[vtkusers] Repositioning Image within Render Window

[Gib Bogle]

On 21/10/2010 11:40 a.m., David Gobbi wrote:
> On Wed, Oct 20, 2010 at 4:33 PM, David Doria<daviddoria at gmail.com>  wrote:
>> On Wed, Oct 20, 2010 at 6:31 PM, David Gobbi<david.gobbi at gmail.com>  wrote:
>>>
>>> Hi Alexis,
>>>
>>> The vtkImageActor is the most common way of displaying an image.  It
>>> assumes that the image data is already in the correct coordinate
>>> system (and if the image is not yet in the right coordinate system,
>>> then its Origin and Spacing can be adjusted with
>>> vtkImageChangeInformation).  That is usually the best method for
>>> displaying an image.  If you try displaying an image with vtkTexture
>>> instead, then you have to take care of all the details like aspect
>>> ratio, position, texture coords, etc. yourself.
>>>
>>> And, as John said, you must also consider the camera, because it is
>>> what determines how the "World Coordinates" of the 3D scene are
>>> translated into view that you see on the computer screen.  For 2D
>>> image viewing, you usually want to set ParallelProjectionOn() and use
>>> SetParallelScale() to set how large the view is, in world coordinates.
>>>   Then set the camera FocalPoint to the center of your image, set the
>>> camera Position about 1000mm away from the focal point (i.e. looking
>>> towards it), and then set the ViewUp() so that the image will be
>>> correctly oriented on the screen.
>>>
>>>    David
>>
>> Here is an example of using an ImageActor as David G. suggested:
>> http://www.vtk.org/Wiki/VTK/Examples/Cxx/Images/InteractWithImage
>
> Except that example doesn't do anything with the camera positioning.
> It is impossible to adjust the image position without moving the
> camera, because VTK's default camera setting will always center the
> actor within the window.

Quibble: That's the case with a single actor.  Otherwise VTK aims the camera at 
the average actor position (or something like that), with the camera located at 
(xave,yave,zave+zoffset).  This must be documented somewhere.