vtkFixedPointVolumeRayCastMapper

Section: Visualization Toolkit Volume Rendering Classes

Usage

This is a software ray caster for rendering volumes in vtkImageData. It works with all input data types and up to four components. It performs composite or MIP rendering, and can be intermixed with geometric data. Space leaping is used to speed up the rendering process. In addition, calculation are performed in 15 bit fixed point precision. This mapper is threaded, and will interleave scan lines across processors.

This mapper is a good replacement for vtkVolumeRayCastMapper EXCEPT: - it does not do isosurface ray casting - it does only interpolate before classify compositing - it does only maximum scalar value MIP

The vtkVolumeRayCastMapper CANNOT be used in these instances when a vtkFixedPointVolumeRayCastMapper can be used: - if the data is not unsigned char or unsigned short - if the data has more than one component

This mapper handles all data type from unsigned char through double. However, some of the internal calcultions are performed in float and therefore even the full float range may cause problems for this mapper (both in scalar data values and in spacing between samples).

Space leaping is performed by creating a sub-sampled volume. 4x4x4 cells in the original volume are represented by a min, max, and combined gradient and flag value. The min max volume has three unsigned shorts per 4x4x4 group of cells from the original volume - one reprenting the minumum scalar index (the scalar value adjusted to fit in the 15 bit range), the maximum scalar index, and a third unsigned short which is both the maximum gradient opacity in the neighborhood (an unsigned char) and the flag that is filled in for the current lookup tables to indicate whether this region can be skipped.

To create an instance of class vtkFixedPointVolumeRayCastMapper, simply invoke its constructor as follows

  obj = vtkFixedPointVolumeRayCastMapper

Methods

The class vtkFixedPointVolumeRayCastMapper has several methods that can be used. They are listed below. Note that the documentation is translated automatically from the VTK sources, and may not be completely intelligible. When in doubt, consult the VTK website. In the methods listed below, obj is an instance of the vtkFixedPointVolumeRayCastMapper class.