Identifying Problem Areas

Whilst modeling for animation, it's vital to identify key areas that are going to take most of the stick (by which I mean which areas will require the most deformation) when animated, and ensure that there's enough geometry to support it. Failure to do so will cause headaches when it comes to weight painting the verts.

Wings

Wings are very important! I think i've covered the surface areas of the wings by virtue of the very nature of their creation, so that should suffice. Where the wings and body meet is a different story however. The picture left identifies areas that are worrying me at the moment - there's too much of a gap between verts for this area. Fortunately shouldn't be too much of a biggie to rectify. I could just stick an edgeloop in and wire it into where four edges meet, to bring five edges together.

But I don't want to do this. As I discovered with the Toxic Boy geometry, this just creates massive issues when it comes to weight painting it, its best to have four verts coming together are better than five.  So what i'll do is move these verts down and add an extra edgeloop above that will go around the wing. More Geometry where it matters, four sided geo gives better more predictable deformation.

Better Wings

I've gone into that area, added the geometry and given the whole thing a lick with the relax brush. It's beggining to look like something thats going to behave when animated. What is paramount when modeling geometry intended for animation is to make sure the interior angles where verst meet are as broad as possible. I shall further elaborate below.

Further Elaboration

Imagine this were a perfect square and all its edges were perpendicular to each other, that would make each angle 90° to each other. This will equate to a nice even deformation, by which I mean each angle will reduce or expand proportionately and not crease unless moved through extremity.

Trapezoid

Now imagine this is an isolated section in a piece of geometry in a model. In order to follow the contours, the geometry has to be pushed around, angles have to compromised. In this instance two of the angles are 80° and two are 100°. This is ok but not as sturdy as foolhardy as a nice and solid 90° square.

Triangle

Ever since I first switched Maya on the computer, I have always been told "make sure your geometry is is at least four sided" and this quickly became my mantra. But I never fully understood why, but abided by it. A triangle consists of 180°, so the biggest interior angle a triangle point can have is 60° (if it were equalateral). In this instance (imagine it being the corner of an eye) it goes down to a meagre 20°. Not much of an issue when the deformation moves 90° and 70° together, but anything else and you will begin to see sharp edges in the geometry - not so good in an animation (unless its one about Picasso's cubist period).

Pentagon

Inevitably, you are going to get instances where five vertices converge (usually where limbs meet torso's, or where two pieces of geo meet), this is unavoidable, not ideal but tolerable. As the illustration demonstrates an equalateral pentagon consists of five converging edges, separated by 72°.  This amount is probably the smallest angle you'd wish to stretch to avoid those nasty tell-tale lines appearing in your geometry when your character bends over (imagine watching "Finding Nemo" and seeing loads of sharp edges appearing when the fishes start swimming. i don't think so!).

Hexagons's

In a tutorail I saw for Nurbs modeling It said pentagons were ok (by which I mean five converging verts) but not hexagon's. So what's so bad about hexagons? Well if you break it down in terms of angles, an equalateral hexagon will have interior angles of 60°. Going back to the equalateral triangle, it too has interior angles of 60°. So from a Mayan modelers perspective, a hexagon is just as bad as a triangle. Infact it's just six triangles placed side by side - six times worse.

The Golden Rule of Modeling

I think the general rule of thum is keep interior angles between 90° and 72°. Obviously this will be pretty difficult to do by eye (possible scripting opportunity perhaps??), but the experienced modeler would surely be able to develop an eye for it? When it comes to the crunch and you have 5 verts converging, keep the angles as near to 72° as possible, and keep the  joining verts close as possible so it's not spanning too greater distance - if necessary add an extra edge loop in to keep things local. These are the areas that will get the stick when it comes to moving and animating it around and those nasty non-planar edges will begin to appear, like a crack in the very fabric of your workflow!

If you have to use a triangle or angle thats less than 72°, make sure its in an area where its only going to collapse down on itself, and won't be visible when deformed, imagine the geometry performing the animation's its required to do. Still uncertain? Skin it, move it, and try weght paint out the nasty edges and angles; you'll soon discover its impossible! 

Nobody has ever explained why it is imporatant to keep things four sided. It's a very simple principle, if you stick to it, you can't go far wrong!