ess.beer.mcstas.load.mcstas_source_position

ess.beer.mcstas.load.mcstas_source_position(fname, sample_position)

Return the effective source position for the McStas geometry.

sourceMantid is close to the choppers and its direction towards the sample is the incident-beam direction at the sample. It is not the moderator, however, so using it directly would make the source-to-sample distance too short. Conversely, the line from Origin to the sample has the correct length but not the incident direction because the guide is curved.

The coordinate transformations use the source-to-sample vector both to define the incident beam and, through its length, to define Ltotal. We therefore construct an effective source whose direction is given by sourceMantid and whose distance from the sample is given by Origin.

Return type:

Position[NXsource, TypeVar(RunType, ess.reduce.nexus.types.SampleRun (int), ess.powder.types.VanadiumRun (int), ess.powder.types.EmptyCanRun (int))]