Glossary

You will find some explanation about technical terms often used in pyFAI and its documentation.

AzimuthalIntegrator

The azimuthal integrator (ai hereafter) is an object, in the sense of Object Oriented Programming which can transform an image into a powder diffraction pattern using the integrate1d or integrate2d methods. It contains (inherits) a Geometry and caches the look-up table for optimized integration. Ai objects are usually obtained from loading a PONI-file obtained after calibration. See AzimuthalIntegrator

Calibration

Action of determining the geometry of an experiment geometry using a reference sample. Calibration is performed using the pyFAI-calib tool to generate the PONI-file., See its Calibration

Detector

Detectors are all area detectors in pyFAI, which mean pixels are indexed by 2 indices often references as (slow, fast) or (row, column) or simply (1, 2). Indices are using the C-convention. The detector object is responsible for calculating the pixel position in space (so in 3D). and assumes each pixel is defined by 4-corners. Detectors can be defined by many ways: from a shape and a pixel size, from a tabulated detector (there are over 60 detector defined) or from a NeXus file. See Simple detector

Distortion

Distortion correction is the action of correcting the spatial distortion from an image due to a detector. The object is defined from detector and the target is an image with a regular grid and a given pixel size and shape.

Geometry

The geometry object is in charge of calculating all kind of coordinates (cartesian, polar, …) for any point in the image, a step both needed for integration and calibration. The geometry object composes (contains) a detector and contains the 3 translations (dist, poni1 and poni2) and 3 rotations (rot1, rot2, rot3) of the detector in space. It knows in addition about the wavelength. The object is saved in a PONI-file, see Detector position

Image

2D array of pixels which intensity is proportionnal to the number of photons. see Image representation in Python

PONI

Acronym for Point Of Normal Incidence. It is the pixel coordinates of the orthogonal projection of the sample position on the detector (for plane detectors, or the plane z=0 for other). The PONI coincide with the beam center in the case of orthogonal setup but most of the time differs. see Detector position

PONI-File

Small text file generated from the calibration or when saving a geometry which contains the detector description, its position in space and the wavelength. Typically used to initialize an AzimuthalIntegrator or a Geometry object.

Worker

A worker allow, once parameterized, to perform always the same processing on all images in a stack, for example azimuthal integration, distortion correction or simple pixel-wise operation.