“Is It Within My Reach?”-An Agents Perspective

Zhisheng Huang, Anton Eliens, and Cees Visser

Vrije University Amsterdam

The Netherlands

http://wasp.cs.vu.nl/step

Outline of This Talk

• Virtual Agent Platform: DLP+Web3D

• Scripting Language STEP

• Reach by Hand: Inverse Kinematics

• Reach by Body: Decision Making

• Reach by Moving: Reasoning about Environments

• Conclusions and Future Work

Why DLP

• Object-oriented parallel Prolog

• Web3D support

• TCP/IP support for network communication

• Java-based. All DLP programs are compiled into Java classes

• Efficiency for programming

• Reasonably good performance

Implementation

• STEP has been implemented by using Distributed Logic Programming Language (DLP)

• STEP (version 1.0) and its authoring tools are available from the STEP website:

http://wasp.cs.vu.nl/step

FACT : STEP Source Code (1.0)

FACT: Web_oriented• Web deliverable animation. No need to

install any software or tool to run and test STEP scripts. No DLLs are needed to run STEP facial animation engine.

• Animation and presentation can be created on-the-fly, well suitable for web agents which need interaction with users in real time with reasonably good performance.

Reach by HandInverse Kinematics

Interaction Operators in STEP for Computation

High-level interaction operators are used to access the computational capabilities of the meta language in order to find the computation solutions, which involve inverse kinematics.

STEP script: Touch

script(getABvalue(Agent,position(X0,Y0,Z0),Hand,A,B),Action):- Action = seq([getDvalue(Agent,position(X0,Y0,Z0),Hand, D), get_upperarm_length(Agent,L1), get_forearm_length(Agent,L2), do(D1 is L1 + L2), if_then_else(sign(D1-D)>sign(0.001-D), seq([do(cosine_law(L1,L2,D,A)), do(cosine_law(L1, D, L2, B))]), seq([do(A is 1.57*(1+sign(D-0.001))), do(B is 0.0)]))]).

script(getVvalue(Agent,position(X0,Y0,Z0),Hand,V),Action):- Action = seq([get_shoulder_center(Agent,Hand, position(X2,Y2,Z2)), do(direction_vector(position(X2,Y2,Z2),position(X0,Y0,Z0),V))]).

script(touch(Agent, position(X0,Y0,Z0),l),Action):- Action = seq([getABvalue(Agent,position(X0,Y0,Z0),l,A,B), do(R1 is 3.14-A), getVvalue(Agent,position(X0,Y0,Z0),l,V), get_arm_vector(Agent,l,V0),

do(vector_cross_product(V0,V,vector(X3,Y3,Z3),C)), do(R2 is C-B),

par([turn(Agent,l_shoulder,rotation(X3,Y3,Z3,R2),fast), turn(Agent,l_elbow,rotation(X3,Y3,Z3,R1),fast), turn(Agent,l_wrist,rotation(X3,Y3,Z3,-0.5),fast)])]).

script(touch_absolutePosition(Agent,position(X1,Y1,Z1),Hand),Action):-

Action = seq([do(getPosition(Agent,X,Y,Z)), do(getRotation(Agent, X2,Y2,Z2,R)),

do(X3 is X1-X), do(Y3 is Y1-Y),

do(Z3 is Z1-Z), do(R1 is -R),

do(position_rotation(position(X3,Y3,Z3), rotation(X2,Y2,Z2,R1),position(X4,Y4,Z4))),

touch(Agent,position(X4,Y4,Z4), Hand)]).

Reach by Body

• Reasoning about Situations to find a proper list of involved joints

• Use a rule-based decision making model

A Simplified Reaching Model• If the object is lower than the agent’s knee, then

the agent should squat to reach it;

• If the object is higher than the hip and lower than the head, the agent should turn the torso to reach it;

• If the object is higher than the head and is not reachable by hand, the agent should jump to reach it;

• ……

Torso Bending

At least 4 joints

Squat to Reach

At least 5 joints

Reach by Movingreach with knowldge approach

• A set of rational postulates for reaching with knowledge

• Define a preference relation on positions.

• Agents would move to the most-preferred

position to find a path to reach the object

Reach with Knowledge

Rational Postulates

(A)Reachability

The agent prefers a reachable position to unreachable position d(p1, object) < dmax and d(p2, object) > dmax => pref(p1,p2)

(B0) Nearness

The agent prefers a position which is closer to the object

d(p1, object)<d(p2, object) => pref(p1,p2)

• (C0) Shortness

The agent prefers a position for which the move path is shorter.

d(p1,agent)< d(p2,agent)=> pref(p1, p2)

Rational Postulates (continued)

Rational Postulates (continued)(B) (Conditional Nearness) If the object is unreachable, then the agent prefers a position which is closer to the object.\\

d(p1,object)>dmax and d(p2,object)>dmax and d(p1,object)< d(p2,object)\ => pref( p1, p2).

(C) (Conditional Shortness) If the object is reachable, then the agent prefers a position for which the move path is shorter.\\

d(p1,object)<dmax and d(p2,object)<dmax and d(p1,agent)< d(p2,agent) => pref( p1, p2)

Accepted Reachable Distance (ARD)

ARD denotes the distance from which the agent can reach the object with an acceptable bending of the torso.

Rational Postulates (continued)

(D) (Acceptable Nearness) If the object is not acceptably reachable, then the agent prefers a position which is closer to the object.\\

d(p1,object)>ARD and d(p2,object)>ARD and d(p1,object)< d(p2,object)=> pref(p1, p2).

(E) (Acceptable Shortness) If the object is acceptably reachable, then the agent prefers a position for which the move path is shorter.

d(p1,object)<ARD and d(p2,object)< ARD and d(p1,agent)< d(p2,agent) => pref(p1, p2)

Future Work

• Reach by Hand: More complicated hand shapes for grasp and hold;

• Reach by Body: more fine-grained models for decision making models and inverse kinematics

•Reach by Moving: More comprehensive scenarios for planning and reasoning