[vtk-developers] Re: Adding vtkAbstractTransform::Shear() method

David Gobbi david_gobbi at rogers.com
Tue Oct 17 13:15:13 EDT 2006


Hi Will,

I didn't add shear originally because it could be performed by the appropriate combination of rotation and scale operations.

Shear can be tough because (as with rotation) there are many ways to parameterize it.  It isn't possible to write a Shear method that will make everyone happy.

I'd like to see it left out, personally, because Rotation, Scale, and Translation already form an orthogonal set that can be used to compose any linear transformation.  For an Affine widget (and this is just my opinion) it might be easiest to have code in the widget itself to build a vtkMatrix4x4.

 - David


----- Original Message ----
From: Will Schroeder <will.schroeder at kitware.com>
To: David Gobbi <david_gobbi at rogers.com>
Cc: vtk-developers at vtk.org
Sent: Tuesday, October 17, 2006 8:40:41 AM
Subject: Adding vtkAbstractTransform::Shear() method

David-

I am working on a VTK widget:: vtkAffineWidget and its representation 
vtkAffineRepresentation2D. I would like to support shears which as you 
know are affine transformations. To do this I've thought about adding a 
vtkAbstractTransform::Shear() method to do the actual fiddling with the 
transformation matrix, patterning it after the basic linear 
transformations Translate, Scale and Rotate (i.e., using the internal 
vtkTransformConcatenation). Are you okay with this? Other suggestions?

Will






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