Cutting a cloth under stress #3161

sin3point14 · 2022-07-22T08:58:41Z

sin3point14
Jul 22, 2022

I was seeing the TriangleSurfaceCutting.scn demo in SOFA framework. I want to model cutting a membrane with a haptic device.
For starters, I want to change this example by disabling gravity(I know how to do this) and stretching the 4 edge points to put the cloth under stress at rest position. So when I cur an incision through the cloth, I can observe a membrane collapsing. How can this be achieved?

Answered by epernod

Nov 4, 2022

The idea is to compute all your position switching from the 3D world coordinates to the local frame of your triangles.
I.e:

you start from the stressed triangle, and your rupture point 3D position
you compute the direction of your cut
you check for triangles in this direction
you navigate using topology structure from one triangle to another and you propagate your cut direction
etc...

In fact the pipeline I just described is used in the Tearing plugin which looks like what you want to do: https://github.com/InfinyTech3D/Tearing
It is implemented somewhere here: https://github.com/InfinyTech3D/Tearing/blob/eba7b4f25cfec15b3d733be2511886b0799dda36/src/Tearing/TearingAlgorithms.inl#L54

Let…

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hugtalbot · 2022-07-25T16:18:34Z

hugtalbot
Jul 25, 2022
Maintainer

Hi @sin3point14

welcome on the SOFA forum!
I am not sure to understand cause "under stress at rest position" sounds contradictory to me.

Do you want to do something like this:

<?xml version="1.0"?>
<Node name="root" dt="0.05" showBoundingTree="0" gravity="0 -0 0">
    <RequiredPlugin name="Sofa.Component.Collision.Detection.Algorithm"/> <!-- Needed to use components [BVHNarrowPhase BruteForceBroadPhase DefaultPipeline] -->
    <RequiredPlugin name="Sofa.Component.Collision.Detection.Intersection"/> <!-- Needed to use components [MinProximityIntersection] -->
    <RequiredPlugin name="Sofa.Component.Collision.Geometry"/> <!-- Needed to use components [TriangleCollisionModel] -->
    <RequiredPlugin name="Sofa.Component.Collision.Response.Contact"/> <!-- Needed to use components [DefaultContactManager] -->
    <RequiredPlugin name="Sofa.Component.Constraint.Projective"/> <!-- Needed to use components [FixedConstraint] -->
    <RequiredPlugin name="Sofa.Component.IO.Mesh"/> <!-- Needed to use components [MeshOBJLoader] -->
    <RequiredPlugin name="Sofa.Component.LinearSolver.Iterative"/> <!-- Needed to use components [CGLinearSolver] -->
    <RequiredPlugin name="Sofa.Component.Mapping.Linear"/> <!-- Needed to use components [IdentityMapping] -->
    <RequiredPlugin name="Sofa.Component.Mass"/> <!-- Needed to use components [DiagonalMass] -->
    <RequiredPlugin name="Sofa.Component.ODESolver.Backward"/> <!-- Needed to use components [EulerImplicitSolver] -->
    <RequiredPlugin name="Sofa.Component.SolidMechanics.FEM.Elastic"/> <!-- Needed to use components [TriangularFEMForceField] -->
    <RequiredPlugin name="Sofa.Component.SolidMechanics.Spring"/> <!-- Needed to use components [TriangularBendingSprings] -->
    <RequiredPlugin name="Sofa.Component.StateContainer"/> <!-- Needed to use components [MechanicalObject] -->
    <RequiredPlugin name="Sofa.Component.Topology.Container.Dynamic"/> <!-- Needed to use components [TriangleSetGeometryAlgorithms TriangleSetTopologyContainer TriangleSetTopologyModifier] -->
    <RequiredPlugin name="Sofa.Component.Visual"/> <!-- Needed to use components [VisualStyle] -->
    <RequiredPlugin name="Sofa.GL.Component.Rendering3D"/> <!-- Needed to use components [OglModel] -->

    <VisualStyle displayFlags="showVisual showBehaviorModels" />
    <DefaultPipeline verbose="0" />
    <BruteForceBroadPhase/>
    <BVHNarrowPhase/>
    <DefaultContactManager response="PenalityContactForceField" />
    <MinProximityIntersection name="Proximity" alarmDistance="0.8" contactDistance="0.5" />
    <Node name="SquareGravity">
        <EulerImplicitSolver name="cg_odesolver" printLog="false"  rayleighStiffness="0.1" rayleighMass="0.1" />
        <CGLinearSolver iterations="25" name="linear solver" tolerance="1.0e-9" threshold="1.0e-9" />
        <MeshOBJLoader name="meshLoader" filename="mesh/square_2594_triangles.obj" scale="10" createSubelements="true" />
        <TriangleSetTopologyContainer  name="Container" src="@meshLoader"/>
        <TriangleSetTopologyModifier   name="Modifier" />
        <TriangleSetGeometryAlgorithms name="GeomAlgo" template="Vec3d" />
        <MechanicalObject name="Mo"/>
        <DiagonalMass massDensity="0.08" />
        <FixedConstraint indices="617 618 57 1301 1302 49" />
        <TriangularFEMForceField name="FEM" youngModulus="60" poissonRatio="0.3" method="large" />
        <TriangularBendingSprings name="FEM-Bend" stiffness="300" damping="1.0" />
        <TriangleCollisionModel />
        <ConstantForceField indices="621" force="-800 -800 0" showArrowSize="0.1"/>
        <ConstantForceField indices="1360" force="800 -800 0"  showArrowSize="0.1"/>
        <Node >
            <OglModel name="Visual" texcoords="@../meshLoader.texcoords" texturename="textures/colorMap.png" />
            <IdentityMapping input="@.." output="@Visual" />
        </Node>
    </Node>
</Node>
```

2 replies

sin3point14 Jul 26, 2022
Author

It does do the trick by stretching the cloth(I reduced the stiffness)

But to do this we had to apply forces to 2 vertices to displace the, is it possible to constraint 2 vertices to 2 fixed locations? for example, in this simulation if I a 3rd force the 2 vertices would end up shifting(new rest position). I want to stretch the cloth and constraint its edges, so it behaves like a fixed stretched membrane, like a drum. Later I'll add logic to cut it, and I want my edges to be fixed even when I cut it.

sin3point14 Jul 26, 2022
Author

Another supplementary question: why do we need TriangularFEMForceField AND TriangularBendingSprings. TriangularFEMForceField has properties like youngModulus and poisonRatio which should effectively describe the property of a material. But then we are also using TriangularBendingSprings to define a stiffness. The documentation says this stiffness defines the stiffness of a spring between each triangle sharing a common edge. But doesn't youngModulus also do that same thing?
Sorry, but I'm trying to understand the components on a theoretic mechanical basis, I know that we can't simulate mechanical properties exactly hence I'd like to know what exactly both of these components do mechanically.

I changed your file to

        <TriangularFEMForceField name="FEM" youngModulus="60" poissonRatio="0.3" method="large" />
        
        <TriangularBendingSprings name="FEM-Bend" stiffness="30" damping="1.0" />

This is what I observed:

Unchanged Scene
Removed TriangularBendingSprings node (the cloth stretches a lot more and the system in unstable)
Removed TriangularFEMForceField node (the cloth stretch is normal but now some triangles are behaving weirdly)

PS: I tried recording a video
But it failed and I found this in my logs

[INFO]    [VideoRecorderFFMPEG] Start recording to D:/Users/Manas/SOFA/v21.12.00/screenshots/ClothStretch__r60_0001.mp4 ( yuv420p, 60 FPS, 5120000 b/s) using D:\Users\Manas\SOFA\v21.12.00/bin/
'D:\Users\Manas\SOFA\v21.12.00/bin/' is not recognized as an internal or external command,
operable program or batch file.
D:/Users/Manas/SOFA/v21.12.00/screenshots/ClothStretch__r60_0001.mp4 written

I have ffmpeg on my path at D:\bin\ffmpeg.exe but somehow sofa is not detecting it

hugtalbot · 2022-07-28T13:57:48Z

hugtalbot
Jul 28, 2022
Maintainer

Hi @sin3point14

A first important point is that the so-called "rest shape" of an object is the reference shape (the positions) of this object when it is undergoing NO force. This rest state is not supposed to change during the simulation.

To create the tension you are looking for, you can avoid applying forces as I did, but you can instead impose a motion of some vertices (e.g. border vertices). You can for instance take a look at the LinearMovementConstraint.

Regarding the need to use both TriangularFEMForceField and TriangularBendingSprings comes from the fact that:

TriangularFEMForceField is a in-plane FEM model of a linear elastic material, therefore only valid in the plane of each triangle of the mesh
TriangularBendingSprings is therefore needed to provide a bending effect, mimicking a thickness for your material. Without it, any out of plane force (e.g. any force with any contribution orthogonal to the plan) would generate instabilities and lead the simulation to diverge

Finally, the issue with video recording (VideoRecorderFFMPEG) looks strange : do you have indeed a video exported at the given path D:/Users/Manas/SOFA/v21.12.00/screenshots/ClothStretch__r60_0001.mp4 written ?

Hugo

0 replies

sin3point14 · 2022-07-29T07:55:26Z

sin3point14
Jul 29, 2022
Author

Thanks a lot for your explanations!

I am trying to integrate this with a geomagic touch haptic device. The cloth is deforming as expected but I can't feel any force feedback. Can you please check the scenes, I can't really figure out the issue as I am basing this of work someone else had done earlier and I'm pretty new to sofa

<?xml version="1.0"?>
<Node name="root" dt="0.05" showBoundingTree="0" gravity="0 -0 0">
    <RequiredPlugin name="SofaBoundaryCondition"/> <!-- Needed to use components [FixedConstraint] -->  
    <RequiredPlugin name="SofaConstraint"/> <!-- Needed to use components [FreeMotionAnimationLoop, LCPConstraintSolver, LocalMinDistance, UncoupledConstraintCorrection] -->  
    <RequiredPlugin name="SofaGeneralDeformable"/> <!-- Needed to use components [TriangularBendingSprings, VectorSpringForceField] -->  
    <RequiredPlugin name="SofaImplicitOdeSolver"/> <!-- Needed to use components [EulerImplicitSolver] -->  
    <RequiredPlugin name="SofaLoader"/> <!-- Needed to use components [MeshOBJLoader] -->  
    <RequiredPlugin name="SofaMeshCollision"/> <!-- Needed to use components [LineCollisionModel, PointCollisionModel, TriangleCollisionModel] -->  
    <RequiredPlugin name="SofaMiscFem"/> <!-- Needed to use components [TriangularFEMForceField] -->  
    <RequiredPlugin name="SofaRigid"/> <!-- Needed to use components [RigidMapping] -->  
    <RequiredPlugin name="SofaUserInteraction"/> <!-- Needed to use components [MechanicalStateController] -->  
    <RequiredPlugin name="SofaOpenglVisual"/>
    <RequiredPlugin pluginName='SofaHaptics'/>
    <RequiredPlugin name="Geomagic plugin" pluginName="Geomagic" />

    <VisualStyle displayFlags="showVisual showBehaviorModels" />
    <DefaultPipeline verbose="0" />
    <BruteForceBroadPhase/>
    <BVHNarrowPhase/>
    <DefaultContactManager response="PenalityContactForceField" />
    <MinProximityIntersection name="Proximity" alarmDistance="0.8" contactDistance="0.5" />
    <LCPConstraintSolver tolerance="0.001" maxIt="1000"/>
    <GeomagicDriver name="GeomagicDevice" deviceName="Default Device" scale="10" drawDeviceFrame="1" positionBase="50 50 5" drawDevice="0" orientationBase="0 0.707 0 -0.707"  />

    <Node name="SquareGravity">
        <EulerImplicitSolver name="cg_odesolver" printLog="false"  rayleighStiffness="0.1" rayleighMass="0.1" />
        <CGLinearSolver iterations="25" name="linear solver" tolerance="1.0e-9" threshold="1.0e-9" />
        <MeshOBJLoader name="meshLoader" filename="mesh/square_2594_triangles.obj" scale="10" createSubelements="true" />
        <TriangleSetTopologyContainer  name="Container" src="@meshLoader"/>
        <TriangleSetTopologyModifier   name="Modifier" />
        <TriangleSetGeometryAlgorithms name="GeomAlgo" template="Vec3d" />
        <MechanicalObject name="Mo"/>
        <DiagonalMass massDensity="0.08" />
        <FixedConstraint indices="617 618 57 1301 1302 49 621 1360" />
        <TriangularFEMForceField name="FEM" youngModulus="60" poissonRatio="0.3" method="large" />
        <TriangularBendingSprings name="FEM-Bend" stiffness="100" damping="1.0" />
        <TriangleCollisionModel />
        <!-- <ConstantForceField indices="621" force="-800 -800 0" showArrowSize="0.1"/>
        <ConstantForceField indices="1360" force="800 -800 0"  showArrowSize="0.1"/> -->
        <Node >
            <OglModel name="Visual" texcoords="@../meshLoader.texcoords" texturename="textures/colorMap.png" />
            <IdentityMapping input="@.." output="@Visual" />
        </Node>
    </Node>


    <!-- ADDED: the Mechanical state Controller gathers events from the Omni driver and populates the Mechanical state -->
    <Node name="Omni">
        <MechanicalObject template="Rigid3d" name="DOFs" position="@GeomagicDevice.positionDevice"/>
        <MechanicalStateController template="Rigid3d" listening="true" mainDirection="-1.0 0.0 0.0" handleEventTriggersUpdate="true"/>
        <Node name="VisuAvatar" activated="false" >
            <MeshObjLoader name="meshLoader_0" filename="mesh/sphere.obj" scale="10" handleSeams="1" />
            <OglModel name="Visual" src="@meshLoader_0" color="gray"/>
            <RigidMapping input="@.." output="@Visual" index="0"/>
        </Node>
        <Node name="RefModel">
            <MeshObjLoader filename="Demos/Dentistry/data/mesh/dental_instrument_centerline.obj"  name="loader"/>
            <MeshTopology src="@loader"  />
            <MechanicalObject src="@loader" name="instrumentRefState1" ry="-180" rz="-90" dz="3.5" dx="-0.3" />
            <RigidMapping />
        </Node>
        <Node name="RefModelRight" >
            <MeshObjLoader filename="Demos/Dentistry/data/mesh/dental_instrument_centerline.obj"  name="loader"/>
            <MeshTopology src="@loader" />
            <MechanicalObject src="@loader" name="instrumentRefState2" ry="-180" rz="-90" dz="3.5" dx="-0.3" dy="0.5" />
            <RigidMapping />
        </Node>
        <Node name="RefModelLeft" >
            <MeshObjLoader filename="Demos/Dentistry/data/mesh/dental_instrument_centerline.obj"  name="loader"/>
            <MeshTopology src="@loader"  />
            <MechanicalObject src="@loader" name="instrumentRefState3" ry="-180" rz="-90" dz="3.5" dx="-0.3" dy="-0.5" />
            <RigidMapping />
        </Node>
    </Node>

    <Node name="Instrument" >
        <EulerImplicitSolver name="ODE solver" rayleighStiffness="0.05" rayleighMass="1.0" />
        <CGLinearSolver name="linear solver" iterations="25" tolerance="1e-10" threshold="10e-10" /> 
        <MechanicalObject name="instrumentState" template="Rigid3d" />
        <UniformMass name="mass" totalMass="0.05" />
        <LCPForceFeedback activate="true" forceCoef="0.1"/> <!-- ADDED : Compute a force-feedback for the device -->
        <UncoupledConstraintCorrection/>
        <Node name="VisualModel" >
            <MeshObjLoader name="meshLoader_1" filename="Demos/Dentistry/data/mesh/dental_instrument.obj" handleSeams="1" />
            <OglModel name="InstrumentVisualModel" src="@meshLoader_1" color="1.0 0.2 0.2 1.0" ry="-180" rz="-90" dz="3.5" dx="-0.3"/>
            <RigidMapping name="MM->VM mapping" input="@instrumentState" output="@InstrumentVisualModel" />
        </Node>
        <Node name="CollisionModel" >
            <MeshObjLoader filename="Demos/Dentistry/data/mesh/dental_instrument_centerline.obj"  name="loader"/>
            <MeshTopology src="@loader"  />
            <MechanicalObject src="@loader" name="instrumentCollisionState1"  ry="-180" rz="-90" dz="3.5" dx="-0.3" />
            <LineCollisionModel contactStiffness="10" />
            <PointCollisionModel contactStiffness="10" /> 
            <RigidMapping name="MM->CM mapping" input="@instrumentState" output="@instrumentCollisionState1" />
        </Node>
        <Node name="RefModelRight" >
            <MeshObjLoader filename="Demos/Dentistry/data/mesh/dental_instrument_centerline.obj"  name="loader"/>
            <MeshTopology src="@loader"  />
            <MechanicalObject src="@loader" name="instrumentCollisionState2"  ry="-180" rz="-90" dz="3.5" dx="-0.3" dy="0.5" />
            <RigidMapping name="MM->CM mapping" input="@instrumentState" output="@instrumentCollisionState2" />
        </Node>
        <Node name="RefModelLeft" >
            <MeshObjLoader filename="Demos/Dentistry/data/mesh/dental_instrument_centerline.obj"  name="loader"/>
            <MeshTopology src="@loader"  />
            <MechanicalObject src="@loader" name="instrumentCollisionState3"  ry="-180" rz="-90" dz="3.5" dx="-0.3" dy="-0.5" />
            <RigidMapping name="MM->CM mapping" input="@instrumentState" output="@instrumentCollisionState3" />
        </Node>
        <VectorSpringForceField  template="Vec3d" object1="@Omni/RefModel/instrumentRefState1" object2="@Instrument/CollisionModel/instrumentCollisionState1" stiffness="10" viscosity="0" />
        <VectorSpringForceField  template="Vec3d" object1="@Omni/RefModelRight/instrumentRefState2" object2="@Instrument/RefModelRight/instrumentCollisionState2" stiffness="10" viscosity="0" />
        <VectorSpringForceField  template="Vec3d" object1="@Omni/RefModelLeft/instrumentRefState3" object2="@Instrument/RefModelLeft/instrumentCollisionState3" stiffness="10" viscosity="0" />
    </Node>  
</Node>

For the ffmpeg issue, I don't have access to that system right now, but afair there was no video file generated there.

4 replies

hugtalbot Aug 9, 2022
Maintainer

Hi @sin3point14 are you still using the binary version v21.12.00 ?
If so, I will do the same answer than here: in the SOFA binary release, the Geomagic plugin only emulates a Geomagic device but no haptic feedback features is available. This is due to the libopenhaptics which is not owned and distributed by the SOFA community.

To have the plugin, it must be compiled aside. @griffinandrew has the same issue, we could see to build only the Geomagic plugin from sources while keeping the SOFA binary release.

epernod Aug 11, 2022
Maintainer

I think there is also a problem in the scene. You should use the FreeMotionAnimationLoop . You can refer to the examples inside the GeomagicPlugin.
Btw do you have force feedback in those examples?

sin3point14 Aug 15, 2022
Author

I have built Sofa from source, I tried the DeformableCubes scene, and it works perfectly. I used that scene as a baseline and tried copy-pasting the haptics-related nodes but got some really weird behaviour of cloth flying in random directions whenever I touched the cloth with my pointer. The haptic device also started going crazy. I tried tuning the parameters, but I couldn't get any close to desirable behaviour. I did not understand FreeMotionAnimationLoop, LCPForceFeedback well(I don't know about lagrangian mechanics) and was stuck in a blind so went ahead with incrementally building a scene from scratch. It would be great if you could help me understand those nodes, at least in the context of my problem or how should I use them :)

epernod Aug 23, 2022
Maintainer

Hi,

in you case you should look more at the scene with the Geomagic liver interaction (something like DeformableLiver.scn, I don't remember the exact name). The deformable object should have a ConstraintCorrection component such as LinearSolverConstraintCorrection for example.

Regarding constraints resolution with Lagrangian multiplier, I suggest to have a look to the documentation here or maybe see with @hugtalbot for help or a training.

sin3point14 · 2022-08-28T20:25:04Z

sin3point14
Aug 28, 2022
Author

For the stress-based incision, I've calculated the triangle of maximum principal stress and want to insert a cut in the direction perpendicular to the principal stress. However, since the cloth is wobbling in 3 dimensions, how can I calculate 2 points:

x distance away from maximum principal stress triangle centroid
in the plane of cloth
vector joining centroid and required point perpendicular to the principal stress direction

Also, I'm using TopologyChangeManager::incisionCollisionModel to insert the cut, but it needs both indices and positions of the 2 endpoints. How can I find the index from a position(which I can get if you answer the above question), so I can supply it to the method? Also, is there some better way to go about this?

@hugtalbot @epernod any advice?

2 replies

hugtalbot Sep 2, 2022
Maintainer

Hey @sin3point14
Sorry I do not recall are you indeed writing this in C++ ?

epernod Nov 4, 2022
Maintainer

The idea is to compute all your position switching from the 3D world coordinates to the local frame of your triangles.
I.e:

you start from the stressed triangle, and your rupture point 3D position
you compute the direction of your cut
you check for triangles in this direction
you navigate using topology structure from one triangle to another and you propagate your cut direction
etc...

In fact the pipeline I just described is used in the Tearing plugin which looks like what you want to do: https://github.com/InfinyTech3D/Tearing
It is implemented somewhere here: https://github.com/InfinyTech3D/Tearing/blob/eba7b4f25cfec15b3d733be2511886b0799dda36/src/Tearing/TearingAlgorithms.inl#L54

Let me know if it helps and do not hesitate to test the Tearing plugin, I would be happy to have some feedback

Answer selected by epernod

@sin3point14 · 2023-12-14T09:31:45Z

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@sin3point14 · 2024-02-26T06:12:03Z

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Cutting a cloth under stress #3161

sin3point14 Jul 22, 2022

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