# 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

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.

## PONI-File

Small text file generated from pyFAi-calib or when saving a geometry object which contains the detector description, its position in space and the wavelength. Used to initialize AzimuthalIntegrator or Geometry objects.

## 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.