(Advanced) This is the underlying constraint for unilateral contact with friction but must be combined with contact and friction conditions. More...

Inheritance diagram for SimTK::Constraint::PointOnPlaneContact:

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" PointOnPlaneContact element (in the manner of an assignment operator) so they can be chained in a single expression.
	PointOnPlaneContact (MobilizedBody &planeBody, const Transform &defaultPlaneFrame, MobilizedBody &followerBody, const Vec3 &defaultFollowerPoint)
	Construct a point-in-plane normal constraint and two no-slip friction constraints as described in the Constraint::PointOnPlaneContact class documentation. More...

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

PointOnPlaneContact &	setDefaultPlaneFrame (const Transform &defaultPlaneFrame)
	Replace the default plane frame that was supplied on construction. More...

PointOnPlaneContact &	setDefaultFollowerPoint (const Vec3 &defaultFollowerPoint)
	Replace the default follower point that was supplied on construction. More...

MobilizedBodyIndex	getPlaneMobilizedBodyIndex () const
	Return the MobilizedBodyIndex of the plane MobilizedBody. More...

MobilizedBodyIndex	getFollowerMobilizedBodyIndex () const
	Return the MobilizedBodyIndex of the follower MobilizedBody. More...

const Transform &	getDefaultPlaneFrame () const
	Return the default plane frame as set during construction or by the most recent call to setDefaultPlaneFrame(). More...

const Vec3 &	getDefaultFollowerPoint () const
	Return the default follower point as set during construction or by the most recent call to setDefaultFollowerPoint(). More...

Visualization
If you are allowing the SimbodyMatterSubsystem to generate default geometry, this constraint element will attempt to represent the plane and sphere that it connects. Methods here give you some limited control over the generated default geometry; if you need more control you should disable the generation of default geometry and make your own.
PointOnPlaneContact &	setPlaneDisplayHalfWidth (Real halfWidth)
	This affects only generated decorative geometry for default visualization; the plane is really infinite in extent. More...

PointOnPlaneContact &	setPointDisplayRadius (Real radius)
	This affects only generated decorative geometry for default visualization; the point is really zero radius. More...

Real	getPlaneDisplayHalfWidth () const
	Return the plane half-width that will be used if we're asked to generate default visualization geometry. More...

Real	getPointDisplayRadius () const
	Return the sphere radius that will be used to visualize the follower point if we're asked to generate default visualization geometry. More...

Runtime Changes
These refer to Position-stage discrete state variables that determine the sphere and plane 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" SphereOnPlaneContact element (in the manner of an assignment operator, except read-only) so they can be chained in a single expression.
const Transform &	getPlaneFrame (const State &state) const
	Return the plane frame X_SP that is currently in effect for this Constraint. More...

const Vec3 &	getFollowerPoint (const State &state) const
	Return the plane frame X_SP that is currently in effect for this Constraint. 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 &state) const
	The returned position error can be viewed as a signed distance. More...

Vec3	getVelocityErrors (const State &state) const
	The velocity error vector is the velocity of the follower point in the contact frame. More...

Vec3	getAccelerationErrors (const State &state) const
	This vector is the time derivative of the value returned by getVelocityError(). More...

Vec3	getMultipliers (const State &state) const
	These are the Lagrange multipliers required to enforce the three constraint equations generated here. More...

Vec3	getForceOnFollowerPoint (const State &state) const
	This is the force applied by the plane body to the follower point, expressed in the contact frame. 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

(Advanced) This is the underlying constraint for unilateral contact with friction but must be combined with contact and friction conditions.

This enforces the same normal condition as Constraint::PointInPlane but also adds two velocity-level no-slip constraints. Thus there are three constraints, one position (holonomic) constraint and two velocity (nonholonomic) constraints. Note that this is a bilateral constraint and will push or pull as necessary to keep the point in contact with the plane, and that sticking is enforced regardless of the amount of normal force being generated. If you want to make this unilateral, you must handle switching it on and off separately; when this constraint is enabled it always enforces the contact and no-slip conditions.

There are two mobilized bodies involved. MobiliedBody S, the plane "surface" body, has a plane P fixed to it, with the plane defined by a frame P given relative to body S by the transform X_SP. MobiliedBody B, the "follower" body has a station point F (a vertex) fixed to it, given with respect to body B at location p_BF. The coordinate axes of the plane frame P (fixed in S) are used for parameterization of the Constraint. The z direction Pz of that frame is the plane normal; the Px,Py directions are used to express the tangential velocity; the P frame origin Po provides the height h=dot(Po,Pz) of the plane over the surface body's origin in the direction of the plane normal Pz.

The position constraint equation for contact enforces that the follower point F must always be in the plane P, that is, pz_PF=p_PF[2]=0, or equivalently

    (1) perr = pz_PF = dot(p_SF,Pz)-h

That constraint equation is enforced by an internal (non-working) scalar force acting at the spatial location of the follower point, directed along the plane normal, and equal and opposite on the two bodies at F on B and at the instantaneously coincident point p_SF on S. Because position constraints are not enforced perfectly, contact will occur slightly above or slightly below the plane surface, wherever the follower point is.

The two velocity constraint equations enforce that the follower point has no relative tangential velocity when measured in the plane frame P, that is we want to enforce vx_PF=vy_PF=0. The time derivative of the normal constraint is also enforced at the velocity level so we have vz_PF=0. Taken together the velocity-level constraints are just

    (2) verr = v_PF = ~R_SP * v_SF

Equation (2) is the same as the velocity-level constraints for a ball joint between frame P on S and point F on B. The acceleration-level constraints are just the time derivative of (2), i.e.

    (3) aerr = a_PF = ~R_SP * a_SF

The assembly condition is that the follower point must be in the plane; there is no assembly condition in the tangential direction since those constraints are at the velocity level only.

Constructor & Destructor Documentation

SimTK::Constraint::PointOnPlaneContact::PointOnPlaneContact	(	MobilizedBody &	planeBody,
		const Transform &	defaultPlaneFrame,
		MobilizedBody &	followerBody,
		const Vec3 &	defaultFollowerPoint
	)

Construct a point-in-plane normal constraint and two no-slip friction constraints as described in the Constraint::PointOnPlaneContact class documentation.

SimTK::Constraint::PointOnPlaneContact::PointOnPlaneContact ( )

inline

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

Member Function Documentation

PointOnPlaneContact& SimTK::Constraint::PointOnPlaneContact::setDefaultPlaneFrame ( const Transform & defaultPlaneFrame )

Replace the default plane frame that was supplied on construction.

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

PointOnPlaneContact& SimTK::Constraint::PointOnPlaneContact::setDefaultFollowerPoint ( const Vec3 & defaultFollowerPoint )

Replace the default follower point that was supplied on construction.

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

MobilizedBodyIndex SimTK::Constraint::PointOnPlaneContact::getPlaneMobilizedBodyIndex ( ) const

Return the MobilizedBodyIndex of the plane MobilizedBody.

MobilizedBodyIndex SimTK::Constraint::PointOnPlaneContact::getFollowerMobilizedBodyIndex ( ) const

Return the MobilizedBodyIndex of the follower MobilizedBody.

const Transform& SimTK::Constraint::PointOnPlaneContact::getDefaultPlaneFrame ( ) const

Return the default plane frame as set during construction or by the most recent call to setDefaultPlaneFrame().

const Vec3& SimTK::Constraint::PointOnPlaneContact::getDefaultFollowerPoint ( ) const

Return the default follower point as set during construction or by the most recent call to setDefaultFollowerPoint().

PointOnPlaneContact& SimTK::Constraint::PointOnPlaneContact::setPlaneDisplayHalfWidth ( Real halfWidth )

This affects only generated decorative geometry for default visualization; the plane is really infinite in extent.

If you don't set this the default half width is 1 length unit. Set this to zero to disable any attempt to generate default visualization for the plane.

PointOnPlaneContact& SimTK::Constraint::PointOnPlaneContact::setPointDisplayRadius ( Real radius )

This affects only generated decorative geometry for default visualization; the point is really zero radius.

If you don't set this the default radius is .05 length unit. Set this to zero to disable any attempt to generate default visualization for the point.

Real SimTK::Constraint::PointOnPlaneContact::getPlaneDisplayHalfWidth ( ) const

Return the plane half-width that will be used if we're asked to generate default visualization geometry.

If this is zero we won't generate any plane visualization geometry.

Real SimTK::Constraint::PointOnPlaneContact::getPointDisplayRadius ( ) const

Return the sphere radius that will be used to visualize the follower point if we're asked to generate default visualization geometry.

If this is zero we won't generate any point visualization geometry.

const Transform& SimTK::Constraint::PointOnPlaneContact::getPlaneFrame ( const State & state ) const

Return the plane frame X_SP that is currently in effect for this Constraint.

Note that the origin of the returned frame will be exactly on the plane surface; that is not necessarily where contact occurs since the follower point may be above or below the surface by position constraint tolerance.

const Vec3& SimTK::Constraint::PointOnPlaneContact::getFollowerPoint ( const State & state ) const

Return the plane frame X_SP that is currently in effect for this Constraint.

Note that the origin of the returned frame will be exactly on the plane surface; that is not necessarily where contact occurs since the follower point may be above or below the surface by position constraint tolerance.

Real SimTK::Constraint::PointOnPlaneContact::getPositionError ( const State & state ) const

The returned position error can be viewed as a signed distance.

It is positive when the follower point is above the plane and negative when it is below the plane. The given state must have already been realized through Stage::Position.

Vec3 SimTK::Constraint::PointOnPlaneContact::getVelocityErrors ( const State & state ) const

The velocity error vector is the velocity of the follower point in the contact frame.

The contact frame is parallel to the plane frame but with its origin shifted to the spatial location as the follower point. Note that the coordinates are ordered x-y-z so the first two numbers are the tangential slip velocity and the third is the velocity in the normal direction, with positive indicating separation and negative indicating approach. The z value here is the time derivative of the quantity returned by getPositionError(). The given state must have already been realized through Stage::Velocity.

Vec3 SimTK::Constraint::PointOnPlaneContact::getAccelerationErrors ( const State & state ) const

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

The given state must have already been realized through Stage::Acceleration.

Vec3 SimTK::Constraint::PointOnPlaneContact::getMultipliers ( const State & state ) const

These are the Lagrange multipliers required to enforce the three constraint equations generated here.

For this Constraint they have units of force, but the sign convention for multipliers is the opposite of that for applied forces. Thus the returned vector may be considered the force applied by the follower point to the coincident point of the plane body, expressed in the contact frame.

Vec3 SimTK::Constraint::PointOnPlaneContact::getForceOnFollowerPoint ( const State & state ) const

This is the force applied by the plane body to the follower point, expressed in the contact frame.

For this Constraint, the value returned here is identical to the vector returned by getMultipliers(), but with the opposite sign.

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

Constraint_PointOnPlaneContact.h

Public Member Functions

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation