[vtkusers] Drawing an image mask per slice on top of VtkImageViewer2 for a 3D data set

[Dan Liew]

On 02/03/12 15:45, Delcypher wrote:
> Hi, I have two 3D data sets
> 
> VtkStructuredPoints  named "original" of dimensions [512x512x120] 
> VtkStructuredPoints named "mask" of dimensions [512x512x120]
> 
> I'm currently using the VtkImageViewer2 class to view a slice at a 
> time of the image "original" and this seems to be working quite 
> nicely.
> 
> What I want is to have an image mask that is drawn on top of the 
> "original" image for each slice. I want the mask to come from
> "mask" i.e. for every slice in "original" there is one
> corresponding mask for that slice in "mask". When I switch slice
> using imageViewer I need a way to make sure that the corresponding
> mask from "mask" is drawn on the newly displayed slice.
> 
> I started looking at 
> http://www.vtk.org/Wiki/VTK/Examples/Cxx/Images/Transparency which
> is a good example but it is only for 2D images.
> 
> I took a look at the source code for VtkImageViewer2 and I think
> it does the following...
> 
> 1. Place the entire 3D image in the world co-ordinate system and
> place the camera outside of this. 2. To select a particular slice
> VtkImageViewer2 seems to call SetDisplayExtent(x_min , x_max,
> y_min, y_max,  NEWSLICE_NUMBER, NEWSLICE_NUMBER) on its Actor so
> that only the relevant slice is visible (assuming slices are
> arranged along the Z-axis). I presume that these co-ordinates are
> local to the actor and are not world co-ordinates, is that
> correct?
> 
> I'm quite happy to call SetDisplayExtent() myself on the
> VtkImageActor for my "mask" image so that the right slice is used
> but what I'm really unsure of is.... Where do I put the
> VtkImageActor for my "mask" image in the world co-ordinate system
> so everything works (i.e. the mask's slices line up perfectly for
> all slices)??
> 
> I consider placing the "mask" image Actor completely outside the
> block of data for "original" but I have a strong suspicion this
> won't work because VtkImageViewer2 adjusts the cliping planes of
> the Active Camera of the renderer everytime the slice is changed so
> my "mask" may be outside the clipping planes.
> 
> Or could I just place "mask" directly on top of "original" in the 
> world co-ordinate system?
> 
> Or better yet could I use a second VtkImageViewer2 for my "mask"
> image and have both "VtkImageViewer2"s use the same renderer?
> 
> What's the best approach?
> 
> Regards,
> 
> Dan Liew.
Well I tried using two "VtkImageViewer2"s the program crashed. So I
tried the approach in the example and added another actor to the
renderer.
It is sort of working but for some reason the slices are not correctly
lining up in the XY plane despite the actors both sharing the same
origin.

Here's a screenshot illustrating what I see
http://www.doc.ic.ac.uk/~dsl11/simi-qt.png

The green square should be lined on top of the "blackish" image
underneath it. Instead the bottom corner of the "mask" is aligned with
the centre of the "original" image in the XY plane.

Here is the code if anyone wishes to see it
https://github.com/delcypher/simi-qt/blob/restructure/src/viewmanager.cpp

Does anyone know what's wrong?