Conversion from U3D to PLY is not supported yet :(

Universal 3D (U3D) is a compressed file format standard for 3D computer graphics data.

The format was defined by a special consortium called 3D Industry Forum that brought together a diverse group of companies and organizations, including Intel, Boeing, HP, Adobe Systems, Bentley Systems, Right Hemisphere and others whose main focus had been the promotional development of 3D graphics for use in various industries, specifically at this time manufacturing as well as construction and industrial plant design. The format was later standardized by Ecma International in August 2005 as ECMA-363.

The goal is a universal standard for three-dimensional data of all kinds, to facilitate data exchange. The consortium promoted also the development of an open source library for facilitating the adoption of the format.

PLY is a computer file format known as the Polygon File Format or the Stanford Triangle Format. It was designed to store three-dimensional data from 3D scanners. The data storage format supports a relatively simple description of a single object as a list of nominally flat polygons.