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, Castle Park, Cambridge CB3 0AX United Kingdom
