How to display .stl files so that they can be deformed by mouse dragging

[cdy123456-HUB]

I'm a SOFA beginner. I want to use the finger.stl file that comes with sofa to realize the elastic deformation of the model.
After my attempts, I found that the following code execution effect is not ideal.
The inside of the model seems to be missing some kind of support, and when dragged by the mouse, it collapses into it, like a cloth.
Here's my code.

<?xml version="1.0"?>

<Node name="root" dt="0.01" gravity="0 0 0">
	
	<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.Mass"/> <!-- Needed to use components [MeshMatrixMass] -->
  	<RequiredPlugin name="Sofa.Component.ODESolver.Backward"/> <!-- Needed to use components [EulerImplicitSolver] -->
  	<RequiredPlugin name="Sofa.Component.SceneUtility"/> <!-- Needed to use components [InfoComponent] -->
  	<RequiredPlugin name="Sofa.Component.SolidMechanics.FEM.Elastic"/> <!-- Needed to use components [TriangleFEMForceField] -->
  	<RequiredPlugin name="Sofa.Component.StateContainer"/> <!-- Needed to use components [MechanicalObject] -->
  	<RequiredPlugin name="Sofa.Component.Topology.Container.Dynamic"/> <!-- Needed to use components [TriangleSetTopologyContainer] -->
  	<RequiredPlugin name="Sofa.GL.Component.Rendering3D"/> <!-- Needed to use components [OglModel] -->
	<RequiredPlugin name="Sofa.Component.Mapping.Linear"/> <!-- Needed to use components [IdentityMapping] -->
	<RequiredPlugin name="Sofa.Component.Constraint.Projective"/> <!-- Needed to use components [FixedProjectiveConstraint] -->

	<DefaultAnimationLoop/>

	<MeshSTLLoader name="meshLoader" filename="finger.stl" />
	
	<Node name="finger">
		<EulerImplicitSolver/>
		<CGLinearSolver iterations="200" tolerance="1e-09" threshold="1e-09"/>
		
		<TriangleSetTopologyContainer src="@../meshLoader" name="topo" />
		<MechanicalObject template="Vec3d" name="MechanicalModel" showObject="false" />
		<!--<FixedProjectiveConstraint  name="FixedProjectiveConstraint" indices="1" />-->
		<MeshMatrixMass massDensity="1" topology="@topo"/>

		<TriangleFEMForceField name="FEM" youngModulus="1000" poissonRatio="0.4" method="large"/>

		<Node name="ExtractSurface">	
			<Node name="Visual">
				<OglModel name="VisualModel" color="red"/>
				<IdentityMapping name="Mapping" input="@../.." output="@VisualModel"/>		
			</Node>
		</Node>

	</Node>
</Node>

Please tell me how I can change the Node named finger to achieve the effect I want.

[bakpaul]

Hello !

You are using a TriangleFEMForceField. This only gives stiffness on the element itself, but noting between elements. Meaning that no bending between triangles is computed : thus the resulting 'cloth-like' behavior.

For the lack of internal structure, it might be because the stl file only contains surface triangle and is meant either for contact handling or visualization (I don't know what is in this file, I am just pointing potential issues, but the fact that you are using a TriangleFEMForceField makes me think that you tried with a TerahedronFEMForceField but it didn't work because no Tetrahedron were present in the loaded topo...)

What I suggest is to make sure first that the loaded topology contains volumetric elements: either tetrahedron or hexaedron. Then, use the corresponding forcefield : TerahedronFEMForceField or HexaedronFEMForceField

Tell me how it goes !

[cdy123456-HUB]

Hello！

Thank you very much for your reply. After my attempts, as you said, the lack of internal structure in the .stl file I used led to this result. I used another file containing tetrahedrons and got a satisfactory result.

In addition, I am curious if this means that files like .stl and .obj are not suitable for 3D deformations and are more suitable for simulating rigid bodies that do not require deformations.

[bakpaul]

I am delighted to know that my comment helped you. If so, could you kindly mark it as answer so the next one will know this question have found an answer.

No, they are suitable. It just depends what's inside. Obj can also contain volumetric elements. I don't know much about the stl format, but if it can encodes volumetric element then it is suitable. It only depends on what's inside !

[cdy123456-HUB]

Thank you. I learned a lot from reading your reply.