Keeping your feet on the ground

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  04 April 2013
Keeping your feet on the ground

Hi Everyone,

I've been trying to figure this out for a while and wondering how it's done. It's probably something like creating a script or some sort of computer code but as I've used Maya before for simple animation, the thing I've always wondered is how when you animate a character on a surface, how do you make it look like he's actually walking on the ground and not have his feet fall through the floor? I simply just click the floor and move it to meet his feet.

On more advanced projects, on CG animated movies I always wonder what the techniques are for vehicles, people or animals that are interacting with a surface--like a a street, building, forest car, ship, etc. In other words, what do they do that that keeps the character or vehicle from cutting into the other polygons it's interacting with?

For example, like Wreck-it Ralph, when he's climbing the Candy Cane tree how do his limbs like his feet or legs not poke through or fall into the tree since in reality the Tree and Ralph himself are just hollow polygons. Are people painstakingly animating him so he doesn't conflict with the tree? I've been wondering about this for a while and trying to figure out how it's done. It would be great if anyone could enlighten me on the process?
 
  04 April 2013
Look up some tutorials on rigging. Basically the rig gives you controls which can be animated, so you say, position the foot, and then you have little tweak controls you can use to make it deform a little so it LOOKS like it's contacting the surface. This is why good animation is so painstaking, you have to have a rig built for those kinds of things, and then the animator has to spend a lot of time placing and keying and tweaking to achieve those things, especially on the big screen.

There are also dynamics, which are a whole different ballgame in and of themselves. Basically you're letting the computer assist you with calculating the physics of something, but again, it has to be set up, simulated, tweaked, re-simulated, tweaked more, etc. to get that final animation.
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  04 April 2013
Ralphs hands don't go through the tree, because that's how he was animated. IK helps, and there may be extra deformers to smoosh the skin against the surface, but ultimately it's the animator's job to make sure the characters appear solid.
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  04 April 2013
After I typed this I then thought about physics in like game engines. As I can recall with the original Counter-Strike getting stuck in walls or falling through walls and the same with Dark Age of Camelot. Still, those are all games that use game engines and physics built in and I wonder how it works with CG animated films since I guess you could make a physics engine but that wouldn't be very economical for a linear film that lasts about 90-120 minutes as oppose to an interactive game where a player has control over the character and they move about in a 3d environment as opposed to watching predetermined movements created by animators for animated films.

It always amazes me to see 3D characters walking on uneven surface and all weird terrain cause all the time I'm thinking "Ah man, how long did that take to create and move around?"
 
  04 April 2013
I wouldn't like having constraints limiting where I could push a rig to, animators create the illusion of characters contacting and interacting with the scene by using proper placement of contact points. When it comes to feet the master control is usually on the ground with the feet flat on the surface so if I need to place feet flat on the flat surface I can just change my T-Y back to "0".
 
  04 April 2013
render them on separate layer. then composite them over the bg.
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  04 April 2013
Different rigging systems have solutions for feet. The only ones I am familiar with are character studio which has a footsteps system, CAT which also has an editable footstep system that will adhere to a specified surface and motionbuilder which has a floor system that interacts with foot and hand markers. These are only three solutions but I bet there is a lot more.
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  04 April 2013
Nearly anywhere it boils down to animators grunting the coarse work, and if additional subtleties are needed CharFX/AnimFX (or whatever the department is named in the eventual facility) will do a de-intersection pass (usually we have tools/rigs to do it) after FX has done the footprint pass.
It can be grunt work, it could be some assistance scripts tweaking or offering keys, very rarely it's an interactive system as looking up a well enough diced terrain for a set of controls every time the character is moved is unnecessarily costly, but occasionally that gets tried too.
The preference of the anim supe will usually steer things one way or another.

You rarely want the animators to have controls to de-intersect the whole foot manually to the fine details, it usually ends up either noisy or sloppy, and often enough too distant, and if there's no compenetration whatsoever FX will have a nightmare of a time doing a footsteps pass for any soft ground. It's a waste of time as well.

In Char FX de-intersecting a mesh out of terrain is relatively trivial in any established pipeline, and it usually doesn't even require simulation or tweaks unless the intersections are (intentionally) severe and it's a special shot.
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  04 April 2013
Originally Posted by ThE_JacO: Nearly anywhere it boils down to animators grunting the coarse work, and if additional subtleties are needed CharFX/AnimFX (or whatever the department is named in the eventual facility) will do a de-intersection pass (usually we have tools/rigs to do it) after FX has done the footprint pass.
It can be grunt work, it could be some assistance scripts tweaking or offering keys, very rarely it's an interactive system as looking up a well enough diced terrain for a set of controls every time the character is moved is unnecessarily costly, but occasionally that gets tried too.
The preference of the anim supe will usually steer things one way or another.

You rarely want the animators to have controls to de-intersect the whole foot manually to the fine details, it usually ends up either noisy or sloppy, and often enough too distant, and if there's no compenetration whatsoever FX will have a nightmare of a time doing a footsteps pass for any soft ground. It's a waste of time as well.

In Char FX de-intersecting a mesh out of terrain is relatively trivial in any established pipeline, and it usually doesn't even require simulation or tweaks unless the intersections are (intentionally) severe and it's a special shot.


I'm not quite sure what compenetration means but I'll guess and say it means composition penetration in which someone is messing with someone's composition. Otherwise, I have no idea what that means. So from your post I'm guessing animators are separate from fx artists who are dealing with like footprints in the sand, footprints in snow, footprints in mud...but what about puddles? I'm just wondering because I have no idea how any of this is done and I'm just trying to grasp how complicated it all is.
 
  04 April 2013
Simply put, when you are animating you usually want to have a switch between IK and FK controls. Those are usually on the hands and feet. When you are animating gestures for the hands usually you'd want FK control for more fluid animation, but when the character places his hand on a wall for instance, you'd keyframe a transition to IK control and the hand can stay put while the body moves.

From there it is just key framing from pose to pose, let's say on an uneven surface or tree or ladder, whatever the case may be.

The idea is you keep the weight supporting limb in place for the duration of the time it is planted.

What can happen in this case is when you have two keyframes spread apart that do not move in position or rotation but are surrounded by two other keyframes that move in position or rotation, they will have an arc. In the case of the foot, it could slide, or a hand could penetrate an object and so on.

So you'd flatten that arc like so in the graph editor:



When you animate a walk cycle usually the foot is in IK mode. And will not move when you key it in place - other than the arc that will happen on the Z (usually not the Y but it could happen), say on a rough terrain. You just have to eye it for each plant on terrain. On a flat surface, your rig should be set up that 0 on the Y has the foot on the ground. Then as mentioned, always just reset to 0 on the Y as needed.

MotionBuilder has very sophisticated controls for hand and feet penetration when you are using the Human IK rig.

Maya also uses the same HIK system. So that is something that might be interesting to you. MotionBuilder/Maya HIK also has a nice IK FK switching system. And Maya also has hands and feet contact. But I have not used it in Maya.

Something to search for more information on.
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Last edited by cineartist : 04 April 2013 at 06:37 AM.
 
  04 April 2013
Originally Posted by ebbandflow: I'm not quite sure what compenetration means but I'll guess and say it means composition penetration in which someone is messing with someone's composition. Otherwise, I have no idea what that means. So from your post I'm guessing animators are separate from fx artists who are dealing with like footprints in the sand, footprints in snow, footprints in mud...but what about puddles? I'm just wondering because I have no idea how any of this is done and I'm just trying to grasp how complicated it all is.

Compenetration simply means two volumes occupy the same place at the same time (screw you, physics!).
Yes, animators are separate from fx and finalling artists that deal with ground interaction, that includes things such as water puddles and so on.

How complicated depends enirely on how much money and/or time you have at hand.
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  04 April 2013
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