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Havok 1 World/Havok 3 World Rollout 809
warnings are provided for g uidance and can be
safely ignored if you are happy with the behavior
of your animation. The default Gra vity value
reflects "real-world" gravity: –9.8 m/s
2
(–386.22
inches/s
2
) on the Z axis. For more information,
see Scale (page 2–711).
World S cal e—Thedistancein3dsMaxworldunits,
that represents one meter in the reactor world, and
hence determines the size of every object in your
simulation.
Note: Changing the World Scale value can
drastically alter simulated objects’ behavior. For
more information, see Scale (page 2–711).
Col. Tolerance—(Collision Tolerance) One of the
tasks that reactor performs at each simulation
step is detection of whether any objects in the
scene are colliding, and then updating the scene
accordingly. If objects are closer together than the
Collision Tolerance value, reactor considers them
to be colliding. A high Collision Tolerance value
results in a stable simulation, but it can also cause
gaps between "colliding" objects.
The default value is 1/10th of World Scale (10 cm if
you are modeling using real-world sizes), and it is a
good rule of thumb to always keep it above 1/40th
(4 mm), due to floating point precision limits in
the processor. For standard scenes and object
sizes, the default parameters for world scale and
toleranceshouldbeadequate.Ifyouaresimulating
very smal l objects w here the tolerance is still to
visible, t ry reducing the World Scale value and the
Collision Tolerance and Gravity accordingly. For
more information, see Scale (page 2–711).
Add Dea ctiva tor—When on, reactor adds a
deactivator to the simulation.
Thedeactivatorkeepstrackoftheobjectsinthe
simulation and deactivates (stops simulating)
objects that it determines are at rest. This keeps
reactor from wasting system resources simulating
objectsthataren’tdoinganything.
When Add Deactivator is on, you have access to
two distance parameters for determining whether
an object is moving or not. The reason that there
are two properties rather than just one is for
bodies that vibrate. It’s possible that a body can
end up vibrating after a collision or some other
occurrence. A vibrating body might vibrate a few
millimeters in distance, which would keep it active
for a typical Short Frequency test. However, the
object is not really moving anywhere, so keeping
it active wastes CPU time. However, if it vibrates
in place, it fails the Long Frequenc y test and is
deactivated.
•
Short Frequency—The m inimum distance,
usuallyinmillimeters,thatanobjectmustmove
during each step of a simulation. If an object
in a simulation does not move the specified
distance in each step, reactor deact ivates it.
•
Long Freq uency—Also sets a distance, usually
larger than the Short Frequency value. Long
Frequency checks every few steps simulation
rather than at every step. Any object that do es
not move the required Long Frequency distance
is deactivated.
Add Dr ag Action—When on, ensures that rigid
bodies are subject to constant drag. This damps
theirlinearandangularvelocities,sotheycometo
rest sooner. This is useful, for example, w here rigid
bodies are joined with constraints (page 2–724),
as it helps the constrained bodies to come to rest
despite the forces applied by the constraints.
•
Lin—The linear damping applied by A dd Drag
Action.
•
Ang—The angular damping applied by Add
Drag Action.
Do Not Simulate Friction—When on, reactor
ignores all Friction values during the simulation,
and objects slide easily across each other.
Fracture Penetrations—These p arameters let you
adjust how reactor simulates Fracture objects. For