How to Motion Capture a Horse

by Graham Edwards

How to motion capture a horse, courtesty of Animatrik

Motion capture is easy, right? You just put your actors in those funky suits with the bobbles on, record their antics, and use the data to drive your characters.

If only it were so simple. Any motion capture session is merely the start of a long, complex process that relies on skilled animators to adapt and interpret the data, before adding their own creative input. That’s true for human characters, and it’s also true for animals.

Sara Cameron, producer at performance capture and virtual production studio Animatrik, shared her recent experiences capturing the movement of horses for a videogame project currently in development.

Animatrik motion captured horses for a videogame project by mounting over 44 cameras on the walls and in the rafters of a riding stables.

Animatrik motion captured horses for a videogame project by mounting over 44 cameras on the walls and in the rafters of a riding stables.

First and foremost, any large animal needs a correspondingly large amount of space to move around in – and even the most well-trained horse can be unpredictable. Animatrik therefore sourced suitable riding stables in which to stage the action. “A studio just isn’t set up to have horses galloping through it,” commented Cameron.

Before the shoot, Animatrik undertook tests at an indoor riding arena specifically chosen for its low light levels – beneficial for a motion capture system that uses infrared light. The next step involved renting a life-size plastic horse. The team covered its body with retro-reflective markers to ensure the data would accurately reflect bone length, joint change and other specific elements of motion. Since the markers would need to stay in place at speeds of up to 30 miles per hour, the team also tracked down a sweat-resistant adhesive made specifically for horses.

The team undertook initial tests using a plastic horse.

The team undertook initial tests using a plastic horse.

“I tested the markers on my Rottweiler and got her to run around the studio,” recalled Cameron. “The tape didn’t bother her, which is important – the animal’s safety and comfort is our first concern. But, as we discovered through shooting, dogs don’t sweat through their skin the way horses do. On the first day, the horses were dripping with sweat and markers kept falling off!”

The solution was to tape up four horses at once. If the markers fell off one horse during a gallop, the others could continue while that animal went back to a motion capture specialist to be recalibrated. As each horse dropped out, another was always available to take its place.

Each horse wore sweat-resistant markers, which were tracked by the motion capture camera array.

Each horse wore sweat-resistant markers, which were tracked by the motion capture camera array.

The final shoot lasted for two full days, during which the crew used Animatrik’s motion capture road kit to track a total of seven horses. For safety reasons, putting cameras on tripods at ground level was not an option. Instead the team mounted cameras on walls and rafters, and positioned themselves above the action on a boom lift.

Complicating the process was the fact that – just like humans – no two horses are the same. Movements that come naturally for certain animals will inevitably cause others to recoil or rear up. Managing choreography for each individual horse across over 200 shots was therefore a significant challenge.

“Going from a standstill straight into a gallop wouldn’t be suitable, or healthy, for some of the horses on set,” Cameron explained. “ I broke up the moves, grouping the shots into skills for each horse. From there, I organized them into a sequence of moves that allowed the horse to go from walking to trotting and more, all with fluidity.”

Successfully concluding the motion capture process was, of course, simply the first step down a much longer path. “The priority for our specialists was to achieve true motion properly scaled to each horse,” said Cameron. “That way, the post production team would have raw size and rotation information, and could decide on an artistic level how to add them into the game engine.”

All photographs courtesy of Animatrik. Special thanks to Georgia Dawson.