1. A method for decoding a bitstream representing a 3D model comprising repetitive structures organized into patterns and instances, an instance being represented as a transformation of a corresponding pattern and a pattern being representative of a geometry of a repetitive structure of said 3D model, the method comprising: decoding from the bitstream a mode flag indicating whether an instance of a pattern uses texture coordinates of the pattern for determining texture coordinates of said instance; and when said mode flag indicates that said instance of the pattern uses texture coordinates of the pattern, determining texture coordinates of the instance using texture coordinates of the pattern, when said mode flag indicates that said instance of the pattern does not use texture coordinates of the pattern, decoding texture coordinates of the instance from said bitstream.