pymrm.particles.Sphere

class Sphere(Particle):
    """Sphere (any dimension; in 2-D this is a disk — see :class:`Circle`).

    Fully analytic: exact level function, normals, and segment intersections.
    """

    def __init__(self, center, radius):
        super().__init__(center)
        self.radius = float(radius)

    def level_body(self, coords):
        return np.linalg.norm(np.asarray(coords, dtype=float), axis=-1) - self.radius

    def normal_body(self, coords):
        return np.asarray(coords, dtype=float)

    def bounding_box_body(self):
        r = self.radius
        return tuple((-r, r) for _ in range(self.ndim))

    def intersect(self, p0, p1):
        p0 = np.asarray(p0, dtype=float)
        p1 = np.asarray(p1, dtype=float)
        d = p1 - p0
        m = p0 - self.position
        a = np.sum(d * d, axis=-1)
        b = np.sum(d * m, axis=-1)
        c = np.sum(m * m, axis=-1) - self.radius**2
        disc = np.sqrt(np.maximum(b * b - a * c, 0.0))
        t1 = (-b - disc) / a
        t2 = (-b + disc) / a
        # Endpoints straddle the surface: entering picks the first root,
        # exiting (p0 inside) the second.
        return np.where(c > 0.0, t1, t2)