UpdateInstrumentFromFile-v1.rst

Description

Some instrument definition file (:ref:`IDF <InstrumentDefinitionFile>`) positions are only approximately correct and the true positions are located within data files. This algorithm reads the detector positioning from the supplied file and updates the instrument accordingly. It currently supports ISIS Raw, ISIS NeXus files and ASCII files.

It is assumed that the positions specified in the file are all with respect to the a coordinate system defined with its origin at the sample position. Note that this algorithm moves the detectors without subsequent rotation, hence this means that detectors may not for example face the sample perfectly after this algorithm has been applied.

Related or similar algorithms

See :ref:`algm-LoadDetectorInfo` which can do similar job modifying the detector parameters and positions and working with special format ASCII files or ISIS raw or special nexus files.

Additional Detector Parameters Using ASCII File

The ASCII format allows a multi-column text file to provide new positions along with additional parameters for each detector. If a text file is used then the AsciiHeader parameter is required as it identifies each column in the file as header information in the file is always ignored. There is a minor restriction in that the first column is expected to specify either a detector ID or a spectrum number and will never be interpreted as anything else.

The keywords recognised by the algorithm to pick out detector position values & spectrum/ID values are: spectrum, ID, R,theta, phi. The spectrum/ID keywords can only be used in the first column. A dash (-) is used to ignore a column.

As an example the following header:

spectrum,theta,-,-,R

and the following text file:

1   0.0000  -4.2508  11.0550  -2.4594
2   0.0000   0.0000  11.0550   2.3800
3 130.4653  -0.4157  11.0050   0.6708
4 131.9319  -0.5338  11.0050   0.6545
5 133.0559  -0.3362  11.0050   0.6345

would tell the algorithm to interpret the columns as:

1. Spectrum number
2. Theta position value
3. Ignored: Detector's electronics delay time -- the difference of pulse synchronization signal time and the time DAE starts measuring frame time of given spectra.
4. Ignored: Sample to source distance for the particular detector
5. Sample-detector distance R.

Usage

Example - Update Instrument:

Output: