space_ops.py

import numpy as np

from constants import OUT
from constants import RIGHT
from constants import PI
from constants import TAU
from functools import reduce
from utils.iterables import adjacent_pairs


def get_norm(vect):
    return sum([x**2 for x in vect])**0.5


# Quaternions
# TODO, implement quaternion type


def quaternion_mult(q1, q2):
    w1, x1, y1, z1 = q1
    w2, x2, y2, z2 = q2
    return np.array([
        w1 * w2 - x1 * x2 - y1 * y2 - z1 * z2,
        w1 * x2 + x1 * w2 + y1 * z2 - z1 * y2,
        w1 * y2 + y1 * w2 + z1 * x2 - x1 * z2,
        w1 * z2 + z1 * w2 + x1 * y2 - y1 * x2,
    ])


def quaternion_from_angle_axis(angle, axis):
    return np.append(
        np.cos(angle / 2),
        np.sin(angle / 2) * normalize(axis)
    )


def angle_axis_from_quaternion(quaternion):
    axis = normalize(
        quaternion[1:],
        fall_back=np.array([1, 0, 0])
    )
    angle = 2 * np.arccos(quaternion[0])
    if angle > TAU / 2:
        angle = TAU - angle
    return angle, axis


def quaternion_conjugate(quaternion):
    result = np.array(quaternion)
    result[1:] *= -1
    return result


def rotate_vector(vector, angle, axis=OUT):
    quat = quaternion_from_angle_axis(angle, axis)
    quat_inv = quaternion_conjugate(quat)
    product = reduce(
        quaternion_mult,
        [quat, np.append(0, vector), quat_inv]
    )
    return product[1:]


def thick_diagonal(dim, thickness=2):
    row_indices = np.arange(dim).repeat(dim).reshape((dim, dim))
    col_indices = np.transpose(row_indices)
    return (np.abs(row_indices - col_indices) < thickness).astype('uint8')


def rotation_matrix(angle, axis):
    """
    Rotation in R^3 about a specified axis of rotation.
    """
    about_z = rotation_about_z(angle)
    z_to_axis = z_to_vector(axis)
    axis_to_z = np.linalg.inv(z_to_axis)
    return reduce(np.dot, [z_to_axis, about_z, axis_to_z])


def rotation_about_z(angle):
    return [
        [np.cos(angle), -np.sin(angle), 0],
        [np.sin(angle), np.cos(angle), 0],
        [0, 0, 1]
    ]


def z_to_vector(vector):
    """
    Returns some matrix in SO(3) which takes the z-axis to the
    (normalized) vector provided as an argument
    """
    norm = get_norm(vector)
    if norm == 0:
        return np.identity(3)
    v = np.array(vector) / norm
    phi = np.arccos(v[2])
    if any(v[:2]):
        # projection of vector to unit circle
        axis_proj = v[:2] / get_norm(v[:2])
        theta = np.arccos(axis_proj[0])
        if axis_proj[1] < 0:
            theta = -theta
    else:
        theta = 0
    phi_down = np.array([
        [np.cos(phi), 0, np.sin(phi)],
        [0, 1, 0],
        [-np.sin(phi), 0, np.cos(phi)]
    ])
    return np.dot(rotation_about_z(theta), phi_down)


def angle_between(v1, v2):
    return np.arccos(np.dot(
        v1 / get_norm(v1),
        v2 / get_norm(v2)
    ))


def angle_of_vector(vector):
    """
    Returns polar coordinate theta when vector is project on xy plane
    """
    z = complex(*vector[:2])
    if z == 0:
        return 0
    return np.angle(complex(*vector[:2]))


def angle_between_vectors(v1, v2):
    """
    Returns the angle between two 3D vectors.
    This angle will always be btw 0 and TAU/2.
    """
    l1 = get_norm(v1)
    l2 = get_norm(v2)
    return np.arccos(np.dot(v1, v2) / (l1 * l2))


def project_along_vector(point, vector):
    matrix = np.identity(3) - np.outer(vector, vector)
    return np.dot(point, matrix.T)


def normalize(vect, fall_back=None):
    norm = get_norm(vect)
    if norm > 0:
        return np.array(vect) / norm
    else:
        if fall_back is not None:
            return fall_back
        else:
            return np.zeros(len(vect))


def cross(v1, v2):
    return np.array([
        v1[1] * v2[2] - v1[2] * v2[1],
        v1[2] * v2[0] - v1[0] * v2[2],
        v1[0] * v2[1] - v1[1] * v2[0]
    ])


def get_unit_normal(v1, v2):
    return normalize(cross(v1, v2))


###


def compass_directions(n=4, start_vect=RIGHT):
    angle = TAU / n
    return np.array([
        rotate_vector(start_vect, k * angle)
        for k in range(n)
    ])


def complex_to_R3(complex_num):
    return np.array((complex_num.real, complex_num.imag, 0))


def R3_to_complex(point):
    return complex(*point[:2])


def complex_func_to_R3_func(complex_func):
    return lambda p: complex_to_R3(complex_func(R3_to_complex(p)))


def center_of_mass(points):
    points = [np.array(point).astype("float") for point in points]
    return sum(points) / len(points)


def line_intersection(line1, line2):
    """
    return intersection point of two lines,
    each defined with a pair of vectors determining
    the end points
    """
    x_diff = (line1[0][0] - line1[1][0], line2[0][0] - line2[1][0])
    y_diff = (line1[0][1] - line1[1][1], line2[0][1] - line2[1][1])

    def det(a, b):
        return a[0] * b[1] - a[1] * b[0]

    div = det(x_diff, y_diff)
    if div == 0:
        raise Exception("Lines do not intersect")
    d = (det(*line1), det(*line2))
    x = det(d, x_diff) / div
    y = det(d, y_diff) / div
    return np.array([x, y, 0])


def get_winding_number(points):
    total_angle = 0
    for p1, p2 in adjacent_pairs(points):
        d_angle = angle_of_vector(p2) - angle_of_vector(p1)
        d_angle = ((d_angle + PI) % TAU) - PI
        total_angle += d_angle
    return total_angle / TAU