This constraint consists of one constraint equation that enforces a constant distance between a point on one body and a point on another body. More...

Inheritance diagram for SimTK::Constraint::Rod:

Public Member Functions
Construction
Methods in this section refer both to constructors, and to methods that can be used to set or change contruction (Topology-stage) parameters; these specify the values assigned by default to the corresponding state variables. Note: Changing one of these default parameters invalidates the containing System's topology, meaning that realizeTopology() will have to be called and a new State obtained before subsequent use. The set...() methods return a reference to "this" Rod constraint element (in the manner of an assignment operator) so they can be chained in a single expression. The default parameters can be overridden in any given State, and modified without affecting Topology; see the "Runtime Changes" section below.
	Rod (MobilizedBody &mobod1, const Vec3 &defaultPointOnBody1, MobilizedBody &mobod2, const Vec3 &defaultPointOnBody2, Real defaultRodLength)
	Construct a Rod (constant distance) constraint as described in the Constraint::Rod class documentation. More...

	Rod (MobilizedBody &mobod1, MobilizedBody &mobod2, Real defaultRodLength)
	Construct a Rod (constant distance) constraint as described in the Constraint::Rod class documentation, but using the body origins as the Rod end points. More...

	Rod ()
	Default constructor creates an empty handle that can be used to reference any Rod Constraint. More...

const MobilizedBody &	getMobilizedBody1 () const
	Return a reference to the first MobilizedBody given in the constructor. More...

const MobilizedBody &	getMobilizedBody2 () const
	Return a reference to the second MobilizedBody given in the constructor. More...

Rod &	setDefaultPointOnBody1 (const Vec3 &defaultPoint)
	Replace the default location for the point attached to the first body, mobod1, that was supplied on construction. More...

Rod &	setDefaultPointOnBody2 (const Vec3 &defaultPoint)
	Replace the default location for the point attached to the second body, mobod2, that was supplied on construction. More...

Rod &	setDefaultRodLength (Real defaultRodLength)
	Replace the default rod length (distance), replacing whatever value was supplied on construction. More...

const Vec3 &	getDefaultPointOnBody1 () const
	Return the default location for the point attached to the first mobilized body, mobod1, as set during construction or by the most recent call to setDefaultPointOnBody1(). More...

const Vec3 &	getDefaultPointOnBody2 () const
	Return the default location for the point attached to the second mobilized body, mobod2, as set during construction or by the most recent call to setDefaultPointOnBody2(). More...

Real	getDefaultRodLength () const
	Return the default rod length (distance) as set during construction or by the most recent call to setDefaultRodLength(). More...

Runtime Changes
These refer to Position-stage discrete state variables that determine the sphere parameters to be used to calculate constraint forces from a given State object. If these are not set explicitly, the parameters are set to those provided in the constructor or via the correponding setDefault...() methods. Note: Changing one of these parameters invalidates the given State's Stage::Position, meaning that the State's stage will be no higher than Stage::Time after the parameter change. That ensures that position constraint errors will be recalculated before they are used. The set...() methods here return a const reference to "this" SphereOnSphereContact element (in the manner of an assignment operator, except read-only) so they can be chained in a single expression. You can also modify and examine the default parameters; see the "Construction" section above.
const Rod &	setPointOnBody1 (State &state, const Vec3 &p_B1P) const
	Modify the location of the point P on the first body, mobod1, in this state by providing a new vector p_B1P giving the location of P measured from body 1's origin, and expressed in the B1 frame. More...

const Rod &	setPointOnBody2 (State &state, const Vec3 &p_B2Q) const
	Modify the location of the point Q on the second body, mobod2, in this state by providing a new vector p_B2Q giving the location of Q measured from body 2's origin, and expressed in the B2 frame. More...

const Rod &	setRodLength (State &state, Real rodLength) const
	Modify the rod length (distance) in this state. More...

const Vec3 &	getPointOnBody1 (const State &state) const
	Return the position on body 1 of the rod end point P on the first body, mobod1, as currently set in the given state. More...

const Vec3 &	getPointOnBody2 (const State &state) const
	Return the position on body 2 of the rod end point Q attached to the second body, mobod2, as currently set in the given state. More...

Real	getRodLength (const State &state) const
	Return the rod length (distance) as currently set in the given state. More...

Computations
Methods here provide access to values already calculated by this constraint element, and provide operators you can call to calculate related values.
Real	getPositionError (const State &) const
	This is the signed violation of the position constraint, in length units. More...

Real	getVelocityError (const State &) const
	This is the time derivative of the value returned by getPositionError(); in this case it is the relative velocity of the two points projected onto the direction of the line between them. More...

Real	getAccelerationError (const State &) const
	This is the time derivative of the value returned by getVelocityError(). More...

Real	getMultiplier (const State &) const
	This is the Lagrange multiplier required to enforce the constraint equation generated here. More...

Real	getRodTension (const State &) const
	This returns the tension in the Rod being used to enforce the constraint. More...

UnitVec3	findRodOrientationInG (const State &state) const
	Return the instantaneous orientation of the Rod in the Ground frame. More...

Real	findLengthViolation (const State &state) const
	Calculate the amount by which this constraint is violated. More...

Advanced/Obscure/Obsolete/Debugging
You probably don't want to use the methods in this section.
MobilizedBodyIndex	getBody1MobilizedBodyIndex () const
	(Obscure) Use getMobilizedBody1() instead. More...

MobilizedBodyIndex	getBody2MobilizedBodyIndex () const
	(Obscure) Use getMobilizedBody2() instead. More...

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 one constraint equation that enforces a constant distance between a point on one body and a point on another body.

This is like connecting them by a rigid, massless rod with ball joints at either end. The constraint is enforced by a force acting along the rod with opposite signs at either end. When positive, this represents tension in the rod pulling the points together; when negative it represents compression keeping the points separated.

Warning: You can't use this to enforce a distance of zero between two points. That takes three constraints because there is no restriction on the force direction. For a distance of zero (i.e., you want the points to be coincident) use a Ball constraint, a.k.a. CoincidentPoints constraint.

Constructor & Destructor Documentation

SimTK::Constraint::Rod::Rod	(	MobilizedBody &	mobod1,
		const Vec3 &	defaultPointOnBody1,
		MobilizedBody &	mobod2,
		const Vec3 &	defaultPointOnBody2,
		Real	defaultRodLength
	)

Construct a Rod (constant distance) constraint as described in the Constraint::Rod class documentation.

Parameters

mobod1	The first MobilizedBody object to which one of the rod endpoints is fixed.
defaultPointOnBody1	This is the location of a point P on mobod1, given as a vector p_B1P from the B1 frame origin to the point P, expressed in the mobod1 body frame B1. This is the point location that will be present in a default State; you can modify it later.
mobod2	The second MobilizedBody object to which the other rod endpoint is fixed.
defaultPointOnBody2	This is the location of a point Q on mobod2, given as a vector p_B2Q from the B2 frame origin to the point Q, expressed in the mobod2 body frame B2. This is the point location that will be present in a default State; you can modify it later.
defaultRodLength	The rod length (required distance between points P and Q). This is the value that will be present in a default State; you can modify it later.

SimTK::Constraint::Rod::Rod	(	MobilizedBody &	mobod1,
		MobilizedBody &	mobod2,
		Real	defaultRodLength
	)

Construct a Rod (constant distance) constraint as described in the Constraint::Rod class documentation, but using the body origins as the Rod end points.

Parameters

mobod1	The first MobilizedBody object whose origin is used as one of the end points. This is the same as specifying Vec3(0) for defaultPointOnBody1 in the preceding constructor. This is the value that will be present in a default State; you can modify it later.
mobod2	The second MobilizedBody object whose origin is used as one of the end points. This is the same as specifying Vec3(0) for defaultPointOnBody2 in the preceding constructor. This is the value that will be present in a default State; you can modify it later.
defaultRodLength	The rod length (required distance between points P and Q). This is the value that will be present in a default State; you can modify it later.

SimTK::Constraint::Rod::Rod ( )

inline

Default constructor creates an empty handle that can be used to reference any Rod Constraint.

Member Function Documentation

const MobilizedBody& SimTK::Constraint::Rod::getMobilizedBody1 ( ) const

Return a reference to the first MobilizedBody given in the constructor.

This cannot be changed after construction.

const MobilizedBody& SimTK::Constraint::Rod::getMobilizedBody2 ( ) const

Return a reference to the second MobilizedBody given in the constructor.

This cannot be changed after construction.

Rod& SimTK::Constraint::Rod::setDefaultPointOnBody1 ( const Vec3 & defaultPoint )

Replace the default location for the point attached to the first body, mobod1, that was supplied on construction.

This is a topological change; you'll have to call realizeTopology() again if you call this method.

See also: setPointOnBody1()

Rod& SimTK::Constraint::Rod::setDefaultPointOnBody2 ( const Vec3 & defaultPoint )

Replace the default location for the point attached to the second body, mobod2, that was supplied on construction.

This is a topological change; you'll have to call realizeTopology() again if you call this method.

See also: setPointOnBody2()

Rod& SimTK::Constraint::Rod::setDefaultRodLength ( Real defaultRodLength )

Replace the default rod length (distance), replacing whatever value was supplied on construction.

This is a topological change; you'll have to call realizeTopology() again if you call this method.

See also: setRodLength()

const Vec3& SimTK::Constraint::Rod::getDefaultPointOnBody1 ( ) const

Return the default location for the point attached to the first mobilized body, mobod1, as set during construction or by the most recent call to setDefaultPointOnBody1().

See also: getPointOnBody1()

const Vec3& SimTK::Constraint::Rod::getDefaultPointOnBody2 ( ) const

Return the default location for the point attached to the second mobilized body, mobod2, as set during construction or by the most recent call to setDefaultPointOnBody2().

See also: getPointOnBody2()

Real SimTK::Constraint::Rod::getDefaultRodLength ( ) const

Return the default rod length (distance) as set during construction or by the most recent call to setDefaultRodLength().

See also: getRodLength()

const Rod& SimTK::Constraint::Rod::setPointOnBody1	(	State &	state,
		const Vec3 &	p_B1P
	)		const

Modify the location of the point P on the first body, mobod1, in this state by providing a new vector p_B1P giving the location of P measured from body 1's origin, and expressed in the B1 frame.

This overrides the defaultPointOnBody1 in the given state, whose Stage::Position is invalidated.

See also: getPointOnBody1(), setDefaultPointOnBody1()

const Rod& SimTK::Constraint::Rod::setPointOnBody2	(	State &	state,
		const Vec3 &	p_B2Q
	)		const

Modify the location of the point Q on the second body, mobod2, in this state by providing a new vector p_B2Q giving the location of Q measured from body 2's origin, and expressed in the B2 frame.

This overrides the defaultPointOnBody2 in the given state, whose Stage::Position is invalidated.

See also: getPointOnBody2(), setDefaultPointOnBody2()

const Rod& SimTK::Constraint::Rod::setRodLength	(	State &	state,
		Real	rodLength
	)		const

Modify the rod length (distance) in this state.

This overrides the defaultRodLength in the given state, whose Stage::Position is invalidated.

See also: getRodLength(), setDefaultRodLength()

const Vec3& SimTK::Constraint::Rod::getPointOnBody1 ( const State & state ) const

Return the position on body 1 of the rod end point P on the first body, mobod1, as currently set in the given state.

The value is returned as a vector p_B1P from body 1's origin to the point P, expressed in the B1 frame.

See also: setPointOnBody1(), getDefaultPointOnBody1()

const Vec3& SimTK::Constraint::Rod::getPointOnBody2 ( const State & state ) const

Return the position on body 2 of the rod end point Q attached to the second body, mobod2, as currently set in the given state.

The value is returned as a vector p_B2Q from body 2's origin to the point Q, expressed in the B2 frame.

See also: setPointOnBody2(), getDefaultPointOnBody2()

Real SimTK::Constraint::Rod::getRodLength ( const State & state ) const

Return the rod length (distance) as currently set in the given state.

See also: setRodLength(), getDefaultRodLength()

Real SimTK::Constraint::Rod::getPositionError ( const State & ) const

This is the signed violation of the position constraint, in length units.

It is positive when the two points are separated by more than the required distance; negative when closer than the required distance. The given state must have already been realized through Stage::Position.

Real SimTK::Constraint::Rod::getVelocityError ( const State & ) const

This is the time derivative of the value returned by getPositionError(); in this case it is the relative velocity of the two points projected onto the direction of the line between them.

Real SimTK::Constraint::Rod::getAccelerationError ( const State & ) const

This is the time derivative of the value returned by getVelocityError().

Real SimTK::Constraint::Rod::getMultiplier ( const State & ) const

This is the Lagrange multiplier required to enforce the constraint equation generated here.

For this Constraint it has units of force, but recall that the sign convention for multipliers is opposite that of forces. Use the other provided methods if you want to get meaningful forces. The given state must already be realized to Stage::Acceleration.

Real SimTK::Constraint::Rod::getRodTension ( const State & ) const

This returns the tension in the Rod being used to enforce the constraint.

It is positive if the Rod is in tension, negative if in compression. The result is zero if the constraint is currently disabled. The given state must already be realized to Stage::Acceleration.

UnitVec3 SimTK::Constraint::Rod::findRodOrientationInG ( const State & state ) const

Return the instantaneous orientation of the Rod in the Ground frame.

This is a unit vector along the direction from point1 (on body 1) to point2 (on body 2), unless the points overlap in which case it is an arbitrary direction. This method calculates a valid value even if this constraint is currently disabled. The given state must already be realized to Stage::Position.

Real SimTK::Constraint::Rod::findLengthViolation ( const State & state ) const

Calculate the amount by which this constraint is violated.

It is positive when the distance between the points is greater than the specified Rod length, negative when less. If the constraint is currently enabled then this returns the same value as getPositionError(); however, this method calculates a valid value even if the constraint is currently disabled. The given state must be realized to Stage::Position.

MobilizedBodyIndex SimTK::Constraint::Rod::getBody1MobilizedBodyIndex ( ) const

(Obscure) Use getMobilizedBody1() instead.

MobilizedBodyIndex SimTK::Constraint::Rod::getBody2MobilizedBodyIndex ( ) const

(Obscure) Use getMobilizedBody2() instead.

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

Constraint_Rod.h

Public Member Functions

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation