Volume Rendering with iVolume

The Tool Palette interface and interactive iVolume tools allow you great flexibility in manipulating and visualizing true volume data. Both methods display the visualization in the IDL iVolume tool, which allows you to visualize, modify, and manipulate volumes in an interactive environment.

Displaying a Volume using the Tool Palette

In this example, we load some volume data and visualize it using the Tool Palette volume tool.

Make sure you are viewing the IDL Visualize Perspective. (Click the Visualize button (

) in the upper right of the Workbench.)

At the IDL command line, read the example volume data with the following commands:

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

These commands designate a file location and how to read the file into IDL. The variables FILE and HEAD_DATA are loaded into memory and display in the Variables view in the Workbench.

From the Variables View, drag the HEAD_DATA variable to the Volume tool in the Tool Palette.

Displaying a Volume using IVOLUME

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

At the IDL command line, read the example volume data as described above.

Now invoke the iVolume tool to visualize the volume:

iVolume, head_data

To display the volume in color, as the Tool Palette visualization does, enter the following command:

iVolume, head_data, RGB_TABLE0=21

Volume Rendering Quality

In the iVolume tool, Auto Rendering is turned on by default. A 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.

Displaying an Isosurface

An isosurface is a set of points in a three-dimensional array that have the same value. In volume data, an isosurface generally defines a structure of some sort. To display an isosurface using the iVolume tool:

Click on the volume data to select it.

Select Operations → Volume → Isosurface from the iVolume menu.

Select the isosurface value and quality using the Isosurface Value Selector dialog. (Choose an isosurface value of 50 for a good result in this example.) Click OK.

Note
If you have checked the Auto-Render checkbox on the Volume tab, both the isosurface and the original volume will be rendered together. To see only the isosurface, uncheck the Auto-Render checkbox and click in the iVolume window.

Displaying Image Planes

An image plane is a two-dimensional slice taken through a three-dimensional volume. When presented as an image, image planes allow you to look at structures inside the volume.

To view an image plane:

Click on the volume data to select it. Make sure the Auto-Render checkbox on the Volume tab is unchecked.

Select Operations → Volume → Image plane from the iVolume menu.

Click on the image plane and drag back and forth to move the plane across the volume. To change the orientation of the image plane, double-click to display the image plane's property sheet, then select X, Y, or Z from the Orientation field.

You can also display the image slice in an iImage tool:

Click on the image plane to select it.

Select Operations → Image Plane → Launch iImage from the iVolume menu.

A new iImage tool is created to contain the image. Moving the image plane or changing its orientation in the iVolume tool automatically updates the image displayed in the iImage tool.

For much more information on working with the iVolume tool, see the Working with Volumes topic in the IDL Online Help.