Defer scipy imports in spline.py

Author: RoboX2020

spatialmath/spline.py

@@ -11,8 +11,6 @@
 from typing import TYPE_CHECKING, List, Optional, Tuple
 
 import numpy as np
-from scipy.interpolate import BSpline, CubicSpline
-from scipy.spatial.transform import Rotation, RotationSpline
 
 from spatialmath import SE3, SO3, Twist3
 from spatialmath.base.transforms3d import tranimate
@@ -122,6 +120,9 @@ def __init__(
             self.timepoints = self.timepoints - self.timepoints[0]
             self.timepoints = self.timepoints / self.timepoints[-1]
 
+        from scipy.interpolate import CubicSpline  # deferred, scipy is slow to import
+        from scipy.spatial.transform import Rotation, RotationSpline
+
         self.spline_xyz = CubicSpline(
             self.timepoints,
             np.array([pose.t for pose in self.control_poses]),
@@ -292,6 +293,8 @@ def __init__(
             )  # ensures the curve ends on the last control pose
         self.knots = knots
 
+        from scipy.interpolate import BSpline  # deferred, scipy is slow to import
+
         self.splines = [
             BSpline(knots, self.control_pose_matrix[:, i], degree)
             for i in range(0, 6)  # twists are length 6