How is tangent continuity calculated?

For curves, the tangent vector goes from the common endpoint to the next CV on the second curve. The Align tool moves the next CV of the first curve onto the tangent vector where the end tangent magnitude of the first curve is preserved.

For surfaces, the Align tool uses the same procedure as for curves, for each corresponding column of CVs across the common edge. The Alignment Type option controls how the tool modifies the CVs.

If the first curve selected has one end point touching another curve (or surface isoparm), then the Align tool aligns the curve at the location of the intersection, rather than at the end point.

Intersection

This option is only available when Continuity is Tangent or Curvature and Modify is set to Both.

Fixed – Keeps the endpoints fixed and moves the tangent CVs to achieve continuity.

Free – Keeps the tangent CVs fixed and moves the endpoints to achieve continuity.

Alignment Type

DEFAULT – Moves the CVs of the surface so they have the same proportional layout as the CVs of the target object.

Default is the “standard” alignment, and gives the most mathematically correct geometric alignment.

Default may show the effect of the alignment more than other alignment types.

ALIGN BY PROJECT – Projects the tangents of the modified surface onto the tangent ribbon of the target surface along the common edge.

COLINEAR – Aligns the hulls of the modified object with the hulls of the target object.

This alignment allows you to “impose” the CV/hull layout of one object on another, by forcing the hulls of the aligned object to be parallel.

DIRECTIONAL – Only allows the CVs to move along one direction. The Align tool attempts the best alignment given this constraint.

Directional is useful for creating the proper visual alignment in one view, saving the alignment with the Accept button, and then aligning again in another view.

When Alignment Type is Directional, you can use the Vector Options to specify a vector that defines the direction along which CVs can move.

Note

When aligning two curves, or when Continuity is Position, all alignment types are the same except Directional.

Tip

Remember that this alignment type only allows the CVs to move along a single direction. Some of the controls in the Align window (such as skew) may behave counter-intuitively because the CVs are so constrained.

PERPENDICULAR TO EDGE – Align the hulls of the modified object at 90 degrees to the edge of the target object.

This alignment allows you to maintain smooth hull placement in the common case of aligning a radial surface to a curved trim edge.

Lock Position CV Row

Locks the position of the aligned edge CVs to prevent them from moving as you change options.

Lock Tangent CV Row

Locks the position of the tangent CVs (the next CV row back from the aligned surface edge, or the next CV back from the aligned curve end) to prevent them from moving as you change options.

This option is only available when Continuity is Curvature. When this option is on, the tool attempts to achieve continuity by moving the curvature CV row.

Explicit Control

Gives you options (in the Explicit Control Options section) for the degree and number of spans in the first object.

Explicit Control Options

These options allow you to control the degree and spans of the first surface when Explicit Control is turned on. These options are only available when the first object is a surface.

These options always affect the first surface, regardless of the Modify setting.

U degree, V degree

Rebuild the first surface to have this degree in U and V.

U spans, V spans

Rebuild the first surface to have this many spans in U and V.

Vector Options

These options only appear when Alignment Type is set to DIRECTIONAL.

X,Y, Z

Select one of these options to specify a vector along that axis.

View

Select this option to specify a vector normal to the current view. The vector is not drawn in the view windows.

If the current view is changed, click Refresh View Vector to update the vector.

Picked

Selecting this option lets you specify the name of an existing vector in the Picked Vector field, or pick the vector in the view.

Refresh View Vector

This button only appears if View is selected. Click it to update the vector if the view has been modified.

Retain Vector

Click this button to create a vector construction object in the view windows. If you do not click this button, the tool uses the vector direction you specified, but you are not able to see and to re-use the vector.

Partial Align Options

Partial joins

Off – Aligns the entire edge of the first surface to the entire edge of the second surface.

T-Join – Aligns the entire edge of one surface to part of the edge of the other surface.

General – Aligns part of one surface to part of the other surface.

When Partial Joins is set to T-Join or General, small manipulators appear on the common edge. You can drag them to control what portion of the edge is aligned, or you can manually set the Partial Start and Partial End options.

This option is only available when the align is modifying a surface.

Modify Interior Allowed

Modify interior allowed means to reshape the surface to connect the original position of an outside edge and the interior join point. If an outside edge does not have modify interior allowed, the entire edge is reshaped to meet the interior join.

This option controls which outside edges have modify interior allowed: both the start and end, only at the start, or only at the end.

This option is only available when Partial Joins is General.

Attach hardness

Soft – Reshapes the aligned surface outside the aligned portion to meet the partial join.

Hard – Inserts multi-knots to create a much more abrupt join. This limits the effect of the alignment to the aligned portion and preserves the shape of the non-aligned portion.

This option is only available when Partial Joins is General.

Partial Start, Partial End

The start and end parameters of the alignment. These values reflect the positions of the start and end manipulators on the surface.

This option is only available when Partial Joins is T-Join or General.

Directional Alignment Options

Directional Align Vector Name

The name of the vector reference object that defines how the CVs can move when the Alignment Type is Directional. Click a vector reference object to use it. You can also manually type the name of a vector object.

Directional Align Vector

A manual vector value that defines how the CVs can move when the Alignment Type is Directional.

Blending (Curve/Surface 1, Curve/Surface 2)

Extra CV Rows

Allows the Align tool to take control of this many extra rows of CVs to achieve a smoother transition to tangency in the interior of the surface.

Other tools cannot affect the CVs controlled by the Align tool and its construction history.

Decay degree

The degree to which the influence of the alignment falls off as it moves out to the extra CV rows. Higher numbers gives less influence on the extra CV rows.

The decay degree is on an exponential scale, so the influence drops quickly as you increase this value by small amounts.

This option is only available if Extra CV Rows is greater than zero.

Tangent Scale, Curvature Scale

Controls the distance of the tangent/curvature CV rows from the aligned edge.

Start skew, End skew

Rotates the tangent at the start/end of the aligned edge.

This option is only available when Continuity is Tangent or Curvature, and Alignment Type is Align by Project, Directional or Perpendicular to Edge.

Blend Interior From Ends

Moves the interior CVs of the aligned surface to form a smooth transition between CVs of the outer edges when Continuity is set to Tangent or Curvature.

Show Manipulators

Displays manipulators for tangent/curvature scale and skew on the aligned edge.

Manipulators are only available when you are aligning two surfaces, and Continuity is Tangent or Curvature.

Manipulators

The number of manipulators displayed along the aligned edge.

The manipulators allow you to control tangent/curvature scale and skew on the aligned edge manually.

Slide Surface Edge On Reference

Surface 1/2 Join parameter

The parameter on the target surface at which the aligned surface will contact.

Insert At Param.

Create an edit point or isoparametric curve at the point on the target object where the align makes contact.

This option is useful in combination with the Join Parameter option to insert an edit point or edit point isoparametric curve at the interior alignment point for use with Object Edit > Attach > Detach.

Control Options

Create history

Saves the construction history of the alignment so you can edit the objects aligned or the tool options and the alignment automatically updates.

Auto recalc.

Automatically recalculates the alignment as you change controls in the window.

Continuity check

Adds a surface continuity locator to the aligned edge, giving a pass/fail indication on continuity and showing any discontinuities.

See Check the deviation and continuity on surface edges.

Specify continuity check, Continuity check type

Turn Specify Contin. Check on to show the Continuity Check Type option, which allows you to check for a specific level of continuity.

When Specify Contin. Check is off, the tool checks for the continuity you specified for the alignment (with the Continuity option).

These options appear when Continuity check is on.

Buttons

Recalc.

Updates the surface to match the current options when Auto recalc. is off.

Revert

Reverts to the last time you saved the alignment by clicking Accept. If you have not clicked Accept, this button reverts to the unaligned state or to the state at which the file was opened.

Accept

Saves the current state of the alignment, locking in the current shapes of the objects. Further editing takes place “on top of” this state, and clicking Revert returns to this state.