Importing Crystal Orientations

A list of crystal orientations usually arrives as a text file with one orientation per row. Unlike an EBSD map, the list has no spatial positions. Importing it requires the numeric representation, the crystal symmetry, and the reference frames in which the numbers were defined.

This page assumes the orientation map introduced in Defining Orientations and the Euler-angle conventions from Defining Rotations. It uses a three-column file of Bunge Euler angles in degrees.

plottingConvention.default('y↑→x');

% load the quartz symmetry and its crystal reference frame from a CIF file
cs = crystalSymmetry.load('quartz.cif');

Name the Columns

The file contains three numeric columns but no header. Their names tell orientation.load that the columns are the Bunge angles \((\varphi_1,\Phi,\varphi_2)\).

fname = fullfile(mtexDataPath,'orientation','Tongue_Quartzite_Bunge_Euler');

ori = orientation.load(fname,cs,'ColumnNames',{'phi1','Phi','phi2'})

ori = orientation (Quartz → y↑→x)
  size: 382 × 1

The display reports a \(382 \times 1\) orientation array. It also identifies the quartz crystal symmetry and the specimen frame. MTEX stores all 382 orientations in this one vectorized object.

Check the Imported Texture

A pole figure is a useful first sanity check, although it cannot prove a convention by itself. Here the \((0001)\) and \((10\bar{1}0)\) poles should show the texture carried by the imported orientations.

plotPDF(ori,Miller({0,0,0,1},{1,0,-1,0},cs));

Notice that the \((0001)\) poles concentrate around ND, whereas many \((10\bar{1}0)\) poles lie closer to the rim. The imported population is therefore textured rather than randomly distributed.

What the Options Are For

For Euler input, the three angle columns are mandatory. Further named columns are returned in a struct when a second output is requested, as in [ori,properties] = orientation.load(...). The field names are converted to lower case and have whitespace removed.

The names and positions solve different problems. For example, 'Columns',[4 2 7] selects physical columns 4, 2, and 7, while 'ColumnNames',{'phi1','Phi','phi2'} assigns their meanings in that order.

The generic importer advertises quaternion columns named {'Quat real','Quat i','Quat j','Quat k'}. In the current implementation, however, that path passes all four columns as one matrix to a constructor that expects four arrays and raises an error. Until it is fixed, read the numeric columns separately and construct orientation(quaternion(a,b,c,d),cs). Quaternions avoid the Euler-angle sequence and angular-unit questions, but they do not identify the mapping direction or either reference frame.

Four Questions to Answer Before Trusting the Result

A plain numeric file does not contain enough information to distinguish several valid interpretations. All four questions below must be answered from its header, accompanying documentation, or a known physical feature.

The generic text importer currently applies |'passive'| twice, so the
two inversions cancel and the option has no effect. Until that defect is
fixed, import first and use |ori = inv(ori)| only when an independent
convention check establishes that the stored map is the inverse.

A known direction provides the strongest check. Verify that one indexed crystal direction maps to the specimen direction observed in the experiment. A plausible pole figure alone cannot distinguish every wrong combination of convention and frame.

References

Next

Writing orientations back to a file is Export. Orientations measured on a grid across a specimen are imported as a map instead; see Importing EBSD Data.