How to create a smooth, closed spline?

[sambaPython24]

Hey, I would like to create a closed but smooth spline.

The following is the example:

from cadquery import Workplane
sPnts = [
    (2.75, 1.5),
    (2.5,  1.75),
    (2.0,  1.5),
    (1.5,  1.0),
    (1.0,  1.25),
    (0.5,  1.0),
    (0,    1.0)
]

r = Workplane("XY").spline(listOfXYTuple = sPnts,makeWire = True, periodic = True)
display(r)

but I get the following

What is your strategy to make it smooth?

[adam-urbanczyk]

It is actually smooth, you might need to add more points to define your shape better

[sambaPython24]

@adam-urbanczyk Thank you for your answer. When I close the spline manually like this

from cadquery import Workplane

sPnts = [
    (2.75, 1.5),
    (2.5,  1.75),
    (2.0,  1.5),
    (1.5,  1.0),
    (1.0,  1.25),
    (0.5,  1.0),
    (0,    0.0),
    (2.75, 1.5)
]

r = Workplane("XY").spline(
                        listOfXYTuple = sPnts,
                        periodic = False
                          )
display(r)

I get this curve:

which might be technically smooth on a microscopic, but even after zooming quite a bit it appears to be discontinous.

To create a smooth spline, it seems like you have to adjust the tangents of the starting and the ending point.
But how do you find an "optimal" tangent in this case?

[adam-urbanczyk]

Actually with periodic=False it won't be smooth, my screenshot above was based on your original post. So, use periodic=True and add more points or specify better parametrization to get a nicer shape.