1. Blend Curves and Blending Surfaces
An Introduction to the Advanced Surfacing Tools in Alias

2. Main Surface Blends A smooth, continuous surface...
... will be modeled from surface patches...
Curvature Continuity
Curvature Continuity
Positional Continuity
... that have continuity between them.

3. Features and Complex Forms
Complex topologies that cannot be sculpted from a single surface can be constructed from blended surfaces.
Sculpted features can be added to a design and blended in.
Patch Layouts:

4. Workflow Example
Create a licence plate recess using a bi-rail surface.
Create a surface with continuity.
Create the main surfaces.
Trim a gap for the blended surface.
Use curves to design the character of the blend.

5. Curve to Surface Continuity
Object Edit>Align
If a surface edge, isoparm, or curve-on-surface is selected as the master, the CVs of the input curve will align to the U or V direction of the line.
If the curve doesn’t meet a line, then the ‘vector’ option should be used.
Master
Master
Input
Input
Other Tools for Aligning Curves to Surfaces
Blend Curves
Blend curves are a relatively recent tool in Alias. They are very useful but also quite sophisticated, so they will be covered later in this lesson in detail.
Using a Curve-on-surface with Align
An alternative to using the ‘vector’ option. First create a curve-on-surface as a guide, then align the curve to the c-o-s.
Curve Edit>Project Tangent
This is an older tool, used specifically to align a curve to a surface. Largely replaced by the functionality of blend curves and the Align tool.
The CVs will move only in the direction specified in the vector options to achieve the requested continuity.

6. Surface Tools and Continuity
Tangent Continuity Only
Tangent and Curvature Continuity: Limited Control
Tangent and Curvature Continuity: Low-Quality Surface
Tangent and Curvature Continuity: Full Control
Round
The Round tool is useful for small detail fillets, particularly where corners are required.
Quick and easy to use but limited to tangency.
Surface Fillet and Freeform Blend
The advantages of these tools are their speed, ease of use, and how they work with construction history—updating when surfaces are altered. In many circumstances, they create good-quality surfaces. However, these tools aren’t flexible enough to deal with the more complex blending situations.
n-sided
The n-sided tool will create poor-quality surfaces with tangency and curvature—but it is an acceptable tool to use for concept models or small areas.
Rail and Square
The rail and square surfaces have two attributes that make them suitable for creating blend surfaces: continuity and rebuild.
The rail and square surfaces have two attributes that make them suitable for creating blend surfaces: continuity and rebuild.

7. Continuity and Rebuild
Continuity allows you to set the continuity separately for each edge.
Experienced users work with the option window open so they can modify the continuity and rebuild options to refine a surface.
Continuity
The position, tangent, and curvature settings are the same as used in the Align tool.
The Square tool has two settings for Positional Fixed and Free. Fixed works in the same way as Position. Free is more relaxed and will deviate from the chosen edge if the continuity on the adjacent edges need some help.
Forced to Use Rebuild
In some situations, you are forced to use the rebuild ticks. The surface will fail to build, and you will get an error message in the prompt line: Or
The message will go on to tell you how to solve the problem:
Rebuild
Rebuild improves the parameterization of edges, in particular if they have been trimmed.

8. Implied Tangent
Try to keep tangency with an implied surface that shares this edge.
The implied surface is the surface that would be created by mirroring the new surface.
Implied Tangent: Only for Center-lines
Don’t use Implied Tangent when you want the edge of your surface to be smooth with another surface. In this situation, use Tangent.
Only use Implied Tangent for a surface edge which lies on the center-line of a symmetrical design.
Implied Tangent: Alternatives
The Implied Tangent setting won’t always guarantee a good result along a center-line. If this is the case, you have two alternatives:
Build a tangent surface perpendicular to the center-line, and make the new surface tangent to it. Then, discard the first surface (sometimes called a ‘slave’ surface).
Use Object Edit>Symmetry Plane Align after creating the surface. This has the disadvantage of losing the construction history and may cause continuity problems on the other edges of the surface.
With Position, there is a small tangency break between the mirrored surfaces.
With Implied Tangency, the surface is held tangent to the mirrored surface along its length.

9. Blend Surface Errors Continuity Failure
If a blend surface fails, use the Continuity Check within the Bi-rail and Square tools to get more information.
Use the Evaluate>Surface Continuity tool to check other edges to locate the source of the problem.
Evaluation by Numbers or by Eye?
If you are developing a concept design, then you should use the continuity check as a guide only. Also, if a rail or square surface ‘fails’ don’t panic! Use the information as a warning to evaluate the surface before continuing.
Sometimes, a ‘failure’ is minor, and, when you use shading to evaluate the surface, the result is acceptable.
In other situations, the failure will be a real problem caused by some error in the way the curves or surfaces were set up. In these cases, you will have to do some work to remedy the problem.
In any case, if there is a problem, the first thing to do is use Diagnostic Shading to evaluate the problem.
Curvature ‘Flat’
It is possible for a ‘failure’ to be reported and measured as ‘curvature = flat’. You can ignore this failure as the surfaces will be visually smooth.

10. Exercises EX1-Square-rebuild.wire EX2-Bi-rail-rebuild.wire
EX3-N-sided.wire
EX4-Feature-bi-rail.wire
EX5-Patch-layout.wire

11. Blend Curves What Is a Blend Curve? Blend Curve Attributes
A blend curve is a normal NURBS curve with extra controls called ‘blend points’.
Don’t Forget What You Have Already Learned about Curves
Everything you have learned about good-quality curves applies to blend curves.
Turn on the CVs for blend curves so that you can spot if hull lines zig-zag or double-back.
Use the Curve Curvature locator to evaluate the flow of the curve and continuity with adjacent curves and surfaces.
Blend Curve Attributes
Blend points are ‘sticky’—if placed on an existing curve or surface, they become associated and stay attached.
Blend points lie on the curve (unlike CVs) and can be used successfully to shape the curve.
Blend curves are automatically created at G2 (curvature) continuity when associated with an existing surface.
Blend curve are modified using manipulators, not by moving CVs directly.

12. Blend Curve Tools Blend Curve Toolbox Pick>Blend Point
Clicking on the Blend Curve icon opens a separate toolbox for working with blend curves.
Pick>Blend Point
Use Pick>Blend Point and Transform>Move to modify the blend curve shape.
Control Panel>Display
Use Control Panel>Display to turn on and off blend points.
Blend Curve Toolbox
Many of the tools are ‘context-sensitive’, which means they are only available when it is possible to use them.
So, for example, the Blend Curve Edit Point tool will be ‘greyed out’ until a blend point is selected, and then it can be applied.
Tip:
You can drag the Blend Curve toolbox onto the shelf. Click and drag the tab at the top of the toolbox.
On the shelf, the tools are more visible.
Golden Rule!
Turn on the CVs for blend curves to understand the CV structure of the curve and to help diagnose problems.

13. Blend Curve Basic Tools
Create Blend Curve
Click to place blend points.
If you click on a curve or surface, the blend point becomes associated to the object and will stay attached as the object is moved.
The Blend Point icon changes if the point is associated or free.
Blend Curve Add Points
Select the tool, and then click on a blend curve to add a blend point.
To Delete a Blend Point
Use Pick>Blend Point and then delete.
Blend Point Associativity
If a blend point has been associated with an object, then, when you pick and move the point, it will stay attached.
Associativity
If you click on a shared edge when placing a blend point, the pick chooser will pop up.
Choose which surface to associate with the blend point and drag the cursor across to the black finger.
The point will then be associated to the surface, and you can drag it to the required location.

14. Blend Curve Continuity
Blend Curve Edit
Use to display and adjust the continuity locator.
Click on the green dotted lines to align to the surface U and V.
Click and drag on the square and circle to adjust the CV positions and the shape.
Continuity Locator
Clicking on any of the green dotted lines will maintain the tangency.
Clicking on the black dotted lines will be at an angle to the surface.
Adjusting CVs with the Locator
The only way to adjust the shape of the blend curve is to use the square and circle icon on the locator. Turn on the CVs for the curve as you adjust these to see the effect more clearly.
Green Lines: Surface Alignment
Blue Arrows: Direction Constraint
Tangency CV Adjustment
(Square)
Curvature CV Adjustment
Circle

15. Tools for a Selected Curve
Blend Curve Degree
Blend curves will default to degree 5.
To change the degree, pick the curve and select the required degree.
Comparison of Align and Blend Curves
Some users don’t use blend curves since the same results can be achieved using the Align or Project Tangent tools.
However, the results can often be achieved more quickly using blend curves, and construction history will often update more successfully.
Blend Curve Construction History
The blend curve will update as its associated objects are modified.

16. Tools for a Selected Blend Point
Pick>Point Types>Blend Point
Continuity
Pick the blend point and choose the continuity required.
Continuity defaults to G2 (curvature) when associated to a surface.
Blend Constraint Interpolation
Changes the locator so that you can align the curve to the XYZ axes or to the surface parameterization.
Dissociate Blend Constraint
Makes a blend point free.
G3 and G4 Continuity
Blend curves are the only tools in Alias that offer higher levels of continuity.
While G3 and G4 will be ‘smoother’ than lower continuities, they will also increase the number of CVs in the blend curve.
Most experienced users use alternative, advanced techniques for more smooth connections.
G0, G1, and G2 will be sufficient for the concept models you will be creating.
Blend Constraint Direction
Switch to point ray when you need to change the direction of a blend point.

17. Exercises EX6-Blend-curves.wire EX7-Blend-surfaces.wire
EX8-Ketchup-bottle.wire

18. Projects P1-Vehicle-blends.wire P2-Detergent-bottle.wire
P3-Vehicle-features.wire
P4-Handset-blends.wire