# SPDX-License-Identifier: BSD-3-Clause
# Copyright (c) 2023 Scipp contributors (https://github.com/scipp)
"""
Coordinate transformations for powder diffraction.
"""
import scipp as sc
import scippneutron as scn
from .correction import merge_calibration
from .logging import get_logger
from .types import (
CalibrationData,
DataWithScatteringCoordinates,
DspacingData,
ElasticCoordTransformGraph,
MaskedData,
NormalizedByProtonCharge,
RunType,
)
def _dspacing_from_diff_calibration_generic_impl(t, t0, a, c):
"""
This function implements the solution to
t = a * d^2 + c * d + t0
for a != 0.
It uses the following way of expressing the solution with an order of operations
that is optimized for low memory usage.
d = (sqrt([x-t0+t] / x) - 1) * c / (2a)
x = c^2 / (4a)
"""
x = c**2 / (4 * a)
out = (x - t0) + t
out /= x
del x
sc.sqrt(out, out=out)
out -= 1
out *= c / (2 * a)
return out
def _dspacing_from_diff_calibration_a0_impl(t, t0, c):
"""
This function implements the solution to
t = a * d^2 + c * d + t0
for a == 0.
"""
out = t - t0
out /= c
return out
def _dspacing_from_diff_calibration(
tof: sc.Variable,
tzero: sc.Variable,
difa: sc.Variable,
difc: sc.Variable,
_tag_positions_consumed: sc.Variable,
) -> sc.Variable:
r"""
Compute d-spacing from calibration parameters.
d-spacing is the positive solution of
.. math:: \mathsf{tof} = \mathsf{DIFA} * d^2 + \mathsf{DIFC} * d + t_0
This function can be used with :func:`scipp.transform_coords`.
See Also
--------
ess.powder.conversions.to_dspacing_with_calibration
"""
if sc.all(difa == sc.scalar(0.0, unit=difa.unit)).value:
return _dspacing_from_diff_calibration_a0_impl(tof, tzero, difc)
return _dspacing_from_diff_calibration_generic_impl(tof, tzero, difa, difc)
def _consume_positions(position, sample_position, source_position):
_ = position
_ = sample_position
_ = source_position
return sc.scalar(0)
[docs]
def to_dspacing_with_calibration(
data: sc.DataArray,
calibration: sc.Dataset,
) -> sc.DataArray:
"""
Transform coordinates to d-spacing from calibration parameters.
Computes d-spacing from time-of-flight stored in `data`.
Attention
---------
`data` may have a wavelength coordinate and dimension,
but those are discarded.
Only the stored time-of-flight is used, that is, any modifications to
the wavelength coordinate after it was computed from time-of-flight are lost.
Raises
------
KeyError
If `data` does not contain a 'tof' coordinate.
Parameters
----------
data:
Input data in tof or wavelength dimension.
Must have a tof coordinate.
calibration:
Calibration data.
Returns
-------
:
A DataArray with the same data as the input and a 'dspacing' coordinate.
See Also
--------
ess.powder.conversions.dspacing_from_diff_calibration
"""
out = merge_calibration(into=data, calibration=calibration)
out = _restore_tof_if_in_wavelength(out)
graph = {"dspacing": _dspacing_from_diff_calibration}
# `_dspacing_from_diff_calibration` does not need positions but conceptually,
# the conversion maps from positions to d-spacing.
# The mechanism with `_tag_positions_consumed` is meant to ensure that,
# if positions are present, they are consumed (mad unaligned or dropped)
# by the coordinate transform similarly to `to_dspacing_with_positions`.
if "position" in out.coords or (
out.bins is not None and "position" in out.bins.coords
):
graph["_tag_positions_consumed"] = _consume_positions
else:
graph["_tag_positions_consumed"] = lambda: sc.scalar(0)
out = out.transform_coords("dspacing", graph=graph, keep_intermediate=False)
out.coords.pop("_tag_positions_consumed", None)
return DspacingData[RunType](out)
def _restore_tof_if_in_wavelength(data: sc.DataArray) -> sc.DataArray:
out = data.copy(deep=False)
outer = out.coords.pop("wavelength", None)
if out.bins is not None:
binned = out.bins.coords.pop("wavelength", None)
else:
binned = None
if outer is not None or binned is not None:
get_logger().info("Discarded coordinate 'wavelength' in favor of 'tof'.")
if "wavelength" in out.dims:
out = out.rename_dims(wavelength="tof")
return out
[docs]
def add_scattering_coordinates_from_positions(
data: NormalizedByProtonCharge[RunType], graph: ElasticCoordTransformGraph
) -> DataWithScatteringCoordinates[RunType]:
"""
Add ``wavelength`` and ``two_theta`` coordinates to the data.
The input ``data`` must have a ``tof`` coordinate, as well as the necessary
positions of the beamline components (source, sample, detectors) to compute
the scattering coordinates.
Parameters
----------
data:
Input data with a ``tof`` coordinate.
graph:
Coordinate transformation graph.
"""
out = data.transform_coords(
["two_theta", "wavelength"], graph=graph, keep_intermediate=False
)
return DataWithScatteringCoordinates[RunType](out)
[docs]
def convert_to_dspacing(
data: MaskedData[RunType],
graph: ElasticCoordTransformGraph,
calibration: CalibrationData,
) -> DspacingData[RunType]:
if calibration is None:
out = data.transform_coords(["dspacing"], graph=graph, keep_intermediate=False)
else:
out = to_dspacing_with_calibration(data, calibration=calibration)
for key in ('wavelength', 'two_theta'):
if key in out.coords.keys():
out.coords.set_aligned(key, False)
out.bins.coords.pop('tof', None)
out.bins.coords.pop('wavelength', None)
return DspacingData[RunType](out)
providers = (
powder_coordinate_transformation_graph,
add_scattering_coordinates_from_positions,
convert_to_dspacing,
)
