Re: [ccp4bb] Rotation axis

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: Ammonium citrate tribasic buffer
From: E rajakumar e_rajakumar {- at -} YAHOO {- dot -} COM
Date: 2008-08-07

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Subject: interface
From: "Skrzypczak-Jankun, Ewa" Ewa {- dot -} Skrzypczak-Jankun {- at -} UTOLEDO {- dot -} EDU
Date: 2008-08-07

Subject: Re: Rotation axis
From: Phil Evans pre {- at -} MRC-LMB {- dot -} CAM {- dot -} AC {- dot -} UK
Date: 2008-08-07

My original posting on this question generated quite a few replies,
for which many thanks.

I found the most useful pointer to the required algorithm was the link
to Mark Gerstein's site given by Ian,
and I have now programmed this in a C++ class using Clipper routines,
which I can make available if anyone wants it.

There are many programs which will give the direction of the rotation
axis, but defining a point lying on the axis, such that the minimal
translation is just along the axis (ie a screw) is a bit more elusive.

Thanks
Phil

On 29 Jul 2008, at 12:30, Ian Tickle wrote:

>
> Phil
>
> What I suggested works only if the point x is transformed onto itself,
> i.e. there's no screw component.
>
> The general solution is here:
> http://bioinfo.mbb.yale.edu/geometry/screw-axis/
>
> There may be a neater way of deriving this in the general case using a
> homogeneous matrix & co-ordinates but I haven't worked it out yet!
>
> Cheers
>
> -- IAn
>
>> -----Original Message-----
>> From: owner-ccp4bb@jiscmail.ac.uk
>> [mailto:owner-ccp4bb@jiscmail.ac.uk] On Behalf Of Phil Evans
>> Sent: 29 July 2008 09:11
>> To: CCP4BB@JISCMAIL.AC.UK
>> Subject: 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
>>
>>
>
>

CCP4bb navigation

CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: Ammonium citrate tribasic buffer
From: E rajakumar e_rajakumar {- at -} YAHOO {- dot -} COM
Date: 2008-08-07

Next message:
Subject: interface
From: "Skrzypczak-Jankun, Ewa" Ewa {- dot -} Skrzypczak-Jankun {- at -} UTOLEDO {- dot -} EDU
Date: 2008-08-07