In this section we explain how to extract specific grain boundaries. Therefore we start by importing some EBSD data and reconstructing the grain structure.
close all; plotx2east
% import the data
mtexdata forsterite silent
% restrict it to a subregion of interest.
ebsd = ebsd(inpolygon(ebsd,[5 2 10 5]*10^3));
[grains,ebsd.grainId] = calcGrains(ebsd('indexed'));
% remove very small grains
ebsd(grains(grains.grainSize <= 5)) = [];
% and recompute grains
[grains,ebsd.grainId] = calcGrains(ebsd('indexed'));
% smooth the grains a bit
grains = smooth(grains,4);
% visualize as a phase map
plot(ebsd)
hold on
plot(grains.boundary,'linewidth',2)
hold off

The output of
grains.boundary
ans = grainBoundary
Segments length mineral 1 mineral 2
439 27383 µm notIndexed Forsterite
18 1550 µm notIndexed Enstatite
22 1350 µm notIndexed Diopside
1386 55739 µm Forsterite Forsterite
656 26512 µm Forsterite Enstatite
519 20576 µm Forsterite Diopside
35 1296 µm Enstatite Enstatite
112 4827 µm Enstatite Diopside
28 1250 µm Diopside Diopside
tells us the number of boundary segments between the different phsaes. Those segments with notIndexed phase include also those boundary segments where the grains are cutted by the scanning boundary. To restrict the grain boundaries to a specific phase transistion you shall do
hold on
plot(grains.boundary('Fo','Fo'),'lineColor','blue','micronbar','off','lineWidth',2)
hold off

Similarly we may select all Forsterite to enstatite boundary segements.
hold on
plot(grains.boundary('Fo','En'),'lineColor','darkgreen','micronbar','off','lineWidth',2)
hold off

Note, that the order of the phase names matter when considering the corresponding misorintations
grains.boundary('Fo','En').misorientation(1)
grains.boundary('En','Fo').misorientation(1)
ans = misorientation (Forsterite → Enstatite)
Bunge Euler angles in degree
phi1 Phi phi2
24.399 50.2291 261.351
ans = misorientation (Enstatite → Forsterite)
Bunge Euler angles in degree
phi1 Phi phi2
278.649 50.2291 155.601
In the fist case the misorientation returned is from Forsterite to Enstatite and in the second case its exactly the inverse
The selection of grain boundaries according to specific misorientationsm according to twist / tild character or twinning is explained in linked sections.