Allow Goniometer to save Rotation Matrix directly to nexus file

[andy-bridger]

Description of work

Summary of work

When saveNexus is called by Goniometer it now saves a flattened copy of the rotation matrix

Fixes #39487

Further detail of work

Now the rotation matrix can be directly saved and loaded, which has been identified as an issue because of the new functionality to set goniometer matrices directly: #39219 (comment) but may have also been causing issues in user scripts where goniometer has been set with setR or similar

To test:

run script:

# import mantid algorithms, numpy and matplotlib
from mantid.simpleapi import *
import matplotlib.pyplot as plt
import numpy as np

cuboid = " \
<cuboid id='some-cuboid'> \
<height val='2.0'  /> \
<width val='2.0' />  \
<depth  val='0.2' />  \
<centre x='10.0' y='10.0' z='10.0'  />  \
</cuboid>  \
<algebra val='some-cuboid' /> \
"

# just set this as a folder you are happy to have some files appear
root = "C:/Users/kcd17618/Documents/MantidScripts/SaveGoniometerBug"
ws = CreateSampleWorkspace()
other_ws = CreateSampleWorkspace()

# gon mat is a 30 degree rotation around (1,1,1)            
gon_mat = np.array([[ 0.9106836,  -0.24401694,  0.33333333],
 [ 0.33333333,  0.9106836,  -0.24401694],
 [-0.24401694,  0.33333333,  0.9106836 ]])
 
# try setting the matrix directly and using an equivalent axis definition
SetGoniometer(Workspace = ws, GoniometerMatrix = gon_mat)
SetGoniometer(Workspace = other_ws, Axis0 = "30,1,1,1,1")
SetSample(ws, Geometry={'Shape': 'CSG', 'Value': cuboid})
SetSample(other_ws, Geometry={'Shape': 'CSG', 'Value': cuboid})

# verify this is the same
print("Set with GoniometerMatrix: ",ws.run().getGoniometer().getR())
print("Set with Axis0: ",other_ws.run().getGoniometer().getR())

# Save the files
SaveNexus(InputWorkspace = ws, Filename= f"{root}/tmp_ws.nxs")
SaveNexus(InputWorkspace = other_ws, Filename= f"{root}/tmp_other_ws.nxs")

# Load the files
load_ws = Load(Filename = f"{root}/tmp_ws.nxs")
load_other_ws = Load(Filename = f"{root}/tmp_other_ws.nxs")

# Results should not have changed
print("Reloaded - Set with GoniometerMatrix: ",load_ws.run().getGoniometer().getR())
print("Reloaded - Set with Axis0: ",load_other_ws.run().getGoniometer().getR())

Also worth checking that the sample is orientated correctly on all four workspaces (right click on ws, Show Sample Shape)

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[sf1919]

I think the issue is labelled v6.13 so this needs to be pointed at release-next and have appropriate milestone and labels added.

[andy-bridger]

I think this could be pushed down the line to 6.14 as not technically a regression but since it is a bug that is much more accessible due to the change to SetGoniometer if this fix is suitable (doesn't break anything else) I think it is worth getting in.

[RichardWaiteSTFC]

Thanks for this, changes and tests look great. Test instructions worked as expected and sample shapes correctly set. I agree this deserves a release note as it preserves some precision on the saved/loaded rotation. Just one really nit-picking comment, apologies I had to find something!

[RichardWaiteSTFC]

Very minor -but I think the naming convention for such member variable (if that is the right term?) is m_initFromR - obviously this wasn't introduced in this PR (apologies for missing it before), but it helps to make the scope of the variable clear!

[RichardWaiteSTFC]

Thanks for that! Looks good to me!