Cooking this node can generate many USD time samples, rather than just a single time sample at the current time. This can be equivalent to having a Cache LOP following this node, but it will evaluate much faster, and does not cache data from any other nodes. This allows animated data to be authored to USD without introducing a node time dependency which would then cause all following nodes to also be time dependent. This can vastly improve playback performance of some LOP Networks.

In all sampling modes, if a parameter on this node does not vary with time, and does not rely on other time sampled data from the stage, only a single default value will be generated in USD for the corresponding attribute. USD time samples are only generated for parameters that may vary over time.

When the Sampling behavior is Sample Frame Range, this parameter controls the number and spacing of base time samples to be generated by this node. The default values of this parameter are @fstart, @fend, and @finc. These values correspond to the start, end, and step size of the global Houdini animation settings when interacting with Houdini. When using a ROP node to generate a range of frames, these values correspond to the start, end, and increment values specified on the ROP node being executed. This default ensures that a USD file written to disk will contain time samples for exactly the frame range requested by the ROP (regardless of the Houdini animation settings).

For each primary sample generated by this node, these parameters can cause additional samples to be generated around that primary sample time. This is most often used to ensure that accurate data exists at exactly the camera shutter open and close times, as well as at the primary sample time.

Controls the method used to specify the shutter open and close times relative to the primary sample times.

When Shutter is set to Specify Manually, these two offset values are added to the primary sample time to indicate the shutter open and close times. The open time should be less than or equal to zero, and the close time should be greater than or equal to zero.

When Shutter is set to Use Camera Prim, this is the scene graph path of a camera prim on the input node’s stage. The shutter open and close attribute values are read from this primitive.

The number of subframe samples to create for each primary sample. These samples are evenly distributed between the shutter open and close times. Note that such an even distribution may or may not create a sample at exactly the primary sample time.

When turned on, forces a sample to be created at exactly the primary sample time. If the Samples value, together with the shutter open and close times, already place a sample at the primary sample time, turning on this option has no effect. Otherwise, this option causes an addition sample to be added. This means that the actual number of samples per primary sample may in fact be one more than the number specified in the Samples parameter.

Whether the source (the thing constrained to follow a path) is a regular primitive, or a point instance. You cannot use a nested point instance as a source.

When Source Type is Primitive, the scene graph path to the prim to use.

When Source Type is Point Instancer, the point instance to use, using /‹path›[‹instance_index›] syntax (for example, /geometry/instancer[1]).

Where to get the path curve to follow, either the first input or the second input.

Whether the path is a regular primitive, or a point instance. (You can use a nested point instance as a target.)

When Target Type is Primitive, the scene graph path to the prim to use.

When Target Type is Point Instancer, the point instance to use, using /‹path›[‹instance_index›] syntax (for example, /geometry/instancer[1]).

When Target Source is First Input and Type is Primitive, whether to hide set the path’s visibility to “hidden”.

Specify the frame at which the source and/or target geometry are imported into the embedded SOP network to build the constraints.

The default $FF expression forces the constraint LOP to be time dependent, which is needed when operating on a non time-dependent network that has time samples driving the source or target primitives.

However, for better performance with a non time-dependent network with no time samples, it is recommended to use a static value instead.

When this is off (the default), the source object snaps onto the path it follows. When this is on, the object maintains the same relative distance between itself and the path as it follows the shape of the path.

How to map the Position value onto the path.

When Parameterization is Distance Point Attribute, the name of the primvar containing the distance value (not including the primvar: prefix). The primvar must be a vector3, but only the first (X) component is used.

Where to position the source object along the path. To animate the source object along the path, this should be an expression based on the current frame ($F) or time ($T).

For example, if Parameterizaiton is Normalized Distance, you might set this to $F/100.

Set the position using a VEX snippet. The snippet should write the position value to the pos variable. You can use the variables typically available to an Attribute Wrangle SOP. @ptnum is the index of the current prim being constrained. You can use npoints(0) to get the total number of prims being constrained. You can use @Frame and @Time to make the snippet time-dependent.

The initial value of pos (at the start of the snippet) is the evaluated value of the Position parameter. So you can use an expression in that parameter to compute a “base” value, and modify it using the snippet.

How to compute the direction the source object points along.

When Look At Mode is From Primitive, where to get the primitive to look at (the first or second input).

When Look At Mode is From Primitive, the scene graph path of the prim to look at. (This does not support looking at a point instance.)

When Look At Mode is Direction Attribute From Path, the name of a vector3f primvar (minus the primvar: prefix) to use as the look at direction.

How to compute the up vector.

When Look Up Mode is From Primitive, where to get the primitive to point the up vector at (the first or second input).

When Look Up Mode is From Primitive, the scene graph path of the prim to point the up vector at. (This does not support point instances.)

Which axis on the source object to match to the look at vector. You can use this to compensate for the orientation the source object was created in. This can’t be the same as the Look Up Axis.

Which axis on the source object to match to the up vector. You can use this to compensate for the orientation the source object was created in. This can’t be the same as the Look At Axis.

When Look Up Mode is Up Attribute From Path, the name of a vector3f primvar (minus the primvar: prefix) to use as the look up vector.

Roll angle in degrees around the look at direction. You can use this, for example, to animate “banking” as the source object goes around curves.

Set the roll using a VEX snippet. The snippet should write the roll degrees to the roll variable. You can use the variables typically available to an Attribute Wrangle SOP. @ptnum is the index of the current prim being constrained. You can use npoints(0) to get the total number of prims being constrained. You can use @Frame and @Time to make the snippet time-dependent.

The initial value of roll (at the start of the snippet) is the evaluated value of the Roll parameter. So you can use an expression in that parameter to compute a “base” value, and modify it using the snippet.