
- Accuracy of sampling rate (time consistency)
- Image quality
- Sampling rate, shutter speed, aperture
- Lighting
- Background
- Calibration
In addition to those presented in 2D recording, list and explain further problems and sources of
error when performing 3D recording.
- Calibration
- All points must be clearly viewed by majority of cameras
- Must have known 3D co-ordinates and good accuracy
- Minimum of 6 control points required for Direct Linear Transformation (DLT)
- Camera placement
- Position must relate to the algorithm chosen for reconstruction of the movement space co-ordinates
