# Usage¶

LiberTEM-blobfinder can evaluate the position of convergent beam electron diffraction disks or precession electron diffraction peaks to generate input data for strain maps in three automated steps:

Identify peaks using

`get_peaks()`

Extract a probable lattice from the peak positions using

`libertem.analysis.fullmatch.FullMatcher.full_match()`

Refine the lattice for each frame using

`run_refine()`

The algorithms are currently focused on the initial data extraction step, i.e. they work purely in pixels in frame coordinates and derive only parameters for each individual peak and for a 2D lattice in the detector reference frame. They don’t try to index peaks in crystallographic indices of the sample or to derive a 3D orientation. However, they can extract relevant input data such as peak positions and intensities very efficiently for such subsequent processing steps.

The algorithms are designed to be robust against intensity variations across a diffraction disk, between disks and between frames by calculating a correlation for each potential peak position, measuring the quality of each correlation and using the quality and position with subpixel refinement in a weighted least square optimization to derive the parameters for each frame. At the same time, the algorithms are optimized for efficiency and scalability so that they generate a full strain map on 32 GB of raw data within a few minutes on a suitable workstation and scale on a cluster, making full use of LiberTEM’s distributed processing capabilities.

Relevant input parameters are

- Matching template
Instance of

`MatchPattern`

Available options are

`RadialGradient`

,`BackgroundSubtraction`

,`RadialGradientBackgroundSubtraction`

, and`UserTemplate`

`search`

parameter to define the search area around the expected position

- Matcher: Instance of
`libertem.analysis.gridmatching.Matcher`

. `tolerance`

for position errors in the matching routine

- Matcher: Instance of
Number of disks to find in the initial step

See Examples for practical application!