A method for generating a compressed bitstream from data representing a 3D mesh model, the 3D mesh model including repetitive structures, a repetitive structure being a structure having geometric features that repeat in various positions, scales, and orientations in the 3D model, wherein the repetitive structures are represented by instances of patterns, an instance of a pattern being a transformation of a corresponding pattern, the corresponding pattern being a representative geometry of the corresponding repetitive structure, the method comprising: accessing information related to an instance of a pattern associated with a structure, the pattern being one of a plurality of patterns, the information including a pattern identifier and transformation information associated with the pattern, wherein the transformation information includes information types corresponding to at least one of a reflection part, a translation part, a rotation part, and a scaling part; and generating a bitstream comprising a header portion having an indicator indicative of a mode for packing the information in the bitstream among one of a first data packing mode and a second data packing mode, and a data portion including a pattern identifier and transformation information associated with the pattern disposed in the bitstream according to the indicator, wherein: if the indicator indicates the first data packing mode, generating the bitstream includes, for each one of the instances, grouping together the pattern identifier and its respective transformation information; if the indicator indicates the second data packing mode, generating the bitstream includes grouping together pattern identifiers and grouping together the transformation information of all of the instances based on the information type. accessing information related to an instance of a pattern associated with a structure, the pattern being one of a plurality of patterns, the information including a pattern identifier and transformation information associated with the pattern, wherein the transformation information includes information types corresponding to at least one of a reflection part, a translation part, a rotation part, and a scaling part; and generating a bitstream comprising a header portion having an indicator indicative of a mode for packing the information in the bitstream among one of a first data packing mode and a second data packing mode, and a data portion including a pattern identifier and transformation information associated with the pattern disposed in the bitstream according to the indicator, wherein: if the indicator indicates the first data packing mode, generating the bitstream includes, for each one of the instances, grouping together the pattern identifier and its respective transformation information; if the indicator indicates the second data packing mode, generating the bitstream includes grouping together pattern identifiers and grouping together the transformation information of all of the instances based on the information type. if the indicator indicates the first data packing mode, generating the bitstream includes, for each one of the instances, grouping together the pattern identifier and its respective transformation information; if the indicator indicates the second data packing mode, generating the bitstream includes grouping together pattern identifiers and grouping together the transformation information of all of the instances based on the information type.