Discussion List Archives

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Imgcif-l] Cylindrical detectors

> Is it reasonable to use _array_structure_list_axis.angle_increment instead
> of displacement_increment?

Yes

> Note that the radius of curvature of the detector is implied by the offset
> of the other detector axis, and once this is given the pixel displacement
> increment can be converted to degrees.

I suspect it would be better to use two axes for the circular section
of the cylinder, and another for the axis of the cylinder.  The
circle would then be described an angular axis coupled to
a radial axis.  The offset of the radial axis would then be
placed at the center of the circle, and the displacement
would give the (constant) radius of the circle.  The coupled
angular axis would then step through the pixels.  A third
axis would go along the axis of the cylinder.  I'll work
up a detailed example later today.

=====================================================
 Herbert J. Bernstein, Professor of Computer Science
   Dowling College, Kramer Science Center, KSC 121
        Idle Hour Blvd, Oakdale, NY, 11769

                 +1-631-244-3035
                 yaya@dowling.edu
=====================================================

On Wed, 1 Aug 2007, James Hester wrote:

> I have a question relating to describing cylindrical detectors (e.g.
> Debye-Scherrer camera using image plates) in imgCIF.  There appear to be no
> examples in the 'canonical' imgCIF literature relating to such non-flat
> detectors, let me give my best shot here - I would appreciate any feedback
> as to the correctness of this description, particularly the characterisation
> of the array structure axis as a detector rotation axis located at the
> sample.
>
> Is it reasonable to use _array_structure_list_axis.angle_increment instead
> of displacement_increment?
>
> Note that the radius of curvature of the detector is implied by the offset
> of the other detector axis, and once this is given the pixel displacement
> increment can be converted to degrees.
>
> For a cylindrically curved detector located 573mm from the sample, I would
> guess the following axis definitions:
>
> ##########
> loop_
> _axis.id
> _axis.type
> _axis.equipment
> _axis.depends_on
> _axis.offset[1] _axis.offset[2] _axis.offset[3] _axis.vector[1]
> _axis.vector[2] _axis.vector[3]
>
> source       .        source       .        0 0 0   0 0 1
> omega  rotation   goniometer .        0 0 0   1 0 0
> det_up       .        detector     .        0 0 -573  1 0 0   #parallel to
> sample rotation axis but on surface of
> det_along  rotation  detector  .        0  0 0   1 0 0     #coincident with
> sample rotation
>
> # the image that comes off is 2000x4000 pixels, with the fast and short
> direction in the cylindrical z #direction:
>
> loop_
> _array_structure_list.axis_set_id
> _array_structure_list.dimension
> _array_structure_list.precedence
>
> det_up   2000  1
> det_along 4000 2
>
> #vertical and horizontal pixels are 100 microns in size...
>
> loop_
> _array_structure_list_axis.axis_id
> _array_structure_list_axis.displacement_increment
>
> det_up    0.1
> det_along  0.1
> _______________________________________________
> imgcif-l mailing list
> imgcif-l@iucr.org
> http://scripts.iucr.org/mailman/listinfo/imgcif-l
>
_______________________________________________
imgcif-l mailing list
imgcif-l@iucr.org
http://scripts.iucr.org/mailman/listinfo/imgcif-l

Reply to: [list | sender only]
International Union of Crystallography

Scientific Union Member of the International Science Council (admitted 1947). Member of CODATA, the ISC Committee on Data. Partner with UNESCO, the United Nations Educational, Scientific and Cultural Organization in the International Year of Crystallography 2014.

International Science Council Scientific Freedom Policy

The IUCr observes the basic policy of non-discrimination and affirms the right and freedom of scientists to associate in international scientific activity without regard to such factors as ethnic origin, religion, citizenship, language, political stance, gender, sex or age, in accordance with the Statutes of the International Council for Science.

Useful links