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====== 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 [[processing:indexing_with_grainspotter|Grain indexing with GrainSpotter]] and [[processing:indexing_with_imaged11|Grain indexing with ImageD11]]. Typically, ''gve'' files are generated while [[processing:compute_gvectors|Computing G-vectors]].

Below is an example, extracted from the [[software:imaged11|ImageD11]] manual at [[https://pythonhosted.org/ImageD11/fileformats.html]].

<code>
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
</code>

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 [[software:grainspotter|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.
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