[mattia.riviera]

This is my solution for the problem:

Code:

Dim gm3D As System.Windows.Media.Media3D.GeometryModel3D ' My model already transformed
Dim msh As System.Windows.Media.Media3D.MeshGeometry3D     ' Mesh to subtract

Dim bool As Ab3d.Meshes.BooleanMesh3D = Nothing
         
bool =
    New Ab3d.Meshes.BooleanMesh3D(
        TryCast(
            gm3D.Geometry,
            System.Windows.Media.Media3D.MeshGeometry3D),
        gm3D.Transform)

Call bool.Subtract(msh)

gm3D.Transform = New System.Windows.Media.Media3D.MatrixTransform3D

gm3D.Geometry = bool.Geometry