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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 ¶
To... | Do this |
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Place the null anywhere in the scene |
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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.
Parameters ¶
Transform ¶
Note
The transform of objects are also determined by the presence of any added node properties.
Transform Order
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.
Translate
Translation along XYZ axes.
Rotate
Degrees rotation about XYZ axes.
Scale
Non-uniform scaling about XYZ axes.
Pivot
Local origin of the object. See also setting the pivot point .
Uniform Scale
Scale the object uniformly along all three axes.
Modify Pre-Transform
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.
Clean Transform
This reverts the translate, rotate, scale parameters to their default values while maintaining the same overall transform.
Clean Translates
This sets the translate parameter to (0, 0, 0) while maintaining the same overall transform.
Clean Rotates
This sets the rotate parameter to (0, 0, 0) while maintaining the same overall transform.
Clean Scales
This sets the scale parameter to (1, 1, 1) while maintaining the same overall transform.
Extract Pre-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.
Reset Pre-transform
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.
Child Compensation
When the object is being transformed, maintain the current world transforms of its children by changing their transform parameters.
Enable Constraints
Enable Constraints Network on the object.
Constraints
Path to a CHOP Constraints Network.
Tip
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.
Note
Lookat and Follow Path parameters on object nodes are deprecated in favor of Look At and Follow Path constraints. The parameters are only hidden for now and you can set their visibility if you do edit the node’s parameter interface.
Render ¶
Display
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.
Misc ¶
Set Wireframe Color
Use the specified wireframe color
Wireframe Color
The display color of the object
Viewport Selecting Enabled
Object is capable of being picked in the viewport.
Select Script
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.
Geometry Scale
Uniform scaling about the xyz axes.
Display
Whether to display only the icon, only the axis, or both.
Icon
Displays only the icon geometry.
Axis
Displays only the axis.
Icon and Axis
Displays both the icon and axis.
Control Type
Switches between the type of geometry to display.
Null
Displays null geometry (i.e. cross).
Circles
Displays circle primitives.
Box
Displays box primitive.
Planes
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.
Custom
If an input source is specified, this option will display the geometry of the input.
Orientation
Used in conjunction with circle or plane primitives. Determines which circles or planes to display.
All planes
Displays circle or plane primitives on the YZ, ZX and XY planes.
YZ plane
Displays a circle or plane primitive on the YZ plane.
ZX plane
Displays a circle or plane primitive on the ZX plane.
XY 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.
Shaded Mode
Determines whether to display the primitives as shaded objects or as wireframe objects.
off
Displays primitives in wireframe mode.
on
Displays primitives in shaded mode.