Skip navigation links
(CGNS Documentation Home Page) (Steering Committee Charter) (Overview and Entry-Level Document) (A User's Guide to CGNS) (Mid-Level Library) (Standard Interface Data Structures) (SIDS File Mapping Manual) (CGIO User's Guide) (Parallel CGNS User's Guide) (ADF Implementation) (HDF5 Implementation) (Python Implementation) (CGNS Tools and Utilities)

(Brief Description of CGNS) (CGNS Documentation) (CGNS Background) (General CGNS File Mapping Concepts) (Detailed CGNS Node Descriptions) (CGNS File Mapping Figures)

CGNS Background

The information in this section is supplied for the sake of completeness. It is identical with the information found in the Overview.


The purpose of CGNS is to provide a standard for recording and recovering computer data associated with the numerical solution of the equations of fluid dynamics. The format implemented by this standard is (1) general, (2) portable, (3) expandable, and (4) durable.

The CGNS system consists of a collection of conventions, and software implementing those conventions, for the storage and retrieval of CFD (computational fluid dynamics) data. The system consists of two parts: (1) a standard format for recording the data, and (2) 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 standard, applied through the use of the supplied software, is intended to do the following:

Participation and Brief History

The CGNS project originated around 1994-1995 through a series of meetings between Boeing external link and NASA external link that addressed improved means for transferring NASA technology to industrial use. It was held that a principal impediment to technology transfer was the disparity in I/O formats employed by various flow codes, grid generators, and so forth. The CGNS system was conceived as a means to promote "plug-and-play" CFD.

Agreement was reached to develop CGNS at Boeing, under NASA Contract NAS1-20267, with active participation by a team of CFD researchers from

Also participating in the discussions at various times have been researchers from


The principal target of CGNS is the data normally associated with compressible viscous flow (i.e., the Navier-Stokes equations), but the standard is also applicable to subclasses such as Euler and potential flows.

CGNS Version 1.0, released 5/15/98, was limited to problems described by multiblock structured grids. Version 1.1 addresses grids, flowfields, boundary conditions, and block-to-block connection information. Also included are a number of auxiliary items, including nondimensionalization, reference state, and equation set specifications. The extension to time-dependent flows and unstructured grids is addressed in Version 2. Also included are links between CGNS data and CAD geometry. Any mix of the following types of field data can be recorded:

Block connections can be of the following types:

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.