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Re: [Imgcif-l] imgCIF X axis
- To: James Hester <james.r.hester@gmail.com>, The Crystallographic Binary File and its imgCIF application to image data<imgcif-l@iucr.org>
- Subject: Re: [Imgcif-l] imgCIF X axis
- From: "Herbert J. Bernstein via imgcif-l" <imgcif-l@iucr.org>
- Date: Wed, 15 Jun 2022 07:33:34 -0400
- Cc: "Herbert J. Bernstein" <yayahjb@gmail.com>
- In-Reply-To: <CAM+dB2c5Hv=g03gGkC4==awB_ygVL6Hvdp-vf6R86pVOoRSmYQ@mail.gmail.com>
- References: <CAM+dB2c5Hv=g03gGkC4==awB_ygVL6Hvdp-vf6R86pVOoRSmYQ@mail.gmail.com>
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 _______________________________________________ imgcif-l mailing list imgcif-l@iucr.org http://mailman.iucr.org/cgi-bin/mailman/listinfo/imgcif-l
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