CGNS stands for CFD General Notation System. It is a general, portable, and extensible standard for the storage and retrieval of CFD analysis data. It consists of a collection of conventions, and free and open software implementing those conventions. It is self-descriptive, cross-platform also termed platform or machine independent, documented, and administered by an international steering committee. It is also an American Institute of Aeronautics and Astronautics recommended practice. The originated in 1994 as a joint effort between Boeing and NASA, and has since grown to include many other contributing organizations worldwide. In 1999, control of CGNS was completely transferred to a public forum known as the . This Committee is made up of international representatives from government and private industry. The CGNS system consists of two parts: a standard format for recording the data, and software that reads, writes, and modifies data in that format. The format is a conceptual entity established by the documentation; the software is a physical product supplied to enable developers to access and produce data recorded in that format. The CGNS system is designed to facilitate the exchange of data between sites and applications, and to help stabilize the archiving of aerodynamic data. The data are stored in a compact, binary format and are accessible through a complete and extensible library of functions. The application programming interface is cross-platform and can be easily implemented in C, C++, Fortran and Fortran 90 applications. A MEX interface also exists for calling the CGNS API in high-level programming languagesMATLAB and GNU Octave. Object oriented interface and Python module exist. The principal target of CGNS is data normally associated with compressibleviscous flow, but the standard is also applicable to subclasses such as Euler and potential flows. The CGNS standard includes the following types of data.
Structured, unstructured, and hybrid grids
Flow solution data, which may be nodal, cell-centered, face-centered, or edge-centered
Multizone interface connectivity, both abutting and overset
Much of the standard and the software is applicable to computational field physics in general. Disciplines other than fluid dynamics would need to augment the data definitions and storage conventions, but the fundamental database software, which provides platform independence, is not specific to fluid dynamics. CGNS is self-describing, allowing an application to interpret the structure and contents of a file without any outside information. CGNS can make use of either two different low-level data formats:
an internally developed and supported method called Advanced Data Format, based on a common file format system previously in use at McDonnell Douglas
