These parameters are used to set motion blur properties on a per-object basis.

Transform Type

Specifies what type of motion the object has. Options are linearrotate_about_center, and rotate_about_originlinear corresponds to the linear interpolation between matrices. rotate_about_origin corresponds to curved_motionblur=true. Unlike, rotate_about_origin which sets the rotation pivot at the origin, rotate_about_center will rotate about the object's center. This is the default mode and is useful for wheels, propellers, and other objects which spin.

Transform Keys

Overrides the Arnold ROP settings for Transform Keys.

The number of sub-steps used for motion blur can be set in the keys attribute within the Motion Blur settings. For situations where there is a direct movement, such as translation and rotation with constant speed, two keys are enough. However, if the object moves erratically during the exposure interval or performs any other kind of non-linear movement, you will need to increase the number of keys. 

Increasing the number of keys does not usually have much effect on rendering times, although it requires more memory to store the additional geometry at multiple times, especially for large polygon meshes. 

Below are examples where an increase in the number of keys is required. Notice that increasing the number of keys rounds off the corners of the spinning wheel:


The effect is more apparent when animating a deforming object along a motion path:

Keys 2 (default). Rollover image.

Keys 4 (rollover image).

Keys 8 (rollover image).

Deform Keys

Overrides the Arnold ROP settings for Deform Keys.

The number of motion keys for deformation transformation. Can only be used to motion blur objects with moving but same numbered vertices. Cannot be used for objects with changing topology. In that case use Velocity blur (on the object motion blur properties).

Adding motion blur to fur requires Deform Keys.

Velocity Blur

Velocity blur can be used to add motion blur to objects with changing topology like the polygon result of a fluid sim.

Requires the velocity point attribute to use for velocity blur. The Houdini convention is 'v'.


Acceleration Blur

Adjusts the velocity by acceleration at each motion step. Acceleration is often available in particle systems or simulations and is used in HtoA to curve the traditional velocity blur. The Houdini < 12.5 convention is 'accel'. In Houdini 13 and later, 'force / mass' can be used instead.

Although this would also be possible by using many motion keys, it simplifies the computations of motion keys on changing topology such as particles.

Enabled only if Velocity Blur is checked, as both the velocity and acceleration attributes are need for acceleration blur. Uses the keys set in Deform Keys. 

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