International
Tables for Crystallography Volume G Definition and exchange of crystallographic data Edited by S. R. Hall and B. McMahon © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. G. ch. 5.6, p. 551
Section 5.6.2.4. Goniometer geometry functions
a
Stanford Linear Accelerator Center, 2575 Sand Hill Road, Menlo Park, CA 94025, USA, and bDepartment of Mathematics and Computer Science, Kramer Science Center, Dowling College, Idle Hour Blvd, Oakdale, NY 11769, USA |
A CBF/imgCIF file includes a geometric description of the goniometer used to orient the sample during the experiment. Practical use of this information, however, is not trivial as it involves combining data from several categories and analysing in three dimensions the nested axes in which the description is framed (see Section 3.7.3
for a discussion of the axis system). CBFlib provides six functions to facilitate this task:
cbf_construct_goniometer uses the data in the categories DIFFRN_MEASUREMENT, DIFFRN_MEASUREMENT_AXIS, AXIS, DIFFRN_SCAN_FRAME_AXIS and DIFFRN_SCAN_AXIS to construct a geometric representation of the goniometer and initializes the cbf_goniometer handle, goniometer. cbf_free_goniometer frees the goniometer structure. cbf_get_rotation_axis and cbf_get_rotation_range get the normalized rotation vector, and the starting value and increment of the first rotating axis of the goniometer, respectively. The cbf_rotate_vector call applies the goniometer axis rotation to the given initial vector, with the ratio value specifying the goniometer setting from 0.0 at the beginning of the exposure to 1.0 at the end, irrespective of the actual rotation range. Finally, cbf_get_reciprocal transforms the given real-space vector (real1, real2, real3) to the corresponding reciprocal-space vector (reciprocal1, reciprocal2, reciprocal3). As before, the transform corresponds to the goniometer initial position with a ratio of 0.0 and the goniometer final position with a ratio of 1.0.