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
GPH 338 Computer Animation Survey
GPH 338 Computer Animation Survey
Polygons Polygonal surfaces (Mesh)
GPH 338 Computer Animation Survey
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
GPH 338 Computer Animation Survey
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!)
GPH 338 Computer Animation Survey
Mesh Editing
1. Moving the mesh around, without changing its underlying topology (structure)
• Manipulate vertices, edges, faces
• Translate (Move)• Rotate• Scale
GPH 338 Computer Animation Survey
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)
GPH 338 Computer Animation Survey
Poly Boolean operations
• Intersection• Union• Difference• Good for solids• Many animators avoid them
– Messy mesh– Loss of control
GPH 338 Computer Animation Survey
Polygon examples
GPH 338 Computer Animation Survey
GPH 338 Computer Animation Survey
Polygon Texture unwrap Sample
GPH 338 Computer Animation Survey
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)
GPH 338 Computer Animation Survey
GPH 338 Computer Animation Survey
Flexible rectangles
GPH 338 Computer Animation Survey
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
GPH 338 Computer Animation Survey
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
GPH 338 Computer Animation Survey
NURBS Primitives
GPH 338 Computer Animation Survey
• 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
GPH 338 Computer Animation Survey
Attaching NURBS Surfaces
GPH 338 Computer Animation Survey
Trimmed NURBS Surface
GPH 338 Computer Animation Survey
NURBS
• A particular model may be made up of many NURBS surfaces
• Not necessary one patch, can be several patch stitched together
GPH 338 Computer Animation Survey
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 ($!)
GPH 338 Computer Animation Survey
Subdivision Surfaces- Subdivided Polygons
GPH 338 Computer Animation Survey
Subdivision Surfaces
• Subdivide polygons– Hierarchy of polygons– Manipulate at different levels
GPH 338 Computer Animation Survey
GPH 338 Computer Animation Survey
Poly to Subdiv examples
GPH 338 Computer Animation Survey
SubDiv Surface
Subdivision Surfaces
• Good for complicated topology• (This is difficult to make out of rectangles)
GPH 338 Computer Animation Survey
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!
GPH 338 Computer Animation Survey
It will be really useful to use drawings as reference.
GPH 338 Computer Animation Survey
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 …
GPH 338 Computer Animation Survey
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