Long Term Archival
Archiving CAD data is a bigger challenge than performing ordinary backups. There are some factors to keep in mind so you don't wind up with a collection of inaccurate or irretrievable CAD models. In addition to the storage medium and the archiving methodology, a major consideration is the format to archive CAD models. Native CAD data will be obsolete in a few years and copy the installation media for the applications that create the data and the operation system environment is a non-solution. STEP or JT are currently the main long therm archiving formats use in engineering and manufacturing industry.
Historically only 2D drawing data has been archived in formats like TIFF and CGM. Development of 3D data content leads to a change of methods and tools:
- before 1980: Mainly manual paper drawings and microfilm;
- between 1980-1995: Mainly 2D CAD drawings, a minor number of manual paper drawings and additionally 3D surface CAD design;
- As from 1995-2006: The usage of 3D solid & assembly CAD design, generated 2D drawings from 3D master models are used;
- afterwards the usage of 3D solid & assemblies with extended GD&T design information might be implemented;
So neutral formats such as STEP and JT are currently considered the safest formats for long term storage, however choosing a format is not enough. Automated validation and checking procedures need to be introduced to prevent storage of inaccurate, corrupt or invalid legacy data.
LOTAR is an international consortium to develop and maintain standards for long-term archiving (LTA) of 3D CAD data. These standards define archiving and retrieval processes. The documents for the standard are published as the EN 9300 series and NAS 9300 series (National Aerospace Standard).
LOTAR members are Airbus, BAE Systems, Boeing, Dassault Aviation, EADS, Eurocopter, General Dynamics, Goodrich, IAI, Lockheed Martin, SAFRAN, Sandia, and Spirit.
Document any quality defects in the design model to set appropriate expectations for the reusability of the archive data. Verify that any derived forms of the design model, e.g. STEP, are equivalent in quality and shape to the master model. If using STEP, add validation properties to the STEP model which can be used by a future recipient to validate that a future translated (imported STEP) CAD model is equivalent to the master model. These validation properties could also be used to verify the equivalence of any archive data format conversions which are required to maintain the archive over time.
