CA2517463A1 - System and method for defining t-spline and t-nurcc surfaces using local refinements - Google Patents

System and method for defining t-spline and t-nurcc surfaces using local refinements Download PDF

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CA2517463A1
CA2517463A1 CA002517463A CA2517463A CA2517463A1 CA 2517463 A1 CA2517463 A1 CA 2517463A1 CA 002517463 A CA002517463 A CA 002517463A CA 2517463 A CA2517463 A CA 2517463A CA 2517463 A1 CA2517463 A1 CA 2517463A1
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control
spline
mesh
knot
local
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CA2517463C (en
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Thomas W. Sederberg
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Autodesk Inc
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    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06FELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00Digital computing or data processing equipment or methods, specially adapted for specific functions
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T17/00Three dimensional [3D] modelling, e.g. data description of 3D objects
    • G06T17/20Finite element generation, e.g. wire-frame surface description, tesselation
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06FELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00Computer-aided design [CAD]

Abstract

A system and method is provided for defining a bi-cubic spline surface in a computing environment. One operation in the method is creating a control mesh with a substantially rectangular structure (150). A further operation is inferring from the control mesh the tensor product B-spline basis functions for each control point (152). The surface can then be computed based on the basis functions and the control mesh (154).

Claims (22)

1. A method for defining a bi-cubic spline surface in a computing environment, comprising the steps of:
creating a control mesh with a substantially rectangular structure;
inferring from the control mesh the tensor product B-spline basis functions for each control point; and computing the surface based on the basis functions and the control mesh.
2. A method as in claim 1, further comprising the step of determining the basis function for each control point using one non-hierarchical set of rules.
3. A method for locally refining a control mesh of a bi-cubic spline surface in a computing environment, comprising the steps of:
defining the control mesh having a substantially rectangular structure;
inserting a control point into a pre-image of the control mesh; and computing the Cartesian coordinates of the control point and of the neighboring control points such that the bi-cubic spline surface is not geometrically altered.
4. A method as in claim 3, wherein the step of computing the Cartesian coordinates of the control points further comprises the steps of:
splitting basis functions which have fewer knots than are called for by the control mesh; and adding control points to the control mesh in locations where basis functions have more knots than are called for by the control mesh.
5. A method as in claim 3, further comprising the step of creating a sharpness feature in the surface by inserting one or more adjacent partial rows of control points with zero knot intervals thereby creating a sharp crease.
6. A method as in claim 3, further comprising the step of creating a sharpness feature in the surface by inserting one or more adjacent partial rows of control points with small knot intervals thereby creating a less sharp crease.
7. A method as in claim 3 further comprising the step of providing two surfaces having control meshes that are desired to be merged into a single surface;
positioning the two surfaces with common edges that are in close proximity;
performing local refinement on the control meshes of the two surfaces and adjustment of knot intervals such that a sequence of knot intervals agree along a common boundary edge of the two surfaces; and joining the control points of the two surfaces along the common boundary.
8. A method for subdividing control meshes in order to provide local refinements to control meshes of arbitrary topology in a computing environment, comprising the steps of:
selecting an extraordinary point for which local refinement is desired;
using T-junction control points to prevent the refinement operation from propagating to the entire surface.
9. A method for defining bicubic spline surfaces that provides local refinement to control meshes in a computing environment, comprising the steps of:
specifying knot intervals associated with the spline control mesh;
imposing a local knot coordinate system based on the knot intervals;
inferring local knot vectors for control points in order to produce basis functions for the control points; and inserting a single control point into the control mesh without altering the bicubic spline surface.
10. A method as in claim 9, wherein the step of inserting a single control point further comprises the step of inserting a single control point into the control mesh without altering the bicubic spline surface and permitting partial rows of control points terminating in a T-junction.
11. A method as in claim 9, wherein the step of imposing a local knot coordinate system further comprises the step of assigning local knot coordinates (s;,t;) to the pre-image of each control point P i.
12. A method for subdividing a cubic spline control mesh in order to provide local refinements to control meshes of arbitrary topology in a computing system, comprising the steps of:
imposing local knot coordinate systems on the cubic spline mesh of arbitrary topology;
specifying knot intervals for edges of the cubic spline control mesh;
inserting a T-junction into the cubic spline control mesh;
inferring knot vectors for the T-junction; and defining basis functions for the T-junction using the knot vectors.
13. A method as in claim 12, wherein the step of inserting a T-junction further comprises the step of requiring a sum of knot intervals on opposing edges of a face in the cubic spline mesh to be equal.
14. A method as in claim 129 wherein the step of inserting a T-junction further comprises the step of requiring a T-junction on one edge of a face to be connected to a T-junction on an opposing edge of the face when the sum of the knot intervals on opposing edges of a face in the cubic spline mesh are equal.
15. A method as in claim 12, further comprising the step of applying shading to the cubic spline mesh that can be viewed by an end user.
16. A method as in claim 12, further comprising the step of creating a sharpness feature in the spline mesh by inserting a plurality of adjacent rows of control points with zero knot intervals.
17. A method as in claim 16, further comprising the step of controlling the sharpness feature by placement of the inserted control points and adjusting the knot intervals.
18. A method for extracting Bezier patches from a T-spline, comprising the steps of identifying all Bezier domains by extending all T junctions two bays;
performing local knot insertion such that each Bezier domain is surrounded by a 4X4 grid of control points;
choosing the knot intervals for the local knot insertion such that pairs of zero knot intervals separate each pair of adjoining Bezier domains.
19. A method for merging at least two B-spline surfaces with unaligned knot vectors into a single T-spline, comprising the steps of:
identifying a first B-spline control mesh and second B-spline control mesh;
identifying locations in the first B-spline control mesh for additional control points on an edge configured to align with a knot vector in the second B-spline control mesh which will intersect the edge;
inserting offset control points at each identified location in the first control mesh;
joining the control points of the first B-spline control mesh with the corresponding knot vectors frown the second mesh in order to join the two B-splines and create a T-spline.
20. A method as in claim 19, further comprising the steps of identifying locations in the second B-spline control mesh for additional controls points on an edge configured to align with a knot vector in the first B-spline control mesh which will intersect the edge;
inserting offset control points at each identified location in the second B-spline control mesh;
joining the control points of the second B-spline control mesh with the corresponding knot vectors from the first mesh in order to join the two B-splines and create a T-spline.
21. A method as in claim 19, wherein the step of inserting offset control points at each identified location, further comprises the step of inserting triple knot intervals along the shared boundary in order to provide a C2 merge.
22. A method for defining a locally refineable tensor-product spline surface of any degree in a computing environment, comprising the steps of:
defining a control mesh with a substantially rectangular structure;
inferring from the control mesh the tensor product B-spline basis functions for each control point; and computing the surface based on the basis functions and the control mesh.
CA2517463A 2003-03-26 2004-03-26 System and method for defining t-spline and t-nurcc surfaces using local refinements Expired - Lifetime CA2517463C (en)

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US45823103P 2003-03-26 2003-03-26
US60/458,231 2003-03-26
PCT/US2004/009309 WO2004088468A2 (en) 2003-03-26 2004-03-26 System and method for defining t-spline and t-nurcc surfaces using local refinements

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EP1606692A4 (en) 2011-05-04
WO2004088468A2 (en) 2004-10-14
US7274364B2 (en) 2007-09-25
KR20060002856A (en) 2006-01-09
CA2517463C (en) 2012-12-11
US20040189633A1 (en) 2004-09-30
JP2006523891A (en) 2006-10-19
EP1606692A2 (en) 2005-12-21
KR101177131B1 (en) 2012-08-24
WO2004088468A3 (en) 2005-09-29

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