Game Development Reference
In-Depth Information
Figure 16.3 Haptic rendering calculation principle
chapter 17. Penalty-based approach consists of calculating a non-interpenetration force
on the basis of an interpenetration measurement. If one of the objects affected by the
collision is the avatar itself, it is enough to use the resultant (vector sum of forces) and
the total torque created by the collisions (in case of a rigid virtual object) as the set
The device is thus directly interfaced to the simulation. Use of other response cal-
culation methods is more difficult to implement. In fact, the impulse or constraint
methods require imposing a contact position between the objects, i.e. no interpene-
tration. Though this hypothesis is possible for objects whose position is decided by
the simulation, it cannot compel the device to adopt a position compatible with the
obstacles. In reality, the constraints are respected through returned forces, which can be
compared to a secondary control, i.e. a system correcting (after stabilisation) the differ-
ences with respect to the constraints. Such a system always exposes the interpenetration
situations that the response calculation algorithm cannot manage.
16.2.2 Rendering by admittance patterns:
calculations of constraints
When the haptic interface is operated in admittance mode, it involves being able to use
the forces measured by the device and providing it with a position to be maintained.
A natural approach is simulating the avatar physically. The measured forces are first
added to the forces resulting from the simulation and then the sum is integrated twice
to obtain the new position of the avatar. This position is then returned to the device,
because this is the position that the virtual environment asks to maintain. Collision is
thus managed directly by the simulation and any collision response method (impulses,
constraints and if required penalties) can be used. The devices in admittance mode
are found to be well suited to the restitution of interactions with a rigid body avatar,
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