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Geometry building is divided into five subphases. They must be performed in this order:
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1.
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Analytic solver
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2.
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Isospline solver
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3.
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Sharp edge solver
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4.
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Generic spline solver
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5.
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Wrap up
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Any subphase except wrap up may be skipped if it is not needed. Wrap up must be performed, because it recomputes any new pcurves.
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Analytic Solver
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The analytic solver subphase attempts to heal all edges and vertices shared by analytic surfaces. This operation is designed to satisfy both the G0 and G1 constraints on analytic junctions in a body. The analytic solver first builds a graph of all the analytic tangent junctions, and then solves the graph using the set of liner transformations. After the tangent constraints have been satisfied, all the analytic-analytic edge geometry is recomputed by using the
ACIS surface-surface intersection routines.
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Isospline Solver
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The isospline solver (also referred to as the isoparametric spline solver, or
uv spline solver) attempts to heal all edges shared by tangential isoparametric surfaces (e.g., the intersection curve is an isoparametric curve of both splines in the intersection). The new edge geometry is defined as the isoparametric edge of one of the surfaces, and the adjoining surface is modified to pass through this edge curve (by knot insertion techniques).
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G1 Continuity in Isospline
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The isospline solver subphase uses an algorithm that makes the spline surfaces meeting at an isospline edge G1 continuous. This algorithm is a step toward improving the quality of the healed model in order to increase the success of post-healing operations, such as Booleans, blending, shelling etc. Refer to Figure 1-9.
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Figure 1-9. G1 Isospline Junction
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To ensure that an isospline junction in isolation is C1 continuous,
HEAL positions the penultimate row of control points of the spline surfaces such that they maintain collinearity across the spline surfaces, and also maintains a certain ratio of distances between the respective control points (determined by the knot vectors of the two spline surfaces). If there is a sequence of isospline junctions connected to each other at the ends, then to maintain C1 continuity across the entire sequence,
HEAL maintains the same ratio of distances between control points (normalized with respect to the knot values) across the entire sequence. In cases where four isospline surfaces meet at a vertex (unstable isospline edges),
HEAL also attempts to make the twist consistent across all four spline surfaces meeting at the vertex.
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Only simple isospline junctions (where complete surface boundaries match at the edge) are handled. Isospline junctions with partial boundaries, degenerate triangular patches, and spline/analytic junctions are not handled.
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In cases where the part contains a cyclic sequence of isospline edges, or contains unstable vertices at which some edges are complete range isospline junctions and the others are not,
HEAL may fail to make some of the isospline junctions G1, because it may fail to compute a proper sequence of edges for G1 solving.
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Sharp Edge Solver
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The sharp edge solver attempts to heal all edges and vertices that are shared by surfaces that intersect sharply. The geometries of edges that connect two faces are computed by surface-surface intersections of the underlying face geometries. The geometries of edges that lie on a single face (open edges) are computed using projection routines. Vertex geometries are also recomputed using curve-curve intersectors or projectors.
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Generic Spline Solver
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The generic spline solver attempts to heal nonisospline tangential spline junctions, (e.g., the intersection curve is
not an isoparametric curve of both splines in the intersection). This subphase uses the standard
ACIS net surfaces to fit the spline surface. The surface edge curves are projected onto the adjoining surface (to satisfy G0 continuity). These curves become the boundary curves of the new net surface. The interior grid of curves are computed by linear offsets of the boundary curves in parameter space. The new fitted set of curves defines the net surface.
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Wrap Up
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The wrap up subphase recalculates coedge geometry (pcurves on spline surfaces) for all coedges.
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