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Implement base change directly in NXtransformations
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@lukaspie
lukaspie committed Aug 30, 2024
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110 changes: 92 additions & 18 deletions base_classes/NXtransformations.nxdl.xml
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# For further information, see http://www.nexusformat.org
-->
<definition xmlns="http://definition.nexusformat.org/nxdl/3.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" category="base" type="group" ignoreExtraGroups="true" ignoreExtraFields="true" ignoreExtraAttributes="true" name="NXtransformations" extends="NXobject" xsi:schemaLocation="http://definition.nexusformat.org/nxdl/3.1 ../nxdl.xsd">
<symbols>
<doc>
These symbols will be used below to coordinate fields with the same
shape.
</doc>
<symbol name="n_dim">
<doc>
number of dimension in the coordinate_system (typically 3).
</doc>
</symbol>
</symbols>
<doc>
Collection of axis-based translations and rotations to describe a geometry.
May also contain axes that do not move and therefore do not have a transformation
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vertical:NXdetector
depends_on=position/distance
position:NXtransformations
distance=10 # move downstream from the sample
distance=10 # move downstream from the sample
@depends_on=polar
@units=cm
@vector=[1 0 0]
polar=5 # title above the horizontal plane
polar=5 # title above the horizontal plane
@depends_on=azimuth
@units=degrees
@vector=[0 -1 0]
azimuth=0 # stay in the vertical plane
azimuth=0 # stay in the vertical plane
@depends_on=/entry/coordinate_system/beam
@units=degrees
@vector=[-1 0 0]
horizontal:NXdetector
depends_on=position/distance
position:NXtransformations
distance=11 # move downstream from the sample
distance=11 # move downstream from the sample
@depends_on=polar
@units=cm
@vector=[1 0 0]
polar=6 # title above the horizontal plane
polar=6 # title above the horizontal plane
@depends_on=azimuth
@units=degrees
@vector=[0 -1 0]
azimuth=90 # rotate to the horizontal plane
azimuth=90 # rotate to the horizontal plane
@depends_on=/entry/coordinate_system/beam
@units=degrees
@vector=[-1 0 0]
transmission:NXdetector
depends_on=position/distance
position:NXtransformations
distance=20 # move downstream from the sample
distance=20 # move downstream from the sample
@depends_on=/entry/coordinate_system/beam
@units=cm
@vector=[1 0 0]
coordinate_system:NXtransformations
beam=NaN # value is never used
@depends_on=gravity
@vector=[1 0 0] # X-axis points in the beam direction
gravity=NaN # value is never used
@depends_on=. # end of the chain
@vector=[0 0 -1] # Z-axis points up
@vector=[1 0 0]
@direction=X-axis points in the beam direction
gravity=NaN
@depends_on=/entry/analyser_cs/gravity # end of the chain
@vector=[1 0 0]
@transformation_type=rotation
@direction=Z-axis points up

**Example 3: base changes between different coordinate systems**

Define transformations to change bases from the NeXus coordinate frame (McStas)
with the Z-axis along the beam to a new laboratory reference based on X-, Y-, and Z-axes of
the sample stage. The new coordinate system is left-handed, whereas McStas is defined as
right-handed. Thus, the following transformatios need to be applied:

- rotation about y-axis by `180-source_polar_angle`, where `source_polar_angle` is the angle between the Z-axis
of the new CS and the beam axis.
- rotation about z-axis (by the azimuthal angle of the source w.r.t the projection
of the source axis of the new CS)
- change of handedness: x = - x

.. code-block::

entry:NXentry
transformations:NXtransformations
sample_stage_coordinate_system:NaN # value is never used
@depends_on=y_rotation
@direction="X-axis points in sample stage x direction,
Y-Axis points in sample stage y direction (towards the operator),
Z-axis points upwards,
forming a left-handed coordinate_system"
@matrix = [[1 0 0], [0 1 0], [0 0 1]]
y_rotation:180-source_polar_angle
@transformation_type=rotation
@depends_on=sample_stage_cs
@vector=[0, 1, 0]
z_rotation:source_azimuth_angle
@transformation_type=rotation
@depends_on=base_change
@vector=[0, 0, 1]
base_change=1 # no magnification
@transformation_type=base_change
@depends_on=.
@matrix = [[-1 0 0], [0 1 0], [0 0 1]]
</doc>
<field name="AXISNAME" type="NX_NUMBER" nameType="any" units="NX_TRANSFORMATION" maxOccurs="unbounded">
<doc>
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in which case the values are angular rotations around the axis.

If this attribute is omitted, this is an axis for which there
is no motion to be specifies, such as the direction of gravity,
is no motion to be specified, such as the direction of gravity,
or the direction to the source, or a basis vector of a
coordinate frame.

The transformation_type may be ``base_change``, in which case a matrix containing
n_dim column vectors of n_dim length should be supplied.
</doc>
<!--<item value="general" />-->
<enumeration>
<item value="translation"/>
<item value="rotation"/>
<item value="base_change"/>
</enumeration>
</attribute>
<attribute name="vector" optional="true" type="NX_NUMBER">
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should be chosen.
</doc>
<dimensions rank="1">
<dim index="1" value="3"/>
<dim index="1" value="n_dim"/>
</dimensions>
</attribute>
<attribute name="direction">
<doc>
Human-readable field telling in which direction the axis points. This is to be used
to a define a reference frame (i.e, for axes with no transformation_type).

If `@matrix` is filled, then this field shall contain the direction of all n-dim matrix
elements.

Exemplar values for one axis could be the direction of gravity.
</doc>
</attribute>
<attribute name="matrix" optional="true" type="NX_NUMBER">
<doc>
For axes of transformation_type ``base_change``, this matrix contains n_dim column vectors
of n_dim length.
</doc>
<dimensions rank="2">
<dim index="n_dim" value="n_dim"/>
</dimensions>
</attribute>
<attribute name="offset" type="NX_NUMBER">
Expand All @@ -302,7 +377,7 @@
as the mechanical offset from mounting the axis to its dependency.
</doc>
<dimensions rank="1">
<dim index="1" value="3"/>
<dim index="1" value="n_dim"/>
</dimensions>
</attribute>
<attribute name="offset_units" type="NX_CHAR">
Expand All @@ -312,9 +387,8 @@
</attribute>
<attribute name="depends_on" type="NX_CHAR">
<doc>
Points to the path of a field defining the axis on which this instance of
NXtransformations depends or the string ".". It can also point to an instance of
``NX_coordinate_system`` if this transformation depends on it.
Points to the path to a field defining the axis on which this
depends or the string "." when at the end of the chain.
</doc>
</attribute>
<attribute name="equipment_component" type="NX_CHAR">
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the corresponding axis moves during the exposure of a frame. Ideally, the
value of this field added to each value of ``AXISNAME`` would agree with the
corresponding values of ``AXISNAME_end``, but there is a possibility of significant
differences. Use of ``AXISNAME_end`` is recommended.
differences. Use of ``AXISNAME_end`` is recommended.
</doc>
</field>
<attribute name="default">
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