Rail Sweep Quick Help

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  Overview  

The Pwr_RailSweep command sweeps one or more shape curves along a set of one or more rail curves with optional tangency constraints.  If you are using surfaces to construct your objects, the Rail Sweep will likely be one of the most valuable tools that you have.  We have gone to great lengths and developed new technology to give you a rail sweep that is extremely powerful in it's ability to create a desired shape. There are also a lot of different ways to control the sweep making it a very complex command. The defaults should be a good starting point for most sweeping operations.

Here is how to use Power Rail Sweep :  

  1. Start the command and pick one or more shapes (no particular order is required).

  2. Hit the "Pick Rails" button and start selecting rails  Note that the shapes should intersect or nearly intersect all specified rails.  No particular ordering is required for picking the rails.
  3. Adjust the parameters of the rail sweep to achieve the desired shape.

Right Click menu Options:

  1. Uniform Scale - toggle Uniform Scale of Shapes on/off
  2. Don't Use Rails - toggle using rails and rail knots in construction of sweep
  3. Use Rail Rotations - toggle using rail rotations in construction of sweep
  4. Adaptive Surface - toggle between Adaptive Surface and Number of Curves


  Rail Sweep Selection  

Pick Rails:  Choose the rail curves
Pick Shape/Edges:  Pick this button and then you can begin selecting the curves that the sweep will follow.
Pick Entire Loop:  This option will automatically choose an entire loop (of connected curves) when it is turned on.

Blend Options

Cubic with Bias:  This is the default option for blending between shapes when there is more than one shape specified.  Typically this option is used when precise control over multiple shapes is required using the shape bias to control the strength of the contribution of from each shape.   
Linear Shape Blend:  Do a linear blend between shapes.  This option is typically used when only 2 shapes are specified and a direct proportional blend between them is required.
Quadric Shape Blend:  This option gives a cosine wave based quadric blend between the shapes.  There is no biased control with the quadric blend. 


Blend with 3 Shapes and 2 Rails at default Cubic with Bias:


Side View of Blend with 3 Shapes set to "Linear Shape Blend" - note linear transition between shapes.


Side View of Blend with 3 Shapes set to "Quadirc Shape Blend" - note smoother transition between shapes.


Side View of Blend with 3 Shapes set to "Cubic With Bias" at default Bias values of 50% for all shapes.


Side View of Blend with 3 Shapes set to "Cubic With Bias". Middle curve has high bias (100%) in both directions to increase it's influence over the surface. First Curve has 20% bias in forward direction to decrease it's influence. Last Curve has a 20% bias in reverse direction to decrease it's influence.

 

Continuity Options

Tangent Continuity:  Utilize geometric tangent (G1) continuity along interior rails in cases where there are 3 or more rails. This is the default and recommended setting.
Curvature Continuity:  Utilize geometric curvature continuity along interior rails in cases where there are 3 or more rails.  
No Continuity:  Don't enforce continuity on interior rails.  It may produce discontinuous breaks in the tangency of the surface (G0 continuity). 


Curves used Sweep of Single Shape Along 3 Rails - Red is Shape


"No Continuity" option used - note crease along middle rail.


"Tangent Continuity" option used - note smooth transition across interior Rail

 

Creation Options

Uniform Scaling of Shapes:  If this option is specified the shapes will be scaled uniformly as they move between two rails where the distance varies.  This option is required for sweeping to a single point. The default value is true.


Single Shape with 2 Rails that vary in distance between the rails


"Uniform Scaling of Shapes" is checked - note that the height of the curve
grows and shrinks with the distance between the rails. The shape of the
curve remains the same as it moves along the rails because it does
a "Uniform" scaling.


"Uniform Scaling of Shapes" is not checked - note that the height of the curves
remain constant along the sweep. The shape of the curve changes along the
sweep becuase it does a "Non-Uniform" scaling.


Rotational:  This option is only applicable in cases where there is one rail and the second rail degenerates to a single point.  It takes the end point of the first shape as the second rail.  This option is good for producing capping surfaces. Normally this option should utilize "Rail Rotations" set to TRUE.


Curves used for Rotational Sweep Example


Result of sweep around closed curve without "Rotational" checked


Result with "Rotational" checked


Rotational Sweep Curves with 2 Shapes - note that they share
the same end point


Rotational sweep with 2 different shapes along closed curve
    
Cap Ends:  Cap the ends of the resulting Rail Sweep if it is closed.


Sweep to End of Rails:  If the sweep curve does not extend to the rail curves, this option tells the rail sweep to sweep all the way to the rails (extending past the ends of the sweep curve). This option is very useful when the sweep ends at a singular point.


Two Shapes (red) swept along Two Rails that extend past the Shapes


Original sweep with "Sweep to End of Rails" not checked


Sweep with "Sweep to End of Rails" checked


Arc Length Rails: If this box is checked the rails will be reconstructed and parameterized by Arc Length. What this means is that the shapes will move along the rails relative to the length of the rails not by the underlying construction parameters of the curve. If you have cloned the rails and edited them then you will probably want to keep this off because the curves are syncronized by their natural construction.


Syncronization #:  Specifies that an algorithm should be applied to make the sweep move along the rails and maintain a consistent orientation. This option only applies to two rail sweep cases.


Rail Syncronization Test with "poorly" parameterized Rails. The Blue points are the "knots" of the curves.


Rail Sweep with Syncronization = 0 - note bulge in surface caused by "Uniform Scaling of Shapes" and large distance between the ends of the curves.


Rail Sweep with Syncronization = 1 - note some improvement but still has a bulge


Rail Sweep with Syncronization = 10 - note very nicely shaped surface

 

Shape Synch & Approx

G1 End Continuity:  G1 End Continuity maintains the first derivative of the re approximated curve.  This value is only applicable if the Number Points is > 3 otherwise it is ignored..
G2 End Continuity:  G3 End Continuity maintains the first derivative and second derivative of the re approximated curve.  This value is only applicable if the Number Points is > 3 otherwise it is ignored..
G3 End Continuity:  G3 End Continuity maintains the first derivative, second derivative and third derivative of the re approximated curve.  This value is only applicable if the Number Points is > 3 otherwise it is ignored..   
Number Points:  Number of definition points to use to re approximate and synchronize the profiles.  This will make the knot spacing in cases with multiple profiles much more uniform.

Selected Shape Bias

Back: Specifies the strength of the selected curve in the blending going backward to the start of the sweep.  This is the bias of the curve entering the shape.    
Forw:  This is the strength of the selected curve in the blending going forward to the end of the sweep.  The is the bias of the curve exiting the shape.

 

Rail Rotation Axis

Use Rails Rotation: As the rail curves in space this option enables the shape to rotate with it as it moves along.  If you turn this off, the orientation of the interior generated shapes will remain the same as the original shapes. Note that control can be applied to individual rails - see above "Rail Control Options". The Default is to have Use Rails Rotation checked.


Rail Sweep of single Shape (red) along non-planar Rail


"Use Rails Rotation" is checked. Not how orientation of profile
changes as rail curves around and down. This is the default.


"Use Rails Rotation" is not checked. Note how orientation of
profile remains constant.

X, Y, Z: Allows specification of a vector to constrain the rail rotation.   

Constrain Rot To Axis:  If TRUE the axis specified will constrain the rotation.  For example if you constrain the rail rotation to the Z axis you get a shape like a banister of a curved stair way.  The interior shapes rotation is only in the Z axis.


Same sweep as shown above without any axis constraints. Note how profile rotates
both around the Z axis and around the X axis.


Same sweep as above exeept that "Constrain Rot To Axis:" is checked and the
specified axis is (0,0,1). This allows the shape to rotate only around the Z axis and
not the X axis. This shape is useful for creating shapes like a stair banaster railing.