Using the iVolume Tool

Getting Started with IDL: Volume Visualization

Using the iVolume Tool

The interactive iVolume tool allows you great flexibility in manipulating and visualizing true volume data.

Displaying a Volume

Here is a simple example of one way to visualize a volume using the iVolume tool.

At the IDL command line, specify the location of the data file:

file = FILEPATH('head.dat', $  
   SUBDIRECTORY = ['examples', 'data'])  
data = READ_BINARY(file, DATA_DIMS = [80, 100, 57])

Now invoke the iVolume tool to visualize the volume:

iVolume, data

Volume data does not automatically appear in the tool window since volume rendering can be a time consuming operation. To render the volume, click the Render button on the tool. Auto-render is available but not set by default since it can slow down your iTool session if you have simultaneous operations.

Note
Volume data is only rendered if the volume dataspace is selected. Thus, if you have multiple volumes in your dataspace, auto-render must be turned on in order to render both simultaneously.

The data loaded earlier can be displayed by clicking the Render button.

Figure 8-1: Rendered MRI Head Volume Data

Figure 8-1: Rendered MRI Head Volume Data

Volume Rendering Quality

The volume can be rendered in two quality modes:

Low — Done with a stack of 2D texture-mapped semi-transparent polygons. The polygons are oriented so that the flat sides face the viewer as directly as possible. On most systems, Low-quality mode renders faster than High-quality mode, but not as accurately.

High — Done with the IDLgrVolume ray-casting volume renderer. This quality mode is CPU-intensive and will usually take much longer than the Low-quality mode.

Volume Extents

Since the volume is not always rendered, iVolume draws volume extents to help you locate and select the volume. You can select the volume by selecting on the extents, without rendering the volume. By default, iVolume draws a translucent solid cube with internal extents. You can also select a wire frame, or no extents.

Note
Use caution when turning off extents. If extents are turned off and Auto-Render is also off, you may need to use the Visualization Browser to select the volume again.

Modifying Volume Data

The iVolume tool allows you many options such as displaying multiple planes, manipulating volume color and lighting, filtering, resampling, image planes, isosurfaces, interval volumes, viewing statistics and annotating. For much more information on working with the iVolume tool, see Working with Volumes.

IDL Online Help (March 06, 2007)