Raycasting is an image order algorithm used in computer graphics to render three dimensional scenes by following rays cast from the viewpoint of the observer to the dataset. The technique allows the researcher to view 3-D data without the intermediate step of deriving a geometric representation (i.e., isosurface) of the data.
- Allows the entire data set to be viewed at once.
- Lets the user see features that are obscured by surface techniques.
- Small or weakly defined features can be displayed.
- Typically computationally slower than surface rendering techniques.
- Produces superior images compared to splatting or 3-D Texture mapping.
In the raycasting method, a ray is following from each pixel on the screen into the dataset. As the ray traverses the dataset, samples are taken from the 3-D scalar values. The values are processed by a transfer function  that determines a color and opacity for the sample points. The color and opacity of each sample point along the ray is composited to get the correct color for the pixel on the screen. If a certain value of opacity is reached, the ray is terminated early. By interactively changing the color and opacity transfer functions, various structures are interactively revealed in the spatial domain.
- S. Fang, T. Biddlecome,M. Tuceryan, "Image-Based Transfer Function Design for Data Exploration in Volume Visualization ", Ninth IEEE Visualization 1998 (VIS '98) p. 319