Sweep surface node

Creates a surface by sweeping cross-sections along a backbone curve.

All

Parameters

Inputs

Local variables

Example files

See also: Rails, Skin

The Sweep op sweeps primitives in the Cross-section input along Backbone curve(s), creating ribbon and tube-like shapes. The cross-section primitives are placed at each point of the backbone perpendicular to it. If a Reference Point input is given, each primitive will be oriented to aim at its corresponding reference point.

The backbone curve can be open or closed, but must have at least two points.
If the backbone input has more than one primitive, Sweep will sweep the cross section along each one.
If the cross-section input has multiple primitives, you can control them using the Cycle type parameter.
Sweep places the origin of the cross-section on the backbone by default. You can specify a point on the cross-section to attach to the backbone instead with the Use vertex and Connection vertex parameters.
In most cases, you should build the cross section primitives in the XY plane. Sweep will automatically orient them properly along the backbone.
If the backbone curve(s) have point colors or texture coordinates, they will be maintained and applied to the cross section primitives.

Using Sweep

Click the Sweep tool on the Model tab.
Select the cross-section and press Enter to confirm your selection.

You can attach multiple cross-sections to a backbone by selecting more than one.
Select the backbone and press Enter to confirm your selection.

You can select multiple backbones to attach cross-sections along.

Note

You can specify a Skin Output from the drop-down menu on the parameter editor. However, this only works with polygons, NURBS, or bezier curves.

Parameters

X-Section Group

Only use the geometry in this group as the cross-section, instead of all geometry in the first input.

Path Group

Only use the geometry in this group as the backbone curve(s), instead of all geometry in the second input.

Reference Group

Only use the geometry in this group as reference points, instead of all geometry in the third input.

Cycle Type

How to sweep the primitives.

Angle Fix

Attempt to fix buckling twists.

Fix Flipping

Fixes flipped normals.

Remove Coincident Points on Path

Removes overlapping points.

Aim at Reference Points

Tilt the cross-sections towards their respective reference points from the Reference Points input. The Reference Points input will still be used to roll the cross-sections around the backbone even when this parameter is turned off.

Use Vertex

Connect a specific vertex of the cross-section to the backbone.

Connection Vertex

Specific vertex to connect to backbone.

Scale

Uniform scale of cross-section.

Twist

Cumulative rotation of cross-sections around the backbone.

Roll

Non-cumulative rotation of cross-sections around the backbone.

Create Groups

Creates a group for each backbone.

Sweep Groups

Allows naming of the sweep groups. A separate group is created for each backbone by appending a number to the group name. Thus, if there is only one backbone, the created group will be called sweepGroup1.

Skin Output

How/whether to create a surface connecting the cross-sections along the backbone.

Off	Do not create a surface.
On	Skin each set of swept cross-sections.
On with Auto Close	Skin each set and close if the underlying path is closed.
On with Preserve Shape	Like “On” above, but ensure the swept curves are fully encased in the resulting surface.
On with Preserve Shape and Auto Close	Skin with “Preserve Shape” and “Auto Close” put together.

Fast Sweep

More efficient skinning. Use when the input geometries maintain the same topologies between cooks and each cross-section has the same number of points.

Output Polygons

Outputs meshes as polygons rather than meshes.

Inputs

Cross-section	The geometry to sweep along the backbone curve.
Backbone path	The curve(s) to sweep the cross-section shape along.
Reference Points	If this input is connected, each primitive will be oriented to aim at its corresponding reference point in this geometry.

Local variables

PT	Current vertex.
NPT	Total number of points.
PATH	Path primitive number.
PCT	Percentage along backbone (path).

Example files

SweepBasic

$HFS/houdini/help/examples/nodes/sop/sweep/SweepBasic.cmd

Load | Launch

This example demonstrates how the Sweep SOP copies geometry onto the points of a curve.

The Sweep SOP is unique in that it automatically places the copied geometry perpendicular to the backbone it is copied to. Variations such as the Cross Section’s scale can be adjusted using expressions.

SweepCurve

$HFS/houdini/help/examples/nodes/sop/sweep/SweepCurve.cmd

Load | Launch

This network contains an example of the Sweep SOP. A NURBS curve and NURBS circles are used as the backbone and the cross section geometries of the sweep operation respectively.

By controling the scaling of the cross section geometry in the Sweep SOP various effects can be acheived. Finally, a Skin SOP completes the form by using the swept geometry as a kind of skeleton.

SweepDome

$HFS/houdini/help/examples/nodes/sop/sweep/SweepDome.cmd

Load | Launch

In this example the Sweep SOP a grid is used as the backbone of a sweep operation with arcs (created by a Circle SOP) as the hull (cross sections) of the sweep object.

The final sweep object is then skinned with a Skin SOP to create the dome geometry.

WigglyWorm

$HFS/houdini/help/examples/nodes/sop/sweep/WigglyWorm.cmd

Load | Launch

This network demonstrates how the Sweep SOP can be used to construct geometry that is easily deformable. The Sweep SOP requires a backbone and cross section geometry.

Through a sin() function an expression is created to animate the backbone for a slithering effect. Then the circles are copied at every point on the backbone to create the skeleton of the worm. Finally, a simple skin operation completes the worm body.

Usages in other examples

Example name	Example for
CreepParticleTubeA	Creep surface node	Load \| Launch
CreepBlob	Creep surface node	Load \| Launch
ParticleTube	Particle surface node	Load \| Launch
PrimCenter	Primitive surface node	Load \| Launch
RiverBed	Fluid Object dynamics node	Load \| Launch