[vtk-developers] Add GetPoint function to vtkStructuredGrid

[David Doria]

>
> Close but still no cigar.  Don't use "int", use vtkIdType instead.
> Otherwise your code will not be 64-bit safe.  In fact, to make it
> 64-bit safe you need to do this:
>
>   vtkIdType xrel = x - extent[0];
>   vtkIdType yrel = y - extent[2];
>   vtkIdType zrel = z - extent[4];
>   vtkIdType ind = zrel*dims[1]*dims[0] + yrel*dims[0] + xrel;
>
> Unless xrel, yrel, and zrel are also vtkIdType, the mathematical
> computation of "zrel*dims[1]*dims[0] + yrel*dims[0] + xrel" will be
> done in 32-bit regardless the type of the variable it gets stored in.
>
> This is all kind of moot, though, because you are kinda reinventing
> the wheel here.  After you do the bounds check you should just call
> the following function that will do the rest for you:
>
> vtkStructuredData::ComputePointIdForExtent(int extent[6], int ijk[3]);
>
> It already does everything but the bounds check.
>
>    David
>


Ah, even better. What about something like this (surely the flag name should
change...):

void vtkStructuredGrid::GetPoint(int x, int y, int z, bool
adjustForNonZeroExtentBeginning, double p[3])
{
  int extent[6];
  this->GetExtent(extent);

  if(x < extent[0] || x > extent[1] ||
     y < extent[2] || y > extent[3] ||
     z < extent[4] || z > extent[5])
    {
    return; // out of bounds!
    }

  int pos[3];
  pos[0] = x;
  pos[1] = y;
  pos[2] = z;

  vtkIdType id;

  if(adjustForNonZeroExtentBeginning)
    {
    id = vtkStructuredData::ComputePointIdForExtent(extent, pos);
    }
  else
    {
    int dim[3];
    this->GetDimensions(dim);
    id = vtkStructuredData::ComputePointId(dim, pos);
    }

  grid->GetPoint(id, p);
}

The point is just to access the point via GetPoint as you would with
PolyData and UnstructuredGrid, but rather than a linear index, here (as with
ImageData) a (x,y,z) index is needed. This is opposed to using static
vtkStructuredData functions, which don't seem to be pointed to anywhere in
the vtkStructuredGrid documentation.

Thanks,

David
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