G-vectors are the scattering vector associated with the diffraction. The are notes of the reciprocal space or, in direct space, normal to the diffracting plane.

For a given reflection in the crystal, G_hkl is perpendicular to the diffracting place (hkl) and its norm is 2π/d_hkl. The real space coordinate of G_hkl can be calculated from the experimental measurements, namely the x-ray wavelength λ, the diffraction angle 2θ, the azimuth angle η, and the rotation angle ω (see section on experiment geometry) and the detailed calculation in fable_geometry_version_1.0.8.pdf.

The x-ray wavelength λ is known, so is the rotation angle ω. There are issues, however, to evaluate the diffraction angle 2θ and the azimuth angle η. What is measured is the location of a diffraction spot on a detector. Calculating 2θ and η from the location of a diffraction spot on a detector requires calibration.

a mathematical expression of the orientation of a crystal. Those are necessary for assigning orientations to certain crystals.

For the calculation, the software ImageD11 can be used. First, you have to load the peaks you found (e.g. .flt file from PeakSearch and enter the parameters. You can compute the G-vectors by following three steps:

1. Click Transformation –> Assign peaks to powder rings (nothing will happen)
2. Click Transformation –> Compute g-vectors (nothing will happen)
3. Click Transformation –> Save g-vectors. Make sure they get the ending .gve.