Surface Capping Surface Capping icon

Surface Capping draws planar caps that hide the interior of a surface model sliced by a clipping plane. Surface Capping information is included in saved sessions. See also: Surface Color, Color Zone, clip, mclip

There are several ways to start Surface Capping, a tool in the Depiction and Surface/Binding Analysis categories. It can also be called from the Side View and Per-Model Clipping dialogs, and is implemented as the command sop cap.

Options: Changes in numerical parameters take effect after return (Enter) is pressed. Caps are recalculated automatically when the clipping plane is moved, the surface is moved relative to the clipping plane, or the shape of the surface changes. Exceptions: a change in the resolution of a Multiscale Models surface or the shape of a molecular surface (MSMS model) may not trigger a cap update. An update can be triggered by moving the clipping plane slightly or toggling the Cap surfaces at clip planes option.


Lack of per-model settings. The settings apply to all surfaces. It is not possible to cap one surface but not another, or to use different colors, styles, or other capping parameters for different surfaces. This is a limitation of the user interface, not the underlying implementation.

Slow interactive rotation. Rotating the model causes the cap calculation to check if the near clipping plane intersects the surface at each frame of the rotation. This can slow down interactive rotation.

Artifacts in cap. Artifacts such as streaks and dots in a cap can occur when points in the border are very close together. Slight changes in the surface shape or the position of clipping plane relative to the surface will generally solve the problem.

Surfaces with a boundary. The cap calculation assumes that the intersection of the clipping plane and the surface forms closed loops. If the surface has a boundary (for example, a isosurface might end abruptly at the edge of the corresponding volume data), then its intersection with the clipping plane may form a non-closed curve, which will not be capped. The basic difficulty in this case is that the surface does not separate its interior from its exterior.

UCSF Computer Graphics Laboratory / September 2011