Curves
Curves are the foundation of almost every Rhino model — surfaces are built from them. Learn the curve types, how control points shape them, and how to edit and clean them.
In this lesson you will
- Draw lines, polylines, arcs and circles precisely
- Choose between interpolated and control-point curves
- Edit curves with control points and degree
- Join, offset, fillet and rebuild curves
Basic curves
Line, Polyline, Rectangle, Circle, Arc, Ellipse and Polygon behave much like CAD, with Rhino's precision tools. Join combines touching curves into a polycurve; Explode separates them.
Freeform curves
InterpCrvdraws a curve through the points you pick — intuitive when you know where the curve must pass.
Curvedraws by control points the curve is attracted to — smoother and easier to fair.
Turn on control points with PointsOn (F10) and drag them to reshape. A curve's degree (1 = polyline, 3 = smooth typical, 5 = smoother) affects how points influence it.
Editing
Offset creates parallel curves; Fillet rounds corners; Trim and Split cut curves with other objects; Rebuild redistributes control points for cleaner geometry; Fair smooths bumps. CurvatureGraph shows smoothness visually — spikes mean kinks.
Clean curves, clean surfaces
Surfaces inherit their curves' quality. Use as few control points as needed, avoid tiny gaps (check with ShowEdges or SelOpenCrv / closed status in Properties), and keep curves planar when they're meant to be. Five minutes cleaning curves saves an hour fixing surfaces.
Quick reference
| Command / tool | How to start it | What it does |
|---|---|---|
| InterpCrv / Curve | Command line | Freeform curves |
| PointsOn | F10 | Shows control points |
| Rebuild | Command line | Rebuilds curve structure |
| CurvatureGraph | Command line | Shows curvature quality |
| Join / Explode | Command line | Combine / separate curves |
Common mistakes
Joined curve won't close.
Endpoints don't meet; snap to End or use
CloseCrv/Match.Lumpy curves make lumpy surfaces.
Rebuild with fewer points and check the curvature graph.
Exercise
A chair profile
- Draw a side profile of a chair with Polyline and fillets.
- Draw a smooth backrest curve with Curve (control points).
- Show control points and adjust the curve; check with CurvatureGraph.
- Offset the profile by 20 for material thickness.
You should end up with: Clean, smooth profiles ready for surfacing.
Checklist
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Lesson quiz
Which command draws a curve through picked points?
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Free KitWren tools that help
- Length ConverterConvert between metres, centimetres, millimetres, kilometres, inches, feet, yards and miles.
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- Image ResizerResize images to exact pixel dimensions or by percentage, keeping the proportions if you like.
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Free, independent learning material written for KitWren. Rhinoceros, Rhino and Grasshopper are trademarks of Robert McNeel & Associates. KitWren is not affiliated with, sponsored or endorsed by Robert McNeel & Associates. We never provide software downloads, licence keys or cracks — use the official sources.