Rendering volumetric data in molecular systems

A raster-based computer graphics method of imaging volumetric data (data sampled on a three-dimensional grid) has been added to an existing molecular rendering program. Any molecular property expressed as a 30 grid of scalar data values can be displayed around and inside of the molecular van der Waals surface as a collection of colored clouds and transparent surfaces. Different antical properties, such as color and opacity, are assigned to ranges of the molecular property and are rendered by a ray-tracing technique simulating the shading and shadowing of real objects, making the final images highly readable. We have found useful applications in the visualization of crystallographic electron density, electrostatic potentials and protein active sites. Optical properties, such as opacity and color, are assigned to the array of data values, creating a model image composed of colored clouds and transparent surfaces. The resultant images are very readable, as the rendering technique mimics the shading and shadowing of real objects. Distant parts of the molecule are obscured by foreground objects, so that the distracting build-up often seen in vector images is not a problem.