How to use the pynbody.analysis.angmom.faceon function in pynbody

*compare* (default=True):  whether to include Kennicutt (1998) and
            Bigiel+ (2008) for comparison

       *radial* (default=True):  should bins be annuli or a rectangular grid?

       *bins* (default=10):  How many radial bins should there be?

       *legend*: boolean
         whether to draw a legend or not
    '''

    if not radial:
        raise NotImplementedError, "Sorry, only radial Schmidt law currently supported"

    if center:
        angmom.faceon(sim)

    if isinstance(pretime, str):
        pretime = units.Unit(pretime)

    # select stuff
    diskgas = sim.gas[filt.Disc(rmax, diskheight)]
    diskstars = sim.star[filt.Disc(rmax, diskheight)]

    formkey = 'tform'

    try:
        diskstars['tform']
    except KeyError:
        formkey = 'timeform'

    youngstars = np.where(diskstars[formkey].in_units("Myr") >

density for the entire galaxy based on the half mass cold gas radius.

    **Usage:**
    import pynbody.plot as pp
    pp.oneschmidtlawpoint(h[1])

       *pretime* (default='50 Myr'): age of stars to consider for SFR

       *diskheight* (default='3 kpc'): height of gas and stars above
          and below disk considered for SF and gas densities.

       *rmax* (default='20 kpc'): radius of disk considered
    '''

    if center:
        angmom.faceon(sim)

    cg = h[1].gas[filt.LowPass('temp', 1e5)]
    cgd = cg[filt.Disc('30 kpc', '3 kpc')]
    cgs = np.sort(cgd['rxy'].in_units('kpc'))
    rhgas = cgs[len(cgs) / 2]
    instars = h[1].star[filt.Disc(str(rhgas) + ' kpc', '3 kpc')]
    minstars = np.sum(
        instars[filt.LowPass('age', '100 Myr')]['mass'].in_units('Msol'))
    ingasm = np.sum(
        cg[filt.Disc(str(rhgas) + ' kpc', '3 kpc')]['mass'].in_units('Msol'))
    rpc = rhgas * 1000.0
    rkpc = rhgas
    xsigma = ingasm / (np.pi * rpc * rpc)
    ysigma = minstars / (np.pi * rkpc * rkpc * 1e8)
    return xsigma, ysigma

density for the entire galaxy based on the half mass cold gas radius.

	**Usage:**
	import pynbody.plot as pp
	pp.oneschmidtlawpoint(h[1])

	   *pretime* (default='50 Myr'): age of stars to consider for SFR

	   *diskheight* (default='3 kpc'): height of gas and stars above
		  and below disk considered for SF and gas densities.

	   *rmax* (default='20 kpc'): radius of disk considered
	'''

	if center:
		angmom.faceon(sim)

	cg = h[1].gas[filt.LowPass('temp', 1e5)]
	cgd = cg[filt.Disc('30 kpc', '3 kpc')]
	cgs = np.sort(cgd['rxy'].in_units('kpc'))
	rhgas = cgs[len(cgs) / 2]
	instars = h[1].star[filt.Disc(str(rhgas) + ' kpc', '3 kpc')]
	minstars = np.sum(
		instars[filt.LowPass('age', '100 Myr')]['mass'].in_units('Msol'))
	ingasm = np.sum(
		cg[filt.Disc(str(rhgas) + ' kpc', '3 kpc')]['mass'].in_units('Msol'))
	rpc = rhgas * 1000.0
	rkpc = rhgas
	xsigma = ingasm / (np.pi * rpc * rpc)
	ysigma = minstars / (np.pi * rkpc * rkpc * 1e8)
	return xsigma, ysigma

def faceon_image(sim, *args, **kwargs):
    """

    Rotate the simulation so that the disc of the passed halo is
    face-on, then make an SPH image by passing the parameters into
    the function image

    For a description of keyword arguments see :func:`~pynbody.plot.sph.image`.

    """

    from ..analysis import angmom

    with angmom.faceon(sim):
        return image(sim, *args, **kwargs)

*center(True)*:  Automatically align face on and center?

	*axes(False)*: In which axes (subplot) should it be plotted?

	*filename* (None): name of file to which to save output

	**needs a description of all keywords**

	By default, sbprof will use the formation mass of the star.
	In tipsy, this will be taken from the starlog file.

	'''

	if center:
		logger.info("Centering...")
		angmom.faceon(sim)

	logger.info("Selecting disk stars")
	diskstars = sim.star[filt.Disc(rmax, diskheight)]
	logger.info("Creating profile")
	ps = profile.Profile(diskstars, type=binning)
	logger.info("Plotting")
	r = ps['rbins'].in_units('kpc')

	if axes:
		plt = axes
	else:
		import matplotlib.pyplot as plt
	if clear:
		plt.clf()

	plt.plot(r, ps['sb,' + band], linewidth=2, **kwargs)