Helioprojective¶

class sunpy.coordinates.frames.Helioprojective(*args, **kwargs)[source]¶

Bases: SunPyBaseCoordinateFrame

A coordinate or frame in the Helioprojective Cartesian (HPC) system, which is observer-based.

The origin is the location of the observer.
Tx (aka “theta_x”) is the angle relative to the plane containing the Sun-observer line and the Sun’s rotation axis, with positive values in the direction of the Sun’s west limb.
Ty (aka “theta_y”) is the angle relative to the Sun’s equatorial plane, with positive values in the direction of the Sun’s north pole.
distance is the Sun-observer distance.

This system is frequently used in a projective form without distance specified. For observations looking very close to the center of the Sun, where the small-angle approximation is appropriate, Tx and Ty can be approximated as Cartesian components.

A new instance can be created using the following signatures (note that if supplied, obstime and observer must be keyword arguments):

Helioprojective(Tx, Ty, obstime=obstime, observer=observer)
Helioprojective(Tx, Ty, distance, obstime=obstime, observer=observer)

Parameters:

data (BaseRepresentation or None) – A representation object or None to have no data (or use the coordinate component arguments, see below).
Tx (Angle or Quantity) – The theta_x coordinate for this object. Not needed if data is given.
Ty (Angle or Quantity) – The theta_y coordinate for this object. Not needed if data is given.
distance (Quantity) – The distance coordinate from the observer for this object. Not needed if data is given.
observer (HeliographicStonyhurst, str) – The location of the observer. If a string is provided, it must be a solar system body that can be parsed by get_body_heliographic_stonyhurst at the time obstime. Defaults to Earth center.
rsun (Quantity) – The radius of the Sun in length units. Used to convert a 2D coordinate (i.e., no radius component) to a 3D coordinate by assuming that the coordinate is on the surface of the Sun. Defaults to the photospheric radius as defined in sunpy.sun.constants.
obstime (tuple, list, str, pandas.Timestamp, pandas.Series, pandas.DatetimeIndex, datetime.datetime, datetime.date, numpy.datetime64, numpy.ndarray, astropy.time.Time) – The time of the observation. This is used to determine the position of solar-system bodies (e.g., the Sun and the Earth) as needed to define the origin and orientation of the frame.
representation_type (BaseRepresentation, str, optional) – A representation class or string name of a representation class. This may change the valid coordinate component arguments from the defaults (see above). For example, passing representation_type='cartesian' will make the frame expect Cartesian coordinate component arguments (typically, x, y, and z).
copy (bool, optional) – If True (default), make copies of the input coordinate arrays.

Examples

>>> from astropy.coordinates import SkyCoord
>>> import sunpy.coordinates
>>> import astropy.units as u
>>> sc = SkyCoord(0*u.deg, 0*u.deg, 5*u.km,
...               obstime="2010/01/01T00:00:00", observer="earth", frame="helioprojective")
>>> sc
<SkyCoord (Helioprojective: obstime=2010-01-01T00:00:00.000, rsun=695700.0 km, observer=<HeliographicStonyhurst Coordinate for 'earth'>): (Tx, Ty, distance) in (arcsec, arcsec, km)
    (0., 0., 5.)>
>>> sc = SkyCoord(0*u.deg, 0*u.deg,
...               obstime="2010/01/01T00:00:00", observer="earth", frame="helioprojective")
>>> sc
<SkyCoord (Helioprojective: obstime=2010-01-01T00:00:00.000, rsun=695700.0 km, observer=<HeliographicStonyhurst Coordinate for 'earth'>): (Tx, Ty) in arcsec
    (0., 0.)>
>>> sc = SkyCoord(CartesianRepresentation(1*u.AU, 1e5*u.km, -2e5*u.km),
...               obstime="2011/01/05T00:00:50", observer="earth", frame="helioprojective")
>>> sc
<SkyCoord (Helioprojective: obstime=2011-01-05T00:00:50.000, rsun=695700.0 km, observer=<HeliographicStonyhurst Coordinate for 'earth'>): (Tx, Ty, distance) in (arcsec, arcsec, AU)
    (137.87948623, -275.75878762, 1.00000112)>

Attributes Summary

`angular_radius`	Angular radius of the Sun as seen by the observer.
`default_differential`	Default representation for differential data (e.g., velocity)
`default_representation`	Default representation for position data
`frame_attributes`
`frame_specific_representation_info`	Mapping for frame-specific component names
`name`
`observer`
`rsun`

Methods Summary

`assume_spherical_screen`(center[, only_off_disk])	Context manager to interpret 2D coordinates as being on the inside of a spherical screen.
`make_3d`()	This method calculates the third coordinate of the Helioprojective frame.

Attributes Documentation

angular_radius¶

Angular radius of the Sun as seen by the observer.

The rsun frame attribute is the radius of the Sun in length units. The tangent vector from the observer to the edge of the Sun forms a right-angle triangle with the radius of the Sun as the far side and the Sun-observer distance as the hypotenuse. Thus, the sine of the angular radius of the Sun is ratio of these two distances.

default_differential¶: Default representation for differential data (e.g., velocity)

default_representation¶: Default representation for position data

frame_attributes = {'observer': <sunpy.coordinates.frameattributes.ObserverCoordinateAttribute object>, 'obstime': <sunpy.coordinates.frameattributes.TimeFrameAttributeSunPy object>, 'rsun': <astropy.coordinates.attributes.QuantityAttribute object>}¶

frame_specific_representation_info¶: Mapping for frame-specific component names

name = 'helioprojective'¶

observer = None¶

rsun = <Quantity 695700. km>¶

Methods Documentation

classmethod assume_spherical_screen(center, only_off_disk=False)[source]¶

Context manager to interpret 2D coordinates as being on the inside of a spherical screen.

The radius of the screen is the distance between the specified center and Sun center. This center does not have to be the same as the observer location for the coordinate frame. If they are the same, then this context manager is equivalent to assuming that the helioprojective “zeta” component is zero.

This replaces the default assumption where 2D coordinates are mapped onto the surface of the Sun.

Parameters:

center (SkyCoord) – The center of the spherical screen
only_off_disk (bool, optional) – If True, apply this assumption only to off-disk coordinates, with on-disk coordinates still mapped onto the surface of the Sun. Defaults to False.

Examples

Reprojecting Using a Spherical Screen

Creating a Composite Plot with Three Maps

>>> import astropy.units as u
>>> from sunpy.coordinates import Helioprojective
>>> h = Helioprojective(range(7)*u.arcsec*319, [0]*7*u.arcsec,
...                     observer='earth', obstime='2020-04-08')
>>> print(h.make_3d())
<Helioprojective Coordinate (obstime=2020-04-08T00:00:00.000, rsun=695700.0 km, observer=<HeliographicStonyhurst Coordinate for 'earth'>): (Tx, Ty, distance) in (arcsec, arcsec, AU)
    [(   0., 0., 0.99660825), ( 319., 0., 0.99687244),
     ( 638., 0., 0.99778472), ( 957., 0., 1.00103285),
     (1276., 0.,        nan), (1595., 0.,        nan),
     (1914., 0.,        nan)]>

>>> with Helioprojective.assume_spherical_screen(h.observer):
...     print(h.make_3d())
<Helioprojective Coordinate (obstime=2020-04-08T00:00:00.000, rsun=695700.0 km, observer=<HeliographicStonyhurst Coordinate for 'earth'>): (Tx, Ty, distance) in (arcsec, arcsec, AU)
    [(   0., 0., 1.00125872), ( 319., 0., 1.00125872),
     ( 638., 0., 1.00125872), ( 957., 0., 1.00125872),
     (1276., 0., 1.00125872), (1595., 0., 1.00125872),
     (1914., 0., 1.00125872)]>

>>> with Helioprojective.assume_spherical_screen(h.observer, only_off_disk=True):
...     print(h.make_3d())
<Helioprojective Coordinate (obstime=2020-04-08T00:00:00.000, rsun=695700.0 km, observer=<HeliographicStonyhurst Coordinate for 'earth'>): (Tx, Ty, distance) in (arcsec, arcsec, AU)
    [(   0., 0., 0.99660825), ( 319., 0., 0.99687244),
     ( 638., 0., 0.99778472), ( 957., 0., 1.00103285),
     (1276., 0., 1.00125872), (1595., 0., 1.00125872),
     (1914., 0., 1.00125872)]>

make_3d()[source]¶

This method calculates the third coordinate of the Helioprojective frame. It assumes that the coordinate point is on the surface of the Sun.

If a point in the frame is off limb then NaN will be returned.

Returns:: new_frame (Helioprojective) – A new frame instance with all the attributes of the original but now with a third coordinate.