Hi Phil, If you have a reasonably recent version of the cctbx around (phenix, cci apps, maybe ccp4), try this:
import scitbx.math rotation_matrix = (1,0,0,0,0,1,0,-1,0) fm = scitbx.math.r3_rotation_axis_and_angle_from_matrix(r=rotation_matrix) print fm.axis print fm.angle(deg=True) The implementation (with comments) is in scitbx/include/scitbx/math/r3_rotation.h Ralf ----- Original Message ---- From: Phil Evans <[EMAIL PROTECTED]> To: CCP4BB@JISCMAIL.AC.UK Sent: Tuesday, July 29, 2008 1:10:50 AM Subject: [ccp4bb] Rotation axis If I've go a superposition transformation (x' = Rx + t), as it happens from a superposition in ccp4mg, how do I get the position & direction of the rotation axis (to draw in a picture)? I know that any (orthonormal) transformation can be represented as a rotation about an axis + a screw translation along that axis I'm sure I've done this before ... thanks Phil
