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Forum: Geometry
Re: Warning Direction of rotation - clockwise or counterclockwise (Patrik Eschle)
Re: None Re: Direction of rotation - clockwise or counterclockwise (michel maire)
Re: None Re: Direction of rotation - clockwise or counterclockwise (Patrik Eschle)
Date: 04 Apr, 2015
From: michel maire <michel maire>

On Thu, 02 Apr 2015 13:18:16 GMT, Patrik Eschle wrote:
> Hello
> 
> Now the confusion is complete. Two seemingly equivalent methods rotate
> in different sense.
> 
> But then Michel Maire points me to examples/extended/geometry/transforms.

 Readme of the example does not explain enough the underlying motivations for the this exercise. 
 Let me try to do it here.

 1 - There are 2 constructors to place volumes :
     - G4PVPlacement ( G4Transform3D( rotmA, transl), ... 
     - G4PVPlacement ( rotmB, transl, ...
  rotmA and rotmB must be mutually inverse. 
  The question is : what is exactly the definition of rotmA (and therefore rotmB).
  This is what the first two methods try to explicit : rotmA is what I call direct matrix; rotmB is its inverse.

2- Operators AxialRotation. The function rotateY (or Z) build a direct matrix, e.g. rotmA
    Its inverse can be calculated as : rotmA_inv (theta) = rotmA(-theta)    (Lie group ....)

    This is what we wanted to illustrate in PlaceWithAxialRotations(). The first object is placed with rotmA, the second object with rotmB

 3- Unfortunatly, constructor of rotation matrix with Euler angles choose the opposite convention (inconsistency in clhep) 
      but I guess no one use Euler angles constructor.

  Hope this can help.        Michel

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2015/04/04/08.29-55156-rotm.jpg

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1 None: Re: Direction of rotation - clockwise or counterclockwise   (michel maire - 05 Apr, 2015)
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