Wpf: how to extract mesh positions from 2 model3d to test for collision?

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WPF

model

collisions

In a WPF scene, I have 2 Model3D in a GroupModel3D: one Model3D is a tool, the other is a workpiece and I want to test when they touch. To test when they touch, I need to inspect every coordinate of Model 1 to determine if they intersect the triangles of Model 2. The problem is to get the positions - i.e. the coordinates - of the triangles of Model 1 and Model 2. The meshes are easily extracted from a GeometryModel3D. But I need to convert a Model3D to a GeometryModel3D to get to the meshes, or else, directly convert a Model3D to MeshGeometry3D.

For example, the code shown below is not accepted since the children of MyGlobalGroup3D are Model3D elements which cannot be converted to GeometryModel3D.


Would anybody have a suggestion ?

What I have tried:

Dim imodel1 As GeometryModel3D = TryCast(MyGlobalGroup3D.Children.Item(indexWork), GeometryModel3D)
Dim imodel2 As GeometryModel3D = TryCast MyGlobalGroup3D.Children.Item(indexTool), GeometryModel3D)