I think it's just angles and cross products:
var axisC = {0 0 1/1 }
var axisZ = {0 0 1}
rotAxis = cross(axisZ,axisC)
rotAngle = angle(axisZ, {0 0 0},rotAxis, axisC)
draw {0 0 0} @{rotAxis * 10}
print " " + rotAngle + " " + rotAxis
reset
rotate molecular {0 0 0} @rotAxis @rotAngle
The cross product gets you an axis perpendicular to the other two.
That trick with the rotAngle done as a dihedral gets you a directed angle
rather than just a positive value for which you don't know which way to
turn.
Then you can work out how you want to rotate the others. I'll leave that as
a puzzle for you.
Bob
On Wed, Jul 1, 2009 at 10:40 AM, Brian McMahon <b...@iucr.org> wrote:
> Is there a neat way (perhaps using quaternions) to view a triclinic
> unit cell down its crystallographic axes? i.e. a moveto command so
> that the cell ends up with its c axis normal to the screen and its
> ac face (in projection) lying horizontally?
>
> Thanks
> Brian
>
>
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--
Robert M. Hanson
Professor of Chemistry
St. Olaf College
1520 St. Olaf Ave.
Northfield, MN 55057
http://www.stolaf.edu/people/hansonr
phone: 507-786-3107
If nature does not answer first what we want,
it is better to take what answer we get.
-- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900
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