There are a number of different file formats which can be used to transfer data between Mechanical CAD systems (e.g.: STEP, IGES, DXF, etc.) Most file formats can be produced in a variety of "flavors". Before generating any type of interchange data, the following items must be addressed:
Another very important thing to remember is that this type of translation does not provide bi-directional integration of applications. Yes, these translations can be performed in both directions, but in most cases data is lost or filtered during each translation. For example, at this time there is no file format supported to transfer parametric data contained in a parametric solid. This means, if a parametric solid model is translated into a STEP file and then read directly back into the Parametric CAD Solid Modeler, all parametric information is lost. [Editor's note: extensions to STEP to support parametric data are being developed, but will most likely not appear in COTS STEP translators until 1999 at the earliest. --Steve W.]
Answering the above questions will help in determining what file format to use and how the data should to be represented in the interchange file. Generate and transfer only the data necessary and keep it as simple as possible. It should also be noted, that any translation of geometry between two CAD systems, whether using STEP, IGES, etc., requires testing to develop the right combination of parameters for each translator. A STEP file suitable for importing into CAD Vendor A may not import properly into CAD Vendor B.
The following is a list of CAD representations and some associated file formats to support them:
| Representation | File Formats |
|---|---|
| Parametric Solid Models | Not supported at this time |
| Solid Models | STEP (Some IGES translators) |
| Surface Models | STEP, IGES |
| Wireframe Models | STEP, IGES, DXF |
| Tessellated Models | VRML, STL |
The following is a list of common functionality needed after translation and the associated CAD representations which support them:
| Functionality Needed | Representations Supporting It |
|---|---|
| Mass Properties | Solid Models |
| Detail Design | Solid Models, Surface Models, Wireframe Models |
| Manufacturing | Solid Models, Surface Models, Wireframe Models |
| Assembly Integration | Solid and Surface Models |
| Meshing | Solid and Surface Models |
| 3D Shaded images | Solid, Surface and Tessellated Models |
| Dimension Query | Solid, Surface, Wireframe and Tessellated Models* |
| WEB Access | Tessellated Models, Raster images, Vector images |
*Note: Dimensions can be queried from Tessellated Models, but accuracy becomes an issue due to the approximation of the actual model. Also, certain features such as rounds are converted and radius informaion is not accessible.
Obviously, the best way to share data is by using the same CAD application. If this is not possible, solid models via STEP provide the most functionality after translation of CAD data. If either system does not support solid models, the data must be "filtered" which reduces the amount of functionality and data is lost.
Understanding what the data will be used for, the capabilities of the CAD systems and the limitations introduced from the data translation are the key ingredients for a successful transfer. If mass properties must be calculated using imported data, then transfer of solid models is the only way to satisfy this requirement without having to rebuild geometry. Consideration must be placed on what functionality is required with the imported data and the amount of rework that is necessary to support it.
(HTML Translation by Steve Waterbury)
Webmaster: Stephen Waterbury (email: stephen.c.waterbury@nasa.gov)