Importing Smoothing Groups into Blender

OBSOLETE since Blender 2.79 and Blender Source Tools 2.10. The tools automatically import the smoothing groups properly.

(Learned from TFA)

NOTE: This should make the unsmoothed mesh look like the smoothed mesh but still keep all the faces connected to each other.

Import the properly smoothed mesh by enabling this option: "Preserve SMD normals". (This smooths the mesh but disconnects between the smoothing groups.)

Import the unsmoothed mesh by disabling (unticking) this option: "Preserve SMD normals". (This keeps mesh connected but is not smoothed.)

Select the unsmoothed mesh and enable Auto Smooth. (The Angle value does not seem to matter.)

Select the unsmoothed mesh and add a Data Transfer Modifier.

In the Data Transfer modifier:

    Select the smoothed mesh for Source Object.

    Enable (tick) the Face Corner Data option.

    Select the Topology option beside Face Corner Data.

    Click on Custom Normals below Face Corner Data to enable it.

The Data Transfer modifier keeps the mesh smoothed *and* connected.