The -Y switch suppresses the creation of Steiner points on the exterior boundary. Interior Steiner points may still be created.

This switch is useful when the mesh boundary must be preserved so that it conforms to some adjacent mesh.

Specify this switch twice (`-YY') to prevent all boundary splitting, including interior boundaries.

You can use -Y together with -q switch (to improve the quality of the mesh), TetGen will try, but the resulting mesh may contain tetrahedra of poor quality. However, it works well if all the boundaries are previously subdivided into well shaped and closely spaced patches.