[vtkusers] stenciling problem-- is this code thread safe?
David Gobbi
david.gobbi at gmail.com
Fri Feb 11 16:56:13 EST 2011
I should add: vtkLassooStencilSource is not only much more
efficient than vtkPolyDataToImageStencil, but it is also much
more robust. Internally it is simpler and has fewer heuristics.
- David
On Fri, Feb 11, 2011 at 2:48 PM, David Gobbi <david.gobbi at gmail.com> wrote:
> The old code shouldn't break, it didn't break any of the
> regression tests at least. To be safe, you should be using
> vtkTransformToPolyDataFilter to add a shift to the extruded
> data, just like the TestImageTracerWidget.
>
> Your other option is to use vtkLassoStencilSource (new in VTK 5.8)
> instead of vtkPolyDataToImageStencil. It requires you to build
> your own contours (it takes a list of points as input) but it is more
> efficient than vtkPolyDataToImageStencil and it can take x-aligned
> and y-aligned contours as well as z-aligned. It has a
> SetSliceOrientation() method to allow you to set the orientation.
>
> - David
>
>
> On Fri, Feb 11, 2011 at 2:33 PM, Mark Roden <mmroden at gmail.com> wrote:
>> I guess the question is why the 5.6 method doesn't work with 5.9, if
>> the extrusion/polydatatostencil/stencil pipeline should be good-- ie,
>> if I have contours drawn along the x plane, I'll need this
>> non-z-stacking approach to work (and I do have such contours). Our
>> app allows users to draw their contours on any plane, so the z-aligned
>> contour assumption isn't entirely useful to me.
>>
>> It looks like there's a noop happening somewhere, as if the something
>> in that pipeline just decided that because there are only polys (or
>> something similar), it's not going to do the work. If polys are still
>> a valid input, then why should the old code break?
>>
>> On Fri, Feb 11, 2011 at 1:24 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>> Ah, it looks like TestImageTracerWidget.cxx uses slices that
>>> aren't parallel to the XY plane... so it actually has to use the
>>> old extrusion method to prepare the data.
>>>
>>> - David
>>>
>>>
>>> On Fri, Feb 11, 2011 at 1:57 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>> I was recommending that you visualize the contours as polydata,
>>>> so telling me that you are still getting blank images doesn't help
>>>> to move things forward.
>>>>
>>>> PolyDataToImageStencil still works on polys. It has two modes:
>>>> it can be given a closed polyhedral surface (like before) or,
>>>> in VTK 5.8 and 5.9, it can be given a set of polyline contours.
>>>> But if its input contains any polys, then it will ignore the polylines.
>>>> And if given a set of polys that do not form a closed surface, it
>>>> will usually not work (this depends on the orientation of the polys).
>>>> Given a single, flat poly it will never work, if given polys the polys
>>>> must define an enclosed volume.
>>>>
>>>> The vtkImageTracer widget has not been updated recently, so
>>>> it still uses extrusion in order to generate a surface, instead of
>>>> using the more efficient contour-to-stencil conversion.
>>>>
>>>> The contours should be closed and connected, which they should
>>>> be if they are generated from polygon edges, but vtkCleanPolyData
>>>> can be used as further insurance. An example of contour use is
>>>> Hybrid/Testing/Tcl/TestImageStencilWithPolydata.tcl
>>>>
>>>> But I've gone ahead and merged a patch for the vtkLinearExtrusion
>>>> multithreading bug. I'd prefer if you continued to diagnose the
>>>> contour issue and get it working that way, but that's up to you.
>>>>
>>>> - David
>>>>
>>>>
>>>> On Fri, Feb 11, 2011 at 1:34 PM, Mark Roden <mmroden at gmail.com> wrote:
>>>>> Hi David,
>>>>>
>>>>> Yes, I'm feeding these things into a visualizer. It's the same code
>>>>> path as when I was using 5.6, in that it's going right into a mapper
>>>>> to an actor to a renderer. I'm getting blank images.
>>>>>
>>>>> I'm wondering if it could be easier to avoid this extra filter (that
>>>>> seems to have some kind of angle threshold?) and just redo the gdcm
>>>>> poly reader to report both polys and lines, and then blank the polys
>>>>> if necessary for the stenciling code.
>>>>>
>>>>> rtstructs are just a series of points that are supposed to be linearly
>>>>> connected. right now, the code to feed them into the polys array
>>>>> looks like:
>>>>>
>>>>>
>>>>> vtkCellArray *polys = vtkCellArray::New();
>>>>> for(unsigned int i = 0; i < nitems; ++i){//nitems = number of
>>>>> closed contour polygons
>>>>> ....
>>>>> for(unsigned int i = 0; i < npts * 3; i+=3)
>>>>> {
>>>>> float x[3];
>>>>> x[0] = pts[i+0];
>>>>> x[1] = pts[i+1];
>>>>> x[2] = pts[i+2];
>>>>> vtkIdType ptId = newPts->InsertNextPoint( x );
>>>>> ptIds[i / 3] = ptId;
>>>>> }
>>>>> // Each Contour Data is in fact a Cell:
>>>>> vtkIdType cellId = polys->InsertNextCell( npts , ptIds);
>>>>> }
>>>>> Could you point me to some sample code I can use to construct the
>>>>> lines necessary to make your filter work, as opposed to the polys that
>>>>> the reader is currently producing?
>>>>>
>>>>>
>>>>>
>>>>> On Fri, Feb 11, 2011 at 12:14 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>>>> A better approach would be to visualize the contours to make
>>>>>> sure there's nothing wrong with them. Just feed them into a
>>>>>> vtkDataSetMapper, add that mapper to a vtkActor, and add that
>>>>>> to your renderer. If they don't look right, then do the same for the
>>>>>> polygons. You need to know what kind of input you are feeding into
>>>>>> vtkPolyDataToImageStencil before you start worrying about the output.
>>>>>>
>>>>>> On Fri, Feb 11, 2011 at 1:01 PM, Mark Roden <mmroden at gmail.com> wrote:
>>>>>>> whoops. Thanks for that.
>>>>>>>
>>>>>>> Now theLines has some information in it, although more than I think it should.
>>>>>>>
>>>>>>> Still not showing up in my displays, though, whereas it was in the 5.6 version.
>>>>>>>
>>>>>>> Is there a way to quickly walk through the contents of vtkImageData to
>>>>>>> see if there's anything there produced by the stenciling? I'm
>>>>>>> wondering if something's broken in the visualization code.
>>>>>>>
>>>>>>> On Fri, Feb 11, 2011 at 11:57 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>>>>>> I gotta ask... did you call theEdges.Update() before checking the output?
>>>>>>>>
>>>>>>>> On Fri, Feb 11, 2011 at 12:49 PM, Mark Roden <mmroden at gmail.com> wrote:
>>>>>>>>> Yeah, that doesn't work.
>>>>>>>>>
>>>>>>>>> vtkCellArray thePolys = data.GetPolys();
>>>>>>>>> vtkCellArray theStrips = data.GetStrips();
>>>>>>>>> vtkCellArray theLines = data.GetLines();
>>>>>>>>>
>>>>>>>>> vtkFeatureEdges theEdges = new vtkFeatureEdges();
>>>>>>>>> theEdges.BoundaryEdgesOn();
>>>>>>>>> theEdges.ManifoldEdgesOn();
>>>>>>>>> theEdges.NonManifoldEdgesOn();
>>>>>>>>> theEdges.FeatureEdgesOn();
>>>>>>>>> theEdges.SetInput(data);
>>>>>>>>> vtkPolyData theEdgeData = theEdges.GetOutput();
>>>>>>>>>
>>>>>>>>> thePolys = theEdgeData.GetPolys();
>>>>>>>>> theStrips = theEdgeData.GetStrips();
>>>>>>>>> theLines = theEdgeData.GetLines();
>>>>>>>>>
>>>>>>>>> thePolys, theStrips, and theLines are all zero-sized once
>>>>>>>>> theFeatureEdges filter is run, but thePolys has 25 points (for my test
>>>>>>>>> data) prior to running.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Fri, Feb 11, 2011 at 11:37 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>>>>>>>> You could try vtkFeatureEdges. There is probably a better filter for
>>>>>>>>>> the job, but I don't know.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Fri, Feb 11, 2011 at 12:25 PM, Mark Roden <mmroden at gmail.com> wrote:
>>>>>>>>>>> OK, so it looks like everything's coming back as polys instead of
>>>>>>>>>>> lines. What's the best way to proceed then, modify the reader to get
>>>>>>>>>>> just lines, or is there some way to convert from the polys to lines?
>>>>>>>>>>>
>>>>>>>>>>> On Fri, Feb 11, 2011 at 11:12 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>>>>>>>>>> Just verify that the vtkGDCMPolyDataReader contains no polygons, i.e.
>>>>>>>>>>>> get its output and call output.GetPolys() and output.GetStrips().
>>>>>>>>>>>> Both of these should be null, because a single polygon or strip in the
>>>>>>>>>>>> polydata will keep the contour code from working. The output of
>>>>>>>>>>>> GetLines() should, of course, not be null, since that is what
>>>>>>>>>>>> vtkPolyDataToImageStencil will use to create the stencil.
>>>>>>>>>>>>
>>>>>>>>>>>> - David
>>>>>>>>>>>>
>>>>>>>>>>>> On Fri, Feb 11, 2011 at 12:05 PM, Mark Roden <mmroden at gmail.com> wrote:
>>>>>>>>>>>>> So in this code, which is using a vtkPolyData 'data' that is a series
>>>>>>>>>>>>> of xy contours along the z axis, as restored by the
>>>>>>>>>>>>> vtkGDCMPolyDataReader (and working in 5.6):
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> //vtk 5.9 no longer requires linear extrusion beforehand
>>>>>>>>>>>>> //vtkLinearExtrusionFilter extruder = new vtkLinearExtrusionFilter();
>>>>>>>>>>>>> //extruder.SetInput(data);
>>>>>>>>>>>>> //extruder.SetVector(0, 0, spacing[2]);
>>>>>>>>>>>>> //extruder.Update();
>>>>>>>>>>>>> //vtkPolyData extruderOutput = extruder.GetOutput();
>>>>>>>>>>>>>
>>>>>>>>>>>>> vtkPolyDataToImageStencil pol2Stenc = new vtkPolyDataToImageStencil();
>>>>>>>>>>>>> pol2Stenc.SetTolerance(0);
>>>>>>>>>>>>> //pol2Stenc.SetInput(extruderOutput);
>>>>>>>>>>>>> pol2Stenc.SetInput(data);
>>>>>>>>>>>>> pol2Stenc.SetInformationInput(binaryOrgan);
>>>>>>>>>>>>> pol2Stenc.Update();
>>>>>>>>>>>>> vtkImageStencilData pol2StencOutput = pol2Stenc.GetOutput();
>>>>>>>>>>>>>
>>>>>>>>>>>>> vtkImageStencil stencil = new vtkImageStencil();
>>>>>>>>>>>>> stencil.SetInput(binaryOrgan);
>>>>>>>>>>>>> stencil.ReverseStencilOn();
>>>>>>>>>>>>> stencil.SetStencil(pol2StencOutput);
>>>>>>>>>>>>> stencil.Update();
>>>>>>>>>>>>>
>>>>>>>>>>>>> final vtkImageData stencilOutput = stencil.GetOutput();
>>>>>>>>>>>>> final vtkImageData imageToKeep = new vtkImageData();
>>>>>>>>>>>>> imageToKeep.DeepCopy(stencilOutput);
>>>>>>>>>>>>> stencilOutput.Delete();
>>>>>>>>>>>>>
>>>>>>>>>>>>> The result is a blank image. Is there a call I'm missing here?
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Fri, Feb 11, 2011 at 11:00 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>>>>>>>>>>>> The vtkPolyDataToImageStencil in VTK 5.8 and 5.9 can take a polyline
>>>>>>>>>>>>>> contour or a stack of contours as input and create a stencil from
>>>>>>>>>>>>>> that. Each polylines should lie in an XY plane (though they can be at
>>>>>>>>>>>>>> any Z position). This will not work with a polygon; a polyline is
>>>>>>>>>>>>>> required.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> - David
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Fri, Feb 11, 2011 at 11:51 AM, Mark Roden <mmroden at gmail.com> wrote:
>>>>>>>>>>>>>>> Hi David,
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> How should the stenciling be done in vtk 5.9 then? If I remove the
>>>>>>>>>>>>>>> linear extrusion, no masks are produced.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> This is exciting-- I can now use the vtkSmartVolumeMapper, which I've
>>>>>>>>>>>>>>> been drooling over ever since it was introduced!
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>>> Mark
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> On Fri, Feb 11, 2011 at 10:39 AM, Mark Roden <mmroden at gmail.com> wrote:
>>>>>>>>>>>>>>>> wait, never mind! I had some issues with vtk strings, but it appears
>>>>>>>>>>>>>>>> that this line:
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> outWin.SetInstance(outWin);
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> is now deprecated or something, because having that line active in this snippet:
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> vtkFileOutputWindow outWin = new vtkFileOutputWindow();
>>>>>>>>>>>>>>>> outWin.SetInstance(outWin);
>>>>>>>>>>>>>>>> outWin.SetFileName("MVSVTKViewer.log");
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> throws this exception:
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Exception in thread "main" java.lang.NoSuchFieldError: vtkId
>>>>>>>>>>>>>>>> at vtk.vtkOutputWindow.SetInstance_3(Native Method)
>>>>>>>>>>>>>>>> at vtk.vtkOutputWindow.SetInstance(vtkOutputWindow.java:45)
>>>>>>>>>>>>>>>> at com.mvs.viewer.Application.main(Application.java:63)
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> But that's a different issue (bug?)
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> On Fri, Feb 11, 2011 at 10:35 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>>>>>>>>>>>>>>> If you are reporting the vtkLinearExtrusionFilter, I already did.
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> On Fri, Feb 11, 2011 at 11:31 AM, Mark Roden <mmroden at gmail.com> wrote:
>>>>>>>>>>>>>>>>>> Hi David,
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Unfortunately, the current vtk master branch is seriously broken in
>>>>>>>>>>>>>>>>>> its java wrappings. I'm putting together a bug report now...
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>>>>>> Mark
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> On Fri, Feb 11, 2011 at 10:09 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>> I should add: with the current VTK master and release branches,
>>>>>>>>>>>>>>>>>>> vtkPolyDataToImageStencil no longer requires vtkLinearExtrusionFilter
>>>>>>>>>>>>>>>>>>> to be used beforehand. So you could try that.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> - David
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> On Fri, Feb 11, 2011 at 11:06 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>> I was doubtful about the global memory, but I looked through the
>>>>>>>>>>>>>>>>>>>> filters just to be sure. And guess what I found... here is some
>>>>>>>>>>>>>>>>>>>> highly suspect code in vtkLinearExtrusionFilter:
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> double *vtkLinearExtrusionFilter::ViaNormal(double x[3], vtkIdType id,
>>>>>>>>>>>>>>>>>>>> vtkDataArray *n)
>>>>>>>>>>>>>>>>>>>> {
>>>>>>>>>>>>>>>>>>>> static double xNew[3], normal[3];
>>>>>>>>>>>>>>>>>>>> int i;
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> n->GetTuple(id, normal);
>>>>>>>>>>>>>>>>>>>> for (i=0; i<3; i++)
>>>>>>>>>>>>>>>>>>>> {
>>>>>>>>>>>>>>>>>>>> xNew[i] = x[i] + this->ScaleFactor*normal[i];
>>>>>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> return xNew;
>>>>>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> Code like the above is definitely going to cause thread problems.
>>>>>>>>>>>>>>>>>>>> And this isn't the only place in that class where code like this appears.
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> Yikes!
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> - David
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> On Fri, Feb 11, 2011 at 10:46 AM, Mark Roden <mmroden at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>>> What I mean is, I have a vtkPolyData that has been DeepCopied and a
>>>>>>>>>>>>>>>>>>>>> vtkImageData that is binary and distinct from all other data.
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> When I call the previously listed code with multiple threads (each
>>>>>>>>>>>>>>>>>>>>> with their own polydata and binary image to fill in), the result is
>>>>>>>>>>>>>>>>>>>>> generally a very garbled image. If I call from a single thread in
>>>>>>>>>>>>>>>>>>>>> series, one for each polydata/image pair, then everything works out
>>>>>>>>>>>>>>>>>>>>> fine.
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> So it seems to me that something in the above series isn't thread
>>>>>>>>>>>>>>>>>>>>> safe. Each thread is declaring its own local objects, but is there
>>>>>>>>>>>>>>>>>>>>> some global memory that's being used or accessed here?
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> On Fri, Feb 11, 2011 at 9:23 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>>>> Hi Mark,
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> Explain in more detail what you mean by "call from multiple threads".
>>>>>>>>>>>>>>>>>>>>>> VTK is, in general, not thread safe and you cannot call Update() on
>>>>>>>>>>>>>>>>>>>>>> a filter from more than one thread. Each thread needs to have its own
>>>>>>>>>>>>>>>>>>>>>> set of filters. And in general, you cannot feed a data object into more
>>>>>>>>>>>>>>>>>>>>>> than one thread, because even simple methods like GetBounds() are
>>>>>>>>>>>>>>>>>>>>>> not thread safe.
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> When using VTK from multiple threads, it is necessary to apply
>>>>>>>>>>>>>>>>>>>>>> extreme caution.
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> - David
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> On Fri, Feb 11, 2011 at 10:00 AM, Mark Roden <mmroden at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>>>>> Hi all,
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> This code does not have threads enabled in vtk 5.6.1 (the code is in Java):
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> vtkLinearExtrusionFilter extruder = new vtkLinearExtrusionFilter();
>>>>>>>>>>>>>>>>>>>>>>> extruder.SetInput(data);
>>>>>>>>>>>>>>>>>>>>>>> extruder.SetVector(0, 0, spacing[2]);
>>>>>>>>>>>>>>>>>>>>>>> extruder.Update();
>>>>>>>>>>>>>>>>>>>>>>> vtkPolyData extruderOutput = extruder.GetOutput();
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> vtkPolyDataToImageStencil pol2Stenc = new vtkPolyDataToImageStencil();
>>>>>>>>>>>>>>>>>>>>>>> pol2Stenc.SetTolerance(0);
>>>>>>>>>>>>>>>>>>>>>>> pol2Stenc.SetInput(extruderOutput);
>>>>>>>>>>>>>>>>>>>>>>> pol2Stenc.SetInformationInput(binaryOrgan);
>>>>>>>>>>>>>>>>>>>>>>> pol2Stenc.Update();
>>>>>>>>>>>>>>>>>>>>>>> vtkImageStencilData pol2StencOutput = pol2Stenc.GetOutput();
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> // This is where the memory leak is!!!!
>>>>>>>>>>>>>>>>>>>>>>> vtkImageStencil stencil = new vtkImageStencil();
>>>>>>>>>>>>>>>>>>>>>>> stencil.SetInput(binaryOrgan);
>>>>>>>>>>>>>>>>>>>>>>> stencil.ReverseStencilOn();
>>>>>>>>>>>>>>>>>>>>>>> stencil.SetStencil(pol2StencOutput);
>>>>>>>>>>>>>>>>>>>>>>> stencil.Update();
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> // We're doing this because of an email to Mark
>>>>>>>>>>>>>>>>>>>>>>> // that says this will fix our memory issues
>>>>>>>>>>>>>>>>>>>>>>> final vtkImageData stencilOutput = stencil.GetOutput();
>>>>>>>>>>>>>>>>>>>>>>> final vtkImageData imageToKeep = new vtkImageData();
>>>>>>>>>>>>>>>>>>>>>>> imageToKeep.DeepCopy(stencilOutput);
>>>>>>>>>>>>>>>>>>>>>>> stencilOutput.Delete();
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> When I try to call this code from multiple threads (ie, to create the
>>>>>>>>>>>>>>>>>>>>>>> stencils for multiple organs), Bad Things happen, as in, the data are
>>>>>>>>>>>>>>>>>>>>>>> entirely corrupted. Is this code thread safe?
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> Mark
>>>>>>>>>>>>>>>>>>>>>>> _______________________________________________
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>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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