Match Nurbs Surface Edges Dialog OptionsKeyCreator \ Modify \ Surface \ Match-Nurbs-Surface-Edges-Dialog-Options
Match NURBS Surface Edges Dialog Options
The Match NURBS Surface Edges dialog appears when Match Edges is selected from the Modify>Surface submenu.
This box is checked by default. This means that the surface edges will match with G1 (normal) continuity across the common edge. (The surfaces will always match tangentially along the common edge since they both share the exact same edge curve). If this box is unchecked, then the surface edges will match with G0 (position) continuity across the common edge.
Determine extent of Edge Matching by
The extents of the edges to be matched may have to be determined to handle the cases where the surface on the left is larger than the surface on the right, or the surface edges overlap by some distance. (This only applies to Open surfaces and the setting has no effect on closed surfaces)
Match Surfaces by
When matching the edges of surfaces you can force one surface to match the edge and tangents of the other surface (modifying one surface and keeping the other unchanged), or you can choose to average the surface edges together (modifying both surfaces).
For Closed Surfaces
When two smoothly closed (a.k.a. Periodic NURBS) surfaces are selected, the seams of the surfaces must be aligned properly or the resulting matching of edges might cause the surfaces to twist.
How it Works:
Because the Surface Edge matching function is designed and intended to work only on untrimmed iso-edges of NURB surfaces, the following limitations exist: If you select a surface that is not a NURB surface, it will be converted to a NURB automatically and the result will be a NURB. If you select a Trimmed surface (face) and the underlying surface is modified, then the trimming information will be lost. If you select a face that is stitched into a larger body, it will be unstitched automatically.
The surface edge matching works by making the surfaces compatible with one another through a process of degree elevation, knot parameter insertion, control point snapping and tangent vector length re-proportioning. Any change in surface shape is restricted to the first row of patches closest to the common edge. It will handle any combination of surface degrees. For example, if a cubic (degree 3) surface is matched to a quintic (degree 5) surface, then the result will be that both surfaces now have degree 5. The accuracy of edge matching is guaranteed to produce a zero gap and parallel normals/tangents (to double precision accuracy), but the results can always be verified using the Tools > Verify > Deviations > Edge to Edge function.
After selecting the surfaces, they are redrawn temporarily with flowlines at knot values (patch boundaries). This is so that you can see the full extents of each underlying surface. You are then prompted to indicate the edge on each surface to be matched. Temporary vectors are drawn at the mid point of each edge pointing away from the surface. As you move the cursor near the vectors, they highlight indicating the chosen edge. Specify the edge for each surface
In this figure, both surfaces were modified by averaging the tangents. Notice how the flowlines now line up exactly. This is not a necessary condition for a perfectly matched edge, but will happen if both surfaces are averaged.
Above > In this figure, two closed surfaces with vastly different cross sectional shapes are to be matched. Automatic seam alignment is performed. yellow tubular surface is forced to match the shape of the green surface.
Above > This figure demonstrates two surfaces for which only a portion of each edge overlaps the other. By choosing the option "Matching only the common subset of edges" we can match the portions that make sense to match. After matching the subset of the edges that actually overlap, the red surfaces are now separated off as individual surfaces.