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The Bridge SOP is similar to the Skin SOP but with much greater control over the resulting surface. Given a set of profiles (i.e. curves on surface) and/or spatial faces, the Bridge op builds a NURBS skin with specified tangent and curvature characteristics. The precision of the resulting surface is highly dependent on the number of required cross-sections and on the quality of the profile extraction. High precisions will generate a very dense surface with, potentially, many multiple knots.
In general, the higher the order of the curve, the better the fit the Bridge op will be able to provide. However, it is generally better to stick to cubics (order 4) curves, as the software is optimized for cubics.
Because the Bridge op can join both a set of spatial curves and trim curves, it can be used much like the Skin SOP and/or the Fillet SOP. However, bridging trimmed surfaces is more expensive than bridging carved surfaces.
Use a Trim SOP to cut a hole in the projected surface.
Use a Bridge SOP to skin the profile curve to another profile curve.
Use a Profile SOP to extract the curve on surface or remap it’s position.
To texture-map the resulting skin, use an Orthographic projection rather than a Spline-based projection. This results in better continuity across the surfaces.
Example: Joining Two Trim (Profile) Curves
Place a Circle SOP. Primitive Type: NURBS; Radius = 0.2, 0.2
Place a Grid SOP. Primitive Type: NURBS.
Feed both the Circle and Grid SOPs into a Project SOP. Make it the display SOP. You notice the projected circle on the grid: our trim curve.
Append a Trim SOP and make it the display SOP. Turn on Gouraud shading for the Viewport. You now see the trimmed holes in the surface of the grid.
Append a Copy SOP. Number of Copies: 2; Translation Z: 1.0; Rotation X: 30. Make it the display SOP. Now we have two grids with trimmed holes in them.
Append a Bridge SOP, and make it the display SOP. Scale Tangents: 0, 0, 0; Use Curvature: On; Scale Curvatures: 3, 3, 3 .
To specify which profile curves to skin, turn on Profile Numbers in the Viewport options, (click Plus at the bottom-right of Viewport, and enable the icon). We can see the profile numbers of the two trim curves are 0.0 and 1.0, meaning the 0th profile of the 0th primitive and the 0th profile of the 1st primitive). The strange numbering is because primitive numbers start at 0 instead of 1.
In the Bridge SOP’s Group field enter: *.0. This means to include the 0th (first) curve from all (the * wildcard character) primitives in the skin. You now see the resulting bridge between the two trim curves. The skin bulges outwards.
We can control the bulge by playing with the Scale Curvatures and the Tangent Magnitudes. Set the Scale Curvatures to: -3, -3, -3 . Now we have an inward-bulging tube connecting the two holes.
Experiment with moving the location and size of the holes (change the Translation and Radius in the Circle SOP). The Bridge SOP dynamically updates the geometry connecting the two surfaces. Setting the Scale Curvature to: 0, 0, 0 produces a straight-through connection between the two holes.
Subset of profiles and/or faces to bridge.
Allows bridging of subgroups of N primitives or patterns of primitives.
Pattern of primitives to bridge.
Spline order for both profile extraction and skin.
Minimum number of cross-sections in skin.
Type of normal to use for computing direction.
This sets the local normal according the the frenet frame of the curve. This is the vector perpendicular to both the tangent of the curve and the binormal (the direction of curvature).
This uses the calculated normal of the entire curve as the normal.
Build the skin as a circular fillet, if possible.
The scaling and rotation parameters contain three fields:
Applies to the first face in the input.
Applies to all intermediate faces.
Applies to the last face in the input.
Further rotation of the tangents (degrees).
Further scaling of the tangents. When building a circular fillet, only the sign of the tangents is used.
Take curvature into consideration as well.
Further scaling of the curvature.
The parameters in this tab determine the precision with which to extract profile curves.
Divisions Per Span
Number of 2D points evaluated in each span.
Precision of 2D fitting algorithm.
Preserve Sharp Corners
Enables or disables fitting of sharp turns.