Curve
surface node
Creates polygonal, NURBS, or Bezier curves.
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In the viewer, use the tab menu to select the Curve SOP.
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Use the operation controls toolbar at the top of the viewer, or the parameter editor, to set the type of geometry to create, drawing method, and whether to automatically close the curve.
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Click in the viewer to place points (control vertices or breakpoints, depending on the Method setting).
You can optionally connect geometry to the node’s input and the curve will snap to its points. Use the Keep input geometry to make the snapping template part of the output geometry for this node.
Placing Curves
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Click the
Curve shelf option on the Create tab. -
Select either Polygon, NURBS, or Bezier from the Primitive Type menu on the operation controls toolbar.
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Move the mouse into the scene view and click
to place the points.The points are grounded on the construction plane. You can hold Alt to detach the curve from the construction plane or hold Ctrl to constrain the placement of the points within 45 degree angles.
You can also reorient the construction plane completely before drawing the curve.
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Press Enter or ⇧ Shift +
to finish the curve.
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Delete the last placed point |
Press Del . |
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Move the points of the curve |
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Insert points on an existing curve |
Press
⇧ Shift
+
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Insert points on the curve |
Press
⇧ Shift
+
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Connect the first and last points of the curve |
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Change the order for NURBS and bezier |
Set it in the operation controls toolbar. |
NURBS and Bezier
You can create either NURBS or bezier curves with the curve shelf tool. These types of curves allow you to choose CVs, Breakpoint (knots), or Freehand from the Method menu on the operation controls toolbar. NURBS automatically determine the start and end points of your curve, whereas bezier curves recognize the first point as the start point, the second and third points as control points, and the fourth point as the end point. If the bezier curve has more than four points, the fourth point is also recognized as the start point for the next set of points.
| NURBS Curve |
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| Bezier Curve |
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Polygons
You can also create polygons with the curve shelf tool, and choose either CVs, Breakpoint (knots), or Freehand from the Method menu on the operation controls toolbar; however, when creating polygons both CVs and Breakpoint will act the same way (allow you to place points in the scene view).
| NURBS Curve |
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Parameters
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Primitive Type |
Type of geometry to create.
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Method |
Drawing method (how to interpret mouse clicks in the viewer and coordinates in the field below).
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Coordinates |
Normally you will use this operator in the viewer and simply click to indicate coordinates; however, if you need to you can also use a space-separated list of coordinates in this field to specify points. Coordinates can be specified in the following formats:
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Curve Properties
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Close |
Automatically closes the curve. |
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Normalize Basis |
Normalizes the curve’s basis. |
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Order |
The order of the NURBS or Bezier curve. Higher order curves give more control vertices and smoother curve interpolation between breakpoints. |
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Parameterization |
How to assign U values to breakpoints. This mainly affects the mapping of textures onto surfaces you create with the curve later.
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Fitting Properties
These parameters control the fitting of the curve to the points you draw when Method is “Freehand”.
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Tolerance |
How close the fitted curve should be to the points you drew. Large values give a looser fit but a more efficient curve, while smaller values give a better fit but a heavier, more complex curve. |
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Smoothness |
Extra smoothing of the fitted curve. Use this to smooth out rough patches. |
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Preserve Sharp Corners |
Try to preserve sharp turns in the freehand points. |
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Keep Input Geometry |
Include the input geometry in this node’s output. |
Example files
CurveHood
$HFS/houdini/help/examples/nodes/sop/curve/CurveHood.cmd
This example demonstrates how to use the Curve SOP to create a car’s hood.
It also shows how to make points on a new curve dependent on the points of a previous curve. This way, you can move the points on one curve and affect any curve further in the network.