Tangent difference when curves have G1 continuity



Hello everyone,

What does “tangent difference” practically refers to when you analyze curve geometric continuity (Analyze > Curve > Geometric Continuity) in Rhino 5?

Say we have line A, B and C. A and B are G1 with 0 tangent difference while A and C are G1 with 0.1° tangent difference. B and C are both tangent to A, so what’s the difference between them? Is one “less” tangent than the other?

Thank you to help me clarify this point :slight_smile: !


Continuity has a tolerance to it, which is used when trimming objects, set in the document properties, and that’s what GCon uses. I think the default is 1 degree, which can be rather visibly not tangent, so I set it to 0.1.

Yes A and B are so to speak “more” tangent than A and C. There has to be some tolerance wiggle-room since in the floating-point math on computers “0” tangent difference is probably not actually precisely 0 but 0.000000002 or something, and the tighter you set the tolerance in your geometry the more needlessly heavy and slower to manipulate it becomes.


Ok, got it ! Thanks !


There are 2 settings that affect what Gcon command reports.
The numerical angle it reports depends on your “display precision” setting and the Gx report depends on your “angle tolerance” setting. Both settings are found in the Document Properties>Units
So if your angle tolerance is .1 and the angle is more than that it will tell you the curves are G0 if the ends are within the absolute tolerance. If its less than the angle tolerance then Gcon will report G1 or G2

It looks like you have the display precision set to 1 decimal point. That means when the angle is .05 degrees it will tell you that angle is 0.1 degree and when the angle is .04999 degrees it will tell you the angle is 0.0 degrees. I would recommend that you increase the display precision if you want decimal numbers to be displayed more accurately.