thesis - Computer Graphics Group - Charles University - Univerzita ...

112 CHAPTER 9. RESULTS
desks and non-penetration constraints due to the contacts between the cube and the desks
can not be satisfied.
• TestFriction
Static, dynamic and impulsive friction approximation at contacts is evaluated by this test.
The scene consists of a table, desk and a stack of boxes. The boxes are stacked on the
desk that lies on the table and there is no friction between the desk and the table. A ball
strikes the desk and the impulsive friction between the ball and the desk makes the desk
(as well as the stacked boxes) move. The whole desk can be dragged by just pushing onto
the top-most box.
9.1.2 Joint Tests
Simulator library implements various geometric joints that can be used to attach bodies together
and provides a way to control angles or velocities about joint axes, impose joint angle
limits, control displacements along joint axes, etc. This functionality is presented by TestHinge-
Joint, TestUniversalJoint, TestBallAndSocketJoint, TestSliderJoint, TestMotorJoint
and TestLimitedSpringJoint tests that evaluate the corresponding joint classes. It is assumed
here that the user provides appropriate external influences by dragging the attached bodies to
validate the functionality of the joints and their motors.
9.1.3 Performance and Robustness Tests
To test the performance of the constraint solver and its fitness to handle highly constrained
articulated structures whose segments can collide, the following two tests exercising certain types
of articulated structures were implemented.
• TestChain
A chain consisting of 32 segments connected by various joint types, where each joint removes
at least 3 DOFs, corresponding to a linear articulated structure is presented by this test.
• TestArticulatedStructure
This test implements and evaluates a non-linear highly articulated structure consisting
of 127 segments whose all DOFs are constrained and presents the use of soft constraints
to attract articulated structures to initial states — soft constraints are used to constrain
joint angles to zeroes. Unless the structure’s segments contact, the constraint forces are
computed in the linear time.
TestJointCycles test verifies that articulated structures with loops (rigid body systems
with cycles in the body-joint graph and other auxiliary constraints) are handled correctly by the
linear time constraint solver and that the LCP solver can solve problems whose matrices A are
not positive-definite. The test also demonstrates the handling of redundant constraints, because
more constraints are imposed than is actually needed to achieve the effect.
9.1.4 Integration Precision Tests
These tests simulate the same test scene by integrating the equations of motion using a set of
distinct ODE solvers so that the simulation effects (integration precision of the individual solvers)
could be compared. An articulated structure consisting of a rotating carousel with four chains