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Hi again Rob,
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<div>This one was also overlooked, sorry... :-(</div>
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<blockquote type="cite">
<div>On <i style="background-color: rgb(255, 255, 255);">Tue Aug 12 10:40:26 CEST 2025 </i><i>Robert Dalgliesh - STFC UKRI robert.dalgliesh at stfc.ac.uk wrote:</i></div>
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<pre style="text-wrap-mode: wrap; background-color: rgb(255, 255, 255);">Is there a straightforward way to calculate the absolute interaction position of a neutron within a component after you have used PROP_Z0?
</pre>
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</blockquote>
<div>I am thinking you mean after SCATTER? (PROP_Z0 just puts everything at the z=0 plane of the component? Anyway, the procedure is about the same</div>
<blockquote type="cite">
<div>
<pre style="text-wrap-mode: wrap; background-color: rgb(255, 255, 255);">I would like to know the interaction point in both local (component) coordinates and in the world system so I can then work out the interaction position relative to other components.
Having dug around in the documentation I couldn’t see anything obvious.</pre>
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<div>Yes, there is indeed:</div>
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<div>1) Add USERVARS for measuring local and global coordinates to your instrument file:</div>
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</div>
<div>USERVARS %{</div>
<div> double xloc;</div>
<div> double yloc;</div>
<div> double zloc;</div>
<div> double xglob;</div>
<div>
<div> double yglob;</div>
<div> double zglob;</div>
</div>
<div>%}</div>
<div><br>
</div>
<div>2) Add an EXTEND block on your sample comp:</div>
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</div>
<div>COMPONENT Sample = Something(…)</div>
<div>AT (0,0,0) RELATIVE SamplePos</div>
<div>EXTEND %{</div>
<div> // Measure neutron coordinates in sample frame</div>
<div> // (can be made to depend on e.g. if (SCATTERED) )</div>
<div> xloc=x;</div>
<div> yloc=y;</div>
<div> zloc=z;</div>
<div>%}</div>
<div><br>
</div>
<div>3) Add an Arm located at the Sample position, but ROTATED into the global frame:</div>
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</div>
<div>COMPONENT SemiGlobal = Arm()</div>
<div>AT (0,0,0) RELATIVE SamplePos</div>
<div>ROTATED (0,0,0) ABSOLUTE</div>
<div>
<div>EXTEND %{</div>
<div> // Take comp absolute comps...</div>
<div> coords_get(POS_A_COMP_INDEX(INDEX_CURRENT_COMP), &xglob, &yglob, &zglob);</div>
<div> // … and add the relative coordinates of the neutron in the semi-global frame</div>
<div> xglob+=x;</div>
<div> yglob+=y;</div>
<div> zglob+=z;</div>
<div>%}</div>
</div>
<div><br>
</div>
<div>(There are surely other ways to do that calculation also, but this is the simplest one in my mind.)</div>
<div><br>
</div>
<div>4) Measure on the vars using Monitor_nD(user1=“xglob”…) or Flex_monitor_1/2/3D(user1=“xglob”…)</div>
<div><br>
</div>
All the best and happy easter,
<div>Peter<br>
<br>
<div>
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<div><br>
Peter Kjær Willendrup<br>
Forskningsingeniør, Specialkonsulent<br>
<br>
DTU Physics<br>
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