Module refldata

source code

Reflectometry data representation.

Need to support collections of data from TOF, monochromatic and white beam instruments.

Conceptually each data point is a tuple:

incident angles (sample tilt and rotation)
reflected angles (polar angle of detector pixel)
slit distances and openings
detector pixel distance and size
incident/reflected polarization
wavelength distribution
measurement start and duration
monitor and detector counts
sample environment

Reflectometers are either vertical or horizontal geometry. For vertical geometry (sample surface parallel to gravity), x refers to horizontal slit opening and horizontal detector pixels. For horizontal geometry (sample surface perpendicular to gravity) x refers to vertical slit opening and vertical detector pixels. Other than gravitational corrections to resolution and detector pixels, the analysis for the two instrument types should be identical.

Monochromatic reflectometers have a single wavelength per measurement but scan the measurements. Time-of-flight and polychromatic reflectometers have multiple wavelengths per measurement but perform one measurement. In either case a dataset consists of detector frames versus Q. We will ignore scans on multichannel instruments since these can be treated as combined independent scans with non-overlapping data, and handled outside this data structure.

Data points are gathered together into measurements. Some files may have multiple measurements, and other measurements may be spread over multiple files. Files may be local or remote, ascii or binary. It is up to the individual format reader to assign map measurements to files.

Different polarization states will be treated as belonging to different measurements. These will need to be aligned before polarization correction can be performed. Multiple measurements may occur on the same detector. In this case each measurement should have a separate 'region of interest' to isolate it from the others, presenting a virtual detector to the reduction and analysis program.

Some information about the measurements may be missing from the files, or recorded incorrectly. Changes and additions to the metadata must be recorded in any reduced data file format, along with a list of transformations that went into the reduction.

See notes in properties.py regarding dated values.