AttachProjectiveConstraint

This component belongs to the category of Projective Constraint. The AttachProjectiveConstraint works with a pair of objects and it projects the degrees of freedom (e.g. position) and their derivatives (e.g. velocity), so that both objects are attached. As being a projective constraint, this projective constraints ensures a geometrical connection between both objects at the end of the time step but it does not integrate the physics of both object (contrary to Lagrange based constraints).

Data

The AttachProjectiveConstraint can be initialized using three input data:

object1: link to the first model (MechanicalModel)
object2: link to the second model (MechanicalModel)
indices1: corresponding to the indices of the source points on the first model
indices2: corresponding to the indices of the fixed points on the second model
constraintFactor: allows for the partial application of the constraint using this factor per pair of points constrained (0=the constraint is released. 1=the constraint is fully constrained)
twoWay:
if true, this boolean projects the constraint vertices of both object1 and object2 towards their average degrees of freedom and derivatives:
```
Deriv corr = (dx2-dx1)*0.5*responseFactor*getConstraintFactor(index);
      dx1 += corr;
      dx2 -= corr;
```
if false, the position of the object1 are projected onto the object2. Therefore, object2 only follows object1 without affecting the motion of object1
```
dx2 = Deriv();
```

Usage

The AttachProjectiveConstraint requires two MechanicalObjects so that both degrees of freedom can be accessed and projected to the attached configuration. An integration scheme and a solver are also necessary to solve the linear system at each time step.

Example

This component is used as follows in XML format:

<AttachProjectiveConstraint name="AttachProjectiveConstraint" object1="@M1" object2="@M2" indices1="0 1 2" indices2="10 11 12" constraintFactor="1 1 1"/>

or using SofaPython3:

node.addObject('AttachProjectiveConstraint', object1="@M1", object2="@M2", indices1="0 1 2", indices2="10 11 12", constraintFactor="1 1 1")

An example scene involving a AttachProjectiveConstraint is available in examples/Component/Constraint/Projective/AttachProjectiveConstraint.scn

Target: Sofa.Component.Constraint.Projective

namespace: sofa::component::constraint::projective

parents:

PairInteractionProjectiveConstraintSet

Data:

Name	Description	Default value
name	object name	unnamed
printLog	if true, emits extra messages at runtime.	0
tags	list of the subsets the objet belongs to
bbox	this object bounding box
componentState	The state of the component among (Dirty, Valid, Undefined, Loading, Invalid).	Undefined
listening	if true, handle the events, otherwise ignore the events	0
group	ID of the group containing this constraint. This ID is used to specify which constraints are solved by which solver, by specifying in each solver which groups of constraints it should handle.	0
endTime	The constraint stops acting after the given value. Use a negative value for infinite constraints	-1
indices1	Indices of the source points on the first model
indices2	Indices of the fixed points on the second model
twoWay	true if forces should be projected back from model2 to model1	0
freeRotations	true to keep rotations free (only used for Rigid DOFs)	0
lastFreeRotation	true to keep rotation of the last attached point free (only used for Rigid DOFs)	0
restRotations	true to use rest rotations local offsets (only used for Rigid DOFs)	0
lastPos	position at which the attach constraint should become inactive
lastDir	direction from lastPos at which the attach coustraint should become inactive
clamp	true to clamp particles at lastPos instead of freeing them.	0
minDistance	the constraint become inactive if the distance between the points attached is bigger than minDistance.	-1
positionFactor	IN: Factor applied to projection of position	1
velocityFactor	IN: Factor applied to projection of velocity	1
responseFactor	IN: Factor applied to projection of force/acceleration	1
constraintFactor	Constraint factor per pair of points constrained. 0 -> the constraint is released. 1 -> the constraint is fully constrained

Links:

Name	Description
context	Graph Node containing this object (or BaseContext::getDefault() if no graph is used)
slaves	Sub-objects used internally by this object
master	nullptr for regular objects, or master object for which this object is one sub-objects
mechanicalStates	List of mechanical states to which this component is associated
object1	First object associated to this component
object2	Second object associated to this component