[vtkusers] picking vtkImageSlice using vtkCellPicker?

Miro Drahos mdrahos at robodoc.com
Tue Mar 25 17:25:00 EDT 2014 

David,
thank you very much for valuable feedback. I will heed your advice and 
enforce positive spacing in the images.
This seems like the best approach and avoid other potential issues down 
the road.
Best,
Miro



On 03/25/2014 12:49 PM, David Gobbi wrote:
> Hi Miro,
>
> As far as I know, no VTK components whatsoever are tested for images
> with negative spacing, and no-one is working to fix the components
> that are known to break with negative spacing.
>
> In my own software, whenever I read an image that has negative
> spacing, I always reverse the slice order to make the spacing
> positive.  This means that I have to modify the orientation/position
> matrix to account for the reversal, and it also means that I have to
> create a map that will map imagedata slice indices to the original
> file slice indices.  All of this adds complexity to my programs,
> obviously, but at least it means that I can be confident that all the
> rendering, contouring, filtering, and picking tools will properly work
> with my data.
>
> Since I'm familiar with the image picking code, I can take a look to
> see why it doesn't work for negative spacing.  But I strongly
> recommend that you do not use images with negative spacing in VTK.
> If you use negative spacing, then some things will work, it's true, but
> some things will break.
>
>    David
>
> On Tue, Mar 25, 2014 at 1:24 PM, Miro Drahos <mdrahos at robodoc.com> wrote:
>> Hi David,
>> I investigated this issue further and indeed vtkCellPicker works fine with
>> vtkImageActor/vtkImageSlice when I plug in different images.
>> It so happens that my image has negative spacing (in z-direction), and that
>> seems to cause issues. If I load the same image and flip the z-spacing sign,
>> picking works fine. I had a look at the vtkImageActor class and saw the
>> if-clauses taking care of the spacing sign (when setting display bounds),
>> but I have not seen a similar treatment in vtkImageSliceMapper -- is it
>> possible that the issue is there?
>> I have had issues with images with negative spacing before, in particular
>> marching cubes filter as well as volumeMapper don't support the negative
>> spacing (in vtk 5.10). I was able to work around this by flipping the
>> spacing (and changing the origin) but I would rather keep the negative
>> spacing as is, since that's how the slices were acquired, in the -z
>> direction.
>> Do you (or anyone else?) know where in the vtk codebase could this problem
>> (picking dependent on the spacing sign of the image) be?
>> I believe that picking takes into consideration just the actor bounds, but
>> the rendering works just fine, so I am quite puzzled.
>> I am hoping that once I know where the problem is, I can derive a class
>> implementing the correct behavior and use that instead.
>> Any advice is greatly appreciated, as always.
>> Best,
>> Miro
>>
>>
>>
>>
>> On 03/20/2014 02:29 PM, David Gobbi wrote:
>>> Hi Miro,
>>>
>>> I checked through the git logs, the only recent fix to vtkCellPicker
>>> had to do with the fact that GetMapper() returned null for
>>> vtkImageSlice (but it still returned the prop and position just fine).
>>>    However, I noticed that the only nightly test for picking images uses
>>> a vtkImageActor (a subclass of vtkImageSlice) instead of using
>>> vtkImageSlice directly.  This shouldn't make a difference, but it
>>> might be worth investigating.
>>>
>>>     David
>>>
>>> On Thu, Mar 20, 2014 at 2:17 PM, Miro Drahos <mdrahos at robodoc.com> wrote:
>>>> Hi David,
>>>> thank you for your prompt response.
>>>>
>>>> I am using VTK 5.10 and doing nothing special as far as I can tell. Here
>>>> is
>>>> some more details:
>>>>
>>>> I have a vector of vtkSmartPointer<vtkImageSlice> objects to display
>>>> images
>>>> [my 3D CT image has several segments with different slice thicknesses, so
>>>> that's why I have a vector of them]. All the reslicing and visualization
>>>> is
>>>> working as expected, so I don't suspect an issue there.
>>>> Now I am observing LeftMouseEvent of the interactor and processing it in
>>>> my
>>>> callback class to recognize when the surface model is picked. If it is,
>>>> then
>>>> user can translate and rotate it. The callback class is derived from both
>>>> vtkCommand and QObject (to be able to use signal/slots of Qt that this is
>>>> part of) and I am implementing FindPickedActor(int x, int y) method as I
>>>> have seen it throughout VTK many times.
>>>> I have tried to use different pickers, and decided for vtkCellPicker
>>>> instead
>>>> of vtkPropPicker, to be able to set tolerance (user can make the surface
>>>> model transparent and then might want to pick just the outline --
>>>> intersection of the surface and the image reslice plane. Picking outline
>>>> is
>>>> hard with no tolerance).
>>>> Picking surface model works just fine.
>>>>
>>>> Here is the Print() of one of my vtkImageSlice instance:
>>>>
>>>> vtkImageSlice (0x4ecbd30)
>>>>     Debug: Off
>>>>     Modified Time: 64690
>>>>     Reference Count: 3
>>>>     Registered Events: (none)
>>>>     Dragable: On
>>>>     Pickable: On
>>>>     AllocatedRenderTime: 860.822
>>>>     EstimatedRenderTime: 0
>>>>     NumberOfConsumers: 1
>>>>     RenderTimeMultiplier: 0.863803
>>>>     Visibility: On
>>>>     PropertyKeys: none.
>>>>     useBounds: 1
>>>>     IsIdentity: true
>>>>     Position: (0, 0, 0)
>>>>     Orientation: (0, 0, 0)
>>>>     Origin: (0, 0, 0)
>>>>     Scale: (1, 1, 1)
>>>>     Bounds:
>>>>       Xmin,Xmax: (-100, 100)
>>>>       Ymin,Ymax: (-100, 100)
>>>>       Zmin,Zmax: (-90.625, -2.5)
>>>>     UserTransform: (none)
>>>>     UserMatrix: (none)
>>>>     Property:
>>>>       Debug: Off
>>>>       Modified Time: 64690
>>>>       Reference Count: 3
>>>>       Registered Events: (none)
>>>>       ColorWindow: 260.1
>>>>       ColorLevel: 119.85
>>>>       UseLookupTableScalarRange: Off
>>>>       LookupTable: 0x156088a0
>>>>       Opacity: 1
>>>>       Ambient: 0.3
>>>>       Diffuse: 1
>>>>       InterpolationType: Linear
>>>>       LayerNumber: 0
>>>>       Checkerboard: Off
>>>>       CheckerboardSpacing: 10 10
>>>>       CheckerboardOffset: 0 0
>>>>       Backing: Off
>>>>       BackingColor: 0 0 0
>>>>     Mapper:
>>>>       Debug: Off
>>>>       Modified Time: 96181
>>>>       Reference Count: 3
>>>>       Registered Events: (none)
>>>>       Executive: 0x4ecc950
>>>>       ErrorCode: Success
>>>>       Information: 0x4ecc440
>>>>       AbortExecute: Off
>>>>       Progress: 1
>>>>       Progress Text: (None)
>>>>       TimeToDraw: 0
>>>>       ClippingPlanes: (none)
>>>>       SlicePlane: 0x4691280
>>>>       SliceAtFocalPoint: Off
>>>>       SliceFacesCamera: Off
>>>>       Border: On
>>>>       Background: Off
>>>>       NumberOfThreads: 8
>>>>       JumpToNearestSlice: Off
>>>>       AutoAdjustImageQuality: On
>>>>       SeparateWindowLevelOperation: On
>>>>       ResampleToScreenPixels: On
>>>>       SlabThickness: 0
>>>>       SlabType: Mean
>>>>       SlabSampleFactor: 2
>>>>       ImageSampleFactor: 1
>>>>       Interpolator: 0x4ecf330
>>>>     Bounds: (-100, 100) (-100) (100) (-90.625) (-2.5)
>>>>
>>>> I will make a simple mock program and try to isolate the problem.
>>>> Thank you once again!
>>>> Miro
>>>>
>>>>
>>>>
>>>>
>>>> On 03/20/2014 12:31 PM, David Gobbi wrote:
>>>>> Hi Miro,
>>>>>
>>>>> You'll have to provide more details, because I use vtkCellPicker on
>>>>> vtkImageSlice all the time.  It's even part of the nightly VTK testing.
>>>>> Is there anything special about the way you use the vtkImageSlice?
>>>>> What version of VTK are you using?
>>>>>
>>>>>      David
>>>>>
>>>>> On Thu, Mar 20, 2014 at 1:15 PM, Miro Drahos <mdrahos at robodoc.com>
>>>>> wrote:
>>>>>> Hi all,
>>>>>> I am rendering an image slice using vtkImageSlice and a surface
>>>>>> (vtkActor).
>>>>>> When I perform picking using vtkCellPicker, I always pick the surface
>>>>>> actor,
>>>>>> even if it is in the background, behind the vtkImageSlice.
>>>>>> If I try to pick the vtkImageSlice (and the ray does not intersect the
>>>>>> surface actor), the Pick() method returns 0, as well as
>>>>>> picker->GetPath()
>>>>>> returns NULL. The vtkImageSlice is set to be pickable.
>>>>>> I am quite baffled by this, since I'd expect to be able to pick
>>>>>> vtkImageSlice with vtkCellPicker, since it is a vtkProp3D.
>>>>>> If I use vtkPropPicker, I can pick the image slice fine, but I would
>>>>>> prefer
>>>>>> to use vtkCellPicker so that I can specify picking tolerance.
>>>>>> Can someone shed some light on this?
>>>>>> Thank you tons!
>>>>>> Miro
>>>>
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