K is for Kinematics

by Graham Edwards

K is for KinematicsIn the VFX ABC, the letter “K” stands for “Kinematics”.

If you’ve ever animated a creature using a piece of 3D software like Autodesk’s Maya or 3DSMax, you’ll know all about kinematics.

If you haven’t, here’s a quick primer …

Imagine you’re going to animate a troll. Just an regular troll: twelve feet tall with massive hands and a bad attitude. Let’s call him Tarquin.

The scene you’re going to animate requires Tarquin to reach out his hand and throttle a nearby dwarf. The dwarf’s name, by the way, is Doug.

Forward Kinematics

One way to perform the task is by using forward kinematics.

This is very tricky. Forward kinematics requires you to animate Tarquin’s arm starting from the shoulder and working your way out. In other words, you move his upper arm a bit, then adjust his forearm, then proceed to his hand, and finally manipulate those fat troll fingers.

The reason this is tricky is because what you really want to do is make sure Tarquin’s fingers connect with Doug’s neck in exactly the right place, at exactly the right time. That’s a tough call when those fingers are always the last appendage on the list of things you move.

Inverse Kinematics

If all that sounds like too much hard work, you might prefer to fall back on inverse kinematics.

This is much more satisfactory. With inverse kinematics, you get to focus entirely on Tarquin’s hand, grabbing it with your cursor moving it from its starting position to, you guessed it, the waiting neck of the poor, doomed Doug.

As for the rest of Tarquin’s arm, you simply rely on the software knowing how all the joints are interconnected, and trust it to move the entire limb accordingly. It’s like moving the hand of a jointed puppet and letting the laws of physics do the rest.

Of course, it’s not quite as simple as that. If you want to get any kind of expression into the movement (and, being an animator, that’s precisely your aim) you have to go in and make adjustments to the gross movement that’s been determined by the software. You know, all those small accelerations and delays, not to mention the unexpected muscle twitches caused by Tarquin’s predilection for strong ale.

If you have friendly rigging team, they might cause certain secondary movements to happen automatically. But it’s still up to you to coax a performance out of your troll.

If you want to learn more about kinematics, you’ll need to dig deep into a software tutorial, like the one in this Maya training video:

However, before you get lost down a rabbit hole filled with IK handles and pole vectors, let’s take a moment to consider the long and illustrious history of the word kinematics. Along the way, we might learn what it actually means.

Kinetographs and Kinetoscopes

One of the earliest devices developed for the presentation of moving pictures was the Kinetoscope. Both it and its counterpart, the Kinetograph, were created in the US at the Edison Lab during the 1890s.

Edison's Kinetoscope was developed during the final decade of the 19th century.

Edison’s Kinetoscope, one of the earliest motion picture viewers, was developed during the final decade of the 19th century.

The Kinetoscope presented moving images to its viewers by causing a strip of perforated celluloid film to pass in front of a light source at high speed, with each successive image on the film being isolated by a moving shutter. If that sounds like a movie projector to you, you’re nearly right.

Although the Kinetoscope contained all the essential components of a typical film projector, it was actually a peephole device, and thus could be viewed by only one person at a time.

As for the Kinetograph, that was the camera used to create the celluloid images in the first place.

By the turn of the century, a number of other inventors had jumped on the motion picture bandwagon, including Louis and August Lumière , whose Cinématographe machine was capable of displaying projected moving images to a large audience.

Kinematics in the Kinema

The root of all these words is the Greek word “kinema”, which means “motion”. As with many Greek words, during its journey across Europe and beyond, the “k” has been transformed into a “c”.

Which is why nobody goes to the kinema any more.

However, you can still find the word “kinema”, in all its derived forms, if you look hard enough. The technical and craft organisation that is the British Kinematograph, Sound and Television Society (BKSTS) – originally formed in 1931 as the British Kinematograph Society – is still going strong.

Then there’s the American Society of Cinematographers (ASC), a non-profit organisation dedicated to the art of filmmaking. Its magazine, American Cinematographer, was first published in 1920. It’s still going strong too.

Finally we have kinematics, that esoteric aspect of the modern art of animation, the mastery of which demands the application of both artistic sensibilities and technical smarts.

And the name of which contains a pleasing echo of the long history of the motion picture craft.