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Since  18.0 
Overview
This node takes a crosssection curve from the second input, distributes copies of it along a spine curve from the first input, and creates a surface between the distributed crosssection curves. It is an extremely versatile workhorse for generating procedural geometry.
This node will accept polylines, NURBS curves, or Beziér curves. By default the type of input curves determine the type of surface (for example, polylines produce polygons, NURBS curves produce NURBS surfaces), however you can override the surface type using the Primitive type parameter on the Construction tab.
Instead of using modeled crosssections connected to the second input, you can use automatic circle, square, or line crosssections using the Surface Shape parameter.
This node can handle multiple spines, and/or multiple crosssections.

If there are multiple curves in the first (spine) input, the crosssection(s) is/are swepat along each spine curve separately.

If there are multiple curves in the second (crosssection) input, the crosssections are ditributed along the curve length according to the Cross section order parameter on the Construction tab.
This node can handle closed spines and/or closed crosssections. (Closed means that the curve is a loop — the first and last point of the curve are the same.)

If both the spine and crosssection are open, the node creates an open surface.

If either the spine or crosssection are closed, the node creates a tube.
When one curve is open and the other closed, creating a tube, you can automatically add endcap geometry using the End cap type parameter on the Surface tab.

If both the spine and crosssection are closed, the node creates a torus.
Positioning the curves

Spine curves can be anywhere in space.

This node assumes all cross section curves are modeled at the origin in the XY plane, with +Y up direction.
Do not model the crosssection curve on (or at the beginning of) the spine curve.

When the curve is flat (planar), the node assumes it should orient the up direction of the crosssections perpendicular to the curve plane.
After construction, you can adjust the orientation of the crosssection curve(s) relative to the spine using the Roll and Yaw parameters.
Tip
This is a technical node. It is very useful for procedurally building surfaces from crosssections. It is not as suitable for "artistic" curveup modeling, since this node bases crosssection orientation and positioning on parameters and/or attributes, rather than where/how you modeled the curves.
Tips

The orientations applied to the cross sections are equivalent to those in the Orientation Along Curve node.
Inputs
First (Backbone curves)
Should contain one or more spine curves. If the input has multiple curves, the crosssection(s) is/are surfaced along each spine separately.
Second (Cross section(s))
Should contain one or more crosssection curves. If the input has multiple curves,
Connecting modeled crosssection curves to the second input is optional. Instead, you can use automatic circle, square, or line crosssections using the Surface Shape parameter.
Parameters
Backbone Curve Group
If this is blank, the node uses all curves from the first input, or you can specify a group or set of curves using group syntax. You can also click the Reselect button next to this field to select the curves in the viewport.
Cross Section Group
If this is blank, the node uses all curves from the second input, or you can specify a group or set of curves using group syntax. You can also click the Reselect button next to this field to select the curves in the viewport.
Surface
Surface Shape
What to use as the crosssection shape. The default is to use curves connected to this node’s second input.
Second Input Cross Sections
Use the curve or curves from the second input (taking into account the Cross section group field) as the crosssection(s).
Round Tube
Use a circle as the crosssection, producing a round tube. Scale the tube with the Radius parameter and set the number of sides the circle has with the Columns parameter.
Square Tube
Use a square as the crosssection, producing a boxy tube. Scale the tube with the Width parameter and set the number of subdivisions along each side with the Columns parameter.
Ribbon
Use a line as the crosssection, producing a ribbon shape. Scale the ribbon with the Width parameter and set the number of subdivisions across the line with the Columns parameter.
Surface Type
The surface topology of the generated surface.
The Columns option is useful for creating many curves from each input curve.
Points
Don’t create any primitives, only points.
Rows
Create a curve for each cross section in the grid.
Columns
Create a curve for each vertex around the grid, spanning the full curve.
Rows and Columns
Create curves corresponding with both the Rows option and the Columns option.
Triangles
Create triangles splitting the grid quads in a single direction.
Quadrilaterals
Create the grid quads as is.
Alternating Triangles
Create triangles splitting the grid quads in alternating directions.
Reverse Triangles
Create triangles splitting the grid quads in a single direction opposite that of the Triangles option.
Scale Cross Sections
When Surface shape is "Second Input", this scales the size of all crosssections.
Columns
When Surface shape is "Round tube", "Square tube", or "Ribbon", this controls the density of the crosssection shape. For round, this is the number of sides the circle has. For square, this is the number of subdivisions along each side. For ribbon, this is the number of subdivisions across.
Radius
When Surface shape is "Round tube", the radius of the tube.
Width
When Surface shape is "Square tube" or "Ribbon", the width of the tube/ribbon.
Reverse Cross Sections
Turn this on to reverse the normals of the generated surface.
When this is on, the node treats cross section primitives as if they were reversed, which reverses normals on the generated surface.
Stretch Around Turns
Stretch crosssections in the direction of curvature around turns in the spine. (Default on.) This avoids the crosssection appearing squished in turns. This is usually what you want, unless you have set Surface type to "rows" or "columns".
Max Stretch
When Stretch Around Turns is on, the maximum amount that cross sections will be stretched. The default is 10 (maximum 10× stretch). This prevents the crosssection from scaling wildly if, for example, the spine curve doubles back on itself.
End Cap Type
When the spine curve is open and the crosssection curves are closed, the generated surface is a tube. The node can automatically create endcaps on the open ends of the tube.
None
Do not generate endcaps.
Single Polygon
Cap the ends with a single Ngon.
Grid
Cap the ends with a surface, controlled by the parameters below.
Side Single Polygon
When the spine is closed but the crosssections are open, the sides of the generated surface are open rather then the ends. This closes the sides with an Ngon.
Cap Divisions
When End Cap Type is Grid, the number of rows in the endcap surfaces.
Triangular Poles
When End Cap Type is Grid and this is on, the poles of end caps are made with triangles. When this is off (the default), the poles are made with quads with duplicate vertices.
End Cap Scale
When End Cap Type is Grid, this is the amount each endcap "bulges out" from each end of the tube. Set this to 0
for no bulge, or to a negative number for an inward bulge.
End Cap Roundness
When End Cap Type is Grid, and End cap scale is not 0
, this controls the curvature of the bulge. 1
is convex circular, 0
is linear, and 1
is concave circular.
End Caps Group
When this is on, the output geometry includes a group by this name, containing all endcap geometry. This lets you treat the endcaps separately if necessary in downstream nodes.
Apply Scale Along Curve
Scales the generated surface across the length of the spine curve according to the Scale ramp parameter.
Scale Ramp
When Apply scale along curve is on, this ramp lets you interactively scale the surface inward and outward along the length of the spine curve.
Rotation
Rotate Order
The order in which to apply the Pitch (around X/out), Yaw (around Y/up), and Roll or Twist (around Z/tangent) options below, when more than one can apply.
Pitch and Yaw may be useful to effectively apply a pretransform to the cross sections before using them if they are not in the XY plane in the cross section input, which is why they default to being applied before the Roll or Twist.
These rotations are effectively applied to the cross sections before the transforms from the backbone curves, having the net effect of them being rotations in the space of the backbone curve frames.
Apply Roll or Twist
Apply the Roll and Twist parameters below to the crosssection curves.
Roll
A rotation, in degrees, around the spine curve direction, applied equally to every crosssection. You can use this to correct the orientation of the crosssection in relation to the curve.
Full Twists
A convenience to add full twists (for each interval set in the Twist per parameter). This node multiplies this by 360 and adds it to the number in Partial twist.
Partial Twist
The number of degrees of twist to add (for each interval set in the Twist per parameter).
Twist Per
The interval along each of which the total twist specified by the Full twists and Partial twist parameters is applied to the surface.
See the descriptions and image below.
Per Edge
The twist applies along each edge (the distance from each point in the curve to the next point).
Per Unit Distance
The twist applies each "world unit" of distance along the curve.
Scale by Attribute
The twist value is multiplied at each vertex by the value in the attribute named in the Twist ramp attribute parameter (this can be a vertex, point, primitive, or detail attribute). This product is applied as a roll at each vertex, not as an accumulating twist.
Per Full Curve by Edges
Applies the twist value once across the entire curve, divided equally among each edge.
Per Full Curve by Distance
Applies the twist value once across the entire curve, with the amount proportional to the distance along the curve.
Twist Ramp Attribute
When Twist Per is "Scale By Attribute", this is the name of the vertex, point, primitive, or detail attribute to multiply by the total twist amount (full twists combined with partial twist). This product is applied as a roll at each vertex, not as an accumulating twist.
Apply Yaw
Apply the Yaw parameters below to the crosssection curves. Yaw is a rotation around the crosssection’s "up" vector, usually thought of as "turning left or right".
Yaw
A rotation, in degrees, around the crosssection’s "up" vector, applied equally to every crosssection. (This is usually thought of as "turning left or right".) You can use this to correct the orientation of the crosssection relative to the curve.
Incremental Yaw
A rotation, in degrees, around the crosssection’s "up" vector (usually thought as "turning left or right"), to apply along each interval set in the Yaw per parameter.
Yaw Per
The interval along each of which the total rotation specified by the Incremental Yaw parameter is applied to the surface.
Per Edge
The yaw applies along each edge (the distance from each point in the curve to the next point).
Per Unit Distance
The yaw applies each "world unit" of distance along the curve.
Scale by Attribute
The yaw value is multiplied at each vertex by the value in the attribute named in the Yaw ramp attribute parameter (this can be a vertex, point, primitive, or detail attribute). This product is applied as a yaw at each vertex, not as an accumulating yaw.
Per Full Curve by Edges
Applies the yaw value once across the entire curve, divided equally among each edge.
Per Full Curve by Distance
Applies the yaw value once across the entire curve, with the amount proportional to the distance along the curve.
Yaw Ramp Attribute
When Yaw Per is "Scale By Attribute", this is the name of the vertex, point, primitive, or detail attribute to multiply by Incremental Yaw. This product is applied as a yaw at each vertex, not as an accumulating yaw.
Apply Pitch
Apply the Pitch parameters below to the crosssection curves. Pitch is a rotation around the crosssection’s "out" vector, usually thought of as "tilting up or down".
Pitch
A rotation, in degrees, around the crosssection’s "out" vector, applied equally to every crosssection. (This is usually thought of as "tilting up or down".) You can use this to correct the orientation of the crosssection relative to the curve.
Incremental Pitch
A rotation, in degrees, around the crosssection’s "out" vector (usually thought as "tilting up or down"), to apply along each interval set in the Yaw per parameter.
Pitch Per
The interval along each of which the total rotation specified by the Incremental Pitch parameter is applied to the surface.
Per Edge
The pitch applies along each edge (the distance from each point in the curve to the next point).
Per Unit Distance
The pitch applies each "world unit" of distance along the curve.
Scale by Attribute
The pitch value is multiplied at each vertex by the value in the attribute named in the Yaw ramp attribute parameter (this can be a vertex, point, primitive, or detail attribute). This product is applied as a pitch at each vertex, not as an accumulating pitch.
Per Full Curve by Edges
Applies the pitch value once across the entire curve, divided equally among each edge.
Per Full Curve by Distance
Applies the pitch value once across the entire curve, with the amount proportional to the distance along the curve.
Pitch Ramp Attribute
When Pitch Per is Scale By Attribute, this is the name of the vertex, point, primitive, or detail attribute to multiply by Incremental Pitch. This product is applied as a pitch at each vertex, not as an accumulating pitch.
Construction
Cross Section Order
How the node decides what cross section(s) to use a each point along the spine curve.
All Cross Sections at Each Curve Vertex
Within a single curve’s output grid, at every single vertex, all cross sections will be used.
This is useful for if the cross sections collectively form a unit that should appear at each vertex within each grid, for example, to create a bulge at each vertex.
Each Cross Section At All Curve Vertices
Every curve will be separately surfaced once for each cross section.
This is useful if the cross sections should effectively act like a single, disconnected cross section, for example, to create multiple tubes for each curve.
Cycle Through Cross Section Primitives per Vertex
Within each single curve’s output grid, the cross section selected for each vertex will cycle through the cross sections, starting from the first cross section.
This is useful if the cross sections form all cross sections to be used along the curves in order, for example, if the cross section input contains all cross sections for a corridor in order.
Cycle Through Cross Section Primitives per Primitive
For each curve’s output grid, a single cross section will be selected, selecting the next cross section for each next curve.
This is useful if each curve has a different cross section to be used for it.
Choose Cross Section Primitives by Attribute
For each vertex, select a cross section to use based on the attribute specified in the Cross Section Attribute parameter.
Cross Section Attribute
When Cross Section Order is "Choose Cross Section Primitives by Attribute", this is the name of the attribute to use for selecting cross sections.
This can be a point, vertex, primitive, or detail attribute on the spine curve, or a primitive attribute on the crosssections.

If this is an integer attribute on the spine, it will select cross sections by primitive number.

If this is an integer or string attribute present on both inputs, it will select a cross section with a matching value.
Primitive Type
The type of primitive to output (when Surface Type is not "Points"). "Automatic" generates the same type of surface as the input curves (for example, polylines create a polygon surface, NURBS curves produce a NURBS surface).
Ensure Unique Seam Vertices
If Surface Type is "Rows", "Columns", or "Rows and Columns", and the spine curve or crosssection is closed, this adds an extra vertex (if needed) to each curve to ensure that there are separate vertices for parametric curve u or v coordinate values 0 and 1.
If any output primitives are polygon soups, NURBS surfaces, Bezier surfaces, or bilinear mesh primitives, this option similarly also adds any extra vertices that would be needed to ensure that all uv seams are paramerized correctly.
Swap Rows and Columns
Adjusts the order of the points and primitives in the generated surface(s) to be columnmajor, having all points/primitives of one column before those of the next column, instead of the default (rowmajor, having all point/primitives of one row before those of the next row). Changing this also reverses normals, so you may also want to turn on Reverse Cross Sections to keep the current normals.
Close Implicit Backbone Curve if No Curve Input
If the node finds no spine curve in the first input, the node sweeps the cross sections in the second input as if there is a single curve with one vertex per cross section and all positions at the origin. When this is on, the node makes that implicit curve closed, treating the cross sections as forming a loop, instead of a line.
Target Up Vector
The initial orientation of the crosssection around the direction of the curve. You can use the roll, yaw, and pitch parameters on the Surface tab to further adjust the orientation of the crosssections on top of this.
Curve Normal
Match the crosssection upvector to the curve normal. This is useful when the curve is planar, it orients the crosssections perpendicular to the plane.
X/Y/Z Axis
Match the crosssection upvector to the X, Y, or Z axis.
Attribute
Get the upvector from a percurve value in a primitive attribute, or a shared value in a detail attribute. Set the attribute name in the Start up attribute parameter.
Custom
Match the crosssection upvector to a custom vector. Set the custom vector in the Start upvector parameter.
Target Up Vector at Start (else Average)
When this is on, at each point the node tries to get closest to the initial upvector, while staying perpendicular to the spine curve tangent. When this is off, it tries to get closest to the average of all vertex upvectors, instead of the initial upvector.
Use Target End Up Vector
When Target upvector at Start is on, and this is on, the node adjusts any twist along the spine to ensure the final upvector is as close as possible to the target upvector, without affecting the initial upvector.
If Target upvector is "Attribute" or "Custom", there are separate End Up Attribute and End Up Vector parameters, in order to specify different end upvectors from the start upvectors.
Start Up Attribute
When Target Up Vector is Attribute, this is the name of the primitive or detail attribute to use for each curve’s target upvector.
End Up Attribute
When Target Up Vector is Attribute and Use Target End Up Vector is on, this is the name of the primitive or detail attribute that provides the target upvectors at the end of the curve.
Start Up Vector
When Target upvector is "Custom", this is the target upvector at the end of the curve.
End upvector
When Target upvector is "Custom" and Use Target End Up Vector is on, this is the target upvector at the end of the curve.
Tangent Type
How to compute the spine curve’s tangent direction at each point. If Transform using curve point attributes is on and the spine curve has the required attributes, this is ignored.
(The Stretch Around Turns option always computes the stretch and stretch direction based on the "Average of Edge Directions" tangent, regardless of this setting.)
Average of Edge Directions
Average of the normalized directions of the previous and next edge.
Central Difference
Average of the nonnormalized previous and next edge vectors.
This is similar to the "Central Difference" option for Velocity Approximation on the Trail node.
Previous Edge
Previous edge direction.
Next Edge
Next edge direction.
Z Axis (Ignore Curve)
The tangent will be chosen as the Z axis, regardless of the curve.
This can be useful if the cross sections have already been rotated to the desired orientation.
Make Closed Curve Orientations Continuous
Any extra rotation required to make the start and end orientations match (either because the curve is nonplanar, or you applied a total amount of twist that wasn’t an even multiple of 360) is spread out along the entire curve, instead of possibly coming suddenly along the last edge.
Extrapolate End Tangents
Extrapolate the tangent for the last edge from the previous two edges. When this is off, the tangent for the final edge is just the edge direction.
This is most useful when a backbone curve is intended to represent a circular arc, so the end cross sections will be rotated as expected.
Transform Using Curve Point Attributes
Orient the crosssections using the point attributes P
, N
, up
, orient
, rot
, trans
, pivot
, pscale
, scale
, and/or transform
on the spine curve.

If
N
is present and none ofup
,orient
,rot
, ortransform
are present, the node usesN
as the curve tangent and computes the rest of the rotation as usual. 
If
up
is present and none ofN
,orient
,rot
, ortransform
are present, the node computes the tangent as usual, and usesup
as the upvector at each vertex (before any roll or twist is applied).
UVs and Attributes
Compute UVs
Generate a uv
vertex attribute on the generated surface. If the input curves already have uv
attributes, the node uses the values from those attributes (U corresponds to the cross sections, and V corresponds to the spine curve).
(If Surface Type is "Points", this will generate a point attribute.)
Override Any Existing UVs
When Compute UVs is on, compute new UVs for the surface, even if the input curves already had uv
attributes.
LengthWeighted UVs
Scale the U and V coordinates based on proportional edge lengths so they're even across the whole surface, rather than bunching up where edges bunch up.
(If Normalize Computed Us and/or Normalize Computed Vs are on, the coordinates are still normalized to be within the 0 to 1 range.)
Normalize Computed Us
Normalize computed U coordinates to be in the range 0 to 1 (before applying UV scale). When this is off, U corresponds to the average distance around the cross sections on the mesh (ignoring any stretch applied by Stretch Around Turns).
When this is on and Normalize Computed Vs is off, the node scales V such that U and V appear scaled similarly in space (depending on the Use Max Cross Section Length per Curve for Proportional Scale setting).
This is especially useful for things like applying repeating rope textures, where the texture should be applied isotropically.
Normalize Computed Vs
Normalize computed V coordinates to be in the range 0 to 1 (before applying UV scale). When this is off, V corresponds to the average distance along the surface in V, or the distance along the spine curve, depending on the Use Mesh Edge Lengths instead of Curve Edge Lengths parameter.
When this is on and Normalize Computed Us is off, the node scales U such that U and V appear scaled similarly in space.
Flip Computed Us
Reverse the direction of the computed U values (same as replacing each U value with max(U values)  U
). Use this if a texture appears backward when applied to the surface.
This should be on for textures to appear correct on surfaces viewed from the front, (normals pointing toward the camera), and should be off for textures to appear correct on surfaces viewed from the back, (normals pointing away from the camera).
UV Scale
A scale on the generated UV coordinates. This is applied after any normalization.
This is applied before the adjustments made by Make Computed Us Wrap Seamlessly and/or Make Computed Vs Wrap Seamlessly, so the texture will still wrap correctly.
Use Mesh Edge Lengths Instead of Curve Edge Lengths
When this is on and LengthWeighted UVs is on, the averages of the output mesh edge lengths in the curve direction are used as the lengths in the V direction, instead of the original curve edge lengths.

This is useful when, for example, a curve has coincident points with different cross sections, such as a door jamb in a hallway, so that the surface between the two cross sections gets a nonzero area of texture space.

It is also useful for generating UVs for grid end caps. However, it can be less stable, when changing rotations, than using the original curve lengths.
Use Max Cross Section Length per Curve for Proportional Scale
When Normalize Computed Us is on and Normalize Computed Vs is on, this controls whether the node uses the maximum cross section length for computing the V scale, instead of the average of the previous and next cross section lengths for each V edge.
If the cross section length varies significantly, this can make the texture appear stretched in some places, but can also avoid instability and inconsistency in the V scale along the curve.
Snap U to Nearest Boundary
When Normalize Computed Us is off and this is on, the node rounds the range of U to the nearest positive integer, so textures wrap correctly in the U direction. This node applies this rounding after the UV Scale.
Snap V to Nearest Boundary
When Normalize Computed Vs is off and this is on, the node roounds the range of V to the nearest positive integer, so textures wrap correctly in the V direction. This node applies this rounding after the UV Scale.
From Backbone Curves
Spaceseparated list of attributes to copy from the backbone curve onto the generated surface. You can use patterns here.
By default, P
, N
, up
, pscale
, scale
, orient
, rot
, pivot
, trans
, and transform
are not copied, to avoid copying attributes used for computing transforms.
From Cross Sections
Spaceseparated list of attributes to copy from the crosssection curves onto the generated surface. You can use patterns here.
The transforms attributes that have a transform type (position, vector, normal, quaternion, or transform matrix) appropriately.
Point Row Attribute
Create an integer point attribute with this name on the generated surface, containing the row number.
Point Col Attribute
Create an integer point attribute with this name on the generated surface, containing the column number.
Prim Row Attribute
Create an integer point attribute with this name on the generated surface, containing the quad row number.
Prim Col Attribute
Create an integer point attribute with this name on the generated surface, containing the quad column number.
Cross Section Num Attribute
Create an integer point attribute with this name on the generated surface, containing the primitive number of the cross section curve used to create the point.
Curve Num Attribute
Create an integer point attribute with this name on the generated surface, containing the primitive number of the spine curve used to create the point.
Examples
SweepBasic Example for Sweep geometry node
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 Example for Sweep geometry node
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 Example for Sweep geometry node
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 Example for Sweep geometry node
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.
See also 