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Intersectors
Intersection Algorithms
ACIS represents cones, cylinders, planes, spheres, and tori explicitly, and sculptured faces implicitly as nonuniform rational B-splines (NURBS). Curve algorithms allow for curve/curve intersections (CCI), curve/surface intersections (CSI), surface/surface intersections (SSI), and curve/curve intersections on a surface (CCS). These algorithms are known as intersectors.
Curve/Curve Intersection
The curve/curve intersection algorithm is implemented to find points or intervals where two curves meet or approach one another within a specified tolerance.
Curve/Surface Intersection
The curve/surface intersection algorithm can:
- Intersect implicit curves and surfaces.
- Handle the intersection between a parametric curve and a singular surface when the singularity is due to the degeneracy of the surface boundary to a single point.
Surface/Surface Intersection
The surface/surface intersection algorithm can:
- Handle the intersection between parametric surfaces, either of which can be a singular surface due to the degeneracy of the surface boundary to a single point.
- Calculate surface silhouette curves for any ACIS surfaces, including singular ones.
- Accept help points in the exploration stage, which enable the intersection of implicit surfaces.
- Produce the intersections between two offset surfaces, given a start and an end point. These intersections can then be used to calculate the spline curve during blending.
Curve/Curve Intersection on Surface
The curve/curve intersection on a surface (CCS) algorithm was introduced to improve the performance of many curve/curve intersections. In many cases, when two curves are intersected in ACIS, it is known that both of the curves lie on the same surface. However, the CCI algorithm that is generally used to intersect these curves does not use this information. The CCS algorithm receives a surface and two pcurves, as well as the two curves to be intersected. If this additional information is accurate (that is, each pcurve is an accurate representation of the curve in the surface's parameter space) and used, this can possibly improve the efficiency of the intersection algorithm.
Intersectors Implementation
Intersectors are implemented in low-level C++ classes that are not intended to be accessed directly by applications. They can be thought of as virtual methods of Booleans. When the Boolean operations are used properly, they invoke the correct intersector methods.
Note: Reference material is provided on the intersector classes because they are visible in the header files. Unpredictable results can occur when these intersector classes are used directly by applications.
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