Clothoidal path planner (AtsushiSakai#551)

* Add clothoidal path planner

* Code quality/style fixes

* Open up possibilities a bit by allowing control over theta1 values

* Get line length under 80 chars for code style checks

Author: daniel-s-ingram

PathPlanning/ClothoidalPaths/clothoidal_paths.py

@@ -0,0 +1,144 @@
+"""
+Clothoidal Path Planner
+Author: Daniel Ingram (daniel-s-ingram)
+Reference paper: https://www.researchgate.net/publication/237062806
+"""
+
+import matplotlib.pyplot as plt
+import numpy as np
+import scipy.integrate as integrate
+from collections import namedtuple
+from scipy.optimize import fsolve
+from math import atan2, cos, hypot, pi, sin
+from matplotlib import animation
+
+Point = namedtuple("Point", ["x", "y"])
+
+
+def draw_clothoids(
+    theta1_vals,
+    theta2_vals,
+    num_clothoids=75,
+    num_steps=100,
+    save_animation=False
+):
+    p1 = Point(0, 0)
+    p2 = Point(10, 0)
+    clothoids = []
+    for theta1 in theta1_vals:
+        for theta2 in theta2_vals:
+            clothoid = get_clothoid_points(p1, p2, theta1, theta2, num_steps)
+            clothoids.append(clothoid)
+
+    fig = plt.figure(figsize=(10, 10))
+    x_min, x_max, y_min, y_max = get_axes_limits(clothoids)
+    axes = plt.axes(xlim=(x_min, x_max), ylim=(y_min, y_max))
+
+    axes.plot(p1.x, p1.y, 'ro')
+    axes.plot(p2.x, p2.y, 'ro')
+    lines = [axes.plot([], [], 'b-')[0] for _ in range(len(clothoids))]
+
+    def animate(i):
+        for line, clothoid in zip(lines, clothoids):
+            x = [p.x for p in clothoid[:i]]
+            y = [p.y for p in clothoid[:i]]
+            line.set_data(x, y)
+
+        return lines
+
+    anim = animation.FuncAnimation(
+        fig,
+        animate,
+        frames=num_steps,
+        interval=25,
+        blit=True
+    )
+    if save_animation:
+        anim.save('clothoid.gif', fps=30, writer="imagemagick")
+    plt.show()
+
+
+def get_clothoid_points(p1, p2, theta1, theta2, num_steps=100):
+    dx = p2.x - p1.x
+    dy = p2.y - p1.y
+    r = hypot(dx, dy)
+
+    phi = atan2(dy, dx)
+    phi1 = normalize_angle(theta1 - phi)
+    phi2 = normalize_angle(theta2 - phi)
+    delta = phi2 - phi1
+
+    try:
+        A = solve_for_root(phi1, phi2, delta)
+        L = compute_length(r, phi1, delta, A)
+        curv = compute_curvature(delta, A, L)
+        curv_rate = compute_curvature_rate(A, L)
+    except Exception as e:
+        print(f"Failed to generate clothoid points: {e}")
+        return None
+
+    points = []
+    for s in np.linspace(0, L, num_steps):
+        try:
+            x = p1.x + s*X(curv_rate*s**2, curv*s, theta1)
+            y = p1.y + s*Y(curv_rate*s**2, curv*s, theta1)
+            points.append(Point(x, y))
+        except Exception as e:
+            print(f"Skipping failed clothoid point: {e}")
+
+    return points
+
+
+def X(a, b, c):
+    return integrate.quad(lambda t: cos((a/2)*t**2 + b*t + c), 0, 1)[0]
+
+
+def Y(a, b, c):
+    return integrate.quad(lambda t: sin((a/2)*t**2 + b*t + c), 0, 1)[0]
+
+
+def solve_for_root(theta1, theta2, delta):
+    initial_guess = 3*(theta1 + theta2)
+    return fsolve(lambda x: Y(2*x, delta - x, theta1), [initial_guess])
+
+
+def compute_length(r, theta1, delta, A):
+    return r / X(2*A, delta - A, theta1)
+
+
+def compute_curvature(delta, A, L):
+    return (delta - A) / L
+
+
+def compute_curvature_rate(A, L):
+    return 2 * A / (L**2)
+
+
+def normalize_angle(angle_rad):
+    return (angle_rad + pi) % (2 * pi) - pi
+
+
+def get_axes_limits(clothoids):
+    x_vals = [p.x for clothoid in clothoids for p in clothoid]
+    y_vals = [p.y for clothoid in clothoids for p in clothoid]
+
+    x_min = min(x_vals)
+    x_max = max(x_vals)
+    y_min = min(y_vals)
+    y_max = max(y_vals)
+
+    x_offset = 0.1*(x_max - x_min)
+    y_offset = 0.1*(y_max - y_min)
+
+    x_min = x_min - x_offset
+    x_max = x_max + x_offset
+    y_min = y_min - y_offset
+    y_max = y_max + y_offset
+
+    return x_min, x_max, y_min, y_max
+
+
+if __name__ == "__main__":
+    theta1_vals = [0]
+    theta2_vals = np.linspace(-pi, pi, 75)
+    draw_clothoids(theta1_vals, theta2_vals, save_animation=False)