Global Sweep

InsertSurfaceGlobal Sweep

The Global Sweep command enables you to create surfaces by sweeping one or more section contours (chains of consecutive curves) or a surface — along one or more drive contours.

After selecting making the selection of the drive contours (for the Drive Curves selector), you can choose whether to use section curves or to sweep a surface in the Sweep drop-down list, which has to following two options.

Curves

To use section curves: one or more contours, even if they have sharp points.
If you choose Curves, you can select different groups of contours to be swept (for the Curves (n) selector under Section Group(s) (n)).

The context menu displayed by right-clicking on Curves (n), the following options will be displayed:

Show Invert and Place - Displays the Invert and Position of Section mini-dialog boxes for the corresponding section.
Show All Invert and Place - Displays the Invert and Position of Section mini-dialog boxes for all the sections.
Hide Invert and Place - Hides the Invert and Position of Section mini-dialog boxes for the corresponding section.
Hide All Invert and Place - Hides the Invert and Position of Section mini-dialog boxes for all the sections.

Invert check box:
It enables you to invert the orientation of the section contour.

When selected, the orientation is inverted. This might be required if the sweep result is self-intersecting.
When cleared, the orientation is not inverted.

Position of Section text box:
It enables you to change the position of the contour to be swept on the drive. You can enter the curve parameter value in the corresponding text box. The position of the section curve is represented by a red handle displayed at the projection of the initial point of each section group onto the drive contour. You can interactively drag this red handle to change its position.

Surface

To sweep a surface along the drive curves. This feature is helpful to control section evolutions along a drive in air intake, exhaust manifold designs, etc. If you want to sweep several surfaces, you need to join them first. If you select Surface you can proceed as follows:

Select the surface (Surface) to be swept.

As soon as the surface is selected, two arrows corresponding to the U (U) and V (V) parameters are displayed on the selected surface: you can double-click on each of them to invert the parameterization.

Under the Invert U/V node you can find the Exchange U/V check box, enabling you to invert the two parametric directions of the surface:
- When the box is cleared the parametric directions will be kept as they are.
- When the box is checked, the current U direction will become the V direction and the current V direction will become the U direction.
The shape of the section at parameter U on the drive is defined by the shape of the corresponding U-isoparametric curve of the selected surface. More precisely the section is evaluated in the working plane frame translated along a line defined as the projection of the surface iso-parametric curve {V = 0} on the X-axis of the working plane. Therefore it is important to position well the swept surface in the current axis system.
The options under the Transform node (End Axis Alignment) enable you to change the position of the selected surfaces along the drives.

On the drive contour the selected motion reference is displayed:

T=tangent
N=normal
B=binormal.

By double-clicking on the corresponding arrows you can invert the relative directions.

If any transformation has been applied, you can easily undo it in the same command session by right-clicking on the Transform node in the selection list and by selecting Reset in the context menu.

Please note that when using the Surface option no transition management is available.

In the Motion Mode drop-down list you can choose the method to be used to perform the sweep along the drive:

Constant

The contours will be swept along the drive keeping their orientation constant.

Constant axis

The contours will be swept along the drive while keeping an axis constant through all the motion (the axis Direction can be an existing line, the one identified by two points or an axis of the Work Plane).

Frenet

The contours will be swept along each drive assuming the orientation of the Frenet reference (tangent, normal, binormal) of the latter.

Enhanced Frenet

The contours will still be swept along each drive assuming the orientation of the Frenet reference of the latter as much as possible, with an enhancement enabling the resulting surface to be continuous (G0).

Along one plane

The contours will be swept along each drive assuming the orientation of a plane. An Automatic plane check box enables you to control the selection of such plane.

If the check box is selected, the plane whose orientation will be used to sweep the section contours along the drives is determined automatically as the mean plane of the drive contour. It will obviously be the plane on which the drive contour lies if the latter is planar.
If the check box is cleared, the plane is to be selected using the Plane normal drop-down list.

Surface based

The contours will be swept along the drive keeping an orientation based on the one of the selected surfaces (i.e.: during the motion, the normal will be the one of the surface, while the tangent will be the one of the curve). This method can be very useful to build "lips". The Close Sweep check box shows up when the initial and the final end points of the drive curves coincide. If you select it, the final result will be a closed surface, while if you clear it the resulting surface will not be closed.

Bi-driven

The contours (one or several section curves) will be swept along two drives (selected as Drive Curves and Second Drive Curves), which may be curves or surface boundaries, ensuring G0 continuity along the two drives. Please note the following:

If the end points of the selected section curves initially lie on the two drives, they will be kept on the drives along the whole motion.
If the end points do not initially lie on the drives, they may not lie on the drives along the motion.
Though the selected section may be tangent to two surface boundaries selected as drives, only G0 continuity is ensured along the motion.

When the Bi-driven mode is selected, and when possible, the sections are scaled so as to keep in contact with the drives. The Scaling drop-down list enables you to select one of the following scaling methods:

None	No deformation is applied to the sections. With this choice, the section endpoints may not keep in contact with the drives.
Isotropic	In order to keep the contact between the sections and the drive curves, a scale is applied along the direction of the line joining the two drive curves. This is an axis of the motion frame. The same scale is applied along the two other axes of the motion. In other words, this option applies uniform rescaling: the section curves are scaled equally along the three axes of the motion.
Unidirectional	Same as in the Isotropic mode, but no scale is applied along the two other axes of the motion: rescaling is applied only along the direction of the line joining the two drive curves.

As mentioned, with bi-driven motion, the sections are intended to be scaled so as to keep in contact with the drives. Two parameters on each section are detected, corresponding to the contact points between the section and the two drives or at least the closest points. If all the pairs of parameters are the same, then the scale function is applied. Otherwise, it is not. In this case, a specific warning is displayed.

Note
In the case the contour(s) to be driven lie(s) on the same plane as the drive contour, you can use the transformation handle to move it onto the curve with the orientation you like best.

AutoInvert and AutoPlace Option
A smart mechanism for the automatic assignment of the position (and of the orientation reversal when the Motion Mode is Bi-driven) of the section contour so as to obtain the best fitting result is available.
By default the mechanism is enabled, but you can turn it off, so as to make your own choices manually, in two different ways:

By manually changing the position of the section and/or by changing the status of the corresponding Invert check box.
By right-clicking on the Curves n selector and selecting or clearing the AutoInvert and AutoPlace option in the context menu.

Please note that in associative mode (that is, when the Associative Mode box is selected), if the AutoInvert and AutoPlace box is selected, the position and invert values are not saved. As a consequence, when rebuilding the model they are computed automatically.

Associativity
The surfaces created using this command in both Sweep modes (Curves and Surface) can be associative: associative surfaces are Skins, which are open solids, retaining a link to the base curves, so that if you modify the base curves the surfaces will be modified accordingly; they have a history and are displayed in the Model Structure. See "Associative Surfaces (Skins)" for details. If the Sweep drop-down list is set to Surface), after selecting a surface:

When the Associative Mode box is cleared, no link will be created between the resulting sweep surface and the reference surface you have selected. If you modify the latter, the former will remain unchanged.
When the Associative Mode box is checked, the resulting sweep surface will retain a link to the reference skin you have selected, so that if you modify the latter, the former will change accordingly.

In the following example the green hexagonal skin has been selected as the reference surface to be used for the creation of the final sweep surface. The Associative Mode check box has also been selected. The azure curves are the drive curves.

When you apply the command you obtain the following result.

When you apply a change to the reference skin (in the example the rotation angle has been modified), the skin obtained as result of the Global Sweep command is updated accordingly.

Additional options are available under More Options.

The Transition drop-down list enables you to control the resulting surfaces at each sharp point:

None	No transition is applied. The resulting surfaces will only be positionally continuous.
Global mode	The effect of transition is computed by the global section interpolation process.
Local mode	A local computation of transition is performed that is effective in a restricted area around the transition, as shown in the following images.


Local mode	Global mode

Using the following options in the new Restrict drop-down list under More Options, you can restrict the development of the sweep surface within limits.
- None - No restriction is applied and the sweep will be created over the complete drive curve.
- Between parameters - The sweep is limited between two user defined points on the drive curve.
  
  Regular Complementary
- Between sections - The sweep is limited between the first and the last section curves.
  
  Regular Complementary
The complementary sweep is obtained by selecting the Complementary Shape check box under the Restrict node.

When the command is performed with several sections, there are different ways to match their discontinuities (if any) through the options of the Section Matching node.
In the Matching type drop-down list, you can select the actual matching mode to be used by the application for the section mapping:
By default, the matching type combo-box is set to Discontinuity, and Ignore discontinuities is unchecked.

Curvilinear

The discontinuities of the sections are mapped using their arc length.
In the following example there are three discontinuities on the first section and only two on the second.

The following illustration shows what you get upon the choice of the Curvilinear option (Motion Mode is set to Along one plane and the Automatic plane box is checked):

Discontinuity

Tangency discontinuities are detected. If the number of these discontinuities is the same on each section, a discontinuity-to-discontinuity (from now on, for shortness' sake: D2D) mapping between each section is applicable.

D2D mapping mathematical concept
Given K sets S_i of n discontinuities (ordered values), a D2D matching is an ordered bijection between S_p and S_q, for p, q in {1…K} and p different from q.

If the number of discontinuities is not the same on each section, a D2D mapping is not possible, and the resulting matching is automatically curvilinear. In the example used to show the Curvilinear option (see above), then, even if you had selected the Discontinuity option, the result would have been the same.
A specific Ignore discontinuities check box, though, is available so as to enable you to "skip" discontinuities on some section in order to have the same number of discontinuities on each of them. In this case the D2D match becomes possible.

When the box is cleared, no discontinuities will be skipped by the application during the section matching process. If the discontinuity number is not the same on all sections, then the actual matching mode used by the application will be the curvilinear one.
When the box is checked, optional Skipped discontinuities n marker selectors are displayed under the Section Group(s) n nodes. Each selector enables the selection of the cross markers that are displayed on the corresponding section in this case.

If you select the central discontinuity marker on the first section, the D2D mapping will be possible, as only two discontinuities will be taken into account:

The final result will then be more accurate than the one obtained with the Curvilinear option.

All discontinuities

All the discontinuities (both tangency and curvature) are detected on the sections. If a D2D matching is possible, it is performed. Otherwise the matching remains curvilinear. Please note that this option was the one always applied in the former version of the command.
In the following example the two sections are the side curves. On both sections, there is only one curvature discontinuity (that is, the curve is not more than tangent continuous at this point).

With the All discontinuities option it is possible to obtain a real D2D mapping:

On the contrary, with the Curvilinear or even Discontinuity options (since only tangency discontinuities are taken into account for matching), you would obtain three surfaces which would be tangent continuous.

All discontinuities with reparameterization

It enables you to achieve transversal G1 continuity of surfaces being produced from section curves having same number of G1 continuous spans while preserving their correspondence.

The Match Curve-to-Curve Sections check box enables you to choose the method for joining different contours made of more than one curve each.
- When the box is checked, the sweep will be performed between the curves belonging to the selected groups, rather than between the groups themselves. The number of curves belonging to each different group may be different, so the number of sweep surfaces actually created will be the same as the maximum of the numbers of curves among all the groups.
- When the box is cleared, the groups themselves are taken into account and the number of sweep surfaces may vary depending on the specific situations.
For further details on the Match Curve-to-Curve Sections option, see "Using the Match Curve-to-Curve Sections of the Global Sweep command".
When the More Options node is expanded — and only in this case:
- A Position of Section n (n = 1, 2, 3, ...) handle/mini-dialog box pair is displayed on the drive curves at each of the points where a section is positioned (n is the section number) so that you can modify it either by dragging the handle or by entering a different parameter value (the parameter refers to the whole drive chain).
- An Invert check box enables you to invert the orientation of the section contour in order to remove twists from the resulting surface:
  - When checked, the orientation is inverted.
  - When cleared, the orientation is not inverted.

A warning is displayed at each location where the motion is not continuous (there may be cases where, though the drive is only G0 at a certain location, the selected Motion Mode is such that the resulting motion is continuous).

When the Position of Section handle is dragged just upon a discontinuity, there are actually three possible ways to position the section (on the discontinuity, on the left or on the right). Hence, a context menu can be displayed by right-clicking on the Position of Section handle.

Link to both transition sides	Perform the transition considering the actual section curve you have selected.
Link to left transition side	Perform the transition considering the section as lying before (on the left of) the discontinuity.
Link to right transition side	Perform the transition considering the section as lying after (on the right of) the discontinuity.

Please note that if the Position of Section handle is close to the discontinuity but not just on it, then the same context menu is displayed, but no check box is available on it. If you choose one of the options, the Position of Section handle will be positioned exactly on the discontinuity.

Finally, in order to improve the final shape and to gain better control on its degree and continuity values, you can choose the method to be used for the interpolation of the sections in the Section interpolation drop-down list under More Options.

Max. degree 3	When this option is selected, the final degree along the U direction for the final shape will be 10. When the drive is closed, if the motion is continuous enough, the continuity value at the closure point will be C2. Please note that if the number of sections is lower or equal to 4, then the final U degree of the shape will be lower or equal to 10.
Max. degree 5	When this option is selected, the final degree along the U direction for the final shape will be 12. When the drive is closed, if the motion is continuous enough, the continuity value at the closure point will be C4. Please note that if the number of sections is lower or equal to 4, then the final U degree of the shape will be lower or equal to 12.

Self-intersection Detection
Specific warnings are displayed when self-intersections are detected. In the following example an ellipse has been swept along the drive curves and the resulting surface has a self-intersection which is automatically detected by the program.


Regular	Complementary


Regular	Complementary

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