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Tuesday, October 8, 2013

Motion Analysis and Procedural Animation of Quadruped Character using Hybrid Model

Abstract: In this paper we discuss the technique  of performing Quadruped Motion Analysis from the original video footage of quadruped character in motion. The motion analysis involves calculating the footfall patterns and plotting the diagram, along with generation of Motion Gait Graphs for each leg showing the swing and stance phase of each leg in motion. The developed hybrid system  for  procedural animation proposes the use of Inverse Kinematics along with Dynamic Controllers .The desired motion control input, comes either from the user or from a higher level motion planning system. A motion planning system uses the gait graph and footfall pattern information to produce the desired animal behavior. In our case, the motion control input consists of the desired values for the body’s velocity, and the heading determined by the yaw angle. The dynamic controller computes the aggregate force Fr and torque Tr that should be applied to the body at the center of gravity. The problem can be formulated as a linear constrained minimization and is solved using the Simplex method for linear programming. The leg subsystem is controlled by the kinematic gait controller. Based on these forces, a forward dynamic simulation is performed to compute the new state of the body.


Thursday, May 30, 2013


Character Animation Theories And Principles

By Mike Brown
 

Anticipation & Overshoot:

The most important thing to remember is that great animation doesn't happen from Point A to Point B, it happens at point A and Point B. Meaning that we must show the audience what is going to happen by anticipating the action (Point A) , do the action, then show the audience what just happened by overshooting the pose and settling back in (Point B). I'll use the principles of Squash and Stretch to demonstrate Anticipation and Overshoot.

Download the movie Anticipation.mpg (175kb)

You'll notice 4 balls. The ball on the far left has no anticipation or overshoot. It looks stale and lifeless and doesn't move in a convincing way. The ball in the Left middle has anticipation and overshoot. It anticipates the action by squashing (Pose A), does the action,... then shows the audience what just happened by overshooting it's next resting position (Pose B). We'll call this action the Short Bounce. It has character, moves in a convincing way, and keeps the audience's attention where we want it but it lacks exaggeration.

Exaggerated action is what makes good animation great. Study the Short Bounce for a while and practice the principles behind it in your own animation. It's VERY important to MASTER this action and principles behind it in your own character animation before moving on to The Long Bounce. You must know the basic rules before you can break them.

The next ball in the scene on the Right Middle is very similar to to the Short Bounce except that it breaks a few normal rules of physics by exaggerating the action. We'll call this the Long Bounce. It accelerates much more quickly than the Short Bounce, reaches it pinnacle quicker, shows the audience what it's doing, then finishes the action. Using this principle correctly and in the right spots can add that extra ummph and weight to your action. This is a technique for more advanced animators. Beginners should concentrate on learning how and when to use anticipation and overshoot before attempting to break the rules like this.

The fourth ball on the right hand side is a variation on the long bounce and adds an extra bit of action between Point A and Point B. Its action can be described as Point A to C to B. Instead of traveling in a straight line it follows a slight arc and is even more exaggerated. I call this 'putting the juice in'. For those animators that are more advanced, see how far you can push those extreme poses, then add a little flavor to it by doing something unexpected in between (Point C).

 

Overlapping Action:

The next topic is overlapping action. The easiest way to describe overlapping action is, different parts of your character will move at different speeds and come to rest at different times; meaning... Break up the action. If everything on your character starts and stops at the same time it will look like it was animated on a computer (god forbid that should ever happen).

Download the movie overlap.mpg (175kb)

You'll notice two balls, one resting above the other. Play the animation As the animation plays notice that one ball comes to rest before the other or, OVERLAPS the action of the the first ball. Breaking things up like this is very important for achieving the illusion of life. Make sure your animation has little variations. If you have to repeat the same action three times in a row do each one a little differently.

 

Progressively Breaking Joints

Using the principle of progressively breaking joints is a way to get that snap, crackle and pop into your animation. This principle basically builds on top of the principle of Overlapping Action. It can most easily be described as a whip or a character throwing a football. First the upper arm rotates in an arc, then the forearm breaks or rotates in an arc and finally the wrist breaks and releases the ball

Download the movie Progressive.mpg (326kb)

You'll see two chains of boxes. Play the animation. The chain on the left bends and all the boxes rotate at the same speed. This is a nice effect but it isn't as dynamic and doesn't have the same appeal or, SNAP as the one on the right. Study the chain on the right. You'll notice that the first link in the chain begins moving before the others, then the second link breaks and begins moving and so on down the chain. Using Progressively Breaking Joints is a good method of emphasizing an action or grabbing your audiences attention.

Arcing Actions and Head Turns

Arcing Actions is a way of saying things don't move in a straight line. It helps to break up your action and give a natural feel to your character. NOTHING moves in a straight line. Even bullets have a slight arc to their trajectory.

Download the movie headturn.mpg (155kb)

Play the animation. Notice the head on the Left turns in a straight line. Even anticipation and overshoot can't help this fellow. Now look at the head on the right. It turns in an arc. Always be aware of your action's arc. It will make your character natural and believable and hopefully your audience won't notice you did it on a computer.

Once you feel comfortable with these theories try adding some character to a simple box or sphere. You'll see what I mean in this timidbox.mpg movie.


"Little Talks" - Of Monster and Men

Five sky-sailors discover a crystal meteor containing a lost mythical female creature. An epic journey through fantastical worlds ensues as the sailors struggle to return her to her people. This music video was shown at the SIGGRAPH 2012 Electronic Theater. This animation as well as all SIGGRAPH conference content is documented in the ACM Digital Library. -

 See more at: http://www.siggraph.org/content/little-talks-monster-and-men#sthash.DaVRp8PC.dpuf


Photo Credit

WeWereMonkeys: Mihai Wilson and Marcella Moser

Link Title

EXPLORE SIGGRAPH CONFERENCE CONTENT
- See more at: http://www.siggraph.org/content/little-talks-monster-and-men#sthash.DaVRp8PC.dpuf


Procedural Model of Horse Simulation
In this paper, a procedural model has been developed for synthesizing cyclic horse motion through trigonometric functions.  The system has been developed and implemented using mathematical model derived from trigonometric cyclic equations, along with forward and inverse kinematics, motion dynamics and gait error optimization to produce absolute gait control over the locomotion of horse character. The dynamic motion is calculated independently for each body part with GUI based user interaction and control over the speed, frequency and oscillation during runtime, for high divergence control over the simulation. The user can manipulate the simulation parameters for motion speed, body oscillation, leg impact phases and duration at runtime and our system will automatically adjust the motion of horse  and gait transition according to the user input. At preprocessing level a template based horse skeletal rig is generated automatically with inverse kinematics (IK) controllers for the spine, neck and all four legs. The head, tail, and feet’s are controlled with forward kinematics (FK), along with scapula and sternum joints of the legs. Motion cycle is generated using the stance time and leg cycle time. Our procedural model for horse simulation can currently generate various gaits of motion with variable speed and body oscillation with controllable behavior and transaction of gaits at runtime.

Poster: Zeeshan Bhatti, Asadullah Shah, Farruh Shahidi, ”Procedural Model of Quadruped Simulation”, Poster, Proceeding of Invention and Innovation Exhibition (IRIIE 2013) organized by International Islamic University Malaysia (IIUM), held at CAC, IIUM Malaysia 2013. (Won SILVER Medal).