From SOFAWiki

Description

This engine separate topology in two parts, considering a ROI, a topology inside and a topology outside the ROI which can be a sphere or a box

ROI used in this engine are similar to BoxROI and SphereROI
Topological primitives handle are now:

- dofs/vertices
- edges
- triangles
- tetrahedra

Input Data's

• box

Box defined by two points (xmin,ymin,zmin, xmax,ymax,zmax).

• centers

Center(s) of the sphere(s).

• radii

Radius(i) of the sphere(s).

• direction

Edge direction(if edgeAngle > 0).

• normal

Normal direction of the triangles (if triAngle > 0)".

• edgeAngle

Max angle between the direction of the selected edges and the specified direction.

• triAngle

Max angle between the normal of the selected triangle and the specified normal direction.

Input topology:

• position/rest_position

Rest position coordinates of the degrees of freedom

• edges

Edge Topology array.

• triangles

Triangle Topology array.

• tetrahedra

Tetrahedron Topology array.

Input parameters

For display:

• drawROI

If true, Draw ROI(s).

• drawPoints

If true, Draw Points.

• drawEdges

If true, Draw Edges.

• drawTriangle

If true, Draw Triangles.

• drawTetrahedra

If true, Draw Tetrahedra.

• drawSize

Rendering size for box and elements.

For behaviour:

• localIndices

If true, will compute local dof indices in topological elements. (see examples below)

Output Data's

• indices

Indices of the points contained in the ROI.

• edgeIndices

Indices of the edges contained in the ROI.

• triangleIndices

Indices of the triangles contained in the ROI.

• tetrahedronIndices

Indices of the tetrahedra contained in the ROI.

• pointsInROI

Points contained in the ROI.

• pointsOutROI

Points contained out of the ROI.

• edgesInROI

Edges contained in the ROI.

• edgesOutROI

Edges contained out of the ROI.

• trianglesInROI

Triangles contained in the ROI.

• trianglesOutROI

Triangles contained out of the ROI.

• tetrahedraInROI

Tetrahedra contained in the ROI.

• tetrahedraOutROI

Tetrahedra contained out of the ROI.

• nbrborder

If localIndices option is activated, will give the number of vertices on the border of the ROI (being the n first points of each output Topology).

Simple Examples

Examples using this engine can be found in:

Sofa/examples/Components/engine/SubsetTopology.scn

Same scene, but using the option localIndices:

 Sofa/examples/Components/engine/SubsetTopology_localIndicesOption.scn

More complex Example

This example shows how, from a simple mesh, split the input topology into two independent topologies using the engine SubsetTopology and then use different kind of behaviours.

Sofa/examples/Components/engine/SubsetTopology_refiningMesh.scn

For example, here we take a cylinder composed of Tetrahedra and we use tetrahedral finite element on one part of this cylinder and hexahedra finite element on the other part, using a sparse grid.
As you can see this trick could be use to have a global coarse behaviour of an object and just refine one part wanted for observation. These changes, resulting in much faster computation of the global system.
To to this, you need to use the localIndices option of the SubsetTopology engine. And then basically:

Put the MeshLoader and the engine in the parent node:

<Node name="Group">
	  <MeshGmshLoader name="meshLoader"  filename="mesh/truthcylinder1.msh"/>
	  <SubsetTopology template="Vec3d" box="-5 -20 -5 5 -10 5"  src="@meshLoader" rest_position="@meshLoader.position"  name="Subset" localIndices="1"/>
</Node>

Then create two child nodes for the inside and the outside topology, regarding the ROI.

Inside topology:

<Node name="Group">
		<Node name="in">
		  <MechanicalObject template="Vec3d" name="mecaObj1" position="@../Subset.pointsInROI" />
		  <TetrahedronSetTopologyContainer name="Container"
						   position="@mecaObj1.position" tetrahedra="@../Subset.tetrahedraInROI"/>		  
		  <TetrahedronSetTopologyModifier name="Modifier" />
		  <TetrahedronSetTopologyAlgorithms template="Vec3d" name="TopoAlgo" />
		  <TetrahedronSetGeometryAlgorithms template="Vec3d" name="GeomAlgo" drawTetrahedra="0"/>
 
		  <TetrahedronFEMForceField name="FEM" youngModulus="1116" 
                  ...
</Node>

Outside topology:

<Node name="Group">
		<Node name="Out">
		  <MechanicalObject template="Vec3d" name="mecaObj2" />
		  <SparseGridTopology	n="4 7 4"  vertices="@../Subset.pointsOutROI"
					name="name" drawHexahedra="0"/>
		  <UniformMass totalmass="15" />		  
		  <HexahedronFEMForceField template="Vec3d" name="FEM"  youngModulus="200" />
 
		  <Node name="tetra">		    
		    <TetrahedronSetTopologyContainer name="Container"
						   position="@../../Subset.pointsOutROI" tetrahedra="@../../Subset.tetrahedraOutROI"/>
                   ....		    
</Node>

And finally use springs for example to link both "objetcs". The Data nbrBorder give you the number of vertices which where on the border of the subdivision. Thus, these vertices are present in both topologies and are placed as the n first vertices.