VRML general position/ symmetry diagrams of the 80 layer groups

The crystallographic problem: The standard representations of the general position and symmetry diagrams of three-dimensional groups are two-dimensional diagrams. These are projections onto a plane of, respectively, the general positions and the symbols of the symmetry elements. This is the case for space groups (International Tables for Crystallography, 1995) and for layer groups (Weber, 1929; Wood, 1964; Chapuis, 1996; Grell et al., 1988; International Tables for Crystallography, 1999). Three-dimensional diagrams of only the general position diagrams of the layer groups have been produced by Litvin & Litvin (1993). With this new program we have incorporated both the general position and symmetry diagrams into one three-dimensional diagram for each layer group. Each diagram can be rotated and zoomed to aid the visualization of the general positions and the symmetry of the 80 layer groups. Method of solution: The three-dimensional diagrams were developed using a commercial product (WalkThrough Pro by Virtus Corporation) and converted into VRML format. The general positions are represented by spheres and three-dimensional symbols were introduced and used to represent the symmetry elements. Software environment: Needed to view the diagrams are a World Wide Web (WWW) browser with a VRML viewer plug-in, for example, Netscape with Cosmo, both widely available on the internet. Each diagram is individually loaded from hard disk and viewed within the browser. Hardware environment: The diagrams can be viewed on any platform supporting a WWW browser with a VRML viewer plug-in. Stored on a hard-disk drive, the 80 files use 65 Mbytes of space. Program specifications: The diagrams are stored on a hard disk and loaded individually into a web browser and viewed with a VRML viewer plug-in. Documentation: A symbol file lists the sequential numbering and symbols of the 80 layer groups and the symbols used to represent the positions and symmetry elements. Availability: Zipped files of the 80 diagrams and an Adobe Acrobat readable symbol file containing the documentation can be downloaded from http://www.bk.psu.edu/faculty/litvin. Alternatively, these files can be obtained by sending three formatted 1.44 Mbyte 3.5″ disks to the correspondence author (DBL). Nonzipped files can be obtained by sending a single 100 Mbyte ZIP disk to the correspondence author.