SimTK::Constraint::ConstantAngle Class Reference

This constraint consists of a single constraint equation that enforces that a unit vector v1 fixed to one body (the "base body") must maintain a fixed angle theta with respect to a unit vector v2 fixed on the other body (the "follower body"). More...

Inheritance diagram for SimTK::Constraint::ConstantAngle:

Public Member Functions
	ConstantAngle (MobilizedBody &baseBody_B, const UnitVec3 &defaultAxis_B, MobilizedBody &followerBody_F, const UnitVec3 &defaultAxis_F, Real angle=Pi/2)
	ConstantAngle ()
	Default constructor creates an empty handle. More...
ConstantAngle &	setAxisDisplayLength (Real)
ConstantAngle &	setAxisDisplayWidth (Real)
Real	getAxisDisplayLength () const
Real	getAxisDisplayWidth () const
ConstantAngle &	setDefaultBaseAxis (const UnitVec3 &)
ConstantAngle &	setDefaultFollowerAxis (const UnitVec3 &)
ConstantAngle &	setDefaultAngle (Real)
MobilizedBodyIndex	getBaseMobilizedBodyIndex () const
MobilizedBodyIndex	getFollowerMobilizedBodyIndex () const
const UnitVec3 &	getDefaultBaseAxis () const
const UnitVec3 &	getDefaultFollowerAxis () const
Real	getDefaultAngle () const
const UnitVec3 &	getBaseAxis (const State &) const
const UnitVec3 &	getFollowerAxis (const State &) const
Real	getAngle (const State &) const
Real	getPositionError (const State &) const
Real	getVelocityError (const State &) const
Real	getAccelerationError (const State &) const
Real	getMultiplier (const State &) const
Real	getTorqueOnFollowerBody (const State &) const
Public Member Functions inherited from SimTK::Constraint
	Constraint ()
	Default constructor creates an empty Constraint handle that can be used to reference any Constraint. More...
	Constraint (ConstraintImpl *r)
	For internal use: construct a new Constraint handle referencing a particular implementation object. More...
void	disable (State &) const
	Disable this Constraint, effectively removing it from the system. More...
void	enable (State &) const
	Enable this Constraint, without necessarily satisfying it. More...
bool	isDisabled (const State &) const
	Test whether this constraint is currently disabled in the supplied State. More...
bool	isDisabledByDefault () const
	Test whether this Constraint is disabled by default in which case it must be explicitly enabled before it will take effect. More...
void	setDisabledByDefault (bool shouldBeDisabled)
	Normally Constraints are enabled when defined and can be disabled later. More...
	operator ConstraintIndex () const
	This is an implicit conversion from Constraint to ConstraintIndex when needed. More...
const SimbodyMatterSubsystem &	getMatterSubsystem () const
	Get a const reference to the matter subsystem that contains this Constraint. More...
SimbodyMatterSubsystem &	updMatterSubsystem ()
	Assuming you have writable access to this Constraint, get a writable reference to the containing matter subsystem. More...
ConstraintIndex	getConstraintIndex () const
	Get the ConstraintIndex that was assigned to this Constraint when it was added to the matter subsystem. More...
bool	isInSubsystem () const
	Test whether this Constraint is contained within a matter subsystem. More...
bool	isInSameSubsystem (const MobilizedBody &mobod) const
	Test whether the supplied MobilizedBody is in the same matter subsystem as this Constraint. More...
int	getNumConstrainedBodies () const
	Return the number of unique bodies directly restricted by this constraint. More...
const MobilizedBody &	getMobilizedBodyFromConstrainedBody (ConstrainedBodyIndex consBodyIx) const
	Return a const reference to the actual MobilizedBody corresponding to one of the Constrained Bodies included in the count returned by getNumConstrainedBodies(). More...
const MobilizedBody &	getAncestorMobilizedBody () const
	Return a const reference to the actual MobilizedBody which is serving as the Ancestor body for the constrained bodies in this Constraint. More...
int	getNumConstrainedMobilizers () const
	Return the number of unique mobilizers directly restricted by this Constraint. More...
const MobilizedBody &	getMobilizedBodyFromConstrainedMobilizer (ConstrainedMobilizerIndex consMobilizerIx) const
	Return a const reference to the actual MobilizedBody corresponding to one of the Constrained Mobilizers included in the count returned by getNumConstrainedMobilizers(). More...
const SimbodyMatterSubtree &	getSubtree () const
	Return a subtree object indicating which parts of the multibody tree are potentially affected by this Constraint. More...
int	getNumConstrainedQ (const State &, ConstrainedMobilizerIndex) const
	Return the number of constrainable generalized coordinates q associated with a particular constrained mobilizer. More...
int	getNumConstrainedU (const State &, ConstrainedMobilizerIndex) const
	Return the number of constrainable mobilities u associated with a particular constrained mobilizer. More...
ConstrainedUIndex	getConstrainedUIndex (const State &, ConstrainedMobilizerIndex, MobilizerUIndex which) const
	Return the index into the constrained mobilities u array corresponding to a particular mobility of the indicated ConstrainedMobilizer. More...
ConstrainedQIndex	getConstrainedQIndex (const State &, ConstrainedMobilizerIndex, MobilizerQIndex which) const
	Return the index into the constrained coordinates q array corresponding to a particular coordinate of the indicated ConstrainedMobilizer. More...
int	getNumConstrainedQ (const State &) const
	Return the sum of the number of coordinates q associated with each of the constrained mobilizers. More...
int	getNumConstrainedU (const State &) const
	Return the sum of the number of mobilities u associated with each of the constrained mobilizers. More...
QIndex	getQIndexOfConstrainedQ (const State &state, ConstrainedQIndex consQIndex) const
	Map one of this Constraint's constrained q's to the corresponding index within the matter subsystem's whole q vector. More...
UIndex	getUIndexOfConstrainedU (const State &state, ConstrainedUIndex consUIndex) const
	Map one of this Constraint's constrained U's (or mobilities) to the corresponding index within the matter subsystem's whole u vector. More...
void	getNumConstraintEquationsInUse (const State &state, int &mp, int &mv, int &ma) const
	Find out how many holonomic (position), nonholonomic (velocity), and acceleration-only constraint equations are currently being generated by this Constraint. More...
void	getIndexOfMultipliersInUse (const State &state, MultiplierIndex &px0, MultiplierIndex &vx0, MultiplierIndex &ax0) const
	Return the start of the blocks of multipliers (or acceleration errors) assigned to this Constraint. More...
void	setMyPartInConstraintSpaceVector (const State &state, const Vector &myPart, Vector &constraintSpace) const
	Set the part of a complete constraint-space vector that belongs to this constraint. More...
void	getMyPartFromConstraintSpaceVector (const State &state, const Vector &constraintSpace, Vector &myPart) const
	Get the part of a complete constraint-space vector that belongs to this constraint. More...
Vector	getPositionErrorsAsVector (const State &) const
	Get a Vector containing the position errors. More...
Vector	calcPositionErrorFromQ (const State &, const Vector &q) const
Matrix	calcPositionConstraintMatrixP (const State &) const
Matrix	calcPositionConstraintMatrixPt (const State &) const
Matrix	calcPositionConstraintMatrixPNInv (const State &) const
void	calcConstraintForcesFromMultipliers (const State &, const Vector &lambda, Vector_< SpatialVec > &bodyForcesInA, Vector &mobilityForces) const
	This operator calculates this constraint's body and mobility forces given the complete set of multipliers lambda for this Constraint. More...
Vector	getVelocityErrorsAsVector (const State &) const
	Get a Vector containing the velocity errors. More...
Vector	calcVelocityErrorFromU (const State &, const Vector &u) const
Matrix	calcVelocityConstraintMatrixV (const State &) const
Matrix	calcVelocityConstraintMatrixVt (const State &) const
Vector	getAccelerationErrorsAsVector (const State &) const
	Get a Vector containing the acceleration errors. More...
Vector	calcAccelerationErrorFromUDot (const State &, const Vector &udot) const
Vector	getMultipliersAsVector (const State &) const
	Get a Vector containing the Lagrange multipliers. More...
void	getConstraintForcesAsVectors (const State &state, Vector_< SpatialVec > &bodyForcesInG, Vector &mobilityForces) const
	Given a State realized through Acceleration stage, return the forces that were applied to the system by this Constraint, with body forces expressed in Ground. More...
Vector_< SpatialVec >	getConstrainedBodyForcesAsVector (const State &state) const
	For convenience, returns constrained body forces as the function return. More...
Vector	getConstrainedMobilityForcesAsVector (const State &state) const
	For convenience, returns constrained mobility forces as the function return. More...
Real	calcPower (const State &state) const
	Calculate the power being applied by this Constraint to the system. More...
Matrix	calcAccelerationConstraintMatrixA (const State &) const
Matrix	calcAccelerationConstraintMatrixAt (const State &) const
void	setIsConditional (bool isConditional)
	(Advanced) Mark this constraint as one that is only conditionally active. More...
bool	isConditional () const
	(Advanced) Get the value of the isConditional flag. More...
Public Member Functions inherited from SimTK::PIMPLHandle< Constraint, ConstraintImpl, true >
bool	isEmptyHandle () const
	Returns true if this handle is empty, that is, does not refer to any implementation object. More...
bool	isOwnerHandle () const
	Returns true if this handle is the owner of the implementation object to which it refers. More...
bool	isSameHandle (const Constraint &other) const
	Determine whether the supplied handle is the same object as "this" PIMPLHandle. More...
void	disown (Constraint &newOwner)
	Give up ownership of the implementation to an empty handle. More...
PIMPLHandle &	referenceAssign (const Constraint &source)
	"Copy" assignment but with shallow (pointer) semantics. More...
PIMPLHandle &	copyAssign (const Constraint &source)
	This is real copy assignment, with ordinary C++ object ("value") semantics. More...
void	clearHandle ()
	Make this an empty handle, deleting the implementation object if this handle is the owner of it. More...
const ConstraintImpl &	getImpl () const
	Get a const reference to the implementation associated with this Handle. More...
ConstraintImpl &	updImpl ()
	Get a writable reference to the implementation associated with this Handle. More...
int	getImplHandleCount () const
	Return the number of handles the implementation believes are referencing it. More...

Additional Inherited Members
Public Types inherited from SimTK::Constraint
typedef Rod	ConstantDistance
	Synonym for Rod constraint. More...
typedef Ball	CoincidentPoints
	Synonym for Ball constraint. More...
typedef Ball	Spherical
	Synonym for Ball constraint. More...
typedef Weld	CoincidentFrames
Public Types inherited from SimTK::PIMPLHandle< Constraint, ConstraintImpl, true >
typedef PIMPLHandle < Constraint, ConstraintImpl, PTR >	HandleBase
typedef HandleBase	ParentHandle
Protected Member Functions inherited from SimTK::PIMPLHandle< Constraint, ConstraintImpl, true >
	PIMPLHandle ()
	The default constructor makes this an empty handle. More...
	PIMPLHandle (ConstraintImpl *p)
	This provides consruction of a handle referencing an existing implementation object. More...
	PIMPLHandle (const PIMPLHandle &source)
	The copy constructor makes either a deep (value) or shallow (reference) copy of the supplied source PIMPL object, based on whether this is a "pointer semantics" (PTR=true) or "object (value) semantics" (PTR=false, default) class. More...
	~PIMPLHandle ()
	Note that the destructor is non-virtual. More...
PIMPLHandle &	operator= (const PIMPLHandle &source)
	Copy assignment makes the current handle either a deep (value) or shallow (reference) copy of the supplied source PIMPL object, based on whether this is a "pointer sematics" (PTR=true) or "object (value) semantics" (PTR=false, default) class. More...
void	setImpl (ConstraintImpl *p)
	Set the implementation for this empty handle. More...
bool	hasSameImplementation (const Constraint &other) const
	Determine whether the supplied handle is a reference to the same implementation object as is referenced by "this" PIMPLHandle. More...

Detailed Description

This constraint consists of a single constraint equation that enforces that a unit vector v1 fixed to one body (the "base body") must maintain a fixed angle theta with respect to a unit vector v2 fixed on the other body (the "follower body").

This can be done with a single constraint equation as long as theta is sufficiently far away from 0 and +/-Pi (180 degrees), with the numerically best performance at theta=Pi/2 (90 degrees).

Warning

Do not use this constraint to align the vectors, that is for angles near 0 or +/- Pi; performance will noticeably degrade within a few degrees of these limits and numerical integration will eventually fail at the limits.

If you want to enforce that two axes are aligned with one another (that is, the angle between them is 0 or +/-Pi), that takes two constraint equations since the only remaining rotation is about the common axis. (That is, two rotational degrees of freedom are removed; that can't be done with one constraint equation – the situation is analogous to the inability of a Rod (distance) constraint to keep two points at 0 distance.) Instead, you can use two ConstantAngle constraints on pairs of vectors perpendicular to the aligned ones, so that each ConstantAngle is set to the optimal 90 degrees.

This constraint is enforced by an internal scalar torque applied equal and opposite on each body, about the mutual perpendicular to the two vectors.

The assembly condition is the same as the run-time constraint: the bodies must be rotated until the vectors have the right angle between them.

Constructor & Destructor Documentation

SimTK::Constraint::ConstantAngle::ConstantAngle	(	MobilizedBody &	baseBody_B,
		const UnitVec3 &	defaultAxis_B,
		MobilizedBody &	followerBody_F,
		const UnitVec3 &	defaultAxis_F,
		Real	angle = Pi/2
	)

SimTK::Constraint::ConstantAngle::ConstantAngle ( )

inline

Default constructor creates an empty handle.

Member Function Documentation

ConstantAngle& SimTK::Constraint::ConstantAngle::setAxisDisplayLength

(

Real

)

ConstantAngle& SimTK::Constraint::ConstantAngle::setAxisDisplayWidth

(

Real

)

Real SimTK::Constraint::ConstantAngle::getAxisDisplayLength

(

)

const

Real SimTK::Constraint::ConstantAngle::getAxisDisplayWidth

(

)

const

ConstantAngle& SimTK::Constraint::ConstantAngle::setDefaultBaseAxis

(

const UnitVec3 &

)

ConstantAngle& SimTK::Constraint::ConstantAngle::setDefaultFollowerAxis

(

const UnitVec3 &

)

ConstantAngle& SimTK::Constraint::ConstantAngle::setDefaultAngle

(

Real

)

MobilizedBodyIndex SimTK::Constraint::ConstantAngle::getBaseMobilizedBodyIndex

(

)

const

MobilizedBodyIndex SimTK::Constraint::ConstantAngle::getFollowerMobilizedBodyIndex

(

)

const

const UnitVec3& SimTK::Constraint::ConstantAngle::getDefaultBaseAxis

(

)

const

const UnitVec3& SimTK::Constraint::ConstantAngle::getDefaultFollowerAxis

(

)

const

Real SimTK::Constraint::ConstantAngle::getDefaultAngle

(

)

const

const UnitVec3& SimTK::Constraint::ConstantAngle::getBaseAxis

(

const State &

)

const

const UnitVec3& SimTK::Constraint::ConstantAngle::getFollowerAxis

(

const State &

)

const

Real SimTK::Constraint::ConstantAngle::getAngle

(

const State &

)

const

Real SimTK::Constraint::ConstantAngle::getPositionError

(

const State &

)

const

Real SimTK::Constraint::ConstantAngle::getVelocityError

(

const State &

)

const

Real SimTK::Constraint::ConstantAngle::getAccelerationError

(

const State &

)

const

Real SimTK::Constraint::ConstantAngle::getMultiplier

(

const State &

)

const

Real SimTK::Constraint::ConstantAngle::getTorqueOnFollowerBody

(

const State &

)

const

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The documentation for this class was generated from the following file:

• Constraint.h