rotmat.py

#!/usr/bin/env python
#
# vector3 and rotation matrix classes
# This follows the conventions in the ArduPilot code,
# and is essentially a python version of the AP_Math library
#
# Andrew Tridgell, March 2012
#
# This library is free software; you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published by the
# Free Software Foundation; either version 2.1 of the License, or (at your
# option) any later version.
#
# This library is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
# for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this library; if not, write to the Free Software Foundation,
# Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA

'''rotation matrix class
'''

from math import sin, cos, sqrt, asin, atan2, pi, radians, acos

class Vector3:
    '''a vector'''
    def __init__(self, x=None, y=None, z=None):
        if x != None and y != None and z != None:
            self.x = float(x)
            self.y = float(y)
            self.z = float(z)
        elif x != None and len(x) == 3:
            self.x = float(x[0])
            self.y = float(x[1])
            self.z = float(x[2])
        elif x != None:
            raise ValueError('bad initialiser')
        else:
            self.x = float(0)
            self.y = float(0)
            self.z = float(0)

    def __repr__(self):
        return 'Vector3(%.2f, %.2f, %.2f)' % (self.x,
                                              self.y,
                                              self.z)

    def __add__(self, v):
        return Vector3(self.x + v.x,
                       self.y + v.y,
                       self.z + v.z)

    __radd__ = __add__

    def __sub__(self, v):
        return Vector3(self.x - v.x,
                       self.y - v.y,
                       self.z - v.z)

    def __neg__(self):
        return Vector3(-self.x, -self.y, -self.z)

    def __rsub__(self, v):
        return Vector3(v.x - self.x,
                       v.y - self.y,
                       v.z - self.z)

    def __mul__(self, v):
        if isinstance(v, Vector3):
            '''dot product'''
            return self.x*v.x + self.y*v.y + self.z*v.z
        return Vector3(self.x * v,
                       self.y * v,
                       self.z * v)

    __rmul__ = __mul__

    def __div__(self, v):
        return Vector3(self.x / v,
                       self.y / v,
                       self.z / v)

    def __mod__(self, v):
        '''cross product'''
        return Vector3(self.y*v.z - self.z*v.y,
                       self.z*v.x - self.x*v.z,
                       self.x*v.y - self.y*v.x)

    def __copy__(self):
        return Vector3(self.x, self.y, self.z)

    copy = __copy__

    def length(self):
        return sqrt(self.x**2 + self.y**2 + self.z**2)

    def zero(self):
        self.x = self.y = self.z = 0

    def angle(self, v):
        '''return the angle between this vector and another vector'''
        return acos(self * v) / (self.length() * v.length())

    def normalized(self):
        return self / self.length()
    
    def normalize(self):
        v = self.normalized()
        self.x = v.x
        self.y = v.y
        self.z = v.z
        
class Matrix3:
    '''a 3x3 matrix, intended as a rotation matrix'''
    def __init__(self, a=None, b=None, c=None):
        if a is not None and b is not None and c is not None:
            self.a = a.copy()
            self.b = b.copy()
            self.c = c.copy()
        else:
            self.identity()

    def __repr__(self):
        return 'Matrix3((%.2f, %.2f, %.2f), (%.2f, %.2f, %.2f), (%.2f, %.2f, %.2f))' % (
            self.a.x, self.a.y, self.a.z,
            self.b.x, self.b.y, self.b.z,
            self.c.x, self.c.y, self.c.z)

    def identity(self):
        self.a = Vector3(1,0,0)
        self.b = Vector3(0,1,0)
        self.c = Vector3(0,0,1)

    def transposed(self):
        return Matrix3(Vector3(self.a.x, self.b.x, self.c.x),
                       Vector3(self.a.y, self.b.y, self.c.y),
                       Vector3(self.a.z, self.b.z, self.c.z))

        
    def from_euler(self, roll, pitch, yaw):
        '''fill the matrix from Euler angles in radians'''
        cp = cos(pitch)
	sp = sin(pitch)
	sr = sin(roll)
	cr = cos(roll)
	sy = sin(yaw)
	cy = cos(yaw)

	self.a.x = cp * cy
	self.a.y = (sr * sp * cy) - (cr * sy)
	self.a.z = (cr * sp * cy) + (sr * sy)
	self.b.x = cp * sy
	self.b.y = (sr * sp * sy) + (cr * cy)
	self.b.z = (cr * sp * sy) - (sr * cy)
	self.c.x = -sp
	self.c.y = sr * cp
	self.c.z = cr * cp


    def to_euler(self):
        '''find Euler angles for the matrix'''
        if self.c.x >= 1.0:
            pitch = pi
        elif self.c.x <= -1.0:
            pitch = -pi
        else:
            pitch = -asin(self.c.x)
        roll = atan2(self.c.y, self.c.z)
        yaw  = atan2(self.b.x, self.a.x)
        return (roll, pitch, yaw)

    def __add__(self, m):
        return Matrix3(self.a + m.a, self.b + m.b, self.c + m.c)

    __radd__ = __add__

    def __sub__(self, m):
        return Matrix3(self.a - m.a, self.b - m.b, self.c - m.c)

    def __rsub__(self, m):
        return Matrix3(m.a - self.a, m.b - self.b, m.c - self.c)
    
    def __mul__(self, other):
        if isinstance(other, Vector3):
            v = other
            return Vector3(self.a.x * v.x + self.a.y * v.y + self.a.z * v.z,
                           self.b.x * v.x + self.b.y * v.y + self.b.z * v.z,
                           self.c.x * v.x + self.c.y * v.y + self.c.z * v.z)
        elif isinstance(other, Matrix3):
            m = other
            return Matrix3(Vector3(self.a.x * m.a.x + self.a.y * m.b.x + self.a.z * m.c.x,
                                   self.a.x * m.a.y + self.a.y * m.b.y + self.a.z * m.c.y,
                                   self.a.x * m.a.z + self.a.y * m.b.z + self.a.z * m.c.z),
                           Vector3(self.b.x * m.a.x + self.b.y * m.b.x + self.b.z * m.c.x,
                                   self.b.x * m.a.y + self.b.y * m.b.y + self.b.z * m.c.y,
                                   self.b.x * m.a.z + self.b.y * m.b.z + self.b.z * m.c.z),
                           Vector3(self.c.x * m.a.x + self.c.y * m.b.x + self.c.z * m.c.x,
                                   self.c.x * m.a.y + self.c.y * m.b.y + self.c.z * m.c.y,
                                   self.c.x * m.a.z + self.c.y * m.b.z + self.c.z * m.c.z))
        v = other
        return Matrix3(self.a * v, self.b * v, self.c * v)

    def __div__(self, v):
        return Matrix3(self.a / v, self.b / v, self.c / v)

    def __neg__(self):
        return Matrix3(-self.a, -self.b, -self.c)

    def __copy__(self):
        return Matrix3(self.a, self.b, self.c)

    copy = __copy__

    def rotate(self, g):
        '''rotate the matrix by a given amount on 3 axes'''
	temp_matrix = Matrix3()
        a = self.a
        b = self.b
        c = self.c
	temp_matrix.a.x = a.y * g.z - a.z * g.y
	temp_matrix.a.y = a.z * g.x - a.x * g.z
	temp_matrix.a.z = a.x * g.y - a.y * g.x
	temp_matrix.b.x = b.y * g.z - b.z * g.y
	temp_matrix.b.y = b.z * g.x - b.x * g.z
	temp_matrix.b.z = b.x * g.y - b.y * g.x
	temp_matrix.c.x = c.y * g.z - c.z * g.y
	temp_matrix.c.y = c.z * g.x - c.x * g.z
	temp_matrix.c.z = c.x * g.y - c.y * g.x
        self.a += temp_matrix.a
        self.b += temp_matrix.b
        self.c += temp_matrix.c

    def normalize(self):
        '''re-normalise a rotation matrix'''
	error = self.a * self.b
	t0 = self.a - (self.b * (0.5 * error))
	t1 = self.b - (self.a * (0.5 * error))
	t2 = t0 % t1
        self.a = t0 * (1.0 / t0.length())
        self.b = t1 * (1.0 / t1.length())
        self.c = t2 * (1.0 / t2.length())

    def trace(self):
        '''the trace of the matrix'''
        return self.a.x + self.b.y + self.c.z

def test_euler():
    '''check that from_euler() and to_euler() are consistent'''
    m = Matrix3()
    from math import radians, degrees
    for r in range(-179, 179, 3):
        for p in range(-89, 89, 3):
            for y in range(-179, 179, 3):
                m.from_euler(radians(r), radians(p), radians(y))
                (r2, p2, y2) = m.to_euler()
                v1 = Vector3(r,p,y)
                v2 = Vector3(degrees(r2),degrees(p2),degrees(y2))
                diff = v1 - v2
                if diff.length() > 1.0e-12:
                    print('EULER ERROR:', v1, v2, diff.length())
                    
if __name__ == "__main__":
    import doctest
    doctest.testmod()
    test_euler()