Snapping to vertices on spline

[kizaerf]

I made a spline and there are clear verticies, but autocad just refuses to snap to them. All my osnaps are on and it will snap to some points on the spline but not one where there is a clear vertex. i am stumped.

[RobDraw]

Grip edit will snap to grips. HTH.

[kizaerf]

thank you!

[Dana W]

Those are not vertices, they are modification grips. No vertices are mostly what makes them splines, a continuously varying radius curve. I think, other than grip edit, the only snaps on a spline are end point, intersection, implied intersection, and maybe perpendicular, and even more maybe tangent. It is particularly difficult to be perpendicular or tangent to something with a continuously varying radius. Come to think of it, implied intersection probably cannot be predicted either.

 

Yup, I know it was not necessary to add anything further but I am bored at the moment.

[RobDraw]

I thought they were called control points. Gonna have to check on that when I'm back at work.

[SEANT]

Yes, Control Points or Control Vertices. The Image in the first post of this thread shows that AutoCAD’s Properties Pallet uses both references.

Hidden vertices can be snapped to via the 3d Object Snaps. Select ‘Vertex’ to snap to any of the hidden control points. To isolate just the points directly on the spline use the ‘Knot’ option.

[Dana W]

I thought they were called control points. Gonna have to check on that when I'm back at work.

I'm sure AutoCad has a particular name for them. I guess my generic description is too um, ah, generic to use in a look-up search.

[Dana W]

:lol:Aw come on, there's not a "knot" option.

 

I actually have never heard of it. I am looking it up to see what it does.

[SEANT]

I'd guess that AutoCAD's help file doesn't provide much clarification on Knots. A web search for Knots as they relate to NURBS (B-Splines) would probably be more informative.

[Dana W]

Did that >> From Wiki...

 

Comparison of Knots and Control Points

 

A common misconception is that each knot is paired with a control point. This is true only for degree 1 NURBS (polylines). For higher degree NURBS, there are groups of 2 x degree knots that correspond to groups of (degree+1) control points. For example, suppose we have a degree 3 NURBS with 7 control points and knots 0,0,0,1,2,5,8,8,8. The first four control points are grouped with the first six knots. The second through fifth control points are grouped with the knots 0,0,1,2,5,8. The third through sixth control points are grouped with the knots 0,1,2,5,8,8. The last four control points are grouped with the last six knots.

Some modelers that use older algorithms for NURBS evaluation require two extra knot values for a total of (degree+N+1) knots.

 

OK, I get it now.

 

I have to go apply some white adhesive tape to the nose bridge of my black framed glasses.