LAYERGPD– a program to visualize the three-dimensional layer group general position diagrams

Abstract

Documentation:The write up for MACINPLOTII is approximately 800 lines and can be supplied as an ASCII file or a MS Word 5.0 document.* Availability: Copies of the program can be obtained by writing to the author. The program and documentation will be supplied on a 3.5 in double-sided double-density floppy disk formatted for the Macintosh. A nominal fee will be charged to cover the cost of the disk, or a blank disk can be sent with the request. In addition, the program has been deposited at the University of Illinois NCSA facility and can be accessed via standard file-transfer protocol (ftp.ncsa.uiuc.edu). Crystallography, 1989) and for the layer groups (Weber, 1929;Wood, 1964;Chapuis, 1966; International Tables for Crystallography, 1993). A second twodimensional perspective general position diagram for some layer groups has been given by Grell, Krause & Grell (1988). The goal in developing LAYERGPD was to overcome, for the layer groups, the constraint of a single parallel view of the general positions. We provide the user with options to choose the orientation and type of view, parallel or projective, of the threedimensional general positions. Keywords Method of solution:A PHIGS (programmer's hierarchical interactive graphics system)-based development product (Z-PHIGS by Weiss Software, LL~beck, Germany) was used to create the three-dimensional general position diagrams. At each position, an atom is represented by a multicolored asymmetric triangular pyramid to aid visualization of the symmetry relationships among the general positions.Software environment: LAYERGPD was written in TurboPascal6.0 and is compiled. The PHIGS system necessary to view the general positions is included. There are no overlays.Hardware environment: The program runs under MS-DOS 3.1 or higher on an IBM-compatible PC with a math coprocessor, 2 Mbytes of expanded memory and at least a VGA color monitor. As this is a graphics-intensive program, a 486/25 or better microprocessor is recommended. If stored on hard disk, the program takes up 680 kbytes of disk space.The single view can be rotated independently about all three coordinate axes, zoomed and set to either a parallel or projective view. Documentation:A 'readme' file is provided with initial instructions on running the program from disk or installing it onto and running it from a hard drive. International Tables for Crystallography (1989). Vol. A, 2nd ed., edited by T. Hahn. Dordrecht: Kluwer Academic Publishers. J. Appl. Cryst. (1993). 26, 498 New GK 311/M All-Round Goniospectrometer for Colour Availability: International Tables for Crystallography New Commercial Products Measurement of Special-Effect PaintsSurfaces with pronounced anisotropic scattering, such as metallic and pearl-

PINCER: a portable data-acquisition program based on a command language interpreter

“…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.…”