Support 2 points for cubic spline.

tests/nurbs_tests.py

@@ -6,10 +6,11 @@
 
 from sverchok.utils.testing import SverchokTestCase, requires
 from sverchok.utils.geom import circle_by_three_points
+from sverchok.utils.nurbs_common import SvNurbsMaths, elevate_bezier_degree, from_homogenous
 from sverchok.utils.curve import knotvector as sv_knotvector
 from sverchok.utils.curve.primitives import SvCircle
 from sverchok.utils.curve.nurbs import SvGeomdlCurve, SvNativeNurbsCurve, SvNurbsBasisFunctions, SvNurbsCurve
-from sverchok.utils.nurbs_common import SvNurbsMaths, elevate_bezier_degree, from_homogenous
+from sverchok.utils.curve.nurbs_solver_applications import knotvector_with_tangents_from_tknots
 from sverchok.utils.surface.nurbs import SvGeomdlSurface, SvNativeNurbsSurface
 from sverchok.utils.surface.algorithms import SvCurveLerpSurface
 from sverchok.dependencies import geomdl
@@ -909,6 +910,12 @@ def test_interpolate_4d(self):
         expected_weights = np.array([1, 3, 1])
         self.assert_numpy_arrays_equal(weights, expected_weights, precision=6)
 
+    def test_knotvector_with_tangents_1(self):
+        u = np.array([0.0, 1.0])
+        kv = knotvector_with_tangents_from_tknots(3, u)
+        expected = np.array([0,0,0,0, 1,1,1,1])
+        self.assert_numpy_arrays_equal(kv, expected, precision=4)
+
 class TaylorTests(SverchokTestCase):
     def test_bezier_to_taylor_1(self):
         cpts = np.array([[0,0,0], [1,0,0], [1,1,0], [2,1,0]], dtype=np.float64)

utils/curve/nurbs_solver_applications.py

@@ -170,6 +170,9 @@ def knotvector_with_tangents_from_tknots(degree, u):
         kv.extend([u[-1], u[-1]])
         return np.array(kv)
     elif degree == 3:
+        if len(u) == 2:
+            return np.array([u[0], u[0], u[0], u[0],
+                             u[1], u[1], u[1], u[1]])
         kv = [u[0], u[0], u[0],u[0]]
         kv.append(u[1]/2.0)
         for i in range(1, n-2):
@@ -193,11 +196,14 @@ def interpolate_nurbs_curve_with_tangents(degree, points, tangents,
     tangents = np.asarray(tangents)
     if len(points) != len(tangents):
         raise Exception(f"Number of points ({len(points)}) must be equal to number of tangent vectors ({len(tangents)})")
+    ndim = points.shape[-1]
+    if ndim not in {3,4}:
+        raise Exception(f"Points must be 3 or 4 dimensional, not {ndim}")
 
     if tknots is None:
         tknots = Spline.create_knots(points, metric=metric)
 
-    solver = SvNurbsCurveSolver(degree=degree, ndim=4)
+    solver = SvNurbsCurveSolver(degree=degree, ndim=ndim)
     solver.add_goal(SvNurbsCurvePoints(tknots, points, relative=False))
     solver.add_goal(SvNurbsCurveTangents(tknots, tangents, relative=False))
     knotvector = knotvector_with_tangents_from_tknots(degree, tknots)