Curves

Curves are connected points in a linear fashion.

Types

• Curve: Base Type.
• Curve Operators: Various tools to edit curves.
• Spline (curve.splines): Element of a curve, either NURBS, Bezier or Polyline
• SplinePoint (spline.points): Point on a spline without handles, Poly and NURBS only.
• BezierSplinePoint (spline.bezier_points): Element of a Bezier curve

Details

Curves consist of multiple splines. Each spline can have its own type: Poly, Bezier or NURBS. All of those types can exist in one curve object!

Poly and NURBS curves use points, Bezier curves only use Bezier points.

obj=bpy.context.active_object
if obj.type=="CURVE":
    for spline in obj.data.splines:
        if spline.type=="POLY" or spline.type=="NURBS":
            print(f"Points: {len(spline.points)}")
        elif spline.type=="BEZIER":
            print(f"Bezier Points: {len(spline.bezier_points)}")

It's possible to convert a spline type:

bpy.ops.curve.spline_type_set(type='BEZIER')

Warning: If you convert from bezier to NURBS/Poly, you will lose size and twist data!

Each point has a coordinate as a Vector array, a radius and a tilt.

# Position:
print(obj.data.splines[0].points[0].co)
# Radius, Tilt:
print(obj.data.splines[0].points[0].radius)
print(obj.data.splines[0].points[0].tilt)

Spline points and bezier spline points are not the same! Converting SPs into BSPs isn't possible directly.

data = bpy.context.active_object.data
# get active spline
spl = data.splines.active
# iterate over splines
for spline in data.splines:
    if spline.type in ["NURBS", "POLY"]:
        # selected points
        sel = [p for p in spline.points if p.select]
        for p in sel:
            print(p.co)
    else:
        # selected bezier points
        sel = [p for p in spline.bezier_points if p.select]
        for p in sel:
            print(p.co)

---

Creating Curves from scratch

This is the very basic way of creating curves:

import bpy
from bpy_extras import object_utils

# curve data
coords = [(1,0,1), (2,0,0), (3,0,1)]

# create the Curve Datablock
curveData = bpy.data.curves.new('myCurve', type='CURVE')
curveData.dimensions = '3D'
curveData.resolution_u = 2

# map coords to spline
polyline = curveData.splines.new('POLY')
polyline.points.add(len(coords)-1)
for i, coord in enumerate(coords):
    x,y,z = coord
    polyline.points[i].co = (x, y, z, 1)

# create Object
curveOB = bpy.data.objects.new('myCurve', curveData)

# add the curve as an object into the scene with this utility module
object_utils.object_data_add(bpy.context, curveData)

Further Curve Tutorials

Jeremy Behreandt: Scripting Curves In Blender With Python