Video Analysis and Basic Anatomical Principles (week 3) Flashcards
state 4 facts about the anatomical starting position
- upright standing position, facing forward, legs together, feet flat on floor, hands at sides, palms facing forward
- helps in describing ‘geography’ of the body
- how components relate to each other
- generally in pairs: anterior + posterior, inferior + superior, medial + lateral
state what it is meant by the key term - cardinal planes
the cardinal planes are the 3 imaginary perpendicular reference planes that divide the body in half by mass
state the names, and function, of all three cardinal planes
- sagittal/median plane - splits body left to right
- frontal/coronal plane - splits body front to back
- transverse/horizontal plane - splits body top to bottom
in the anatomical position, where do all the cardinal planes intersect the body
the body’s centre of mass
state what it is meant by the key term - axis
axis are infinite, imaginary lines which pass through joints
state the names of all the anatomical reference axis, and the anatomical reference planes they pair with
- mediolateral axis (and sagittal/median plane)
- anteroposterior axis (and frontal/coronal plane)
- longitudinal axis (and transverse plane)
state the movements possible in the sagittal/median plane, mediolateral axis
- flexion and extension
2. dorsi and planter flexion
state the movements possible in the frontal/coronal plane, anteroposterior axis
- abduction and adduction
- eversion and inversion
- lateral/side flexion (trunk)
- scapula elevation and depression
- ulnar and radial deviation (hand)
state the movements possible in the transverse plane, longitudinal axis
- rotation
- internal and external rotation
- pronation and supination
- horizontal flexion/adduction + extension/abduction
state what it is meant by the key term - sampling (frame) rate
refers to how many frames you can sample per second
state 2 facts about sampling (frame) rate
- standard video in UK works with standard video format, PAL (phase alternating line) - 25 frames, 50 fields
- standard frame rate = 25 Hz
state what it is meant by the key term - shutter speed
indicates how long the sensor is ‘open’ and exposed to light
state 3 facts about shutter speed
- low shutter speed risks blurred images if the movement is fast
- faster shutter speeds can capture fast movements
- however, high shutter speeds can lead to dark images
state what it is meant by the key term - aperture
aperture influences the amount of light and depth of the field
state 2 facts about aperture
- large aperture = much light (smaller F-stop number) = worse depth of field
- smaller aperture = less light (larger F-stop number) = better depth of field
state the calculation to work out the F-stop number
F-stop = focal length (mm) / diameter of aperture (mm)
state what it is meant by the key term - digital gain
digital gain can be used to increase image brightness. but, this is artificial and can make the image grainy (adding noise to the image)
high speed video:
- high speed video overcomes the limitations of low sampling rates (up to 10,000 Hz)
- more light required = more expensive
state the sampling rates required for the following activities: walking, running, football kick, tennis serve/golf swing
- walking - 25-50 Hz
- running - 50 - 100 Hz
- football kick - 100 - 200 Hz
- tennis serve / golf swing - 200 - 500 Hz
state the two steps required to set up a camera for quantitative analysis
- camera positioning/orientation (minimising perspective error)
- calibration (allow scaling the video to real world coordinates)
state what it is meant by the key term - perspective error
perspective error is the error caused in the position of an object when the viewing angle is not perpendicular to the object
state the two considerations for the first step of setting up a camera for quantitative analysis
- camera-object distance as far as possible
2. camera perpendicular to the plane of motion (pan, tilt, and roll)
explain the calibration step (step 2) in setting up a camera for quantitative analysis
need to record a ‘known distance’ so you can scale the video (pixels) to real world distances, to obtain 2D/3D co-ordinates
state 2 benefits of the use of video camera analysis over that of online motion analysis
- flexibility (can be used in more environments - like water)
- allows for visual feedback for the performer (permanent record)
- low cost
- minimal interference to the performer (eg - reflective markers)
equipment considerations: (5 things)
- camera
- recording and storage devises
- playback system
- co-ordinate digester (to allow movements to be taken from the video images)
- processing and analysis software
state 5 video camera considerations:
- picture quality
- frame rate
- manual high speed shutter
- manual aperture adjustment
- light sensitivity
- gen-lock capabilities
- recording medium (eg - tape or hard drive)
equipment set up process for 3D video analysis - 5 steps:
- mount cameras on stable tripods and avoid panning
- position cameras for optimal positioning of landmarks
- ensure control points are visible and recorded by all cameras
- align the performance with the axis of the global co-ordinate system
- make provision for shutter synchronisation and event synchronisation
state what it is meant by the key term - biomechanics
biomechanics is the study of the structure and function of biological systems by means of the methods of mechanics
state what it is meant by the key term - perspective error
perspective error is error caused in the position of an object when the viewing angle is not perpendicular to the object
state the two considerations to be mindful of to reduce perspective error
- camera object distance as far as possible
2. camera is perpendicular to the plane of motion (pan, roll and tilt)
state what it is meant by the key term - video
a video is a sequence of images taken at constant time intervals. it is a 2D representation of a 3D scene
high speed video allows for ‘greater’ what ?
greater temporal resolution
explain temporal resolution (in relation to high speed video)
high speed video takes more frames per second than standard video which means that the time interval between each frame is smaller. This means that you are more likely to see specific events within a movement pattern as these events are less likely to occur at a time inbetween frames
state what it is meant by the key term - focal length
focal length is the distance between the centre of a lens, or curved mirror, and its focus
what is the difference between sample rate (FPS) and shutter speed ?
- Frame rate refers to the number of individual frames that comprise each second of video you record
- Shutter speed refers to the amount of time that each individual frame is exposed for
