MTEX vs. Bunge Convention edit page

For historical reasons MTEX defines orientations in a slightly different way than they have been defined by Bunge. As explained in topic orientations MTEX defines them as coordinate transformations from the crystal reference frame into the specimen reference frame. In contrast to this Bunge orientations are coordinate transformations from the specimen reference frame into the crystal reference frame. Lets demonstrate this by a simple example:

% consider cubic symmetry
cs = crystalSymmetry('cubic')

% and a random orientation
ori = orientation.rand(cs)
cs = crystalSymmetry
 
  symmetry: m-3m   
  elements: 48     
  a, b, c : 1, 1, 1
 
 
ori = orientation (m-3m → xyz)
 
  Bunge Euler angles in degree
     phi1     Phi    phi2    Inv.
  224.968 99.2493 87.5354       0

This is now an MTEX orientation and can be used to translate crystal coordinates, i.e., Miller indices into specimen coordinates,

% either by multiplying from the left
r = ori * Miller({1,0,0},cs)

% or using the command rotate
rotate(Miller({1,0,0},cs),ori)
r = vector3d
          x         y         z
  -0.143909 0.0832224  0.986085
 
ans = vector3d
          x         y         z
  -0.143909 0.0832224  0.986085

A Bunge orientation is exactly the inverse of an MTEX orientation, i.e.,

ori_Bunge = inv(ori)
ori_Bunge = orientation (xyz → m-3m)
 
  Bunge Euler angles in degree
     phi1     Phi    phi2    Inv.
  92.4646 99.2493 315.032       0

and translates specimen coordinates into Miller indices

ori_Bunge * r
ans = Miller (m-3m)
  h k l
  1 0 0

Euler angles

Since the Euler angles are the most common way to describe orientations MTEX implements them such that the Euler angles of an MTEX orientation coincide with the Euler angles of a Bunge orientation. Thus the Euler angles of orientations in MTEX agree with the Euler angles reported by all common EBSD devices, simulation software, text books and paper.

Matrix notation

Due to the above explained inverse relationship of orientations defined in MTEX and in Bunge convention, a matrix generated from an orientation in MTEX is the inverse, or equivallently, the transpose of the matrix in Bunge notation.

ori.matrix
ori_Bunge.matrix^(-1)
ori_Bunge.matrix'
ans =
   -0.1439    0.7020   -0.6975
    0.0832    0.7109    0.6983
    0.9861    0.0424   -0.1607
ans =
   -0.1439    0.7020   -0.6975
    0.0832    0.7109    0.6983
    0.9861    0.0424   -0.1607
ans =
   -0.1439    0.7020   -0.6975
    0.0832    0.7109    0.6983
    0.9861    0.0424   -0.1607

Misorientations

Since, MTEX orientations translates crystal to specimen coordinates misorientations are defined by the formula

ori1 = orientation.rand(cs);
ori2 = orientation.rand(cs);

mori = inv(ori1) * ori2
mori = misorientation (m-3m → m-3m)
 
  Bunge Euler angles in degree
     phi1     Phi    phi2    Inv.
  239.971 88.2688 150.438       0

as they are commonly defined coordinate transformations from crystal to crystal coordinates. This formula is different to the misorientation formula for Bunge orientations

ori1_Bunge = inv(ori1);
ori2_Bunge = inv(ori2);

mori = ori1_Bunge * inv(ori2_Bunge)
mori = misorientation (m-3m → m-3m)
 
  Bunge Euler angles in degree
     phi1     Phi    phi2    Inv.
  239.971 88.2688 150.438       0

However, both formula result in exactly the same misorientation.

Summary

This list summarizes the differences between MTEX orientations and Bunge orientations.

  • formulas involving orientations - invert orientation
  • orientation Euler angles - unchanged
  • orientation matrix - transpose matrix
  • misorientations - unchanged
  • misorientation Euler angles - take Euler angles of inverse misorientation