Lecture 3 - Measuring Human Motion Flashcards
list the pioneers of motion capture technology
Muybridge and Marey
how do Muybridge’s and Marey’s motion capture technology differ?
- > Muybridge’s were a bunch of pictures taken in rapid succession (horse and flip examples)
- > Marey used joint and limb markers. He took a bunch of pictures of the action and composed the whole motion+markers in one frame
- he acheived this with a shutter gun (like a spinning picture wheel)
relate strobe lights to motion capture
if strobe lights flash at the same frequency/rate of an object, it appears as though the object is static
- > this is beneficial as you can observe the object as it’s working but the details are clear (i.e. an engine has to be running for you to be able to see what the problem is but there’s a lot of moving parts that disrupt your view)
list some examples of optical motion capture systems
- > passive marker systems
- > active marker systems
- > markless systems
list some examples of non-optical motion capture systems
- > electrogoniometer
- > inertial systems
- > mechanical systems
- > electromagnetic systems
- > accelerometer
what is a passive optical motion capture system
- > use passive, reflective markers on the subject skin
- > light is transmitted towards the subject, reflected back from the marker to the cameras
- > it is passive because there is no electronics, wires, ect. on the subject
advantages of passive optical systems
- > lightweight and no power supply needed
- > large possible active areas
- > real time available
- > large number of markers can be tracked
- > allows for natural movement patterns
limitations of passive optical systems
- > skin motion vs bone motion
- > cost
- > sensitivity to light/reflection
- > line of sight system (markers might not face the camera)
- > partial marker identification
accelerometers
measure the acceleration of the body segment to which it is attached
- > spring compression system
piezoelectric accelorometer
- > mass pushes on crystal
- > crystal is squeezed
- > crystal generates a voltage
