What is ʼCurve Continuityʼ (G0
Short Answer
Curve continuity in Rhino 3D describes how smoothly two curves meet at a shared end. G0 means positional continuity only: the curve ends touch, but their directions may differ. The fastest professional check is GCon. Limitation: G0 does not guarantee tangency or visual smoothness.
What You Need to Know Before
Warning: Two curves can look connected when zoomed out but still fail continuity checks because their endpoints are slightly apart. In production surfacing, assuming G0 is “good enough” often creates broken trims, bad blends, or visible kinks downstream.
How to Check Curve Continuity in Rhino 3D
Command: GCon
Shortcut: No default shortcut
Quick Steps:
- Run GCon from the command line, or use Tools > Curve Tools > Curve from Objects if you are preparing geometry first, then type the command directly.
- Select the two curves near the ends you want to test.
- Read the command line result for continuity type; use the endpoint selection carefully and confirm whether Rhino reports position only, tangent, or curvature continuity.
Variables & Settings
Key Setting: Endpoint selection
Expert Setting: In Rhino, continuity results depend on which ends of the curves you pick. If you click the wrong ends, the analysis may report an irrelevant condition or appear to fail even though the intended junction is correct.
Why it Fails
Cause 1 (Geometry): The curve endpoints are not actually coincident, so the curves are close visually but fail even basic G0 continuity.
Cause 2 (layers/Locks): One curve may be on a locked layer or be part of referenced geometry, preventing proper editing when trying to fix failed continuity.
Cause 3 (Command/Logic): G0 only checks endpoint contact; users often expect it to confirm smoothness, but tangency requires G1 and curvature smoothness requires G2.
Quick Fix & Best Practice
Quick Fix: Use End object snap and Move or Match to bring the curve endpoints together exactly before rechecking with GCon.
Manager’s Verdict: Use G0 when you only need curves to meet, such as layout or trimmed construction work. Avoid relying on G0 alone for visible product surfaces, Class-A style modeling, or any edge that must look smooth.
FAQ
Is G0 continuity the same as tangent continuity?
No, G0 only means the endpoints touch.
How do I check if curves are smoother than G0 in Rhino?
Use GCon to see whether the connection is G1 or G2.
Can joined curves still have only G0 continuity?
Yes, joined curves can be connected without being tangent or curvature continuous.
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