| iTool User's Guide: Working with Volumes |

## Extracting an Interval Volume

An interval volume is a set of tetrahedra that span a space between two isovalues within a volume. Since a tetrahedral mesh is a solid, iVolume displays the outer surface of the mesh as a set of polygons. This surface cannot be translated, scaled, or rotated relative to the volume but does move with the volume.

To create an interval volume, select Operations Volume Interval Volume, and a dialog appears allowing you to set two isovalues.

Figure 14-8: Interval Volume Value Selector for iVolume

Figure 14-8: Interval Volume Value Selector for iVolume

If the volume is multi channel, you can select a channel for setting the isovalues and then create an interval volume for that channel by selecting OK.

Figure 14-9: Original Volume Visualization and Interval Volume

Figure 14-9: Original Volume Visualization and Interval Volume

Note Vertex colors are not persevered during decimation.

Note Interval volume surfaces often contain a large number of polygons, which can degrade iVolume's display performance. When selecting isovalues, you can specify a decimation percentage to reduce the number of polygons in the resulting surface. This decimation step requires additional time, but the resulting surface will contain fewer triangles and will draw faster.

IDL Online Help (March 01, 2006)