NURBS Curves / NEW: Managing NURBS surface networks
Digital Tutors: Exploring NURBS in Maya
The term NURBS refers to curves and surfaces generated from the position of points. A NURBS curve is generated from a series of points and a NURBS surface is generated from a series of curves. Each NURBS curve or surface has a specific parametric equation that defines its shape and is always a four-sided patch. It can be shaped to take on various forms, but it always remains four-sided. NURBS objects can be defined by up to four contour or any number of profile curves.
Because NURBS surfaces are parameterized, it is easy to assign a coordinate space to a four-sided patch. Their UV space is also parameterized.
NURBS are used for objects with simple and precise curvalinear surface shape. This format is most common in architecture, industrial and product design where the accuracy of form and adherence to blueprints are most important. In the past (and more rarely today) NURBS were used in animation production to control surface smoothness. NURBS are never used as a model format in game design but can be very effective as a stage of a modeling process.
1. In animation production NURBS can be used for the models with many simple precisely shaped elements: a bird cage, a baby crib, a sail ship with masts, sails and ropes.(See NURBScage.mb in Resources/models) NURBS can also be used for making large continuous surfaces, such as fields and terrains, fabric (curtains, simple fabric shape (not true cloth simulation), etc. Older cg workflows for organic-looking smooth complex surfaces, made out of multiple patches. http://www.npowersoftware.com/nurbs/pntutorials_advanced_Car.htm Also see NURBShead.mb model in Resources/Models.
2. In automotive, industrial or product design NURBS patches are used for making high-precision models based on blueprints.
...starts and ends on a control point - has direction - is parameterized - must have at least four control vertices.
Anatomy of a NURBS Curve:
Control Vertex (Vertices) –points that lie outside the curve, allow for manipulation with continuity/smoothness
1. CV curve tool – place Control Vertices , Edit Points will be created accordingly.
- Creating sharp angles in a cubic curve is possible by overlapping consecutive CVs or creating a 1 degree curve and a 3 degree curve and attaching them
Drawing Curves on 3d surfaces:
Curves are used in animation as motion paths
Anatomy of a NURBS Surface:
Control Vertices – can move, rotate and scale (Additional selecting by pressing arrow keys on the keyboard)
NURBS models smoothness display keyboard buttons:
Creating simple NURBS models/patches:
**Render quality for NURBS is controlled via Tesselation settings in Attribute Editor**
Positional and Tangential Continuity
Positional Continuity is established when the borders of adjacent NURBS patches line up, but the seam is noticeable.
Tangential Continuity is established when the borders of adjecent NURBS patches line up and there is no visible seam. This is achieved by ensuring same coodinate values on at least one of the axis on the first and second CV of each isoparm that runs perpendicular to the shared edge...
Using NURBS Curves and Surfaces to Make Polygon Objects
When building an object with NURBS curves it is possible to choose polygon output in the operation settings (ie rotate, loft, etc). It is also possible to convert an existing NURBS surface into polygonal surface using Modify/Convert/NURBS objects to Polygons. Depending on whether you want output a lo-res or a hi-res object work with these settings:
PUTTING IT ALL TOGETHER: Digital Tutors: Interpretive Modeling
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