[Nexus] Suggestions for NeXus from CIF

[freddie.akeroyd at stfc.ac.uk]

Hi Pete,

> Two comments on the axis suggestions.
>
> On 4/6/2010 3:02 AM, Mark Koennecke wrote:
>> Axis Suggestions for NeXus   ---------------------------
>> 1) NeXus stays with the McStas coordinate system.
>
> McStas is not very restrictive.
> It only defines the coordinate axes.
> It does not describe rotations.
>
>
> For those that want to see the McStas definition,
> refer to the components manual, page 11,
>
http://mcstas.risoe.dk/documentation/manual/mcstas-1.12a-components.pdf
>
> "All mentioning of component geometry refer to the local coordinate 
> system of the individual component. The axis convention is so that the

> z axis is along the neutron propagation axis, the y axis is vertical 
> up, and the x axis points left when looking along the z-axis, 
> completing a right-handed coordinate system. Most components 
> 'position' (as specified in the instrument description with the AT 
> keyword) corresponds to their input side at the nominal beam position.

> However, a few components are radial and thus positioned in their 
> centre."
>
>
> Similar information is provided in the user and programmers manual, 
> page 70
> http://mcstas.risoe.dk/documentation/manual/mcstas-1.12a-manual.pdf
>
> "The instrument is given a global, absolute coordinate system. In 
> addition, every component in the instrument has its own local 
> coordinate system that can be given any desired position and 
> orientation (though the position and orientation must remain fixed for

> the duration of a single simulation). By convention, the z axis points

> in the direction of the beam, the x axis is perpendicular to the beam 
> in the horizontal plane pointing left as seen from the source, and the

> y axis points upwards."
>

Mcstas does describe rotations, but this only seems to be mentioned
later in "instrument definitions" rather than in the "conventions"
section of the manual where coordinates are discussed. The orientation
of the local axes of a component with respect to another reference point
are described using AT and ROTATED keywords (page 76 of
http://mcstas.risoe.dk/documentation/manual/mcstas-1.12a-manual.pdf )


Regards,

Freddie
-- 
Scanned by iCritical.