# AstropyDeprecationWarning when making a coordinate transformation that includes a frame **URL:** \ **Category:** Astropy\ **Tags:** astropy\ **Created:** [April 23, 2022, 11:07am UTC](https://community.openastronomy.org/t/astropydeprecationwarning-when-making-a-coordinate-transformation-that-includes-a-frame/343 "2022-04-23T11:07:53Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![mmestre](https://avatars.discourse-cdn.com/v4/letter/m/46a35a/32.png) [@mmestre](https://community.openastronomy.org/u/mmestre)\ **Post date:** [April 23, 2022, 11:07am UTC](https://community.openastronomy.org/t/astropydeprecationwarning-when-making-a-coordinate-transformation-that-includes-a-frame/343/1 "2022-04-23T11:07:53Z")
Hello, I have the following piece of code where I transform coordinates from ICRS to galactocentric: ```auto # Transformation to galactocentric coordinates sky_coord = coord.ICRS(ra=alpha*u.degree, dec=delta*u.degree, distance=distance*u.kpc, pm_ra_cosdec=mu_alpha*np.cos(delta*u.degree)*u.mas/u.yr, pm_dec=mu_delta*u.mas/u.yr, radial_velocity=v_los*u.km/u.s) galcen_distance = r_sun*u.kpc v_sun = coord.CartesianDifferential([11.1, v_circ_sun+12.24, 7.25]*u.km/u.s) z_sun = 0.0*u.kpc frame = coord.Galactocentric(galcen_distance=galcen_distance, galcen_v_sun=v_sun, z_sun=z_sun) galac_coord = sky_coord.transform_to(frame) ``` When running I obtain the following warning: ```auto WARNING: AstropyDeprecationWarning: Transforming a frame instance to a frame class (as opposed to another frame instance) will not be supported in the future. Either explicitly instantiate the target frame, or first convert the source frame instance to a `astropy.coordinates.SkyCoord` and use its `transform_to()` method. [astropy.coordinates.baseframe] ``` I can’t undertand the explanation. I would like to know which modifications should I make to my piece of code in order to solve that warning. Thank you very much in advance. ---
**Author:** ![ayshih](https://dub1.discourse-cdn.com/flex005/user_avatar/community.openastronomy.org/ayshih/32/84_2.png) [@ayshih](https://community.openastronomy.org/u/ayshih)\ **Post date:** [April 24, 2022, 4:57am UTC](https://community.openastronomy.org/t/astropydeprecationwarning-when-making-a-coordinate-transformation-that-includes-a-frame/343/2 "2022-04-24T04:57:54Z")
Can you double-check that this code exactly as you have shared is emitting this warning? The normal way to see this warning is if you had instead typed: ```python galac_coord = sky_coord.transform_to(coord.Galactocentric) ``` That is, the warning would be because you were trying to transform to a frame class (`coord.Galactocentric`) rather than to a frame instance (`coord.Galactocentric(...)`). In the code you have shared, you are correctly transforming to a frame instance, so that warning shouldn’t be emitted, and on my machine it doesn’t emit that warning. I’ll also point out that your `sky_coord` is not actually an instance of the `SkyCoord` class. This warning only appears when you are directly working with frame classes instead of using `SkyCoord`. Had `sky_coord` been a `SkyCoord` instance, this warning would never appear. ---
**Author:** ![mmestre](https://avatars.discourse-cdn.com/v4/letter/m/46a35a/32.png) [@mmestre](https://community.openastronomy.org/u/mmestre)\ **Post date:** [April 27, 2022, 8:10pm UTC](https://community.openastronomy.org/t/astropydeprecationwarning-when-making-a-coordinate-transformation-that-includes-a-frame/343/3 "2022-04-27T20:10:09Z")
Thank you very much for your help. As you say, the warning arises in this two situations: ```auto Iba_coord_ICRS = Iba_coord_GD1.transform_to(coord.ICRS) Iba_coord_GD1 = Iba_coord_ICRS.transform_to(GD1_class.GD1Koposov10) ``` How could I previously instantiate each of them? The GD1\_class is here: ```auto class GD1Koposov10(coord.BaseCoordinateFrame): """ A Heliocentric spherical coordinate system defined by the orbit of the GD1 stream. As described in Koposov et al. 2010 (see: ``_). For more information about this class, see the Astropy documentation on coordinate frames in :mod:`~astropy.coordinates`. Parameters ---------- representation : :class:`~astropy.coordinates.BaseRepresentation` or None A representation object or None to have no data (or use the other keywords) phi1 : angle_like, optional, must be keyword The longitude-like angle corresponding to GD-1's orbit. phi2 : angle_like, optional, must be keyword The latitude-like angle corresponding to GD-1's orbit. distance : :class:`~astropy.units.Quantity`, optional, must be keyword The Distance for this object along the line-of-sight. pm_phi1_cosphi2 : :class:`~astropy.units.Quantity`, optional, must be keyword The proper motion in the longitude-like direction corresponding to the GD-1 stream's orbit. pm_phi2 : :class:`~astropy.units.Quantity`, optional, must be keyword The proper motion in the latitude-like direction perpendicular to the GD-1 stream's orbit. radial_velocity : :class:`~astropy.units.Quantity`, optional, must be keyword The Distance for this object along the line-of-sight. """ default_representation = coord.SphericalRepresentation default_differential = coord.SphericalCosLatDifferential frame_specific_representation_info = { coord.SphericalRepresentation: [ coord.RepresentationMapping('lon', 'phi1'), coord.RepresentationMapping('lat', 'phi2'), coord.RepresentationMapping('distance', 'distance')], } _default_wrap_angle = 180*u.deg def __init__ (self, *args, **kwargs): """Init.""" wrap = kwargs.pop('wrap_longitude', True) super(). __init__ (*args, **kwargs) if wrap and isinstance(self._data, (coord.UnitSphericalRepresentation, coord.SphericalRepresentation)): self._data.lon.wrap_angle = self._default_wrap_angle # TODO: remove this. This is a hack required as of astropy v3.1 in order # to have the longitude components wrap at the desired angle def represent_as(self, base, s='base', in_frame_units=False): """Represent as.""" r = super().represent_as(base, s=s, in_frame_units=in_frame_units) r.lon.wrap_angle = self._default_wrap_angle return r # Rotation matrix as defined in the Appendix of Koposov et al. (2010) R = np.array([[-0.4776303088, -0.1738432154, 0.8611897727], [0.510844589, -0.8524449229, 0.111245042], [0.7147776536, 0.4930681392, 0.4959603976]]) @frame_transform_graph.transform(coord.StaticMatrixTransform, coord.ICRS, GD1Koposov10) def icrs_to_gd1(): """Compute the transformation from Galactic spherical to heliocentric GD1 coordinates.""" return R @frame_transform_graph.transform(coord.StaticMatrixTransform, GD1Koposov10, coord.ICRS) def gd1_to_icrs(): """Compute the transformation from heliocentric GD1 coordinates to spherical Galactic.""" return matrix_transpose(icrs_to_gd1()) # TODO: remove this in next version class GD1(GD1Koposov10): """GD-1 class.""" def __init__ (self, *args, **kwargs): """Init GD-1 class.""" import warnings warnings.warn("This frame is deprecated. Use GD1Koposov10 instead.", DeprecationWarning) super(). __init__ (*args, **kwargs) trans = frame_transform_graph.get_transform(GD1Koposov10, coord.ICRS).transforms[0] frame_transform_graph.add_transform(GD1, coord.ICRS, trans) trans = frame_transform_graph.get_transform(coord.ICRS, GD1Koposov10).transforms[0] frame_transform_graph.add_transform(coord.ICRS, GD1, trans) ``` When I did : ```auto sky_coord = coord.ICRS(ra=alpha*u.degree, dec=delta*u.degree, distance=distance*u.kpc, pm_ra_cosdec=mu_alpha*np.cos(delta*u.degree)*u.mas/u.yr, pm_dec=mu_delta*u.mas/u.yr, radial_velocity=v_los*u.km/u.s) ``` did I instantiate the coord.ICRS class? How would my example be using SkyCoord ? Thank you very much @ayshih ! ---
**Author:** ![mmestre](https://avatars.discourse-cdn.com/v4/letter/m/46a35a/32.png) [@mmestre](https://community.openastronomy.org/u/mmestre)\ **Post date:** [April 27, 2022, 8:38pm UTC](https://community.openastronomy.org/t/astropydeprecationwarning-when-making-a-coordinate-transformation-that-includes-a-frame/343/4 "2022-04-27T20:38:34Z")
Thanks @ayshih, I made a long answer to your question with further questions and my post was removed by Akismet. I will wait the system to bring it back. Otherwise I will write again. ---
**Author:** ![nabobalis](https://dub1.discourse-cdn.com/flex005/user_avatar/community.openastronomy.org/nabobalis/32/14_2.png) [@nabobalis](https://community.openastronomy.org/u/nabobalis)\ **Post date:** [April 27, 2022, 8:53pm UTC](https://community.openastronomy.org/t/astropydeprecationwarning-when-making-a-coordinate-transformation-that-includes-a-frame/343/5 "2022-04-27T20:53:21Z")
I restored the message. Sorry for the trouble! ---
**Author:** ![ayshih](https://dub1.discourse-cdn.com/flex005/user_avatar/community.openastronomy.org/ayshih/32/84_2.png) [@ayshih](https://community.openastronomy.org/u/ayshih)\ **Post date:** [April 28, 2022, 3:49am UTC](https://community.openastronomy.org/t/astropydeprecationwarning-when-making-a-coordinate-transformation-that-includes-a-frame/343/6 "2022-04-28T03:49:14Z")
> [@mmestre](#): > > Thank you very much for your help. As you say, the warning arises in this two situations: > > ```auto > Iba_coord_ICRS = Iba_coord_GD1.transform_to(coord.ICRS) > Iba_coord_GD1 = Iba_coord_ICRS.transform_to(GD1_class.GD1Koposov10) > > ``` > > How could I previously instantiate each of them? In the case of `ICRS`, and your `GD1Koposov10`, all you need to instantiate them is to add empty parentheses, e.g.: ```auto Iba_coord_ICRS = Iba_coord_GD1.transform_to(coord.ICRS()) Iba_coord_GD1 = Iba_coord_ICRS.transform_to(GD1_class.GD1Koposov10()) ``` The need to pass in an instance rather than a class may appear silly for these two classes in particular, but that’s because they do not have any frame attributes (e.g., `obstime`). When a frame has frame attributes, the `transform_to()` call wants the target frame to be a frame instance so that those frame attributes have actual values (which could be default values). > [@mmestre](#): > > When I did : > > ```auto > sky_coord = coord.ICRS(ra=alpha*u.degree, dec=delta*u.degree, > distance=distance*u.kpc, > pm_ra_cosdec=mu_alpha*np.cos(delta*u.degree)*u.mas/u.yr, > pm_dec=mu_delta*u.mas/u.yr, > radial_velocity=v_los*u.km/u.s) > > ``` > > did I instantiate the coord.ICRS class? Yup > [@mmestre](#): > > How would my example be using SkyCoord ? There are several ways to create the `SkyCoord` instance. You could create it much like you create the frame instance: ```auto sky_coord = coord.SkyCoord(ra=..., ..., frame=coord.ICRS) ``` or if you already have the frame instance, you can feed that directly into the `SkyCoord` constructor: ```auto sky_coord = coord.SkyCoord(sky_coord) ``` In your problematic lines, if `Iba_coord_GD1` and `Iba_coord_ICRS` are `SkyCoord` instances, then the two lines will not emit a warning, even without the parentheses. That’s because `SkyCoord.transform_to()` makes assumptions for the values of frame attributes for the target frame if only a frame class is provided. In contrast, `BaseCoordinateFrame.transform_to()` wants the user to be explicit because it is intended as a lower-level call. If you want to read a little more about when/why this was changed, see here: [https://github.com/astropy/astropy/pull/10475](https://github.com/astropy/astropy/pull/10475) ---
**Author:** ![mmestre](https://avatars.discourse-cdn.com/v4/letter/m/46a35a/32.png) [@mmestre](https://community.openastronomy.org/u/mmestre)\ **Post date:** [April 28, 2022, 7:51pm UTC](https://community.openastronomy.org/t/astropydeprecationwarning-when-making-a-coordinate-transformation-that-includes-a-frame/343/7 "2022-04-28T19:51:45Z")
Thank you very much for the patience and detailed explanation! I will read the reference. All the best. ---
**Author:** ![mmestre](https://avatars.discourse-cdn.com/v4/letter/m/46a35a/32.png) [@mmestre](https://community.openastronomy.org/u/mmestre)\ **Post date:** [April 29, 2022, 12:23pm UTC](https://community.openastronomy.org/t/astropydeprecationwarning-when-making-a-coordinate-transformation-that-includes-a-frame/343/8 "2022-04-29T12:23:48Z")
Hi @ayshih, sorry for more related questions. 1- I would like to know if there exist a frame class or a frame is only a particular instantiation of a coordinate class (e.g. coord.galactocentric) where no coordinates are given ? 2- Could you tell me how to define a frame using SkyCoord class ? 3- The objects instantiated using coord.ICRS(…) or SkCoord(…,frame=coord.ICRS) are exactly the same or have different properties? 4- Do you recomend to use SkyCoord or plain coord.ICRS ? Thank you very much in advance. ---
**Author:** ![ayshih](https://dub1.discourse-cdn.com/flex005/user_avatar/community.openastronomy.org/ayshih/32/84_2.png) [@ayshih](https://community.openastronomy.org/u/ayshih)\ **Post date:** [May 2, 2022, 2:58am UTC](https://community.openastronomy.org/t/astropydeprecationwarning-when-making-a-coordinate-transformation-that-includes-a-frame/343/9 "2022-05-02T02:58:37Z")
> [@mmestre](#): > > Hi @ayshih, sorry for more related questions. > > 1- I would like to know if there exist a frame class or a frame is only a particular instantiation of a coordinate class (e.g. coord.galactocentric) where no coordinates are given ? I use the terms “frame class”/“frame instance” regardless of whether coordinate data is included. That is, `ICRS()` is a frame instance without coordinate data, and `ICRS(1*u.deg, 2*u.deg)` is a frame instance with coordinate data. Note that the target of a `transform_to()` call can be a frame instance with coordinate data; the coordinate data is simply ignored in that case. > [@mmestre](#): > > 2- Could you tell me how to define a frame using SkyCoord class ? I’m not clear what you mean by “define a frame”. If you mean create a `SkyCoord` instance for a particular frame and coordinate data, I already gave you examples above. If you mean create a `SkyCoord` instance without any coordinate data, that’s not possible; unlike the frame classes, a `SkyCoord` instance must have coordinate data. If you mean define a frame class, that’s not what the `SkyCoord` class is for. Your `GF1Koposov10` class looks to be defined fine, as a subclass of `BaseCoordinateFrame`. > [@mmestre](#): > > 3- The objects instantiated using coord.ICRS(…) or SkCoord(…,frame=coord.ICRS) are exactly the same or have different properties? They do not instantiate the same object. The `SkyCoord` instance has more functionality than the `ICRS` instance. I’ll point out that if you have a `SkyCoord` instance, you can “downgrade” it to a frame instance by accessing the `.frame` property. > [@mmestre](#): > > 4- Do you recomend to use SkyCoord or plain coord.ICRS ? > > Thank you very much in advance. You should use `SkyCoord` unless you have some reason to intentionally avoid some of the additional logic that `SkyCoord` provides. `SkyCoord` is the higher-level interface to using the frame classes directly. ---
**Author:** ![mmestre](https://avatars.discourse-cdn.com/v4/letter/m/46a35a/32.png) [@mmestre](https://community.openastronomy.org/u/mmestre)\ **Post date:** [May 2, 2022, 7:13pm UTC](https://community.openastronomy.org/t/astropydeprecationwarning-when-making-a-coordinate-transformation-that-includes-a-frame/343/10 "2022-05-02T19:13:58Z")
Thank you very much @ayshih ! Now everything clear. I had misunderstood some concepts. Cheers!