Authors: Doug du Boulay
Contact: Doug du Boulay, Crystallography Centre, University of Western Australia, Nedlands 6907, Australia
PREABS is a screen-based interactive X11 display routine for checking and viewing the crystal shape description required for ABSORB. The diffractometer axes may also be rotated.
PREABS is a work in progress. It is intended to permit graphical editing of crystal size and shape in order to accurately model real crystals of ill defined shape. Unfortunately the editing aspect of this program has not been completed. It does however, permit visualization of crystal models constructed via the usual ABSORB face description methods. The crystal model is displayed, embedded within the ABSORB, internal, equivalent diffractometer specification, corresponding to the Busing and Levy (1967) system. The overall view of the crystal and diffractometer can be rotated with left-mouse-click-drag events, and by switching the right-mouse-button mode, the crystal can be rotated about specific diffractometer circle axes. The position of the telescope is adjustable and an image of the crystal through the telescope can be obtained.
Switches the diffractometer coordinate systems on or off. This is a four mode switch, since both the XTAL coordinate system and the actual diffractometer coordinate system may be different. Setting 0 switches both axes systems off. Setting 1 switches the XTAL coords on, setting 2 switchesthe real coords on, while the final setting displays both sets of axes. Drawing the real diffractometer axes requires the presence of the original UB matrix used to measure the reflection data on the xtal archive.
Switches filling of the front display surfaces of the diffractometer circles on or off. This can result in significantly slower rendering.
This control switches on or off the display of diffractometer faces which face away from the viewing direction.
This control switches on or off the crystal face normals and their associated approximate miller indices.
Three viewing modes are available. The default view is an overall view of the whole diffractometer. The second view has an additional reduced image of the crystal in the lower left corner, as seen through the telescope. The third view is a larger view of the crystal through the telescope. Note that the telescope view has greatly reduced functionality over the default diffractometer view.
This is another three state control for switching on/off the labelling of reciprocal lattice points lying near the Ewald sphere surface.
This controls the default functionality of the Right-Mouse-Button. By default this is set to ω but successive selections change it to χ, φ and back to ω. In any particular mode, rotations about the corresponding diffractometer axis are calculated by representing that particular axis circle as a sphere centred on the crystal and projecting forward out of the screen, but constrained to rotate about its axis. Any right-mouse-motion is mapped to rotations of this sphere about the axis in question.