(self, vx, vy=None, vz=None)
return phi0 - fov / sth / 2.0, phi0 + fov / sth / 2.0
Get the min and max value of phi of the meridians to cover the field
        of view.

        Input:
          - the normalized vector of the direction of the center of the
            projection, in the reference frame of the graticule.
        Return:
          - vmin,vmax : the interval of phi for the
                        meridians crossing the field of view.
Get the min and max value of phi of the meridians to cover the field
        of view.
Get the min and max value of phi of the meridians to cover the field of view .
def get_meridian_interval(self, vx, vy=None, vz=None):
        """Get the min and max value of phi of the meridians to cover the field
        of view.

        Input:
          - the normalized vector of the direction of the center of the
            projection, in the reference frame of the graticule.
        Return:
          - vmin,vmax : the interval of phi for the
                        meridians crossing the field of view.
        """
        if vy is None and vz is None:
            vx, vy, vz = vx
        elif vy is None or vz is None:
            raise ValueError("Both vy and vz must be given or both not given")
        fov = self.proj.get_fov()
        th = np.arccos(vz)
        if th <= fov / 2.0:  # test whether north pole is visible
            return -np.pi, np.pi
        if abs(th - pi) <= fov / 2.0:  # test whether south pole is visible
            return -np.pi, np.pi
        sth = np.sin(th)
        phi0 = np.arctan2(vy, vx)
        return phi0 - fov / sth / 2.0, phi0 + fov / sth / 2.0
def get_meridian_interval ( self , vx , vy = None , vz = None ) : if vy is None and vz is None : vx , vy , vz = vx elif vy is None or vz is None : raise ValueError ( "Both vy and vz must be given or both not given" ) fov = self . proj . get_fov ( ) th = np . arccos ( vz ) if th <= fov / 2.0 : # test whether north pole is visible return - np . pi , np . pi if abs ( th - pi ) <= fov / 2.0 : # test whether south pole is visible return - np . pi , np . pi sth = np . sin ( th ) phi0 = np . arctan2 ( vy , vx ) return phi0 - fov / sth / 2.0 , phi0 + fov / sth / 2.0