Select > Exterior Poly-Face command selects exterior poly-faces region of mesh data. It can be used on volume reconstructed mesh or mesh of multiple layers.

1.

Select Select > Exterior Poly-Face in the menu or click the icon  in the toolbar.

2.

Set Initial Radius to 10, Expand Radius to 5 and Tolerance to 0.3.

3.

Click OK and Edit > Copy to copy selected outside surface.

4.

Exit Mesh mode and click Edit > Paste.

·   Initial Radius – You can use Initial Radius value to extract the outer region roughly.

·   Expand Radius – Expand Radius can be used to get more detailed information of the outer region. But this radius value should not be bigger than the hole radius. If it is bigger, it will extract the inner radius.

·   Tolerance – Margin used to expand the region.