[vtkusers] How to crop a vtkImageData volume?

[Amy Squillacote]

Hi Al,

I'm copying this back to the vtkusers list. Please keep the discussion 
on the list so other people can contribute to the conversation and so 
the discussion is archived.

- Amy

allan.martin at utoronto.ca wrote:
> Hey Amy,
>
> Thanks for your help.  Do you have a brief example of how to use this? 
>  When I do the following, it doesn't seem to get the right region.  I 
> checked the bounds values and they look to be correct (a subset of the 
> original VoxelData bounds), so I'm rather confused.  Thoughts?
>
> vtkPlanes * boxVOIPlanes = vtkPlanes::New();
> boxVOI->GetPlanes(boxVOIPlanes);
> vtkExtractVOI * clipDataSet = vtkExtractVOI::New();
> clipDataSet->SetInput(VoxelData);
> double* bounds = boxVOIPlanes->GetPoints()->GetBounds();
> clipDataSet->SetVOI((int)bounds[0],(int)bounds[1],(int)bounds[2],
>                     (int)bounds[3],(int)bounds[4],(int)bounds[5]);
> clipDataSet->Update();
> mc->SetInput(clipDataSet->GetOutput());
>
> Cheers,
> Al
>
>
>
> Quoting Amy Squillacote <ahs at cfdrc.com>:
>
>> Hi Al,
>>
>> Assuming that you're cropping planes are aligned with the axes of the
>> vtkImageData volume, you could try using vtkExtractVOI instead. Its
>> output is still a vtkImageData, so you wouldn't have a problem with
>> passing it to vtkMarchingCubes.
>>
>> - Amy
>>
>> allan.martin at utoronto.ca wrote:
>>> Hi all,
>>>
>>> I'm trying to take a vtkImageData volume and crop it with a box  
>>> widget to make a smaller volume, so that when I subsequently render 
>>>  an isosurface it isn't so slow.  I think I'm close, but I can't  
>>> seem to get something that vtkMarchingCubes will eat (it wants a  
>>> vtkImageData object, and I don't know how to copy my  
>>> vtkUnstructuredGrid back to a vtkImageData object).  Anyone have an 
>>>  example of how to do this?
>>>
>>> Here is my broken code:
>>>
>>> //Start with a volume, and make it smaller with a box widget
>>> boxVOI = vtkBoxWidget::New();
>>> VoxelData = vtkImageData::New();
>>> ...
>>> //Now take the region defined by the box widget, and make a new  
>>> volume data set
>>> //that is smaller
>>> vtkPlanes* boxVOIPlanes = vtkPlanes::New();
>>> boxVOI->GetPlanes(boxVOIPlanes);
>>> vtkExtractGeometry* clipDataSet = vtkExtractGeometry::New();
>>> clipDataSet->SetInput(VoxelData);
>>> clipDataSet->SetImplicitFunction(boxVOIPlanes);
>>> vtkDataSet* output = (vtkDataSet*) clipDataSet->GetOutput();
>>> vtkImageData* croppedVoxelData = vtkImageData::New();
>>>
>>> //This copy doesn't seem to be sufficient as it doesn't copy the  
>>> number of dimensions and other vtkImageData fields
>>> croppedVoxelData->ShallowCopy(output);
>>> croppedVoxelData->AllocateScalars(); //It complains if scalars  
>>> aren't allocated
>>> mc->SetInput(croppedVoxelData);
>>>
>>>
>>> Thanks for your help,
>>>
>>> Al Martin
>>>
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>>
>> -- 
>> Amy Squillacote                    Phone: (256) 726-4839
>> Computer Scientist                 Fax: (256) 726-4806
>> CFD Research Corporation           Web: http://www.cfdrc.com
>> 215 Wynn Drive, Suite 501
>> Huntsville, AL  35805
>
>
>
> Regards,
>
> Al Martin
>
>
>

-- 
Amy Squillacote                    Phone: (256) 726-4839
Computer Scientist                 Fax: (256) 726-4806
CFD Research Corporation           Web: http://www.cfdrc.com
215 Wynn Drive, Suite 501
Huntsville, AL  35805