Use of "omega" in master pattern simulation and spherical indexing

[cgri2]

Hello,

I have a question about the use of "omega" in programs within the EMSoft and EMSphInx packages. From my understanding, "omega" which is described as the "angle between normal of sample and detector" in the EMSoft documentation corresponds to the azimuthal angle of the detector (as EDAX applications call it). The EBSD detector that I am using has a 2 degree azimuthal angle relative to the normal of the stage tilt axis (sample normal). I have simulated two master patterns using EMSoft with the same exact parameters except for the azimuthal angle: in one simulation, I left omega as 0, and for the other Monte Carlo .nml input file, I specified omega as -2. Then, I converted the h5 master pattern files to the spherical master pattern .sht files. The same data set was indexed using EMSphInx with the same parameters except for the two different master patterns. The spherical indexing solutions are identical. I then used the EMSoft program EMEBSD to output simulated patterns of the indexed orientations to compare with the experimental patterns. The simulated patterns for the same orientation but using the two different master patterns are different. I have attached short videos of the simulated patterns compared to the experimental patterns, where you can see a significant shift in the one where omega=2. This tells me that the master patterns are different due to the 2 degree azimuthal angle and that these differences are reflected in the simulated patterns of the particular orientation generated by the EMEBSD program. (I noticed that a previous version of the EMEBSD template has omega as a parameter to specify, but this was removed in 2020 with the commit saying it is unnecessary.) However, clearly the different master patterns do not affect the spherical indexing solution even though it probably should have. Do you have ideas about what may be going on? I do not know the details of how the master pattern is converted from the h5 to sht format, but is it possible that the information about omega is lost?

Thanks in advance for any advice you can give.

Best,
Claire