Surfaces
Surfaces are built from curves. Learn the main surface commands, when to use each, and how to check that surfaces are smooth and properly connected.
In this lesson you will
- Choose the right surface command for a shape
- Build surfaces with loft, sweep and revolve
- Understand continuity (G0, G1, G2)
- Check and analyse surfaces
The main commands
| Command | Input | Typical use |
|---|---|---|
| ExtrudeCrv | One curve + direction | Walls, extruded profiles |
| Loft | Several cross-section curves | Hulls, towers with varying plans, canopies |
| Sweep1 | Profile(s) along one rail | Handrails, mouldings |
| Sweep2 | Profile(s) between two rails | Shaped roofs, bridges |
| Revolve | Profile around an axis | Domes, vases, columns |
| NetworkSrf | A grid of curves in two directions | Complex double-curved forms |
| Patch | Boundary curves/points | Filling irregular openings |
A lofted canopy
- 1Draw three or four section curves at different positions and heights, all drawn in the same direction.
- 2Select them in order and run
Loft. - 3Choose a style (Normal, Loose, Tight) and preview.
- 4If the loft twists, check curve directions (
Dir) and seam points.
Continuity
Where surfaces meet, G0 means they touch (position), G1 means they're tangent (no crease), G2 means curvature matches (smooth reflections). BlendSrf and MatchSrf create or enforce continuity. Architecture often needs only G0–G1; product design often needs G2.
Checking
Use ShowEdges to find naked edges (edges not joined to another surface), Zebra for reflection-line smoothness, CurvatureAnalysis and EMap. Fix issues at the curve stage where possible.
Quick reference
| Command / tool | How to start it | What it does |
|---|---|---|
| Loft | Command line | Surface through sections |
| Sweep1 / Sweep2 | Command line | Profiles along rails |
| Revolve | Command line | Profile around axis |
| NetworkSrf | Command line | Surface from a curve network |
| Zebra / ShowEdges | Command line | Surface analysis |
Common mistakes
Loft is twisted.
Make curve directions and seams consistent (
Dir,CrvSeam).Visible crease between surfaces.
Use BlendSrf or MatchSrf for tangency or curvature continuity.
Exercise
Three surfaces
- Loft a canopy from four section curves.
- Revolve a column base profile.
- Sweep a handrail profile along a curved rail.
- Check each with Zebra and ShowEdges.
You should end up with: Clean surfaces made with the right command for each shape.
Checklist
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Lesson quiz
Which command builds a surface through several cross-sections?
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