GPH 338 Computer Animation Survey

GPH 338 Computer Animation Survey

GPH 338Computer Animation Survey

Poly/NURBS/Subdiv

--Winny

What are the basic pieces?

• Curves – one dimensional objects– Linear curve: line segments– NURBS: curved pieces (splines) using control vertices– Bezier curve: splines using tangent handles

• Surfaces – two dimensional objects– Polygonal surfaces (Mesh): Polygons – Subdivision surfaces: Subdivided Polygons – NURBS surfaces: flexible rectangles, bounded by NURBS

curves

• Solids – three dimensional pieces



Polygons Polygonal surfaces (Mesh)


Polygons are made up of several components:

Vertices EdgesFaces UVs

Polygon Primitives

• Standard• Parametric – can vary their attributes

vertices, edges, faces, subdivlevel…• Use them when appropriate


Polygons

• Simple pieces, – may need many

• Can build surfaces with strange shapes easily• Rendered directly

– Efficient– Good for games

• Need many polygons for a smooth surface (large files!)


Mesh Editing

1. Moving the mesh around, without changing its underlying topology (structure)

• Manipulate vertices, edges, faces

• Translate (Move)• Rotate• Scale


Mesh Editing

2. Changes to mesh topology (the underlying pieces and the

way they are connected)

• Subdividing• Extruding• Merging Edges• Deleting • Messes up UV coordinates

(texturing)


Poly Boolean operations

• Intersection• Union• Difference• Good for solids• Many animators avoid them

– Messy mesh– Loss of control


Polygon examples



Polygon Texture unwrap Sample


NURBS surfacesNon-Uniform Rational B-Spline

Flexible rectangles, bounded by NURBS curves

NURBS• “Flexible Rectangles” Smooth • Made by Isoparms

– U– V

• Manipulated by Few points (CV)



Flexible rectangles


NURBS surfaces

bounded by NURBS curves

NURBS Curves

• Made up of many spans -piece of curve between two edit points

• Control Vertices (CV’s)– Doesn’t pass through them!– Heads towards them

• Hull - A loop of Control


NURBS curves

Maya Curve Tools• CV tool

– Control vertices• EP

– Edit points• Pencil tool

– Probably want to rebuild

• Degree– 1 – Linear Curve– 3 – default for splines– Higher – can turn

tighter, requires more points


NURBS Primitives


• Standard• Parametric – can vary their attributes

– # of isoparms, Hull, control vertices, etc.• Use them when appropriate

Surfaces from Curves

Loft Extrude / Sweep

Revolve / LatheSurface from boundary


Attaching NURBS Surfaces


Trimmed NURBS Surface


NURBS

• A particular model may be made up of many NURBS surfaces

• Not necessary one patch, can be several patch stitched together


NURBS• Great for organic, flowing surfaces

– Made by a lot of patches, usually not one surface.

• Not many control points needed• Hard to get fine control (e.g., this vertex here!)• UV coordinates are convenient for many reasons

– Can draw on them!– Can put objects on them– Easy to texture??

• Expensive for animation• Expensive for Rendering, Usually converted to

polygons for rendering ($!)


Subdivision Surfaces- Subdivided Polygons


Subdivision Surfaces

• Subdivide polygons– Hierarchy of polygons– Manipulate at different levels



Poly to Subdiv examples


SubDiv Surface

Subdivision Surfaces

• Good for complicated topology• (This is difficult to make out of rectangles)


NURBS/Polygons/SubD’s? It depends…

• Polygons– More efficient for animation and rendering– Good for arbitrary topology and Texture UV

• NURBS– Good for surfaces easily described in terms of flexible

rectangles– Simple manipulation, more natural for many curved

surfaces– Rendering is complicated

• SubD’s– Extremely handy for modeling, go back and forth from

poly to SubD– Heavy…

The best way is combine all together and use all their advantage!


It will be really useful to use drawings as reference.


No matter what…Keep your model Simple & Clean!

• Save a lot of work for Texturing • Save a lot time for rendering• Easy for later modify• Good start for animation …


Documents

GPH 338 Computer Animation Survey