There are three 'Polygon', or Faceted, file types that can be imported into NX. They are VRML, STL and JT. If you can convert the PLY file into one of these formats then perhaps you can do what you're looking for.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA Siemens PLM: UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
