[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Reply to: [list | sender only]
Re: [Imgcif-l] imgCIF X axis
- To: "Herbert J. Bernstein" <yayahjb@gmail.com>
- Subject: Re: [Imgcif-l] imgCIF X axis
- From: James H via imgcif-l <imgcif-l@iucr.org>
- Date: Wed, 22 Jun 2022 10:39:12 +1000
- Cc: James H <jamesrhester@gmail.com>, The Crystallographic Binary File and its imgCIF application to image data<imgcif-l@iucr.org>
- In-Reply-To: <CABcsX25oGH95vP8RLOET9R=BQZHDoizOu4FDht2ZjbXuYyYw8g@mail.gmail.com>
- References: <CAM+dB2c5Hv=g03gGkC4==awB_ygVL6Hvdp-vf6R86pVOoRSmYQ@mail.gmail.com><CABcsX25oGH95vP8RLOET9R=BQZHDoizOu4FDht2ZjbXuYyYw8g@mail.gmail.com>
Just to pick up on something else in Herbert's reply: I've noticed some confusion when talking to people as to what exactly "the principal axis of the goniometer" is. My current working definition is "the bottom-most rotation axis of the goniometer". In terms of the imgCIF AXIS category, this would be the goniometer rotation axis that depends_on no other axis, typically omega on a 4-circle diffractometer, and so by definition of X this axis would have axis vector of [1 0 0] in non-pathological cases. Is my understanding correct? Are there subtleties not covered by my working definition? thanks, James. On Wed, 15 Jun 2022 at 21:34, Herbert J. Bernstein <yayahjb@gmail.com> wrote: > Dear James, > This is a little tricky. The relevant rules are: > > "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." > > "If the axis involved is a rotation axis, it is right-handed, i.e. as > one views the object to be rotated from the origin (the tail) of the > unit vector, the rotation is clockwise. If a translation axis is > specified, the direction of the unit vector specifies the sense of > positive translation" > > So, yes the x-axis starts from the sample, but where it point to in the > goniometer depends on where in the goniometer the "principal" > axis of the goniometer points _and_ in which direction the axis > settings increase and whether the principal axis is a rotation > axis or a translation axis. The only way I have figured out to > do this is to start from the engineering diagrams (or at least > photos) of the goniometer, and even then, I once screwed up > the x-axis for a beamline at DLS (ask Graeme Winter). > > Regards, > Herbert > > On Wed, Jun 15, 2022 at 2:38 AM James H via imgcif-l <imgcif-l@iucr.org> > wrote: > >> Dear imgCIF experts, >> >> Just to double-check, is it correct to say that the imgCIF X axis always >> points from the specimen towards the goniometer base? Closely parsing the >> dictionary and Volume G suggests that the X axis being "aligned" with the >> principal axis could also allow the X axis to point from the specimen away >> from the goniometer base, particularly if the sense of rotation of the >> principal goniometer axis is taken into account when defining X (is it?). >> >> thanks, >> James. >> -- >> T +61 (02) 9717 9907 >> F +61 (02) 9717 3145 >> M +61 (04) 0249 4148 >> _______________________________________________ >> imgcif-l mailing list >> imgcif-l@iucr.org >> http://mailman.iucr.org/cgi-bin/mailman/listinfo/imgcif-l -- T +61 (02) 9717 9907 F +61 (02) 9717 3145 M +61 (04) 0249 4148 _______________________________________________ imgcif-l mailing list imgcif-l@iucr.org http://mailman.iucr.org/cgi-bin/mailman/listinfo/imgcif-l
Reply to: [list | sender only]
- Prev by Date: Re: [Imgcif-l] imgCIF X axis
- Next by Date: Re: [Imgcif-l] imgCIF X axis
- Prev by thread: Re: [Imgcif-l] imgCIF X axis
- Next by thread: Re: [Imgcif-l] imgCIF X axis
- Index(es):