GEOMETRY (EXPERIMENT)

A number of commands are only possible if an experimental geometry has been defined e.g. DIFFRACTION PATTERN which predicts the centres of Bragg peaks on a detector.

GEOMETRY (EXPERIMENT) allows the user to define general aspects of a real or simulated experiment such as energy (or wavelength), sample to detector distance, and pixel sizes.

The centre of the beam on the detector may be defined in one of three different methods:

AVERAGED GRAPHICAL The user clicks on a series of pairs of symmetric points (peaks) and the program calculates the beam centre to be the average of the input coordinates.

ELLIPSE (BEST FIT) The user clicks on five or more coordinates which should lie on an ellipse. From the coordinates entered the best fit ellipse in the least squares sense is found.

GRAPHICAL COORDINATE The user clicks on the estimated centre of the beam (useful for semi-transparent beam-stops).

KEYBOARD The user is prompted for keyboard input of the X and Y coordinates of the beam centre. (The user must know the values by some other method.)

LEAST SQUARES The user clicks on three or more coordinates which should lie on a circle. From the coordinates entered the best fit circle in the least squares sense is found.

(The PEEP command will output angles and corresponding d-spacings once the geometry has been defined.)