[vtkusers] image with variable spacing

[David Gobbi]

Hi Miro,

It is a bit hard for me to guess, but aren't those "clipped" regions
at the boundary of your data?  The vtkImageResliceMapper is generally
not supposed to draw anything beyond the bounds of the vtkImageData.
The Data bounds are the Mapper bounds.  And the Actor bounds are just
the Mapper bounds transformed from the data coordinate system to the
world coordinate system.  So I do not think that the bounds are
incorrect... but I am just guessing because I do not know your data.

A oblique slice through a rectangular volume will produce a
parallelogram, a triangle, a pentagon, or a hexagon.  What you are
seeing in your screenshot is a hexagon.  I think it is the correct
result.

You can try using vtkImageResliceMapper::SetBackground(1), which will
turn off clipping at the boundary, but it might not give the desired
result.

  David


On Tue, Nov 19, 2013 at 2:11 PM, Miro Drahos <mdrahos at robodoc.com> wrote:
> Hi David,
> I have put together the vector of vtkImageResliceMapper's coupled with
> vtkImageSlice's and they work great! Thank you so much for contributing
> these classes! Slicing at the camera focal plane is super convenient and
> really fast.
> I do see clipping that happens at certain angles; I attached a couple
> screenshots to illustrate the problem. The *Clipped.png shot shows the
> clipping in the lower left and upper right corner; I have a feeling it may
> have to do with how the actor's bounds are calculated, but I am not sure how
> to fix this.
> Do you have an idea on how to remediate this?
> Thank you tons once again!
> Miro
>
>
>
> On 11/19/2013 11:28 AM, Miro Drahos wrote:
>>
>> Hi David,
>> thank you very much for the valuable input.
>> I think I will follow your advice and go with a vector of
>> vtkImageResliceMappers, and roll my own reslice widget. It sounds like a
>> much cleaner solution than what I have done so far (vectors of reslice
>> cursors, reps and widgets, with much of the interaction code rewritten
>> to suite my needs).
>>
>> Thank you also for the pointer on how to fill the gaps; I was wondering
>> what would be the best way to do this so that objects behind the plane
>> don't "shine through" the gaps.
>> Best,
>> Miro
>>
>>
>> On 11/19/2013 08:31 AM, David Gobbi wrote:
>>>
>>> Hi Miro,
>>>
>>> There is no easy way to work with images that have variable sampling.
>>> You will almost certainly have to create your own widgets in order to
>>> get the kind of user interaction that you are looking for.  However, I
>>> have some suggestions on how to at least get the data to render
>>> properly:
>>>
>>> 1) You will definitely need to use one vtkImageData object per
>>> segment, given the restrictions on vtkImageData.
>>>
>>> 2) Likewise, each segment will need to have its own mapper (I suggest
>>> using the vtkImageResliceMapper, but of course I'm biased towards it
>>> because I wrote it).
>>>
>>> 3) The mappers for each segment will have to be synchronized to each
>>> other.  For vtkImageResliceMapper, this can be done by using the same
>>> SlicePlane for all the mappers, or alternatively by using
>>> SliceAtFocalPoint/SliceFacesCamera and controlling the slicing via the
>>> camera position and focal point.
>>>
>>> 4) You will have to fill in the gaps between the segments.  One
>>> quick-and-dirty way of doing this with vtkImageResliceMapper is to
>>> call SetBorder(1) to slightly extend the rendered bounds of the image.
>>>
>>> As I mentioned in my first paragraph, none of this will work with
>>> vtkResliceCursorWidget, you'd have to write your own user interaction
>>> code.
>>>
>>>     David
>>>
>>>
>>> On Tue, Nov 19, 2013 at 12:46 AM, Miroslav Drahos <MDrahos at robodoc.com>
>>> wrote:
>>>>
>>>> Hi,
>>>> I am working with medical image (a 3D volume) that consists of several
>>>> segments with different spacing in z-direction. I was hoping to get an
>>>> opinion on how to work with this data; I need to be able to visualize it all
>>>> at once, and reslice it at arbitrary direction.
>>>> One quite natural idea was to resample the image and then work with it
>>>> as one vtkImageData object, use vtkResliceCursorWidget on it, etc. However,
>>>> the origin of the individual image segments changes too, and the gap between
>>>> them is not an integer multiple of z-resolution, so I can't fit an integer
>>>> number of (empty) slices between the segments, and the origin will be
>>>> shifted.
>>>> The other idea that I am about to implement is to store a vector of
>>>> images, and dynamically re-plug the reslice cursor to the segment that it is
>>>> currently on, and have multiple representations that would copy their
>>>> parametric plane representation from the active on and display several
>>>> planes with their own textures.
>>>> But it just seems so clumsy, and makes me feel there must be a more
>>>> elegant and efficient solution.
>>>> I have seen vtkRectilinearGrid, but that cannot be plugged into a
>>>> reslice cursor.
>>>>
>>>> Anybody has an idea of how to work with such data?
>>>> Thank you very much,
>>>> Miro