Final exam date Final exam date has been announced: Articulated Figures III Tuesday, February 27, 2007 2:45 - 4:45pm Motion Capture 70-1435 Projects Project Presentations: Mid-quarter report Dates: All checked… Week 9: Wed, Feb 14 Week 10: Mon, Feb 19 Finals Week: Tues, Feb 27 (2:45-4:45) E-mail if not received 15 minutes / presentation Schedule now on Web Please send me choice of time/day ONLY Week 9 SLOTS AVAILABLE! Assignments Plan for today Assignment 1 -- Framework Next 2 weeks: Articulated Figures Most have been graded Last Wed: Forward Kinematics Assignment 2 -- Keyframing Today: Inverse Kinematics Most have been graded. Wednesday: Motion Capture Assignment 3 -- Billiards Monday: Advanced algorithms 50% graded Then Assignment 4 -- Group Motion Due Feb 7th. Wednesday: Character animation NOTE: Dropbox close dates have been fixed. 1
Thinking About Spring? Thinking About Spring Applications in Virtual Reality (4003-590-09 / 4005-769-09) Procedural Shading The goal of this course is to introduce students to the architectures and mechanisms of procedural shading and to teach them how to use shaders Virtual Theatre effectively in creating stunning visual effects. A distributed computer system whereby performers, stage crew, and Components audience can be in physically separate places yet share in the same live Advanced RenderMan theatrical performance. Real time shaders (Cg) Components Lecture + Lab/Studio Torque Gaming Engine Actual shaders form artists specs. moCap devices Game networking Details 4003-590-01 / 4005-769-01 Details TR 4-6 (ICL6) 4003-590-09 / 4005-769-09 PRE-REQ: Computer Graphics II TR 2-4 (ICL6) Please contact Joe Geigel (jmg@cs.rit.edu) for details Plan for today Motivation Films Next 2 weeks: Articulated Figures Early examples of motion capture Today: Forward Kinematics Monday: Inverse Kinematics Wednesday: Motion Capture Monday: Advanced algorithms Then Wednesday: Character animation Motivational Film Motivational Film Don’t Touch Me (1989) Brilliance (1985) It’s all Apple’s fault! Robert Abel & Associates Diana Walczak and Jeff Kleiser first entirely computer generated TV ad Debuted at Super Bowl XIX (1985) Synthespian, (Synthetic Thesbians) Dojo – First female Who said motion capture was a new technology? Synthespian http://www.kwcc.com/ 2
Plan For Today Role of Animation Topics Degrees of freedom Motion Capture Number of parameters whose values must be defined in order to fully Assignment #5 position the articulated figure Purpose of animation Provide values to each of the DOF for each time step. Motion Capture Rotoscoping The idea between motion capture Used to trace motion of live actors, frame by frame into You want realistic human motion? an animation Go to the source Invented by Max Fleischer in No, not Newton this time… 1916 Use an actual human First used in Koko the Clown cartoons Used extensively by Disney in Snow White Motion Capture in CG Motion Capture First introduced by Abel and Associates What motion capture gives us: for “Brilliance” Sampled values for each DOF in time. Since captured directly from human motion Subtleties of motion come for free. Difficult for an animator to keyframe these subtleties 3
Motion Capture Motion Capture Types of motion capture systems Optical Incorporate directionally-reflective balls referred to as markers which attach to the performer. Three (at least) digital video cameras that track markers. Provides most flexibility for performers. Problem: Markers may be occluded from cameras views. Watt/Policarpo Optical Motion Capture Motion Capture Motion Analysis Corp Types of motion capture systems I Robot Prosthetic set of armatures attached all over the Final Fantasy performer’s body Entirely motion capture Polar Express The armatures are connected to each other by video using a series of rotational and linear encoders. Accurate, though cumbersome for the performer Prosthetic Motion Capture Motion Capture Systems Types of motion capture systems Gypsy 4 Acoustic By MetaMotion An array of audio transmitters are strapped to various parts of the performers body. Three receivers are triangulated to provide a point in 3D space. No occlusion problem. Cables are cumbersome to performers Ambient sound may interfere 4
Motion Capture Systems Electromagnetic Motion Capture Types of motion capture systems MotionStar 2 ElectroMagnetic Ascension Technologies Much like acoustic except magnetic transmitters/receivers used instead of acoustic No occlusion problem. Cables are cumbersome to performers Though now wireless solutions are available Metal / other magnetic fields may interfere. Motion Capture Systems Fiber Optics Motion Capture Types of motion capture systems Shapewrap II Fiber Optic Sensors Measurand Flexible FO sensors strapped to various parts of the performers body. Sensors can directly measure joint rotations Used in conjunction with electromagentic sensor for head and torso. Capturing Human Motion Motion capture Systems Minimal set of Challenges: recording points Signal is not perfect Noisy missing data not perfectly aligned with joints Retargeting Data is only valid for virtual character who possesses same scale as real character. Frey, et. al 5
Motion Capture Systems Motion Capture Systems Challenges: Examples Even if motion capture data was perfect, we still From The Polar Express have the following challenges: Re-use – use the motion for a slightly different purpose Creating impossible motion – Motion capture won’t do it, but may be desired in animation Change of intent – we can’t always predict what motion we will need Take Home Message: Motion Capture captures a particular, single motion. Motion Capture Data Sampling Theory So what CAN we do with motion Signal - function that conveys capture data? information We can Audio signal (1D - function of time) speed up Image (2D - function of space) slow down Continuous vs. Discrete time warp Continuous - defined for all values in range Motion warp Discrete - defined for a set of discrete However, one must remember that points in range. Captured data is Sampled Data. Sampling Theory Sampling Theory Point Sampling start with continuous signal calculate values of signal at discrete, evenly spaced points (sampling) convert back to continuous signal for display or output (reconstruction) Foley/VanDam 6
Sampling Theory Sampling Theory Sampling can be described as creating a Sampling Rate = number of samples per unit set of values representing a function evaluated at evenly spaced samples = 1 f n f ( i ) i 0 , 1 , 2 , K , n = � = f � Δ = interval between samples = range / n. … 0 1 2 n Sampling Theory Sampling Theory Example -- CD Audio Rich mathematical foundation for sampling theory sampling rate of 44,100 samples/sec Δ = 1 sample every 2.26x10 -5 seconds Hope to give an “intuitive” notion of these mathematical concepts Sampling Theory Sampling Theory Spatial vs frequency domains Most well behaved functions can be described as a sum of sin waves (possibly offset) at various frequencies Describing a function by the contribution (and offset) at each frequency is describing the function in the frequency domain Higher frequencies equate to greater detail Foley/VanDam 7
Sampling Theory Sampling Theory Nyquist Theorum Nyquist Theory A signal can be properly reconstructed if Said another way, if you have a signal with the signal is sampled at a frequency (rate) highest frequency component at f h , you that is greater than twice the highest need at lease 2f h samples to represent this frequency component of the signal. signal accurately. Sampling Theory Sampling Theory Example -- CD Audio Nyquist Theory -- examples sampling rate of 44,100 samples/sec CDs can accurately reproduce sounds with frequencies as high as 22,050 Hz. Δ = 1 sample every 2.26x10 -5 seconds Sampling Theory Sampling Theory Aliasing Aliasing - example Failure to follow the Nyquist Theorum results in aliasing . Aliasing is when high frequency components of a signal appear as low frequency due to inadequate sampling. Foley/VanDam 8
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