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 -- ------------------------------------------------------------------------ Herbert J. Bernstein Professor of Mathematics and Computer Science Dowling College, Brookhaven Campus, A210/B205 1300 William Floyd Parkway, Shirley, NY, 11967 +1-631-244-1328 Lab: +1-631-244-1935 Cell: +1-631-428-1397 y...@dowling.edu ------------------------------------------------------------------------ /Users/yaya/Documents/Eudora Folder/Signature Folder/Alternate