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 yaya...@gmail.com
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
Sheraton House,
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Cambridge CB3 0AX
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