When VisIt displays 3D plots, there are a few navigation styles from which you can choose by clicking on the following radio buttons in the Interactors window: Trackball, Dolly, and Flythrough. The default navigation style for 3D plots is: Trackball and it allows you to interactively rotate plots and move around them but it keeps the camera at a fixed distance from the plots and while it can get infinitely close to plots when you zoom in, it can never touch them or go inside of them. The Dolly navigation style behaves like the trackball style except that the when the camera zooms, it is actually moved. The Flythrough navigation style moves the camera and allows you to fly into plots and out the other side.