1. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation A Task Definition Language for Virtual Agents WSCG’03 Spyros Vosinakis, Themis Panayiotopoulos Informatics Dept., University of Piraeus Presenter : Sie-kyung Jang, VR Lab., KAIST

2. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Outline Introduction Approach Related Work 3D Environment with Virtual Agent The Task Definition Language –Actions –Arguments –Defining a Task Example Conclusion

3. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Introduction (1/2) Virtual Environment as a user interface can be important for certain type Virtual Environment is more attractive when they are populated by virtual agents –Virtual Agent Autonomous entity in a virtual environment Look like and behave as a living organism To enhance virtual agent’s autonomy model the agent’s functionality and behavior so as to resemble the real one

4. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Introduction (2/2) Strong dependence between the action definition and context Lack of general-purpose tools for designing and implementing intelligent virtual environment No tool to describe action combinations and sequences needed to achieve specific tasks

5. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Approach Lack of standard architectures, methodologies and general-purpose tools  Context-independent task definition No tool to define action combination and sequences needed to achieve specific tasks  Use of a procedural language Context-independent definition tasks using a high-level language

6. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Related Work Task execution of agents is an important issue Three Important Approaches –Parameterized Action Representation [Bad00] –Smart Object approach [Kal02] –Improv system [Per96]

7. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation 3D Environment with Virtual Agent SimHuman –Tool for creation of 3D Environments with virtual agents –Consists of a programming library Embedded characteristics : Inverse Kinematics, Physically Based Modeling, Collision Detection, Response, Vision Define and animate 3D scenes with an arbitrary number of objects and virtual agents –Consists of two utilities Designing the environments Designing the agents’ animation sequences

8. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation 3D Environment with Virtual Agent SimHuman –Entities Type –Agent : Perform actions and perceive the current state Have an autonomous operation –Object : World, … Tree-structures hierarchy Geometry A set of attributes –

9. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation The Task Definition Language Fill the gap between higher-level decision processes and the agent’s motion and interaction in the environment Combine numerous built-in functions and commands to describe complex task Advantages –Easier for the user to specify action combinations and scenarios for virtual agents –Easily reuse task with different agents, environments

10. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Task Structure Structure #Variables #Body

11. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Actions Process that causes changes to the world, entities Has duration (Fixed or variant) Executed in continuous timeframes Primitive action –Set of commands that an agent can perform in one timeframe –SimHuman Changing the geometric properties of entities Adding / removing entities to / from the world Sending messages to other agents –Agent can execute more than one primitive actions in one timeframes

12. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Actions Representation Implemented as a sequence of primitive action sets Predefined –a 1, a 2, …,a n with duration = n *∆t –a i : set of primitive actions performed in timeframe I Goal-oriented –a i = f(a i-1, I, G) –I : Set of info. About the object & properties the agent receives –G : Goal

13. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Actions Keyframing –Ability to execute predefined animation sequences –Selecting the agent’s body parts and adjusting their rotation Animation library –Set of user defined animation sequences –Anim

14. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Actions Locomotion –Ability to walk inside the environment –Use state machine Ensure that the movement and rotation of the body takes place in a correct and believable manner Inverse Kinematics –IK –Continuous correction sequence Tests at every step the best rotation for each joint to achieve the target –Works with moving targets, avoid collision

15. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Arguments – Variable Variable type –{boolean, integer, float, string, entity, list of entities, vector, list of vectors, relation} - relation : composition type ex) person(‘John’, 28, 1.80, ‘single’) Variable set Types –Agent’s attributes –Task arguments –Task’s internal variables –Other entity's attributes [ ]

16. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Arguments – function Use of function as arguments allow actions to be called with values that are adapted to different environments One can define tasks that may be executed in dynamic world Track the current state of the world, possible relations between entities.

17. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Arguments – function Some functions detect spatial relations –Conditional execution of actions –Managing the agents beliefs about the world –Using current geometric properties (position, size, orientation) –Evaluated by current geometric properties (position, size, orientation) –Near, on, front_of, behind, left_of, right_of, above, below Some function deal with logical properties –Useful for defining complex conditions –and, or, not

18. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Task Structure Structure #Variables #Body -c1; c2; … ci : ci is task commands Possible Commands ‐ ‐ PAR(, ) ‐ DO( ) UNTIL c ‐ IF THEN (block b1>) ELSE ( ) - TASK name (type 1 arg 1,.., type n arg n ) - Defines local variables

19. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Interacting with Object Catch an object using hand –End-effecter on the surface of the hand –Spot on the surface of the object –Use inverse kinematics action –Suitable for large environments that need simplified agent models. Example

20. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Interacting with Object Need complex agent models and skeleton 1)Define many spots Use IK motions using PAR command 2) Constantly rotate all fingers Use DO-UNTIL command Avoids the definition of spots  More general Must use of constant collision detection checks  increase the computational cost Example

21. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Observing the Environment Observing is needed when agent do not know which object to interact with Example

22. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation A complete Scenario Agent visiting a bar –walking around until there is a free table –Sitting on a chair –Calling a waiter –Ordering drink –Drinking from a bottle Decrease every time the agent brings the bottle to the mouth –Communication between agent and waiter

23. KAIST CS780 Topics in Interactive Computer Graphics : Crowd Simulation Conclusion Context-independent definition tasks using a high-level language Future Work –Addition of more complex object interactions ( Facial animation for expressing the agents’ emotions ) –Improve action execution and the world functionality (Able to add more bio-mechanical characteristics to the agent)