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Nominal Geometry |
Nominal Geometry
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Nominal Geometry is a mechanism whereby edges which have local precision may reference a notional accurate curve.
Edges which have local precision carry the geometry which defines the Parasolid body on their fins. The curves on all the fins must lie within a pipe whose diameter is the edge's precision. An edge may also have a nominal curve, which must also lie within the precision pipe. It is expected that, in general, nominal curves are geometrically simpler than the SP-curves on the fins.
An edge with session precision has an accurate curve only for its geometry, which is also its nominal curve. An edge with local precision may optionally have a nominal curve.
An edge with local precision may only acquire a nominal curve when nominal curves are enabled for that edge's body. Once an edge has acquired a nominal curve then that curve is retained - and is available to interrogations - until specifically detached, regardless of whether nominal curves are presently enabled for the edge's body.
All PK identifiers relating to Nominal Geometry use an abbreviation - nmnl. This is to maintain the 31 character limit on identifiers.
Nominal curves may only be attached to edges with local precision when nominal curves are enabled for the edge's body. When bodies are created, nominal curves are initially disabled.
Nominal curves may only be attached to edges with local precision when nominal curves are enabled for the edge's body. There are two means of attaching nominal curves:
| Method | Description |
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When nominal curves are enabled for a body, whenever any of its accurate edges is given a local precision - either directly by a call to PK_EDGE_set_precision, or indirectly as a side effect of a modeling operation - then the pre-existing accurate curve of the edge is retained as its nominal curve. |
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An edge with local precision that does not have a nominal curve may be given one using PK_EDGE_attach_curve_nmnl. The given curve must lie within tolerance of the edge. If the curve is supplied to PK_EDGE_attach_curve_nmnl is already attached to another edge as edge geometry, fin geometry, or nominal geometry, then it is shared if possible. Otherwise, a copy of the curve is used. |
The nominal curve of an edge with local precision may be detached, whether or not nominal curves are enabled for the edge's body. Nominal curves are detached using PK_EDGE_detach_curve_nmnl.
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Note: This function only detacesh the nominal curve of an edge with local precision. It does NOT detach the curve of an accurate edge. |
The nominal geometry of an edge may be interrogated, whether or not nominal curves are enabled for the edge's body. These interrogation functions return information about accurate edges and about edges with local precision and nominal curves.
| Function | Description |
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return the accurate or notionally accurate geometry of an edge |
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return all edges of which this curve is the accurate or notionally accurate geometry |
Nominal geometry can be transmitted by setting the
transmit_nmnl_geometry
field of PK_PART_transmit_o_t to PK_LOGICAL_true.
This table shows what happens to the nominal curve of a tolerant edge during various modeling events.
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