STAFF at two Oxford companies helped to create the stunning special effects for the Christmas blockbuster The Golden Compass.

As well as being filmed in Oxford, the movie used pioneering camera systems made by OMG (Oxford Metrics Group), based in Botley, and digital crowds created by Audiomotion, of Osney Mead.

One of the biggest challenges for the filmmakers was creating hundreds of characters - including polar bears, witches and other imaginary creatures - for the giant battle scenes.

New Line Cinema, the studio behind the Lord of the Rings trilogy, used a technology called motion capture to create "digital extras" in a huge battle that pitches Golden Compass heroine Lyra, played by Dakota Blue Richards, against Tartar guards, and to create a 'gyptian' crew for the film's Noorderlicht ship.

In the story by Oxford writer Philip Pullman, the gyptians are boat people, similar to gypsies, who live beside the canal in Port Meadow.

Audiomotion, now Europe's biggest motion-capture studio, created a replica of the gyptian ship, using rigging from the Cutty Sark restoration company. Vicon cameras were used to film a group of stunt men fighting on the rigging in the Osney Mead studio, and the images were replicated hundreds of times.

Managing director Mick Morris said: "You can digitise it and replicate it, and get the stunt guys to do things which would be too dangerous in practice. When movie people shoot the live action, they will populate just the front two rows of an army with extras, where there should be thousands of soldiers behind them.

"We will get a handful of stunt men to do different moves, and we can replicate them thousands of times. Motion capture is perfect for doing lots of crowd replication."

He added: "It has to be integrated with the live action. If you can see it when the film is released, someone has not done their job."

More than half the motion-capture cameras used by big movie studios are made by Vicon, part of OMG. The technology was developed by Oxford engineering don Julian Morris for surgeons to measure the movement of children with cerebral palsy.

It is now used by coaches analysing the bowling techniques of cricketers, road engineers and satellite navigation systems as well as movie directors creating fantastical characters and computer game makers.

Nick Bolton, who runs Vicon's parent company OMG, said: "Any time that you want to understand human movement in three dimensions, our technology is there."

He added: "Our success has a knock-on effect on the Oxfordshire economy because it helps the businesses that we buy our components from.

"We are recognised as a world leader in motion capture. We are now building a business using the technology in other areas such as unmanned aerial vehicles for surveillance."

Mr Morris said: "It was our good fortune to work on this production, but the work came to the UK as a result of tax breaks for the film industry.

"Pinewood and Shepperton have been making blockbuster movies, and it's good for the economy because of the amount of work it generates - direct employment and tourism."

How motion capture works: The actor or stunt man (or animal - dogs and cats are also used) wears a close-fitting black lycra body suit covered in small glass reflective spheres. As the actor moves, special cameras, which can see only the markers, take hundreds of photos very quickly. The software converts these images into three-dimensional film. Robbie Williams and Wayne Rooney are among stars who have been converted into computerised 'skeletons' by Audiomotion - for a pop video and a computer game, respectively.

Not all Hollywood directors like motion capture. The end of blockbuster cartoon Ratatouille proclaims the movie was made with "100 per cent genuine animation" and "no motion capture or any other performance shortcuts".