VolumeLocatorNodes allow direct modification of the volume dimensions in the Maya view-port by way of context manipulators.
Manipulators are a standard Maya feature which can be accessed by enabling the Show Manipulator Tool (usually the ‘t’ key). You can read about Maya manipulators here:
With the Show Manipulator Tool enabled, selecting a VolumeLocatorNode will draw the manipulators required to modify the currently selected volume type. For example, a sphere volume will have only 1 manipulator, whereas a box volume will have 3. Editing the dimensions of a standard volume is simple. Just click and drag the blue diamond to alter the dimension as shown below.
You can also access the manipulators at any time by holding down the right-mouse button over any VolumeLocatorNode and selecting Edit Volume from the pop-up marking menu as shown below:
You can also choose to reset the volume to its default state via the above marking menu too.
Curve Volumes are a specialised type of volume which require a more complex interaction method. Each curve volume is made up of a series of key points which define the radius of the volume at a specific point along the curve’s length.
When you access the manipulator for a curve volume, each of these key points can be edited in the view-port simply by clicking and dragging the manipulator circle.
Accessing manipulators on a curve is done in the same way as on a standard volume type:
This will draw a blue circle on each of the curve volume’s key points. These blue circles are actually editable context manipulators and can be edited simply by clicking on them and dragging either into or away from the circle’s centre point.