File format for G-vectors

G-vectors are save in a file with a gve extension.

The can be used for indexing grains, as described in the sections on Grain indexing with GrainSpotter and Grain indexing with ImageD11. Typically, gve files are generated while Computing G-vectors.

Below is an example, extracted from the ImageD11 manual at https://pythonhosted.org/ImageD11/fileformats.html.

78.712000 78.712000 78.712000 90.000000 90.000000 90.000000 I
# wavelength = 0.939500
# wedge = -0.051189
# axis 0.000000 0.000000 1.000000
[... the remaining part of the parameter information is snipped ...]
# ds h k l
 0.0179669   -1   -1    0
 0.0179669   -1    0   -1
 0.0179669   -1    0    1
 0.0179669   -1    1    0
 0.0179669    0   -1   -1
 0.0179669    0   -1    1
 0.0179669    0    1   -1
 0.0179669    0    1    1
 0.0179669    1   -1    0
 0.0179669    1    0   -1
 0.0179669    1    0    1
 0.0179669    1    1    0
 0.0254091   -2    0    0
 0.0254091    0   -2    0
 0.0254091    0    0   -2
 [ lots of hkl's snipped ]
#  gx  gy  gz  xc  yc  ds  eta  omega  spot3d_id  xl  yl  zl
-0.006049 -0.006821 -0.011411 1553.000000 1506.534500 0.014605 141.377789 41.000000 35325 211440.500505 -1811.094736 -2266.916293
-0.012846 0.008203 -0.009504 1564.869800 1510.194700 0.017962 121.948198 122.022400 105544 211439.925254 -3027.977786 -1888.286052
0.013156 0.009757 0.007648 1503.726500 1543.564400 0.018077 -64.969351 54.000300 46271 211436.535556 3254.006490 1519.487824
0.000474 0.018005 -0.001647 1500.521000 1525.574600 0.018086 -95.223069 1.993700 3308 211438.759075 3578.198430 -327.094270
-0.003736 0.010752 0.014069 1557.512700 1555.861300 0.018097 38.972120 160.000000 155486 211434.450605 -2261.233048 2795.170225
-0.013099 -0.009687 -0.007903 1566.912500 1513.290200 0.018108 115.878145 53.000000 44665 211439.526323 -3236.750899 -1570.156341
0.017023 -0.001041 -0.006196 1502.350000 1516.761000 0.018145 -109.965181 93.999200 78237 211439.811196 338

Explanations (directly inspired from the ImageD11 manual)

• The first line of the file contains the unit cell parameters and lattice centering (one of P,A,B,C,I,F).
• The wavelength and wedge angle are expected on the next lines (needed to compute ideal two theta, omega and azimuth angles for computed orientations).
• A list of computed theoretical g-vectors for the unit cell with
  • ds = d*= ||G|| = 1/d (expressed in Angstrom)
  • h, k, l values for the unit cell.
• Note that GrainSpotter can override this list of the genhkl option is set in the input file.
• The actual scattering vectors (g-vectors) extracted from the experimental data follow and
  • gx = x-component of scattering vector (along the beam) with all angles at zero (units 1/Angstrom)
  • gy = y-component of scattering vector (toward the door) with all angles at zero (units 1/Angstrom)
  • gz = z-component of scattering vector (roughly up) with all angles at zero (units 1/Angstrom)
  • xc = spatially corrected peak x-position on detector (units: pixels)
  • yc = spatially corrected peak y-position on detector (units: pixels)
  • ds 1/d-spacing - modulus of scattering vector - <math> ds = λ / (2 sin θ)
  • eta = azimuthal angle
  • omega = rotation angle of scan
  • spotid is an spot identifier to follow the individual spot at any process step
  • xl = x-component of scattering vector in the laboratory coordinate system (along the beam) with all angles at zero (units microns)
  • yl = y-component of scattering vector in the laboratory coordinate system (toward the door) with all angles at zero (units microns)
  • zl = z-component of scattering vector in the laboratory coordinate system (roughly up) with all angles at zero (units microns)

These files are written by ImageD11/guitransformer.py and read by ImageD11/indexing.py and GrainSpotter and possibly other programs.