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The Null Object serves as a place-holder in a scene, and does not render. It can be used to designate a place in the space of your scene, or as a "look at" object to help coordinate a camera’s movement and field of view.
The Null Object is also used as an End Affector for constructing chains of bones. Its parameters are similar to those of the Geometry Object’s Transform and Miscellaneous tabs.
To change the null’s display geometry, go inside the node (Alt-click the icon in the network editor or select it and press I) and edit the SOPs defining its shape.
You can use the Null Object’s transform to define coordinate systems in either RIB or IFD renderings using the controls on the Render tab.
Placing a Null in the viewer
Place the null anywhere in the scene
Place the null at the origin
You can change the display, control type, and shading of the null on the Misc tab of the parameter editor.
The left menu chooses the order in which transforms are applied (for example, scale, then rotate, then translate). This can change the position and orientation of the object, in the same way that going a block and turning east takes you to a different place than turning east and then going a block.
The right menu chooses the order in which to rotate around the X, Y, and Z axes. Certain orders can make character joint transforms easier to use, depending on the character.
Translation along XYZ axes.
Degrees rotation about XYZ axes.
Non-uniform scaling about XYZ axes.
Local origin of the object. See also setting the pivot point .
Scale the object uniformly along all three axes.
This menu contains options for manipulating the pre-transform values. The pre-transform is an internal transform that is applied prior to the regular transform parameters. This allows you to change the frame of reference for the translate, rotate, scale parameter values below without changing the overall transform.
This reverts the translate, rotate, scale parameters to their default values while maintaining the same overall transform.
This sets the translate parameter to (0, 0, 0) while maintaining the same overall transform.
This sets the rotate parameter to (0, 0, 0) while maintaining the same overall transform.
This sets the scale parameter to (1, 1, 1) while maintaining the same overall transform.
This removes the pre-transform by setting the translate, rotate, and scale parameters in order to maintain the same overall transform. Note that if there were shears in the pre-transform, it can not be completely removed.
This completely removes the pre-transform without changing any parameters. This will change the overall transform of the object if there are any non-default values in the translate, rotate, and scale parameters.
Keep Position When Parenting
When the object is re-parented, maintain its current world position by changing the object’s transform parameters.
When the object is being transformed, maintain the current world transforms of its children by changing their transform parameters.
Enable Constraints Network on the object.
Path to a CHOP Constraints Network. See also creating constraints.
You can you use the Constraints drop down button to activate one of the Constraints Shelf Tool. If you do so, the first pick session is filled automatically by nodes selected in the parameter panel.
Whether or not this object is displayed in the viewport and rendered. Turn on the checkbox to have Houdini use this parameter, then set the value to 0 to hide the object in the viewport and not render it, or 1 to show and render the object. If the checkbox is off, Houdini ignores the value.
Output transform as render space (RIB/IFD)
If this parameter is turned on, then the transform of the null will be output to render scripts as a named transform space. As well, the pre-include and post-include will be enabled for inclusion into the render stream. Note that the display of the object must be turned on and the null must match the visible objects of the output driver.
Set Wireframe Color
Use the specified wireframe color
The display color of the object
Viewport Selecting Enabled
Object is capable of being picked in the viewport.
Script to run when the object is picked in the viewport. See select scripts .
Cache Object Transform
Caches object transforms once Houdini calculates them. This is especially useful for objects whose world space position is expensive to calculate (such as Sticky objects), and objects at the end of long parenting chains (such as Bones). This option is turned on by default for Sticky and Bone objects.
See the OBJ Caching section of the Houdini Preferences window for how to control the size of the object transform cache.
Uniform scaling about the xyz axes.
Whether to display only the icon, only the axis, or both.
Displays only the icon geometry.
Displays only the axis.
Icon and Axis
Displays both the icon and axis.
Switches between the type of geometry to display.
Displays null geometry (i.e. cross).
Displays circle primitives.
Displays box primitive.
Displays plane primitives.
Null and Circles
Displays null and circle primitives.
Null and Box
Displays null and box primitives.
Null and Planes
Displays null and plane primitives.
If an input source is specified, this option will display the geometry of the input.
Used in conjunction with circle or plane primitives. Determines which circles or planes to display.
Displays circle or plane primitives on the YZ, ZX and XY planes.
Displays a circle or plane primitive on the YZ plane.
Displays a circle or plane primitive on the ZX plane.
Displays a circle or plane primitive on the XY plane.
YZ, ZX planes
Displays circle or plane primitives on the YZ and ZX planes.
YZ, XY planes
Displays circle or plane primitives on the YZ and XY planes.
ZX, XY planes
Displays circle or plane primitives on the ZX and XY planes.
Determines whether to display the primitives as shaded objects or as wireframe objects.
Displays primitives in wireframe mode.
Displays primitives in shaded mode.