Blend Quick Help

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Overview

The Power Pwr_Blend command will create a blended surface between multiple curves/surfaces.  The Pwr_Blend tool can utilize tangent information from one or more of its sketch curves.  This tool and the Rail Sweep will probably be the two tools that are used the most if you are doing surface constructions.  We have gone to great length to make the tool both powerful and easy to use. It has an extensive right click menu available for quick access to the most used parameters for this tool.  

Right Click Menu Options:

  1. Adaptive Surface - Toggle between "Adaptive Surface" and "Number of Curves" in Power Surface Parameters Panel.
  2. Flip Tangents - Flip either all tangents or tangents of selected curve or tangent handle.
  3. Linear Segment, Double-Sided Blend, B-Spline Blending, Optimized Blend - switch between major blending types.
  4. Don't Use Rails - Toggle using rail geometry and knots in surface construction.
  5. Skinning - Ignore Tangents - Toggle "Ignore Shape Tangents" in Power Blend Parameters panel.
  6. No Tangency, Edge Surface #1, Parallel To Vector, Perpendicular to Vector, Parallel to Curvature, Perpendicular to Curvature - selectes the method used to compute the tangent field surface in the Sketch or Composite Sketch.
  7. Along Iso Curves, Perpendicular To Edge, Edge Averaging - selects the techniuqe used to compute the tangent field of edges belonging to surfaces or faces of a NURBS brep. These options are only applicable when "Edge Surface #1" or "Edge Surface #2" are selected for the tangent field method.


Curve Selection Parameters
Pick Shapes/Edges:  Click on this button and then pick the curves that you wish to blend between.

Pick Entire Loop:  This switch will automatically select the entire loop of sketch curve segments.  

Pick Spine Curve:
  The spine curve defines a path for a plane which passes through the spine with normal parallel to the tangent of the curve.  The intersection of these planes with the shapes being blended define the points which are to correspond to each other.    
  Blend Orientation Options  

Auto Orient Curves:  Automatically orient curves so that they are all in the same direction

Auto Orient Tangents:
Automatically orient the tangent surface directions relative to the position of the curves. This will be turned off if you start using the tangent flipping.

Cap Ends:  Cap the ends of the resulting blend if the shapes are closed.

Tangent Strength:  This spinner controls the relative strength of the tangents.  The higher the value the more the surface will bulge. 

Flip Tangents: This is a convenience button allowing you to quickly reorient underlying tangent fields of sub-object shapes. This button is effective only when "Auto Orient Tangents" is off. This button will flip either all of the tangents of the underlying shapes if no sub-object shapes are selected. If one or more shapes are selected in the "Operator Parameters" panel
then only those tangents will be flipped.


Optimized Blend with Tangent Strength of 1.0


Optimized Blend with Tangent Strength of 2.0



Optimized Blend with Tangent Strength of 0.5

  Blend Type  

The blend type specifies how the cross section of the blend is constructed.

Optimized Blend:  The blend produced attempts to optimize curvature changes.  It ignores the magnitude of the shape tangent surfaces and uses just the direction.

B-Spline Blend:
  The blend produces utilizes both magnitude and direction of the specified tangent surfaces.

Circular Arc:
  This option will blend the curves together through a circular arc path.  The blended solution will have a uniform curvature.

Linear Segment:
  Produce a linear segment between each curve.  This produces one or more ruled surfaces.


Conic Section Blend: Produce a blend that has a conic cross section.

Double-Sided Blend: Produce a blend with independent blending control on each side (each curve).  It essentially creates 2 blends (one on each side), with a surface in between.  Use the "Double-Sided Blend Controls" to control the shape of your double-sided blend. See below for examples of double sided blends.


Optimized Blend - Ignores Magnitude of Tangents


B-Spline Blending with Large Tangent Field Magnitues


B-Spline Blending with Smaller Tangent Fields


B-Spline Blending with 3 Different Sized Tangent Control Handles


B-Spline Blend with 1 of 3 tangent handles rotated 90 degrees around curve.


B-Spline Blend with a Flair Angle of 45 degrees on one of Tangent Handles


Linear Segment Blend


Conic Section Blend with Surface Control Polygon Displayed

  Continuity Options  
The continuity options specify the derivative continuity of the blend. Typically the higher order continuities (G2 and G3) produce smoother more organic looking shapes. The G1 continuity tends to produce a manufactured looking object that has a distinct curvature change between the surfaces.

G1- Tangent Continuity:  This option will maintain the geometric tangent (G1) continuity of the surface at interior curves with tangent fields.

G2 - Curvature Continuity:
  This option will maintain the geometric curvature (G2) continuity.

G3 - Third Derivative Continuity:
 This option will maintain the geometric 3rd derivative (G3) continuity. 


Optimized Blend with G1 - Tangent Continuity


Optimized Blend with G2 - Curvature Continuity

Optimized Blend with G3 - Third Derivative Cotninuity

  Blend Rail Options  

These options control how the blend surface utilizes the shapes or rails of the blend.

Don't Use Rails:  This option ignores the rails and rail knots when creating the actual surface.  This option produces the cleanest surface without extra knots but may not exactly interpolate the input shapes. See third image below.

Use Given Rails:
  Uses the shapes and their corresponding knots as rails.  This option exactly interpolates the input shapes but may have extra knots depending upon the knot vector of the shapes.  This option is useful when the input shapes have a consistent knot vector (i.e. they are clones of each other) or they are the result of a previous surface operation which produced a nice knot vector (i.e. edge of a rail sweep).  It is possible to use this option in conjunction with the surface approximation algorithm that uses knots to produce two adjacent surfaces with the same knot vector. 

Reapproximate Rails :
  This option re-approximates the rails using a least squares fitting algorithm.   It does a better job of approximating the given shapes without a poorly constructed interior knot vector.  This option should be used if the shapes have lots of knots but need to be closely approximated.


Blend of Two High Control Point Curves with "Using Given Rails"


Blend of Two High Control Point Curves with "Don't Use Rails" and 20 Curves


Blend with only 8 curves and "Don't Use Rails" - note gap between surface and original curves. If exact interpolation of curves is needed, either have a higher number of curves or "Use Given Rails".

  Tangency Override Options  
This option allows you to ignore the tangent fields and loft or skin through two or more sets of curves. You can use this option instead of using the Pwr_Skin command.

Ignore Shape Tangents: If checked then Lofting or Skinning will be done using the below parameterization options.

Uniform: This option will produce a uniform knot vector in the resulting surface.  This option should be used if there are 3 or more shapes that are equally spaced.
Chord Length:  This option will change the parameterization to be proportional to the distance between the input shapes.   This option should be used there are 3 or more shapes and they are not equally spaced. 
Centripetal:  This option will change the parameterization to be proportional to the square root of the distance between the input shapes.


Three Curve Blend Using Shape Tangents


Three Curve Blend with "Ignore Shape Tangents"

  Blend Parameters  


Syncronization #:  If there are 2 curves only, you may specify a synchronization number to be used along the first curve selected to intersect perpendicular planes. This option is typically used for blending cases where the curves are close to each other but are not cloned from each other. If you display the surface knots, you can see how the curves map to each other. The longer and closer the curves are the higher the syncronization number should be. In the example below only 5 points were needed to get a very nice syncronization. Sometimes as much as 100 syncronization is needed for very long skinny blends. Typically you will know you need a syncronization if you display the surface knots and they tend to bunch up a little in the middle or tend to skew as they go along the curves.


Optimized Blend with Syncronization Number = 0


Optimized Blend with Syncronization Number = 5


Proportional Blending: If this option is specified when doing "B-Spine Blending" it automatically varies the strength of the tangent to be proportional to the distance between the curves.  This option is required to blend between curves which touch at one or both ends.   

  Selected Shape Trimming  

It is often desirable to blend only a portion of a curve. These options allow you to select a shape in the Operator Parameters dialog and change it's minimum and maximum relative parameters. The default of 0 and 100 cover the entire curve. Values of 25 and 75 would blend to the middle half of the curve .


Before and after a 10% trim on one of the shapes

  Double-Sided Blend Controls  

These parameters are used to control the shape of a double-sided type blend. See examples below:

Middle Bulge: This parameter determines how much the surface (between the 2 blends) will bulge up in the middle. The value is interpreted as a percent of the distance between the two blending curves.

Start Blend Size: This parameter tells it how much of a blend to create on the starting side. This is a percent of the distance also. 1% gives a very small tight blend and 20% gives a fairly large blend to the middle section.

End Blend Size: This parameter tells it how much of a blend to create on the ending side.    

Split Double-Sided Blend: When this option is selected, it will split up the resulting blend into 3 separate (but connected) faces.  There will be 2 faces on the ends, and a face in the middle. When this option is turned off, the blend will be created as a single face.

Fade To Normal Blend: If this flag is set to true, one end of the blend will be a Double-Sided Blend while the other end is a normal blend and the surface between them fades from a double sided blend to a normal blend.

Reverse Fade Direction: If true we reverse the direction of the fade so that the double-sided end and normal blend end now are on the opposite sides of the blend.

Fade Weight: This controls how quickly the fade happens. A larger number means that the double sided blend is has more strength than the normal blend. A smaller number means the converse.


Double Sided Blend with 0% Middle Bulge, 10% Start/End Blend Size


Double-Sided Blend with -5% Middle Bulge, 5% Start/End Blend Size


Double-Sided Blend with 2% Middle Bulge, 2% Start/End Blend Size


Double-Sided Blend with "Fade To Normal Blend" at 50% Fade Weight and
0% Middle Bulge, 10% Start Blend Size, and 5% End Blend Size.


Double-Sided Blend with "Fade To Normal Blend" at 90% Fade Weight and
0% Middle Bulge, 10% Start Blend Size, and 5% End Blend Size.


Same Parameters as above with "Reverse Fade Direction" checked.

  Tangent Flipper  

The Tangent Flipper, helps you to flip the tangent of an individual sketch/curve in a blend. When the Tangent Flipper is enabled, a grip is shown in the active viewport as seen in the screen below. The first field selects which sketch/curve you would like to flip. The selected sketch/curve will be surrounded by circles in the viewport as seen in the screen below. When a sketch/curve is selected using the field just mentioned, clicking the Apply button will flip the tangent. Warning: Keep in mind that blends typically have "Auto Orient Tangents" on by default. When you flip a tangent using the Tangent Flipper, it will disable Auto Orient Tangent. This may lead to a result you don't expect.
The Tangent Flipper is automically active when in "Pick Shapes/Edges" mode, but can be activated/deactived at any time by clicking the "Tangent Flipper" button.


Tangent Flipper Grip