Would be good to have clean methods in dials to extend a post-integration reflection table...

[graeme-winter]

... to include direction cosines, Schwarzenbach and Flack's psi angle, ... etc. Direction cosines w.r.t. the true unit cell vectors or the elements of the crystal setting matrix U would be neat.

This is already implemented in export_sadabs.py and export_xds_ascii.py in util, but quicker and tidier C++ implementations would be highly desirable as the current methods in Python are really very slow.

Clearly there are preconditions for this namely test cases.

[graeme-winter]

• add functions to calculate direction cosines in C++
• add function to calculate psi in C++
• add wrapper to dials/command_line
• if directioncosine{xyz}{id} in reflection table; use
• if schwarzenbach_flack_psi in reflection table; use

Elsewise for last two use existing (slow) Python code; will allow testing more easily.

[graeme-winter]

Direction consines:

Given beam := vector from sample to source; s := vector from sample to diffraction spot; z0 is frame with centroid on;

    UB = experiment.crystal.get_A_at_scan_point(int(round(z0)))
    phi = phi_start + z0 * phi_range
    R = axis.axis_and_angle_as_r3_rotation_matrix(phi, deg=True)
    RUB = S * R * F * UB

    x = RUB * (h, k, l)
    s = (s0 + x).normalize()

    astar = (RUB * (1, 0, 0)).normalize()
    bstar = (RUB * (0, 1, 0)).normalize()
    cstar = (RUB * (0, 0, 1)).normalize()

    ix = beam.dot(astar)
    iy = beam.dot(bstar)
    iz = beam.dot(cstar)

    dx = s.dot(astar)
    dy = s.dot(bstar)
    dz = s.dot(cstar)

[rjgildea]

Is there a test somewhere for the python version of the above? Might be possible to do it using flex vector operations avoiding the need to write new C++ code.

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