NURBS Surface Design Intent Preservation via Delta Vector
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Solution Overview
Problem
Existing CAD systems fail to effectively preserve design intent when manipulating Non-Uniform Rational B-spline (NURBS) surfaces, particularly due to unpredictable reactions to geometry changes of parent features and changes in representation, degree, and control points.
Innovation Solution
A method that represents an output surface with control points independent of surface refinement, interpolates a base surface, calculates a delta vector between the output and base surfaces, and transforms it based on a local coordinate system of a normal vector and tangent plane, allowing for design intent preservation without relying on the parent surface's representation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If control points are stored directly as feature parameters, then the system can record design steps, but the system reacts unpredictably to geometry changes of parent features
Solution Approach 1:
The patent segments the control point data into two independent components: (1) control points relative to the output surface geometry, and (2) the output surface representation itself. This segmentation allows the control points to be stored independently from the parent surface's degree and knot sequence, making the system response predictable when parent features change.
Solution Approach 2:
The patent introduces an intermediary computational step that calculates control points based on the output surface geometry rather than storing them directly. This intermediary process acts as a buffer between the parent feature changes and the control point representation, ensuring predictable system behavior.
2Adaptability or versatility
If the NURBS surface of the parent feature changes, then the model can be updated, but the degree, number of patches, and number of control points of the child surface change making direct storage meaningless
Solution Approach 1:
The patent performs preliminary calculation of control points relative to the output surface geometry before any parent feature changes occur. By establishing this relative coordinate system in advance, the control point data remains valid and meaningful even when the parent surface undergoes degree elevation or knot sequence changes.
Solution Approach 2:
The patent creates a universal control point representation that works across different surface refinements. The control points are defined relative to the output surface rather than the parent surface, making them universally applicable regardless of the parent surface's degree, knot sequence, or number of patches.
3Measurement precision
If control points are stored relative to parent surface representation, then the representation is captured, but the design intent does not preserve under representation changes
Solution Approach 1:
The patent changes the reference dimension for control point storage from the parent surface coordinate system to the output surface coordinate system. This dimensional shift ensures that control points maintain their design intent meaning regardless of how the parent surface representation changes, providing both precision and stability.
Data Source
AI summary
A system, method, and computer program for preserving design intent of a Non-Uniform Rational B-spline (NURBS) surface without representation of a parent surface, comprising representing an output surface having control points that is independent from a refinement of the surface; interpolating a base surface from the output surface; calculating a delta vector that is a difference between the output surface and the base surface; and transforming the delta vector based upon a local coordinate system of a normal vector and a tangent plane of the base surface and appropriate means and computer-readable instructions.