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Simbody
3.5
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Simbody
3.5
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This constraint represents a bilateral connection between an edge on one body and a non-parallel edge on another. More...
Inheritance diagram for SimTK::Constraint::LineOnLineContact: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:
The default parameters can be overridden in any given State, and modified without affecting Topology; see the "Runtime Changes" section below. | |
| LineOnLineContact (MobilizedBody &mobod_F, const Transform &defaultEdgeFrameF, Real defaultHalfLengthF, MobilizedBody &mobod_B, const Transform &defaultEdgeFrameB, Real defaultHalfLengthB, bool enforceRolling) | |
| Construct a line-on-line constraint as described in the Constraint::LineOnLineContact class documentation. More... | |
| LineOnLineContact () | |
| Default constructor creates an empty handle that can be used to reference any LineOnLineContact Constraint. More... | |
| const MobilizedBody & | getMobilizedBodyF () const |
| Return a reference to the first MobilizedBody to which a line is attached. More... | |
| const MobilizedBody & | getMobilizedBodyB () const |
| Return a reference to the second MobilizedBody to which a line is attached. More... | |
| bool | isEnforcingRolling () const |
| Report whether this Constraint was constructed to generate rolling constraints (otherwise it is frictionless). More... | |
| LineOnLineContact & | setDefaultEdgeFrameF (const Transform &defaultEdgeFrameF) |
| Replace the default frame of the edge attached to the first body, mobod_F, that was supplied on construction. More... | |
| LineOnLineContact & | setDefaultHalfLengthF (Real defaultHalfLengthF) |
| Replace the default half-length for the edge attached to the first body, mobod_F, that was supplied on construction. More... | |
| LineOnLineContact & | setDefaultEdgeFrameB (const Transform &defaultEdgeFrameB) |
| Replace the default frame of the edge attached to the second body, mobod_B, that was supplied on construction. More... | |
| LineOnLineContact & | setDefaultHalfLengthB (Real defaultHalfLengthF) |
| Replace the default half-length for the edge attached to the second body, mobod_B, that was supplied on construction. More... | |
| const Transform & | getDefaultEdgeFrameF () const |
| Return the default frame of the edge attached to the first body, mobod_F, as set during construction or by the most recent call to setDefaultEdgeFrameF(). More... | |
| Real | getDefaultHalfLengthF () const |
| Return the default half-length for the edge attached to the first body, mobod_F, as set during construction or by the most recent call to setDefaultHalfLengthF(). More... | |
| const Transform & | getDefaultEdgeFrameB () const |
| Return the default frame of the edge attached to the second body, mobod_B, as set during construction or by the most recent call to setDefaultEdgeFrameB(). More... | |
| Real | getDefaultHalfLengthB () const |
| Return the default half-length for the edge attached to the second body, mobod_B, as set during construction or by the most recent call to setDefaultHalfLengthB(). More... | |
Runtime Changes | |
These refer to Position-stage discrete state variables that determine the line 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:
You can also modify and examine the default parameters; see the "Construction" section above. | |
| const LineOnLineContact & | setEdgeFrameF (State &state, const Transform &edgeFrameF) const |
| Modify the frame of the edge on the first body, mobod_F, in this state by providing a new Transform X_FEf measured from and expressed in the F frame. More... | |
| const LineOnLineContact & | setHalfLengthF (State &state, Real halfLengthF) const |
| Modify the half-length hf of the edge on the first body, mobod_F, in this state. More... | |
| const LineOnLineContact & | setEdgeFrameB (State &state, const Transform &edgeFrameB) const |
| Modify the frame of the edge on the second body, mobod_B, in this state by providing a new Transform X_BEb measured from and expressed in the B frame. More... | |
| const LineOnLineContact & | setHalfLengthB (State &state, Real halfLengthB) const |
| Modify the half-length hb of the edge on the second body, mobod_B, in this state. More... | |
| const Transform & | getEdgeFrameF (const State &state) const |
| Return the frame of the edge Ef on the first body, mobod_F, as currently set in the given state. More... | |
| Real | getHalfLengthF (const State &state) const |
| Return the half-length of the edge Ef on the first body, mobod_F, as currently set in the given state. More... | |
| const Transform & | getEdgeFrameB (const State &state) const |
| Return the frame of the edge Eb on the second body, mobod_B, as currently set in the given state. More... | |
| Real | getHalfLengthB (const State &state) const |
| Return the half-length of the edge Eb on the second body, mobod_B, 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 &state) const |
| The returned position error can be viewed as the signed distance between the lines. More... | |
| Vec3 | getVelocityErrors (const State &state) const |
| The returned velocity error vector has the time derivative of the quantity returned by getPositionError() in its z coordinate, and violation of the rolling constraints in its x and y coordinates. 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 constraint equations generated here. More... | |
| Vec3 | findForceOnBodyBInG (const State &state) const |
| Return the force vector currently being applied by this constraint to the point of body B that is coincident in space with the contact point Co. More... | |
| Transform | findContactFrameInG (const State &state) const |
| Return the instantaneous contact frame C in the Ground frame. More... | |
| void | findClosestPointsInG (const State &state, Vec3 &Qf, Vec3 &Qb, bool &linesAreParallel) const |
| Calculate the closest points on each of the two lines, measured and expressed in Ground. More... | |
| Real | findSeparation (const State &state) const |
| Calculate the separation distance or penetration depth of the two edges. 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... | |
This constraint represents a bilateral connection between an edge on one body and a non-parallel edge on another.
On construction you may choose whether the connection enforces non-slipping (which we'll call "rolling" here for consistency with other constraints); otherwise the lines will slip against each other. There is always one position (holonomic) constraint equation: the lines containing the edges must touch at some point. That leaves the edges with five unconstrained degrees of freedom (dofs) to take on any relative orientation and to be touching at any point on their lengths. Optionally, there are also two velocity (nonholonomic) constraint equations that prevent relative slip between the edges. In that case there can be five position dofs but only three unconstrained velocity dofs.
Note that this is a bilateral, unconditional connection and will push or pull as necessary to keep the lines in contact. If rolling is being enforced then whatever tangential forces are necessary to keep the lines from slipping will be generated, regardless of the normal force. These constraints can form the basis for unilateral edge-edge contact with Coulomb friction, but additional conditions must be added to determine when they are active.
There are two mobilized bodies involved, we'll call them F and B. Either or both bodies can move or either can be Ground; however, we will orient the signs in our calculations so that we can think of F as "fixed"; the contact normal points towards the "outside" of F and towards the "inside" of B. That means that if we translate B relative to F in the direction of the normal, the signed distance between them increases (separation increases or penetration decreases). That allows us to say, for example, that a positive position error means separation, that a negative normal velocity error means impact, and that a positive force (negative multiplier) means compression.
Each edge E is defined by a center point P, edge direction d, and exterior "space" direction s used to define the sign convention. The s direction points outward from the solid whose two faces meet to form E, along the midplane between those two faces. We also ask for the edge half-lengths which can be used for visualization and for detecting separation caused by slipping of the end of an edge, but don't actually affect the constraint here which works on the lines containing the edges.
F has an edge Ef attached to it with center point Pf, direction df, half length hf, and outward normal sf. B has edge Eb=(Pb,db,hb,sb). The vector between the defining center points is p_PfPb=Pb-Pf, oriented from Ef's center point to Bf's center point. The contact normal n will be a unit vector aligned with w=df X db, with n=sign*w/||w||. Sign is chosen by examining the dot product of w with sf and sb so that translating Eb along +n would increase the signed distance between the edges.
To locate the contact point Co, we want to find the closest points Qf and Qb on each line, with Qf=Pf + tf*df and Qb=Pb + tb*db for some parameters tf and tb. So we are looking for the solution of this equation:
(1) Pf + tf*df + r*n = Pb + tb*db
where r is the separation distance and n is the contact normal defined above. These are three linear equations in three unknowns, saying that we can get from the closest point Qf on Ef to the closest point Qb on Eb by moving up the contact normal direction from Qf to Qb by a signed distance r (that is, if r<0 then we are moving down the contact normal). Since n is perpendicular to both df and db, we can dot both sides of Eqn. (1) with n to get
(2) (Pf + r*n) . n = Pb . n
==> r*(n.n) = (Pb - Pf) . n
==> (3) r = (Pb - Pf) . n [since n is a unit vector]
Similarly, we can dot with n X db and n X df to solve for tf and tb, resp.
(4) (Pf + tf*df) . (n X db) = Pb . (n X db)
==> tf * (df . (n X db)) = (Pb - Pf) . (n X db) (Pb-Pf).(n X db)
==> (5) tf = ---------------- [can use wXdb here instead of nXdb]
df . (n X db)
and
(6) Pf . (n X df) = (Pb + tb*db) . (n X df)
==> tb * (db . (n X df)) = (Pf - Pb) . (n X df) (Pb-Pf).(n X df)
==> (7) tb = - ---------------- [can use wXdf here instead of nXdf]
db . (n X df)
Then the position constraint we want to enforce is r==0, requiring the lines to touch at their closest points. If the constraint were perfectly enforced, then the contact point Co would be at the same location as the two closest points. Since it won't be enforced perfectly, we'll put the contact point at the midpoint between Qf and Qb, so Co=(Qf+Qb)/2. The exact position of Co does not matter for the position constraint, because the normal force is applied along the line including Qf and Qb. However, it will matter (a little) for the friction constraints.
For any given pose, we will define a contact frame C with origin Co whose z axis Cz=n, Cx=df, Cy=n X df. The instantaneous contact frame in Ground is available as the transform X_GC.
The contact constraints here are enforced by a normal multiplier acting along Cz, and optionally two tangential multipliers acting along Cx and Cy respectively. Together these three multipliers can be interpreted as a force expressed in frame C, and applied equal and opposite to bodies F and B at their material points coincident with contact point Co.
The assembly condition is the same as the position constraint: the two lines must meet at some point. No attempt is made to force the contact point to be within the two edges; we only make the lines containing the edges touch somewhere. There is no assembly condition for the tangential constraints since they do not restrict the allowable pose during assembly.
| SimTK::Constraint::LineOnLineContact::LineOnLineContact | ( | MobilizedBody & | mobod_F, |
| const Transform & | defaultEdgeFrameF, | ||
| Real | defaultHalfLengthF, | ||
| MobilizedBody & | mobod_B, | ||
| const Transform & | defaultEdgeFrameB, | ||
| Real | defaultHalfLengthB, | ||
| bool | enforceRolling | ||
| ) |
Construct a line-on-line constraint as described in the Constraint::LineOnLineContact class documentation.
| mobod_F | The first MobilizedBody object to which a contacting edge is attached. We'll call it F, the "fixed" body just to orient the contact; actually either or both bodies can be moving. |
| defaultEdgeFrameF | This Transform X_FEf defines the location and direction of the edge Ef on mobod_F, measured from and expressed in F. The frame origin is the center point Pf of the edge. Its x axis is direction df aligned with the edge; y is unused; z is Ef's outward ("space") direction sf pointing away from the polygonal solid for which Ef is an edge, midway between the two faces whose intersection defines the edge. This parameter provides the edge frame that will be present in a default State; you can modify it later in any particular State. |
| defaultHalfLengthF | This is the half-length hf of edge Ef. The line segment representing the edge thus runs from Pf-hf*df to Pf+hf*df. This parameter provides the half-length that will be present in a default State; you can modify it later in any particular State. |
| mobod_B | The second MobilizedBody object to which a contacting edge is attached. |
| defaultEdgeFrameB | This Transform X_BEb defines the location and direction of the edge Eb on mobod_B, measured from and expressed in B. The frame origin is the center point Pb of the edge. Its x axis is direction db aligned with the edge; y is unused; z is Eb's outward ("space") direction sb pointing away from the polygonal solid for which Eb is an edge, midway between the two faces whose intersection defines the edge. This parameter provides the edge frame that will be present in a default State; you can modify it later in any particular State. |
| defaultHalfLengthB | This is the half-length hb of edge Eb. The line segment representing the edge thus runs from Pb-hb*db to Pb+hb*db. This parameter provides the half-length that will be present in a default State; you can modify it later in any particular State. |
| enforceRolling | Whether to generate tangential forces to prevent the lines from slipping against one another. Otherwise only a normal force is generated and the lines are free to slip. |
Default constructor creates an empty handle that can be used to reference any LineOnLineContact Constraint.
| const MobilizedBody& SimTK::Constraint::LineOnLineContact::getMobilizedBodyF | ( | ) | const |
Return a reference to the first MobilizedBody to which a line is attached.
This refers to the mobod_F that was given in the constructor and cannot be changed after construction.
| const MobilizedBody& SimTK::Constraint::LineOnLineContact::getMobilizedBodyB | ( | ) | const |
Return a reference to the second MobilizedBody to which a line is attached.
This refers to the mobod_B that was given in the constructor and cannot be changed after construction.
| bool SimTK::Constraint::LineOnLineContact::isEnforcingRolling | ( | ) | const |
Report whether this Constraint was constructed to generate rolling constraints (otherwise it is frictionless).
This cannot be changed after construction.
| LineOnLineContact& SimTK::Constraint::LineOnLineContact::setDefaultEdgeFrameF | ( | const Transform & | defaultEdgeFrameF | ) |
Replace the default frame of the edge attached to the first body, mobod_F, that was supplied on construction.
This is a topological change; you'll have to call realizeTopology() again if you call this method.
| LineOnLineContact& SimTK::Constraint::LineOnLineContact::setDefaultHalfLengthF | ( | Real | defaultHalfLengthF | ) |
Replace the default half-length for the edge attached to the first body, mobod_F, that was supplied on construction.
This is a topological change; you'll have to call realizeTopology() again if you call this method.
| LineOnLineContact& SimTK::Constraint::LineOnLineContact::setDefaultEdgeFrameB | ( | const Transform & | defaultEdgeFrameB | ) |
Replace the default frame of the edge attached to the second body, mobod_B, that was supplied on construction.
This is a topological change; you'll have to call realizeTopology() again if you call this method.
| LineOnLineContact& SimTK::Constraint::LineOnLineContact::setDefaultHalfLengthB | ( | Real | defaultHalfLengthF | ) |
Replace the default half-length for the edge attached to the second body, mobod_B, that was supplied on construction.
This is a topological change; you'll have to call realizeTopology() again if you call this method.
| const Transform& SimTK::Constraint::LineOnLineContact::getDefaultEdgeFrameF | ( | ) | const |
Return the default frame of the edge attached to the first body, mobod_F, as set during construction or by the most recent call to setDefaultEdgeFrameF().
| Real SimTK::Constraint::LineOnLineContact::getDefaultHalfLengthF | ( | ) | const |
Return the default half-length for the edge attached to the first body, mobod_F, as set during construction or by the most recent call to setDefaultHalfLengthF().
| const Transform& SimTK::Constraint::LineOnLineContact::getDefaultEdgeFrameB | ( | ) | const |
Return the default frame of the edge attached to the second body, mobod_B, as set during construction or by the most recent call to setDefaultEdgeFrameB().
| Real SimTK::Constraint::LineOnLineContact::getDefaultHalfLengthB | ( | ) | const |
Return the default half-length for the edge attached to the second body, mobod_B, as set during construction or by the most recent call to setDefaultHalfLengthB().
| const LineOnLineContact& SimTK::Constraint::LineOnLineContact::setEdgeFrameF | ( | State & | state, |
| const Transform & | edgeFrameF | ||
| ) | const |
Modify the frame of the edge on the first body, mobod_F, in this state by providing a new Transform X_FEf measured from and expressed in the F frame.
The origin is the location of the edge center point Pf; the x axis is the edge direction df; z is the outward direction sf; y is unused. This overrides the defaultEdgeFrameF in the given state, whose Stage::Position is invalidated.
| const LineOnLineContact& SimTK::Constraint::LineOnLineContact::setHalfLengthF | ( | State & | state, |
| Real | halfLengthF | ||
| ) | const |
Modify the half-length hf of the edge on the first body, mobod_F, in this state.
This overrides the defaultHalfLengthF in the given state, whose Stage::Position is invalidated.
| const LineOnLineContact& SimTK::Constraint::LineOnLineContact::setEdgeFrameB | ( | State & | state, |
| const Transform & | edgeFrameB | ||
| ) | const |
Modify the frame of the edge on the second body, mobod_B, in this state by providing a new Transform X_BEb measured from and expressed in the B frame.
The origin is the location of the edge center point Pb; the x axis is the edge direction db; z is the outward direction sb; y is unused. This overrides the defaultEdgeFrameB in the given state, whose Stage::Position is invalidated.
| const LineOnLineContact& SimTK::Constraint::LineOnLineContact::setHalfLengthB | ( | State & | state, |
| Real | halfLengthB | ||
| ) | const |
Modify the half-length hb of the edge on the second body, mobod_B, in this state.
This overrides the defaultHalfLengthB in the given state, whose Stage::Position is invalidated.
Return the frame of the edge Ef on the first body, mobod_F, as currently set in the given state.
The value is returned as a Transform X_FEf measured from and expressed in the F frame.
Return the half-length of the edge Ef on the first body, mobod_F, as currently set in the given state.
The returned value is the scalar hf.
Return the frame of the edge Eb on the second body, mobod_B, as currently set in the given state.
The value is returned as a Transform X_BEb measured from and expressed in the B frame.
Return the half-length of the edge Eb on the second body, mobod_B, as currently set in the given state.
The returned value is the scalar hb.
The returned position error can be viewed as the signed distance between the lines.
It is positive when the lines are separated and measures their closest approach distance. It is negative when the spheres are interpenetrating and measures the penetration depth. The given state must have already been realized through Stage::Position.
The returned velocity error vector has the time derivative of the quantity returned by getPositionError() in its z coordinate, and violation of the rolling constraints in its x and y coordinates.
If rolling is not being enforced then the x and y components are returned zero; they will not contain the slip velocity in that case since any slip velocity is acceptable. Note that the returned vector is expressed in the instantaneous contact frame C, considered as fixed on body F. That is, this is the velocity of the contact point on body B's sphere in the F frame, expressed in C. The given state must have already been realized through Stage::Velocity.
This vector is the time derivative of the value returned by getVelocityError().
Note that this is different than the acceleration of the point of sphere B at the contact point because the contact point moves with respect to that sphere. The given state must have already been realized through Stage::Acceleration.
These are the Lagrange multipliers required to enforce the constraint equations generated here.
For this Constraint it has units of force, but recall that the sign convention for multipliers is the opposite of that for applied forces. Thus the returned value is the negative of the force being applied to sphere B at the contact point, expressed in the contact frame C. The x,y coordinates are the tangential force used to enforce rolling (or zero if rolling is not being enforced), and the z coordinate is the force needed to enforce contact. Since this is an unconditional, bilateral constraint the multipliers may have any sign and magnitude. The given state must already be realized to Stage::Acceleration.
Return the force vector currently being applied by this constraint to the point of body B that is coincident in space with the contact point Co.
An equal and opposite force is applied to body F at the same location. This is zero if the constraint is not currently enabled. Tangential forces are generated only when rolling is being enforced, but since this result is in the Ground frame all three vector measure numbers may be non-zero regardless. The given state must already be realized to Stage::Acceleration.
Return the instantaneous contact frame C in the Ground frame.
The actual contact point is the origin Co of the returned frame, which is placed at a point midway along the line segment connecting the closest points of the two lines. This does not imply that the normal constraint is satisifed; point Co could be far from the edges. The z direction of this frame is the contact normal; it is perpendicular to the plane formed by directions df and db, aligned so that it points towards the outside of surface F if the objects are separated. The Cx direction is df, and Cy=Cz X Cx to make a right-handed frame. This method calculates a valid value even if this constraint is currently disabled. The given state must already be realized to Stage::Position.
| void SimTK::Constraint::LineOnLineContact::findClosestPointsInG | ( | const State & | state, |
| Vec3 & | Qf, | ||
| Vec3 & | Qb, | ||
| bool & | linesAreParallel | ||
| ) | const |
Calculate the closest points on each of the two lines, measured and expressed in Ground.
When the constraint is perfectly satisfied, these two points will be in the same location. When the lines are parallel these points are not unique; the returned point on each line will be midway between the line origin point and the projection of the other line's origin point on this line, and linesAreParallel will be returned true. This calculates a valid value even if this constraint is currently disabled. The given state must be realized to Stage::Position.
Calculate the separation distance or penetration depth of the two edges.
It is positive when the closest point Qb on line Lb lies outside the surface containing line Lf, as indicated by the adjacent-face normals provided for Lf. It is negative when point Qb lies below both of line Lf's adjacent faces in which case it measures the penetration depth. This calculates a valid value even if this constraint is currently disabled. The given state must be realized to Stage::Position.
1.8.11