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Calc-ax (which I mentioned in my post a few days ago) calculates the position of the rotation axis such that translation perpendicular to that axis is zero; all remaining translation (if any) is parallel to the axis. Dave David Borhani, Ph.D. D. E. Shaw Research, LLC 120 West Forty-Fifth Street, 39th Floor New York, NY 10036 [log in to unmask] 212-478-0698 http://www.deshawresearch.com > -----Original Message----- > From: CCP4 bulletin board [mailto:[log in to unmask]] On > Behalf Of Winn, MD (Martyn) > Sent: Sunday, August 03, 2008 10:39 AM > To: [log in to unmask] > Subject: Re: [ccp4bb] Rotation axis > > ROTMAT will also do this. But I am not sure that this is what > Phil wants? > > The superposition transformation includes a translation, so > there is no > locus of points that are left unchanged. You can generate an axis of > rotation for polar angles from the R which will be quite > different from t. > You should be able to translate the rotation axis (change the > origin of > the coordinate system) to get a new transformation x' = R'x + t' which > might be better for visualisation. If Phil's last sentence is > right, you > should be able to arrange it so that t' is parallel to the > rotation axis > of R' > > No, I don't know how to do this off the top of my head, but it sounds > very similar to the transformations done in the Schomaker and > Trueblood > TLS paper. > > Or maybe this is over-complicating things ;-) > > Martyn > > -----Original Message----- > From: CCP4 bulletin board on behalf of > [log in to unmask] > Sent: Tue 7/29/2008 1:32 PM > To: [log in to unmask] > Subject: Re: [ccp4bb] Rotation axis > > Dear Phil, > Because question keep popping up in the bullitin board about > conversion > from a rotation matrix into rotation angles, I decided to take the > relevant subroutines from an old program from Groningen and > make a jiffy > to do these conversions. It is a small fortran program and > does not need > any additional libraries or subroutines. The program will take a > rotation matrix and translation vector and print all kind of rotation > angles and also the component of the translation vector > parallel to the > rotation axis, which is the number you want. All other > components of the > translation vector can be made zero by choosing the right position of > the rotation axis. > > Best regards, > Herman Schreuder > > > > -----Original Message----- > From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of > Phil Evans > Sent: Tuesday, July 29, 2008 10:11 AM > To: [log in to unmask] > 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 >