Can you draw a circle use a spline?

spline can construct any curve?

how do you draw a circle with a 3 degree spline? can you do it?

No, it wont be a perfect circle

Why would you want to anyways?

You can however make a partial ellipse with a spline using the offset command

I just want to learn this .

As we know, the nurbs can simulate any curve. include conic curve. but I hant ever seen this sample. thats why I wnat to know about it.

as the circle is 2 degree equation. so the nurbs should be 2 degree function.

but I still wonder how about 3 degree to approach the conic curvel.

thanks

Do it in Rhino and save as dwg

The attached dwg contains one spline.

It's a perfect sircle.

Sirkel fra Rhino.dwg

thanks, I was told rhino is good at nurbs modeling. I noticed the degree is also 2. but why only one control point? what are hte conner points?

and can we draw an ellipse by this curve in autocad2000? its 3 degrees and consistence with ellipse. for example, long shift is 20cm and short one is 10cm.

As Mentioned above, you can do a trick with Offset in acad.

This spline is a result of two offsets from an ellipse.

1) Draw the ellipse

2) Offset 5mm out

3) Delete ellipse

4) Offset 5mm in

5) Delete outer copy

EllipseAsSplineInAcad.dwg

Rhino has a different approach than AutoCAD. In the same way as the Rectangle command results in a Pline object, you have in Rhino many commands that all result in curves. Curves means nurbs cirves, and they can have diffrent degree and each control point can have different weight (gravity). You can move, copye, rotate, scale one or many control points. Quite a different world

What do those blue points mena? in your #6, #9.

control points? or vertex points?

I try tjo draw a circle at cad2000 and an ellipse. but there are some problem.

how to display control point, vertex, knots etc.

greeb cycle (spline drawing)

control point number 7

control point 1

weight -1

fit points number 5

fit points 1

fit point coordinate equal to control point coordinate

degree 3

tangent vector coordiante.

red circle

white amendment cycle from green

whats different between control point number and control number?

as well as fit point number and fit point?

I draw the spline in 4 control points, but attribute display only 1 point?

when I modify the spline. it shows me 6 adjust point? what it these point, and what relation among control point, knots etc. in the acad2000?

now I know the 3degree can be degenerated into one or two degree when coefficient is zero. I dont know why I forget these before.

Autocad will show the Fitpoints for a selected spline. To also have the Control Points displayed, set the SPLFRAME system variable to 1 (then "Regen").

Something else that may be of interest, additional editing of splines is available via the SPLINEDIT command.

What do those blue points mena? in your #6, #9.

control points? or vertex points?

They are control points.

With nurbs of third degree, if you have three control points in line, the curve will touch that line.

Something else that may be of interest, additional editing of splines is available via the SPLINEDIT command.

I didn't find methods for changing degree or removing control points.

I didn't find methods for changing degree or removing control points.

Unfortunatley, it is an "Upward" only process.

Splinedit-Refine-Add control point: Control point removal does not appear to be possible.

Splinedit-Refine-Elevate order: Can only raise the degree (Order = Degree+1)