spec

Software for Diffraction

4.7. - Cut Points



The angles -90° and +270° are at the same position on a circle, but if a motor in spec is sitting at 0°, it will move counter-clockwise by 90° to get to the -90° position and clockwise by 270° to get to the +270° position.

By setting a lower cut point for a particular motor, you can choose what value on the circle the four-circle angle calculations will produce. That is, the calculations will place the angle between the lower cut point and that value plus 360°.

Cut points can be set for the θ, χ and φ four-circle angles. For the 2θ angle, the lower cut point is fixed at -180°. For the azimuth-fixed modes, there is pseudo-cut point for the azimuthal angle. If the cut point is less than zero, the calculated azimuth will be between -180° and 0°, otherwise the azimuth will be between 0° and +180°.


The default cut points are shown below.
 Angle   Default Cut Point 

 θ   -180 
 χ   -180 
 φ   -180 
 ψ   0 

The macro cuts can be used to set or display the cut points. With no arguments, it displays the current cut points. Two arguments are used to set a single cut point. Four arguments set all cut points.
1.FOURC> cuts
Cut Points: th chi phi azimuth -180 -180 -180 0 2.FOURC> cuts phi 90
or
3.FOURC> cuts -180 -180 90 0
4.FOURC>