Raytracing with POV-Ray

1x95 Nucleotides example

The Persistence of Vision Raytracer (POV-Ray) is included with Chimera. POV-Ray images can be saved:

Raytraced images can only be saved in the PNG format. For each raytraced image, Chimera first generates two POV-Ray input files: The raytracing calculation is then run as a background job that can be monitored or canceled using the Task Panel. Several raytracing parameters can be set in the POV-Ray Options preferences.

See also: exporting a scene, tips on preparing images

Lights and Shadows

Chimera includes two light sources, key (dominant) and fill (secondary). Their directions and intensities can be adjusted in the Lighting tool and are propogated to POV-Ray for raytracing. By default, only the key light produces shiny highlights and shadows. Decreasing the key-to-fill ratio will decrease the contrast between shadows and unshadowed regions.

Interactive shadowing in Chimera (the show shadows setting in Effects) can be used to preview where shadows will fall.

Balancing Time Requirements and Results

Sometimes a considerable speedup in raytracing can be obtained with little change in output appearance by adjusting settings in the POV-Ray Options preferences. This is particularly true for movies, which are compressed to some extent during encoding. Changes to consider include:

There is no single answer as to which values will optimally balance time requirements and results, as it will depend on the contents of the scene, the available computational power, and the patience of the user. Running a few tests is recommended before committing to raytracing a large set of images with a particular set of parameters.

Raytracing jobs can be monitored and canceled using the Task Panel.


Using transparency or clipping may increase rendering time significantly.

A raytraced image from POV-Ray may differ from the view in Chimera in several ways. Some differences are desirable, such as the presence of shadows. Others reflect current limitations of the POV-Ray format and/or its implementation in Chimera:

UCSF Computer Graphics Laboratory / August 2009