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Catmull-Clark Surface
Catmull-Clark Surface
=== Curves and Surfaces for CAGD ===
Resume: 1
==== 1 (1) ====
In the French Auto industry both Paul de Castlejau and Pierre Bezier both created equivalent systems to describe the curves on automobiles. At Renault, Bezier developed UNISURF, an early CAD/CAM model.
This chapter provides a bunch of weird analogies for Curves.
==== Points and Vectors (13) ====
A point defines a location. Vectors are the result of subtracting points. Vectors can be added, points cannot.


== B-spline ==
== B-spline ==
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   N<sub>i,j</sub>(t) = (t - t<sub>i</sub>)/(t<sub>i+j</sub> - t<sub>i</sub>)N<sub>i,j-1</sub>(t) + (t<sub>i+j+1</sub> - t)/(t<sub>i+j+1</sub> - t<sub>i+1</sub>)N<sub>i+1,j-1</sub>(t)
   N<sub>i,j</sub>(t) = (t - t<sub>i</sub>)/(t<sub>i+j</sub> - t<sub>i</sub>)N<sub>i,j-1</sub>(t) + (t<sub>i+j+1</sub> - t)/(t<sub>i+j+1</sub> - t<sub>i+1</sub>)N<sub>i+1,j-1</sub>(t)
This forms a triangle because each N where j!= is dependent on two N where j is one less. And the curve itself is the case where i=0 j=n. The ternary acts like a switch that turns on one N where j=0.
This forms a triangle because each N where j!= is dependent on two N where j is one less. And the curve itself is the case where i=0 j=n. The ternary acts like a switch that turns on one N where j=0.
[[Category:Computer Graphics]]

Latest revision as of 14:02, 28 August 2019

I'm leaving this as is, but really my interest is "Computational Geometry"

Notes

BCS

  • Flat shading
  • Gouraud Shading
  • Phong Shading

Catmull-Clark Surface

B-spline

Basis Spline; a curve defined by control points and a knot vector.

  • Joins many low degree Bezier curves

A k degree B-spline deined by n control points will have n-k Bezier curves. So a cubic (k=3) B-spline with 6 control points will have n-k = 6-3 = 3 Bezier curves.

  • C0 continuity means that the last point on each Bezier curve is the same as the first point on the next - there are no gaps.
  • C1 the derivatives of the curves are continuous
  • C2 the second derivatives of the curves are continuous

The length of the knot vector is m=k+n. For a uniform knot vector (most common), the numbers will be integers increasing by one, so m=5 will be T=(0,1,2,3,4).

 S(t) = ∑inNi,k(t)Pi
 Ni,0(t) = (ti <= t < ti+1</sub) ? 1 : 0
 Ni,j(t) = (t - ti)/(ti+j - ti)Ni,j-1(t) + (ti+j+1 - t)/(ti+j+1 - ti+1)Ni+1,j-1(t)

This forms a triangle because each N where j!= is dependent on two N where j is one less. And the curve itself is the case where i=0 j=n. The ternary acts like a switch that turns on one N where j=0.