Coordinates extraction

Hello,

I am working with a SOFA scene.scn where a mesh undergoes a rigid translation in 3D space (no deformation), driven by a set of springs.
The scene is loaded in Unity using SofaContext, and the simulation itself runs correctly.

However, I need to retrieve and record the coordinates of this mesh while it is moving, ideally in SOFA coordinates, but Unity coordinates would also be acceptable.

From my observations:
• The Transform values shown in the Unity Inspector are never updated, even though the objects visibly move.
• I cannot find any SofaUnity component or API that exposes the runtime position of an element of the scene.
• This behavior is consistent not only in my own scene, but also in the official SofaUnity demos and tutorials.

Is there a recommended or supported way to access the runtime position (SOFA or Unity coordinates) of an object in a SofaUnity scene.scn?

Thank you in advance for your help.

Hi,

thank you for your explanation. Yes, depending on the template (Rigid3d or Vec3) of your mechanicalObject in SOFA, there are several ways to get the position in the SOFA or Unity world space.
you can check for example this code for a Rigid3d object:

SofaUnity/Core/Scripts/Modules/Controllers/SofaRigidMapper.cs

Lines 72 to 90 in 58c9660

    
           protected void UpdateFromSofa() 
        
           { 
        
               float[] val = new float[7]; 
        
               m_sofaMesh.GetRawPositions(val); 
        
               // Get raw values from SOFA, need to inverse left-right hand coordinate system 
        
               Vector3 worldPos = new Vector3(-val[0], val[1], val[2]); 
        
               // Project world position into SofaContext frame 
        
               Vector3 localPos = m_sofaMesh.m_sofaContext.transform.TransformPoint(worldPos); 
        
               this.transform.localPosition = localPos; 
        
               // Get SOFA quaternion and inverse rotation 
        
               var rotation = new Quaternion(val[3], val[4], val[5], val[6]); 
        
               Vector3 angles = rotation.eulerAngles; 
        
               this.transform.localEulerAngles = new Vector3(angles[0], -angles[1], -angles[2]); 
        
               // Combine current rotation with SofaContext one 
        
               this.transform.rotation = m_sofaMesh.m_sofaContext.transform.rotation * this.transform.rotation; 
        
           }

More generally in the SofaMesh, the GetRawPositions will return position in the SOFA coordinate system

SofaUnity/Core/Scripts/Core/Components/SofaMesh.cs

Lines 187 to 191 in 58c9660

    
           public void GetRawPositions(float[] vertices) 
        
           { 
        
               if (m_sofaMeshAPI != null) 
        
                   m_sofaMeshAPI.GetRawPositions(vertices); 
        
           }

Otherwise the SofaMesh creates a unity MeshFilter and you can access its vertices which will be in the Unity coordinate system:. For example:

SofaUnity/Core/Scripts/Modules/Controllers/SofaMeshController.cs

Line 63 in 58c9660

Vector3 vert = m_unityMesh.mesh.vertices[i];

Let me know if this works
Best regards

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	protected void UpdateFromSofa()
	{
	float[] val = new float[7];
	m_sofaMesh.GetRawPositions(val);

	// Get raw values from SOFA, need to inverse left-right hand coordinate system
	Vector3 worldPos = new Vector3(-val[0], val[1], val[2]);
	// Project world position into SofaContext frame
	Vector3 localPos = m_sofaMesh.m_sofaContext.transform.TransformPoint(worldPos);
	this.transform.localPosition = localPos;

	// Get SOFA quaternion and inverse rotation
	var rotation = new Quaternion(val[3], val[4], val[5], val[6]);
	Vector3 angles = rotation.eulerAngles;
	this.transform.localEulerAngles = new Vector3(angles[0], -angles[1], -angles[2]);

	// Combine current rotation with SofaContext one
	this.transform.rotation = m_sofaMesh.m_sofaContext.transform.rotation * this.transform.rotation;
	}

	public void GetRawPositions(float[] vertices)
	{
	if (m_sofaMeshAPI != null)
	m_sofaMeshAPI.GetRawPositions(vertices);
	}

Coordinates extraction #223

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epernod commented on Jan 15, 2026

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