OpenCV re-projection matrix

Reference:
[1] Learning OpenCV book.
[2] http://www.xuebuyuan.com/1162766.html

VTK volume dimension

These settings specifies the dimension and position of your vtkImageData object.

SetExtent sets the dimensions in each axis. e.g. a dataset of 50 images and width/height of 512/512

myVtkImageData->SetExtent(0,511,0,511,0,49);

SetSpacing sets the size of a voxel (size in each direction x,y,z) in your dataset.

(default)

myVtkImageData->SetSpacing(1,1,1);

SetOrigin sets the position in 3D space of point 0 0 0 (first pixel)

(default)

myVtkImageData->SetOrigin(0,0,0)




The absolute size of a volume is determined by the 'Extent' x 'Spacing' (i.e. number of voxel multiply by size of the voxel). To downsample the volume (increase spacing), we should:

double scale = 2.0;
// Specify the size of the image data
imageData->SetExtent(-100/scale, 100/scale, -100/scale, 100/scale, -50/scale, 50/scale);

imageData->SetSpacing(scale, scale, scale);

//----------------------------------------------------------------------------
void vtkImageData::GetDimensions(int *dOut)
{
  const int* extent = this->Extent;
  dOut[0] = extent[1] - extent[0] + 1;
  dOut[1] = extent[3] - extent[2] + 1;
  dOut[2] = extent[5] - extent[4] + 1;

}