Sweep1
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Surface Sweep 1 Rail |
The Sweep1 command fits a surface through a series of profile curves that define the surface cross-sections and one curve that defines a surface edge.
Steps
- Select a single rail curve.
- Select cross-section curves in the order that the surface will pass through them.
When multiple closed cross-section curves are selected, there will be an extra step for adjusting curve seams.
Tips
- Cross-section curves with the same structure create a better sweep surface. Cross-section curves will have the same structure if they are all copied from the same curve.
- If the cross-section curves do not have the same structure, use the Rebuild cross sections or Refit cross sections options. The rebuilt or refitted copies of the cross-section curves will be used to sweep.
- When Refit rail is enabled, the refitting tolerance is controlled by Document Properties -> Units -> Absolute tolerance.
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ChainEdges |
Select connected edge/curve segments based on the continuity between segments. |
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Point |
Creates a surface that begins or ends at a point. |
Adjust seam options (Closed curves only)
Flip
Reverses the curve direction.
Automatic
Attempts to align the seam points and directions without intervention.
Natural
Moves the seam points to the way they were at the beginning of the command.
SnapToKnots
Yes
The seam points are always at the knots. You can only move them among the knots.
No
The seam points may leave the knots. You can move them without restriction.
To adjust seams
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Select each seam point and move it along the curve to line up all curve seams.
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Use the Flip option to make all seam arrows point to the same side.
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Press Enter to continue.
Sweep 1 Rail Options
Frame Style
A frame is a 3-D point and three direction vectors. It can be drawn as something that looks like the Rhino world axes icon. It describes a unique coordinate system in space. Frames are calculated along the rail and are used to orient the cross-section curves at those locations. In a simple case with one cross-section, frames are made at the cross-section curve location and where the calculated cross-section is going to go. The 3-D rotation between those two frames determines the rotation of the cross-section curve at its new location.
Freefrom is the default Frame style. The selected Frame style will be remembered in the current Rhino for next use.
Freeform
The cross-section curve rotates to maintain its angle to the rail throughout the sweep.
Roadlike
Specify an axis for calculating the 3-D rotation of the cross-section.
The default Roadlike axis will be different depending on the rail curve. For a planar rail curve, the default axis is perpendicular to the curve plane. For a non-planar rail curve, world-Z axis will be used.
Sets the axis direction for the Roadlike style.
Align with surface (surface edge as rail only)
If the rail is a surface edge, the cross-section curve will twist with the surface edge. If the shapes are tangent to the surface, the new surface should also be tangent.
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Sweep options
Closed sweep
Creates a closed surface, continuing the surface past the last curve around to the first curve.
This option is only available after you select two cross-section curves.
Global shape blending
The sweep is linearly blended from one end to the other, creating sweeps that taper from one cross-section curve to the other. Otherwise, the sweep stays constant at the ends and changes more rapidly in the middle.
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Untrimmed miters
If the sweep creates a polysurface with kinks, the component surfaces will be untrimmed.
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Curve options
Refit rail
Refits the rail curve before creating the sweep.
Allows reversing the direction of the cross-section curves.
Do not change cross sections
Creates the sweep without altering the cross-section curves.
Rebuild cross sections with ___ control points
Rebuilds the cross-section curve's control points before creating the sweep.
Refit cross sections within ___
Refits the cross-section curves before creating the sweep.
Technical notes
To determine the movement of a cross-section, one frame is found at an existing cross-section location and another is calculated at the desired location along the rail. The difference between those frames defines the movement of the cross-section.
The frames are found like this:
- The rail tangent and the fixed direction vector (if they are not parallel) define a plane. The cross product of the tangent vector and the fixed direction produces the normal vector of that plane (frame x) perpendicular to both of the input vectors.
- The cross product of frame x and the rail tangent produces another vector, frame y, perpendicular to the tangent and frame x.
- Taking the rail tangent as frame z, there is a unique 3-D frame at a specific location along the rail with its mutually perpendicular x, y and z coordinate directions.
- The rotation and translation between two of those frames determines how a cross-section will be moved from one location on the rail to another.
If the rail tangent and the arbitrary vector are parallel, they do not define a plane and the cross product does not produce a vector, so the frame is under-defined, and it will twist around the rail tangent since that is the only defined information.
See also
Sweep2
Fit a surface through profile curves and two edge curves.
SubDSweep1
The SubDSweep1 command sweeps a shape curve along a rail curve to create a SubD.
SubDSweep2
The SubDSweep2 command sweeps a shape curve along two rail curves to create a SubD.
Loft
Fit a surface through profile curves that define the surface shape.
NetworkSrf
Fit a surface through a network of crossing curves.