As for GKS, the GKS-3D standard has an Appendix E metafile. The logical format of the 2D and 3D Appendix E metafiles are the same. However, the contents are incompatible, as in one case points are represented by two values, and in the other by three values. The two types of metafile are clearly distinguishable by inspecting the metafile header record. In all other respects, the control and usage of the 2D and 3D metafiles are the same.
The Computer Graphics Metafile, CGM, will not initially have a 3D version. Therefore, if a CGM metafile driver is added to GKS-3D, the output could contain only a 2D projection. This would be sufficient to make a hardcopy, but only with the viewing parameters chosen when the metafile was created. The GKS-3D Appendix E metafile has never been implemented by GTSGRAL. Nevertheless, an additional output workstation is provided to produce a 2D metafile by carrying out the viewing and projection operations before outputting data to the file. This feature is useful for making hardcopies.