Dear Herb,
These things happen.....
I have been interpreting the CBF coordinate system as being a
generalised form of the d*TREK one. I read the definition on page 26 of
the document that I have found here:
<http://www.rigaku.com/downloads/software/free/dTREK%20Image%20Format%
20v1.1.pdf>
to favour your interpretation 1.
Regards,
Peter.
On Thu, 2014-05-08 at 14:57 -0400, Herbert J. Bernstein wrote:
> Dear Colleagues,
>
> Please pardon the shotgun distribution of this query. It may only
> directly concern a few beam-line scientists and software developers,
> but comments from all interested parties are welcome.
>
> Many people have happily used the IUCr imgCIF dictionary definitions
> in data collection and processing software for many years. Just today,
> however, we discovered that there is an ambiguity in the interpretation
> of the CBF laboratory standard coordinate frame definition that comes
> from two alternate readings of the definition of the X-axis. Before
> we put clarifying wording in the dictionary and resolve the ambiguity,
> we would appreciate knowing which of the two interpretations is currently
> in major use so that the resolution will be as non-disruptive as possible.
>
> The imgCIF dictionary says:
>
> Axis 1 (*X*): The*X*-axis is aligned to the mechanical axis pointing from
> the sample or specimen along the principal axis of the goniometer or
> sample positioning system if the sample positioning system has an axis
> that intersects the origin and which form an angle of more than 22.5
> degrees with the beam axis.
>
> Without any intention of saying which of the following intepretations
> is the original intention of this definition by the ordering, here is
> what people have gotten from this:
>
> Interpretation 1: If you treat the sample as the origin, the +X axis runs
> from the sample along the pin _into_ the sample holder; or
>
> Interpretation 2: If you treat the sample as the origin, the -X axis runs
> from the sample along the pin _into_ the sample holder;
>
> There are important implications for processing software on the handedness
> of the resulting scan rotations, so we would appreciate whatever guidance
> any of you can provide as to how you have been reading this spec.
>
> Please send your comments to this list, or, if you prefer, to me personally
> at [log in to unmask]
>
> My apologies to the community for not having resolved this sooner, but
> we only became aware today that some people had been reading the spec one way,
> and others the other way.
>
> With deepest apologies,
> Herbert J. Bernstein
>
--
Peter Keller Tel.: +44 (0)1223 353033
Global Phasing Ltd., Fax.: +44 (0)1223 366889
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