[vtkusers] double vtkDataArray::GetTuple1(vtkIdType i) vs void vtkDataArray::GetTuple(vtkIdType i, double *tuple)

[Maarten Beek]

Hi David,

Thanks so much for your clarification!
I did see issues in the resulting image but was attributing them to noise in the original images. Now I see my code just had a huge bug in it.

I guess I would need a row counter in order to initialize voxelid correctly.

Wouldn't it be nice if the image iterator had a function like getVoxel(int ijk[3])...? I believe ITK has such an iterator.

Maarten


On Wednesday, May 7, 2014 5:26:23 PM, David Gobbi <david.gobbi at gmail.com> wrote:
 
I should add: you actually have to re-initialize the voxelid at the
beginning of each row (i.e. at the beginning of each span of the
iterator).

On Wed, May 7, 2014 at 3:22 PM, David Gobbi <david.gobbi at gmail.com> wrote:
> Hi Maarten,
>
> Since you know it's a vtkUnsignedCharArray, you shouldn't be using
> the SetTuple/GetTuple methods.  Use the SetTupleValue and
> GetTupleValue methods, they're much faster because 1) they aren't
> virtual methods and 2) they don't have to convert to/from double.
> Or even better, if you know that your array only has one component,
> you can use SetValue/GetValue.
>
> Your math for voxelid is too simplistic.  Depending on how the update
> extent is divided amongst the threads, it might give you a location
> that is totally wrong.  To see why, draw a square on a piece of paper.
> That square represents the total extent of the output.  Then divide
> that square into quadrants, and imagine that each quadrant goes
> to a different Execute method.  Then think about how each thread
> is going to march through the data.
>
>   David
>
>
> On Wed, May 7, 2014 at 2:20 PM, Maarten Beek <beekmaarten at yahoo.com> wrote:
>> Hi all,
>>
>> I experienced a crash in my algorithm derived from
>> vtkThreadedImageAlgorithm, that (I think) I solved, but that I don't
>> understand. Is there some one who can shed some light on the following?
>>
>> What I am trying to do is adding a flag identifying the input(s) that
>> contribute to the value of each pixel in the output image
>>
>> //----------------------------------------------------------------------------
>> // This templated function executes the filter for any type of data.
>> template <class OT>
>> void cmvtkTemplatedExecute(cmvtkDRRGenerator2* self,
>>                                vtkDataSetCollection* inputs, vtkImageData*
>> output,
>>                                int extent[6], int threadId, OT*)
>> {
>>     vtkUnsignedCharArray* uchararray =
>> vtkUnsignedCharArray::SafeDownCast(output->GetPointData()->GetScalars("input_flag"));
>>
>>     int numinputs = inputs->GetNumberOfItems();
>>     for( int input_i = 0; input_i < numinputs; ++input_i )
>>     {
>>         vtkImageData* input =
>> vtkImageData::SafeDownCast(inputs->GetItem(input_i));
>>         if( 0 == input )
>>         {
>>             // should not happen
>>             continue;
>>         }
>>         const int* dims= output->GetDimensions();
>>
>>         vtkImageProgressIterator<OT> outIt(output, extent, self, threadId);
>>         vtkIdType voxelid = extent[0] + size[0]*extent[2] +
>> size[0]*size[1]*extent[4];
>>
>>         // Loop through output pixels
>>         while( !outIt.IsAtEnd() )
>>         {
>>             OT* outSI = outIt.BeginSpan();
>>             OT* outSIEnd = outIt.EndSpan();
>>
>>             while( outSI != outSIEnd )
>>             {
>>                 // start with setting pixel to 0.0
>>                 if( input_i == 0 )
>>                 {
>>                     *outSI = 0.0;
>>                 }
>>
>>                 OT result = 0.0;
>>
>>                 //.... some math resulting in a value for result....
>>
>>                 *outSI += result;
>>
>>                 // this input image participates in voxel values; adjust bit
>>                 if( 0.0 < result && 0 != uchararray )
>>                 {
>>                     // The commented code crashes...
>>
>>                     //unsigned char oldvalue =
>> uchararray->GetTuple1(voxelid);
>>                     //unsigned char newvalue = oldvalue | (1<<input_i);
>>                     //uchararray->SetTuple1(voxelid, newvalue);
>>
>>                     double dOldValue;
>>                     uchararray->GetTuple(voxelid, &dOldValue);
>>                     unsigned char chOldValue = static_cast<unsigned
>> char>(dOldValue);
>>                     unsigned char chNewValue = chOldValue | (1<<input_i);
>>                     double dNewValue = static_cast<double>(chNewValue);
>>                     uchararray->SetTuple(voxelid, &dNewValue);
>>                 }
>>
>>                 ++outSI;
>>                 ++voxelid;
>>             }
>>             outIt.NextSpan();
>>         }
>>     } // input_i < numinputs
>> }
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