Align Sections (Misorientation)

Group (Subgroup)

Reconstruction (Alignment)

Description

This Filter attempts to align consecutive 'sections' perpendicular to the Z-direction of the sample by determining the position that results in the minimum amount of misorientation between Cells directly above-below each other. The algorithm of this Filter is as follows:

  1. Calculate the misorientation between each Cell in a section and the Cell directly above it in the next section
  2. Count the number of Cell pairs that have a misorientation above the user defined tolerance and store that as the misalignment value for that position
  3. Repeat steps 1 and 2 for each position when shifting the second slice (relative to the first) from three (3) Cells to the left to three (3) Cells to the right, as well as from three (3) Cells up to three (3) Cells down. Note that this creates a 7x7 grid
  4. Determine the position in the 7x7 grid that has the lowest misalignment value. (It will be the position with the fewest different Cell pairs)
  5. Repeat steps 1-4 with the center of each (new) 7x7 grid at the best position from the last 7x7 grid until the best position in the current/new 7x7 grid is the same as the last 7x7 grid 6) Repeat steps 1-5 for each pair of neighboring sections

Note that this is similar to a downhill simplex and can get caught in a local minimum!

If the user elects to use a mask array, the Cells flagged as false in the mask array will not be considered during the alignment process.

The user can choose to write the determined shift to an output file by enabling Write Alignment Shifts File and providing a file path.

The user can also decide to remove a background shift present in the sample. The process for this is to fit a line to the X and Y shifts along the Z-direction of the sample. The individual shifts are then modified to make the slope of the fit line be 0. Effectively, this process is trying to keep the top and bottom section of the sample fixed. Some combinations of sample geometry and internal features can result in this algorithm introducing a 'shear' in the sample and the Linear Background Subtraction will attempt to correct for this.

Parameters

Name Type Description
Misorientation Tolerance float Tolerance used to decide if Cells above/below one another should be considered to be the same. The value selected should be similar to the tolerance one would use to define Features (i.e., 2-10 degrees)
Write Alignment Shift File bool Whether to write the shifts applied to each section to a file
Alignment File File Path The output file path where the user would like the shifts applied to the section to be written. Only needed if Write Alignment Shifts File is checked
Linear Background Subtraction bool Whether to remove a background shift present in the alignment
Use Mask Array bool Whether to remove some Cells from consideration in the alignment process

Required Geometry

Image

Required Objects

Kind Default Name Type Component Dimensions Description
Cell Attribute Array Quats float (4) Specifies the orientation of the Cell in quaternion representation
Cell Attribute Array Phases int32_t (1) Specifies to which Ensemble each Cell belongs
Cell Attribute Array Mask bool (1) Specifies if the Cell is to be counted in the algorithm. Only required if Use Mask Array is checked
Ensemble Attribute Array CrystalStructures uint32_t (1) Enumeration representing the crystal structure for each Ensemble

Created Objects

None

Example Pipelines

  • (10) SmallIN100 Full Reconstruction
  • (03) SmallIN100 Alignment

Please see the description file distributed with this Plugin

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