3 Things To know about quadrupeds

3D World - - FEATURE -

DNEG an­i­ma­tion Di­rec­tor aaron Gil­man DIS­SECTS the finer points of an­i­mat­ing quadrupeds, Such as the bi­son for the film al­pha

1. know your quads: When an­i­mat­ing quadrupeds such as bi­son, it’s re­ally im­por­tant to un­der­stand all the nu­ances of how they move. There are nu­mer­ous gaits such as walks, trots, can­ters, trans­verse and ro­tary gal­lops. Each of these has a unique foot­fall pat­tern that the an­i­ma­tor needs to be flu­ent in, as well as un­der­stand­ing how these pat­terns tran­si­tion from one to the other. For ex­am­ple, be­sides the ro­tary gal­lop, all quadruped gaits com­mit to the ‘rule of di­ag­o­nals’, which means each fore foot con­tact must have a cor­re­spond­ing op­po­site hind foot con­tact­ing the ground in or­der for the an­i­mal to main­tain bal­ance. This same prin­ci­ple ap­plies to other quadrupeds like cat­tle, dogs and cats, and rep­tiles such as lizards.

2. Leg lock­ing: A lot of quadruped an­i­ma­tion rigs suf­fer from an­kle and el­bow pops or strange in­ter­po­la­tions frame to frame, be­cause the an­i­ma­tor of­ten has to key the con­tact leg pose on ev­ery frame as the weight passes over it. On Al­pha, DNEG made great use of a leg-lock­ing at­tribute we built into our an­i­ma­tion rig. Once the foot made con­tact with the ground, the an­i­ma­tor was able to switch the leg into leg lock mode, which would pre­serve the an­gles of all the joints in the chain, ef­fec­tively stop­ping the leg from chang­ing shape re­gard­less of how the torso moved around it. As the foot re­leases from the ground, the tog­gle gets keyed off, with a seam­less blend into the de­fault IK mode.

3. Mov­ing herds: Noth­ing in na­ture runs in a per­fectly cycli­cal or lin­ear line or re­peats it­self ex­actly from one step to the next. But we needed to go one step fur­ther with this se­quence, be­cause we also needed to un­der­stand how flock­ing be­hav­iour works in a herd. The bi­son needed to bump into each other in nat­u­ral ways, where we con­stantly feel the neg­a­tive space be­tween each an­i­mal com­press­ing and ex­pand­ing. Be­cause they are fol­low­ing a leader, the en­ergy of di­rec­tion change and re­spon­sive­ness to one an­other needs to cas­cade down the length of the herd, so the move­ment of the mass feels like a kind of con­trolled chaos. To un­der­stand this we stud­ied flock­ing be­hav­iour in herds such as buf­falo, horses, gazelles, ze­bra and schools of fish.

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