Sometimes required for comparing GeoVectors if float error has
        occurred. Determine if self and other (another GeoVector) are
        equal to within e km of each other in dx and dy. The default
        (e = 0.000001) will return True if self and other are less than
        1 mm apart in distance.

def almost_equals(self, other, e = 0.000001):
        '''
        Sometimes required for comparing GeoVectors if float error has
        occurred. Determine if self and other (another GeoVector) are
        equal to within e km of each other in dx and dy. The default
        (e = 0.000001) will return True if self and other are less than
        1 mm apart in distance.
        '''
        return abs(self.dx - other.dx) < e and abs(self.dy - other.dy) < e