Source code for astropy.wcs.utils

# Licensed under a 3-clause BSD style license - see LICENSE.rst

import numpy as np

from astropy import units as u
from astropy.utils.misc import unbroadcast
import copy

from .wcs import WCS, WCSSUB_LONGITUDE, WCSSUB_LATITUDE, WCSSUB_CELESTIAL

__doctest_skip__ = ['wcs_to_celestial_frame', 'celestial_frame_to_wcs']

__all__ = ['add_stokes_axis_to_wcs', 'celestial_frame_to_wcs',
           'wcs_to_celestial_frame', 'proj_plane_pixel_scales',
           'proj_plane_pixel_area', 'is_proj_plane_distorted',
           'non_celestial_pixel_scales', 'skycoord_to_pixel',
           'pixel_to_skycoord', 'custom_wcs_to_frame_mappings',
           'custom_frame_to_wcs_mappings', 'pixel_to_pixel',
           'local_partial_pixel_derivatives', 'fit_wcs_from_points']


[docs]def add_stokes_axis_to_wcs(wcs, add_before_ind): """ Add a new Stokes axis that is uncorrelated with any other axes. Parameters ---------- wcs : `~astropy.wcs.WCS` The WCS to add to add_before_ind : int Index of the WCS to insert the new Stokes axis in front of. To add at the end, do add_before_ind = wcs.wcs.naxis The beginning is at position 0. Returns ------- A new `~astropy.wcs.WCS` instance with an additional axis """ inds = [i + 1 for i in range(wcs.wcs.naxis)] inds.insert(add_before_ind, 0) newwcs = wcs.sub(inds) newwcs.wcs.ctype[add_before_ind] = 'STOKES' newwcs.wcs.cname[add_before_ind] = 'STOKES' return newwcs
def _wcs_to_celestial_frame_builtin(wcs): # Import astropy.coordinates here to avoid circular imports from astropy.coordinates import (FK4, FK4NoETerms, FK5, ICRS, ITRS, Galactic, SphericalRepresentation) # Import astropy.time here otherwise setup.py fails before extensions are compiled from astropy.time import Time if wcs.wcs.lng == -1 or wcs.wcs.lat == -1: return None radesys = wcs.wcs.radesys if np.isnan(wcs.wcs.equinox): equinox = None else: equinox = wcs.wcs.equinox xcoord = wcs.wcs.ctype[wcs.wcs.lng][:4] ycoord = wcs.wcs.ctype[wcs.wcs.lat][:4] # Apply logic from FITS standard to determine the default radesys if radesys == '' and xcoord == 'RA--' and ycoord == 'DEC-': if equinox is None: radesys = "ICRS" elif equinox < 1984.: radesys = "FK4" else: radesys = "FK5" if radesys == 'FK4': if equinox is not None: equinox = Time(equinox, format='byear') frame = FK4(equinox=equinox) elif radesys == 'FK4-NO-E': if equinox is not None: equinox = Time(equinox, format='byear') frame = FK4NoETerms(equinox=equinox) elif radesys == 'FK5': if equinox is not None: equinox = Time(equinox, format='jyear') frame = FK5(equinox=equinox) elif radesys == 'ICRS': frame = ICRS() else: if xcoord == 'GLON' and ycoord == 'GLAT': frame = Galactic() elif xcoord == 'TLON' and ycoord == 'TLAT': # The default representation for ITRS is cartesian, but for WCS # purposes, we need the spherical representation. frame = ITRS(representation_type=SphericalRepresentation, obstime=wcs.wcs.dateobs or None) else: frame = None return frame def _celestial_frame_to_wcs_builtin(frame, projection='TAN'): # Import astropy.coordinates here to avoid circular imports from astropy.coordinates import BaseRADecFrame, FK4, FK4NoETerms, FK5, ICRS, ITRS, Galactic # Create a 2-dimensional WCS wcs = WCS(naxis=2) if isinstance(frame, BaseRADecFrame): xcoord = 'RA--' ycoord = 'DEC-' if isinstance(frame, ICRS): wcs.wcs.radesys = 'ICRS' elif isinstance(frame, FK4NoETerms): wcs.wcs.radesys = 'FK4-NO-E' wcs.wcs.equinox = frame.equinox.byear elif isinstance(frame, FK4): wcs.wcs.radesys = 'FK4' wcs.wcs.equinox = frame.equinox.byear elif isinstance(frame, FK5): wcs.wcs.radesys = 'FK5' wcs.wcs.equinox = frame.equinox.jyear else: return None elif isinstance(frame, Galactic): xcoord = 'GLON' ycoord = 'GLAT' elif isinstance(frame, ITRS): xcoord = 'TLON' ycoord = 'TLAT' wcs.wcs.radesys = 'ITRS' wcs.wcs.dateobs = frame.obstime.utc.isot else: return None wcs.wcs.ctype = [xcoord + '-' + projection, ycoord + '-' + projection] return wcs WCS_FRAME_MAPPINGS = [[_wcs_to_celestial_frame_builtin]] FRAME_WCS_MAPPINGS = [[_celestial_frame_to_wcs_builtin]]
[docs]class custom_wcs_to_frame_mappings: def __init__(self, mappings=[]): if hasattr(mappings, '__call__'): mappings = [mappings] WCS_FRAME_MAPPINGS.append(mappings) def __enter__(self): pass def __exit__(self, type, value, tb): WCS_FRAME_MAPPINGS.pop()
# Backward-compatibility custom_frame_mappings = custom_wcs_to_frame_mappings
[docs]class custom_frame_to_wcs_mappings: def __init__(self, mappings=[]): if hasattr(mappings, '__call__'): mappings = [mappings] FRAME_WCS_MAPPINGS.append(mappings) def __enter__(self): pass def __exit__(self, type, value, tb): FRAME_WCS_MAPPINGS.pop()
[docs]def wcs_to_celestial_frame(wcs): """ For a given WCS, return the coordinate frame that matches the celestial component of the WCS. Parameters ---------- wcs : :class:`~astropy.wcs.WCS` instance The WCS to find the frame for Returns ------- frame : :class:`~astropy.coordinates.baseframe.BaseCoordinateFrame` subclass instance An instance of a :class:`~astropy.coordinates.baseframe.BaseCoordinateFrame` subclass instance that best matches the specified WCS. Notes ----- To extend this function to frames not defined in astropy.coordinates, you can write your own function which should take a :class:`~astropy.wcs.WCS` instance and should return either an instance of a frame, or `None` if no matching frame was found. You can register this function temporarily with:: >>> from astropy.wcs.utils import wcs_to_celestial_frame, custom_wcs_to_frame_mappings >>> with custom_wcs_to_frame_mappings(my_function): ... wcs_to_celestial_frame(...) """ for mapping_set in WCS_FRAME_MAPPINGS: for func in mapping_set: frame = func(wcs) if frame is not None: return frame raise ValueError("Could not determine celestial frame corresponding to " "the specified WCS object")
[docs]def celestial_frame_to_wcs(frame, projection='TAN'): """ For a given coordinate frame, return the corresponding WCS object. Note that the returned WCS object has only the elements corresponding to coordinate frames set (e.g. ctype, equinox, radesys). Parameters ---------- frame : :class:`~astropy.coordinates.baseframe.BaseCoordinateFrame` subclass instance An instance of a :class:`~astropy.coordinates.baseframe.BaseCoordinateFrame` subclass instance for which to find the WCS projection : str Projection code to use in ctype, if applicable Returns ------- wcs : :class:`~astropy.wcs.WCS` instance The corresponding WCS object Examples -------- :: >>> from astropy.wcs.utils import celestial_frame_to_wcs >>> from astropy.coordinates import FK5 >>> frame = FK5(equinox='J2010') >>> wcs = celestial_frame_to_wcs(frame) >>> wcs.to_header() WCSAXES = 2 / Number of coordinate axes CRPIX1 = 0.0 / Pixel coordinate of reference point CRPIX2 = 0.0 / Pixel coordinate of reference point CDELT1 = 1.0 / [deg] Coordinate increment at reference point CDELT2 = 1.0 / [deg] Coordinate increment at reference point CUNIT1 = 'deg' / Units of coordinate increment and value CUNIT2 = 'deg' / Units of coordinate increment and value CTYPE1 = 'RA---TAN' / Right ascension, gnomonic projection CTYPE2 = 'DEC--TAN' / Declination, gnomonic projection CRVAL1 = 0.0 / [deg] Coordinate value at reference point CRVAL2 = 0.0 / [deg] Coordinate value at reference point LONPOLE = 180.0 / [deg] Native longitude of celestial pole LATPOLE = 0.0 / [deg] Native latitude of celestial pole RADESYS = 'FK5' / Equatorial coordinate system EQUINOX = 2010.0 / [yr] Equinox of equatorial coordinates Notes ----- To extend this function to frames not defined in astropy.coordinates, you can write your own function which should take a :class:`~astropy.coordinates.baseframe.BaseCoordinateFrame` subclass instance and a projection (given as a string) and should return either a WCS instance, or `None` if the WCS could not be determined. You can register this function temporarily with:: >>> from astropy.wcs.utils import celestial_frame_to_wcs, custom_frame_to_wcs_mappings >>> with custom_frame_to_wcs_mappings(my_function): ... celestial_frame_to_wcs(...) """ for mapping_set in FRAME_WCS_MAPPINGS: for func in mapping_set: wcs = func(frame, projection=projection) if wcs is not None: return wcs raise ValueError("Could not determine WCS corresponding to the specified " "coordinate frame.")
[docs]def proj_plane_pixel_scales(wcs): """ For a WCS returns pixel scales along each axis of the image pixel at the ``CRPIX`` location once it is projected onto the "plane of intermediate world coordinates" as defined in `Greisen & Calabretta 2002, A&A, 395, 1061 <http://adsabs.harvard.edu/abs/2002A%26A...395.1061G>`_. .. note:: This function is concerned **only** about the transformation "image plane"->"projection plane" and **not** about the transformation "celestial sphere"->"projection plane"->"image plane". Therefore, this function ignores distortions arising due to non-linear nature of most projections. .. note:: In order to compute the scales corresponding to celestial axes only, make sure that the input `~astropy.wcs.WCS` object contains celestial axes only, e.g., by passing in the `~astropy.wcs.WCS.celestial` WCS object. Parameters ---------- wcs : `~astropy.wcs.WCS` A world coordinate system object. Returns ------- scale : `~numpy.ndarray` A vector (`~numpy.ndarray`) of projection plane increments corresponding to each pixel side (axis). The units of the returned results are the same as the units of `~astropy.wcs.Wcsprm.cdelt`, `~astropy.wcs.Wcsprm.crval`, and `~astropy.wcs.Wcsprm.cd` for the celestial WCS and can be obtained by inquiring the value of `~astropy.wcs.Wcsprm.cunit` property of the input `~astropy.wcs.WCS` WCS object. See Also -------- astropy.wcs.utils.proj_plane_pixel_area """ return np.sqrt((wcs.pixel_scale_matrix**2).sum(axis=0, dtype=float))
[docs]def proj_plane_pixel_area(wcs): """ For a **celestial** WCS (see `astropy.wcs.WCS.celestial`) returns pixel area of the image pixel at the ``CRPIX`` location once it is projected onto the "plane of intermediate world coordinates" as defined in `Greisen & Calabretta 2002, A&A, 395, 1061 <http://adsabs.harvard.edu/abs/2002A%26A...395.1061G>`_. .. note:: This function is concerned **only** about the transformation "image plane"->"projection plane" and **not** about the transformation "celestial sphere"->"projection plane"->"image plane". Therefore, this function ignores distortions arising due to non-linear nature of most projections. .. note:: In order to compute the area of pixels corresponding to celestial axes only, this function uses the `~astropy.wcs.WCS.celestial` WCS object of the input ``wcs``. This is different from the `~astropy.wcs.utils.proj_plane_pixel_scales` function that computes the scales for the axes of the input WCS itself. Parameters ---------- wcs : `~astropy.wcs.WCS` A world coordinate system object. Returns ------- area : float Area (in the projection plane) of the pixel at ``CRPIX`` location. The units of the returned result are the same as the units of the `~astropy.wcs.Wcsprm.cdelt`, `~astropy.wcs.Wcsprm.crval`, and `~astropy.wcs.Wcsprm.cd` for the celestial WCS and can be obtained by inquiring the value of `~astropy.wcs.Wcsprm.cunit` property of the `~astropy.wcs.WCS.celestial` WCS object. Raises ------ ValueError Pixel area is defined only for 2D pixels. Most likely the `~astropy.wcs.Wcsprm.cd` matrix of the `~astropy.wcs.WCS.celestial` WCS is not a square matrix of second order. Notes ----- Depending on the application, square root of the pixel area can be used to represent a single pixel scale of an equivalent square pixel whose area is equal to the area of a generally non-square pixel. See Also -------- astropy.wcs.utils.proj_plane_pixel_scales """ psm = wcs.celestial.pixel_scale_matrix if psm.shape != (2, 2): raise ValueError("Pixel area is defined only for 2D pixels.") return np.abs(np.linalg.det(psm))
[docs]def is_proj_plane_distorted(wcs, maxerr=1.0e-5): r""" For a WCS returns `False` if square image (detector) pixels stay square when projected onto the "plane of intermediate world coordinates" as defined in `Greisen & Calabretta 2002, A&A, 395, 1061 <http://adsabs.harvard.edu/abs/2002A%26A...395.1061G>`_. It will return `True` if transformation from image (detector) coordinates to the focal plane coordinates is non-orthogonal or if WCS contains non-linear (e.g., SIP) distortions. .. note:: Since this function is concerned **only** about the transformation "image plane"->"focal plane" and **not** about the transformation "celestial sphere"->"focal plane"->"image plane", this function ignores distortions arising due to non-linear nature of most projections. Let's denote by *C* either the original or the reconstructed (from ``PC`` and ``CDELT``) CD matrix. `is_proj_plane_distorted` verifies that the transformation from image (detector) coordinates to the focal plane coordinates is orthogonal using the following check: .. math:: \left \| \frac{C \cdot C^{\mathrm{T}}} {| det(C)|} - I \right \|_{\mathrm{max}} < \epsilon . Parameters ---------- wcs : `~astropy.wcs.WCS` World coordinate system object maxerr : float, optional Accuracy to which the CD matrix, **normalized** such that :math:`|det(CD)|=1`, should be close to being an orthogonal matrix as described in the above equation (see :math:`\epsilon`). Returns ------- distorted : bool Returns `True` if focal (projection) plane is distorted and `False` otherwise. """ cwcs = wcs.celestial return (not _is_cd_orthogonal(cwcs.pixel_scale_matrix, maxerr) or _has_distortion(cwcs))
def _is_cd_orthogonal(cd, maxerr): shape = cd.shape if not (len(shape) == 2 and shape[0] == shape[1]): raise ValueError("CD (or PC) matrix must be a 2D square matrix.") pixarea = np.abs(np.linalg.det(cd)) if (pixarea == 0.0): raise ValueError("CD (or PC) matrix is singular.") # NOTE: Technically, below we should use np.dot(cd, np.conjugate(cd.T)) # However, I am not aware of complex CD/PC matrices... I = np.dot(cd, cd.T) / pixarea cd_unitary_err = np.amax(np.abs(I - np.eye(shape[0]))) return (cd_unitary_err < maxerr)
[docs]def non_celestial_pixel_scales(inwcs): """ Calculate the pixel scale along each axis of a non-celestial WCS, for example one with mixed spectral and spatial axes. Parameters ---------- inwcs : `~astropy.wcs.WCS` The world coordinate system object. Returns ------- scale : `numpy.ndarray` The pixel scale along each axis. """ if inwcs.is_celestial: raise ValueError("WCS is celestial, use celestial_pixel_scales instead") pccd = inwcs.pixel_scale_matrix if np.allclose(np.extract(1-np.eye(*pccd.shape), pccd), 0): return np.abs(np.diagonal(pccd))*u.deg else: raise ValueError("WCS is rotated, cannot determine consistent pixel scales")
def _has_distortion(wcs): """ `True` if contains any SIP or image distortion components. """ return any(getattr(wcs, dist_attr) is not None for dist_attr in ['cpdis1', 'cpdis2', 'det2im1', 'det2im2', 'sip']) # TODO: in future, we should think about how the following two functions can be # integrated better into the WCS class.
[docs]def skycoord_to_pixel(coords, wcs, origin=0, mode='all'): """ Convert a set of SkyCoord coordinates into pixels. Parameters ---------- coords : `~astropy.coordinates.SkyCoord` The coordinates to convert. wcs : `~astropy.wcs.WCS` The WCS transformation to use. origin : int Whether to return 0 or 1-based pixel coordinates. mode : 'all' or 'wcs' Whether to do the transformation including distortions (``'all'``) or only including only the core WCS transformation (``'wcs'``). Returns ------- xp, yp : `numpy.ndarray` The pixel coordinates See Also -------- astropy.coordinates.SkyCoord.from_pixel """ if _has_distortion(wcs) and wcs.naxis != 2: raise ValueError("Can only handle WCS with distortions for 2-dimensional WCS") # Keep only the celestial part of the axes, also re-orders lon/lat wcs = wcs.sub([WCSSUB_LONGITUDE, WCSSUB_LATITUDE]) if wcs.naxis != 2: raise ValueError("WCS should contain celestial component") # Check which frame the WCS uses frame = wcs_to_celestial_frame(wcs) # Check what unit the WCS needs xw_unit = u.Unit(wcs.wcs.cunit[0]) yw_unit = u.Unit(wcs.wcs.cunit[1]) # Convert positions to frame coords = coords.transform_to(frame) # Extract longitude and latitude. We first try and use lon/lat directly, # but if the representation is not spherical or unit spherical this will # fail. We should then force the use of the unit spherical # representation. We don't do that directly to make sure that we preserve # custom lon/lat representations if available. try: lon = coords.data.lon.to(xw_unit) lat = coords.data.lat.to(yw_unit) except AttributeError: lon = coords.spherical.lon.to(xw_unit) lat = coords.spherical.lat.to(yw_unit) # Convert to pixel coordinates if mode == 'all': xp, yp = wcs.all_world2pix(lon.value, lat.value, origin) elif mode == 'wcs': xp, yp = wcs.wcs_world2pix(lon.value, lat.value, origin) else: raise ValueError("mode should be either 'all' or 'wcs'") return xp, yp
[docs]def pixel_to_skycoord(xp, yp, wcs, origin=0, mode='all', cls=None): """ Convert a set of pixel coordinates into a `~astropy.coordinates.SkyCoord` coordinate. Parameters ---------- xp, yp : float or `numpy.ndarray` The coordinates to convert. wcs : `~astropy.wcs.WCS` The WCS transformation to use. origin : int Whether to return 0 or 1-based pixel coordinates. mode : 'all' or 'wcs' Whether to do the transformation including distortions (``'all'``) or only including only the core WCS transformation (``'wcs'``). cls : class or None The class of object to create. Should be a `~astropy.coordinates.SkyCoord` subclass. If None, defaults to `~astropy.coordinates.SkyCoord`. Returns ------- coords : Whatever ``cls`` is (a subclass of `~astropy.coordinates.SkyCoord`) The celestial coordinates See Also -------- astropy.coordinates.SkyCoord.from_pixel """ # Import astropy.coordinates here to avoid circular imports from astropy.coordinates import SkyCoord, UnitSphericalRepresentation # we have to do this instead of actually setting the default to SkyCoord # because importing SkyCoord at the module-level leads to circular # dependencies. if cls is None: cls = SkyCoord if _has_distortion(wcs) and wcs.naxis != 2: raise ValueError("Can only handle WCS with distortions for 2-dimensional WCS") # Keep only the celestial part of the axes, also re-orders lon/lat wcs = wcs.sub([WCSSUB_LONGITUDE, WCSSUB_LATITUDE]) if wcs.naxis != 2: raise ValueError("WCS should contain celestial component") # Check which frame the WCS uses frame = wcs_to_celestial_frame(wcs) # Check what unit the WCS gives lon_unit = u.Unit(wcs.wcs.cunit[0]) lat_unit = u.Unit(wcs.wcs.cunit[1]) # Convert pixel coordinates to celestial coordinates if mode == 'all': lon, lat = wcs.all_pix2world(xp, yp, origin) elif mode == 'wcs': lon, lat = wcs.wcs_pix2world(xp, yp, origin) else: raise ValueError("mode should be either 'all' or 'wcs'") # Add units to longitude/latitude lon = lon * lon_unit lat = lat * lat_unit # Create a SkyCoord-like object data = UnitSphericalRepresentation(lon=lon, lat=lat) coords = cls(frame.realize_frame(data)) return coords
def _unique_with_order_preserved(items): """ Return a list of unique items in the list provided, preserving the order in which they are found. """ new_items = [] for item in items: if item not in new_items: new_items.append(item) return new_items def _pixel_to_world_correlation_matrix(wcs): """ Return a correlation matrix between the pixel coordinates and the high level world coordinates, along with the list of high level world coordinate classes. The shape of the matrix is ``(n_world, n_pix)``, where ``n_world`` is the number of high level world coordinates. """ # We basically want to collapse the world dimensions together that are # combined into the same high-level objects. # Get the following in advance as getting these properties can be expensive all_components = wcs.low_level_wcs.world_axis_object_components all_classes = wcs.low_level_wcs.world_axis_object_classes axis_correlation_matrix = wcs.low_level_wcs.axis_correlation_matrix components = _unique_with_order_preserved([c[0] for c in all_components]) matrix = np.zeros((len(components), wcs.pixel_n_dim), dtype=bool) for iworld in range(wcs.world_n_dim): iworld_unique = components.index(all_components[iworld][0]) matrix[iworld_unique] |= axis_correlation_matrix[iworld] classes = [all_classes[component][0] for component in components] return matrix, classes def _pixel_to_pixel_correlation_matrix(wcs_in, wcs_out): """ Correlation matrix between the input and output pixel coordinates for a pixel -> world -> pixel transformation specified by two WCS instances. The first WCS specified is the one used for the pixel -> world transformation and the second WCS specified is the one used for the world -> pixel transformation. The shape of the matrix is ``(n_pixel_out, n_pixel_in)``. """ matrix1, classes1 = _pixel_to_world_correlation_matrix(wcs_in) matrix2, classes2 = _pixel_to_world_correlation_matrix(wcs_out) if len(classes1) != len(classes2): raise ValueError("The two WCS return a different number of world coordinates") # Check if classes match uniquely unique_match = True mapping = [] for class1 in classes1: matches = classes2.count(class1) if matches == 0: raise ValueError("The world coordinate types of the two WCS do not match") elif matches > 1: unique_match = False break else: mapping.append(classes2.index(class1)) if unique_match: # Classes are unique, so we need to re-order matrix2 along the world # axis using the mapping we found above. matrix2 = matrix2[mapping] elif classes1 != classes2: raise ValueError("World coordinate order doesn't match and automatic matching is ambiguous") matrix = np.matmul(matrix2.T, matrix1) return matrix def _split_matrix(matrix): """ Given an axis correlation matrix from a WCS object, return information about the individual WCS that can be split out. The output is a list of tuples, where each tuple contains a list of pixel dimensions and a list of world dimensions that can be extracted to form a new WCS. For example, in the case of a spectral cube with the first two world coordinates being the celestial coordinates and the third coordinate being an uncorrelated spectral axis, the matrix would look like:: array([[ True, True, False], [ True, True, False], [False, False, True]]) and this function will return ``[([0, 1], [0, 1]), ([2], [2])]``. """ pixel_used = [] split_info = [] for ipix in range(matrix.shape[1]): if ipix in pixel_used: continue pixel_include = np.zeros(matrix.shape[1], dtype=bool) pixel_include[ipix] = True n_pix_prev, n_pix = 0, 1 while n_pix > n_pix_prev: world_include = matrix[:, pixel_include].any(axis=1) pixel_include = matrix[world_include, :].any(axis=0) n_pix_prev, n_pix = n_pix, np.sum(pixel_include) pixel_indices = list(np.nonzero(pixel_include)[0]) world_indices = list(np.nonzero(world_include)[0]) pixel_used.extend(pixel_indices) split_info.append((pixel_indices, world_indices)) return split_info
[docs]def pixel_to_pixel(wcs_in, wcs_out, *inputs): """ Transform pixel coordinates in a dataset with a WCS to pixel coordinates in another dataset with a different WCS. This function is designed to efficiently deal with input pixel arrays that are broadcasted views of smaller arrays, and is compatible with any APE14-compliant WCS. Parameters ---------- wcs_in : `~astropy.wcs.wcsapi.BaseHighLevelWCS` A WCS object for the original dataset which complies with the high-level shared APE 14 WCS API. wcs_out : `~astropy.wcs.wcsapi.BaseHighLevelWCS` A WCS object for the target dataset which complies with the high-level shared APE 14 WCS API. *inputs : Scalars or arrays giving the pixel coordinates to transform. """ # Shortcut for scalars if np.isscalar(inputs[0]): world_outputs = wcs_in.pixel_to_world(*inputs) if not isinstance(world_outputs, (tuple, list)): world_outputs = (world_outputs,) return wcs_out.world_to_pixel(*world_outputs) # Remember original shape original_shape = inputs[0].shape matrix = _pixel_to_pixel_correlation_matrix(wcs_in, wcs_out) split_info = _split_matrix(matrix) outputs = [None] * wcs_out.pixel_n_dim for (pixel_in_indices, pixel_out_indices) in split_info: pixel_inputs = [] for ipix in range(wcs_in.pixel_n_dim): if ipix in pixel_in_indices: pixel_inputs.append(unbroadcast(inputs[ipix])) else: pixel_inputs.append(inputs[ipix].flat[0]) pixel_inputs = np.broadcast_arrays(*pixel_inputs) world_outputs = wcs_in.pixel_to_world(*pixel_inputs) if not isinstance(world_outputs, (tuple, list)): world_outputs = (world_outputs,) pixel_outputs = wcs_out.world_to_pixel(*world_outputs) if wcs_out.pixel_n_dim == 1: pixel_outputs = (pixel_outputs,) for ipix in range(wcs_out.pixel_n_dim): if ipix in pixel_out_indices: outputs[ipix] = np.broadcast_to(pixel_outputs[ipix], original_shape) return outputs[0] if wcs_out.pixel_n_dim == 1 else outputs
[docs]def local_partial_pixel_derivatives(wcs, *pixel, normalize_by_world=False): """ Return a matrix of shape ``(world_n_dim, pixel_n_dim)`` where each entry ``[i, j]`` is the partial derivative d(world_i)/d(pixel_j) at the requested pixel position. Parameters ---------- wcs : `~astropy.wcs.WCS` The WCS transformation to evaluate the derivatives for. *pixel : float The scalar pixel coordinates at which to evaluate the derivatives. normalize_by_world : bool If `True`, the matrix is normalized so that for each world entry the derivatives add up to 1. """ # Find the world coordinates at the requested pixel pixel_ref = np.array(pixel) world_ref = np.array(wcs.pixel_to_world_values(*pixel_ref)) # Set up the derivative matrix derivatives = np.zeros((wcs.world_n_dim, wcs.pixel_n_dim)) for i in range(wcs.pixel_n_dim): pixel_off = pixel_ref.copy() pixel_off[i] += 1 world_off = np.array(wcs.pixel_to_world_values(*pixel_off)) derivatives[:, i] = world_off - world_ref if normalize_by_world: derivatives /= derivatives.sum(axis=0)[:, np.newaxis] return derivatives
def _linear_wcs_fit(params, lon, lat, x, y, w_obj): """ Objective function for fitting linear terms. Parameters ---------- params : array 6 element array. First 4 elements are PC matrix, last 2 are CRPIX. lon, lat: array Sky coordinates. x, y: array Pixel coordinates w_obj: `~astropy.wcs.WCS` WCS object """ cd = params[0:4] crpix = params[4:6] w_obj.wcs.cd = ((cd[0], cd[1]), (cd[2], cd[3])) w_obj.wcs.crpix = crpix lon2, lat2 = w_obj.wcs_pix2world(x, y, 0) resids = np.concatenate((lon-lon2, lat-lat2)) return resids def _sip_fit(params, lon, lat, u, v, w_obj, order, coeff_names): """ Objective function for fitting SIP. Parameters ----------- params : array Fittable parameters. First 4 elements are PC matrix, last 2 are CRPIX. lon, lat: array Sky coordinates. u, v: array Pixel coordinates w_obj: `~astropy.wcs.WCS` WCS object """ from ..modeling.models import SIP, InverseSIP # here to avoid circular import # unpack params crpix = params[0:2] cdx = params[2:6].reshape((2, 2)) a_params = params[6:6+len(coeff_names)] b_params = params[6+len(coeff_names):] # assign to wcs, used for transfomations in this function w_obj.wcs.cd = cdx w_obj.wcs.crpix = crpix a_coeff, b_coeff = {}, {} for i in range(len(coeff_names)): a_coeff['A_' + coeff_names[i]] = a_params[i] b_coeff['B_' + coeff_names[i]] = b_params[i] sip = SIP(crpix=crpix, a_order=order, b_order=order, a_coeff=a_coeff, b_coeff=b_coeff) fuv, guv = sip(u, v) xo, yo = np.dot(cdx, np.array([u+fuv-crpix[0], v+guv-crpix[1]])) # use all pix2world in case `projection` contains distortion table x, y = w_obj.all_world2pix(lon, lat, 0) x, y = np.dot(w_obj.wcs.cd, (x-w_obj.wcs.crpix[0], y-w_obj.wcs.crpix[1])) resids = np.concatenate((x-xo, y-yo)) # to avoid bad restuls if near 360 -> 0 degree crossover resids[resids > 180] = 360 - resids[resids > 180] resids[resids < -180] = 360 + resids[resids < -180] return resids
[docs]def fit_wcs_from_points(xy, world_coords, proj_point='center', projection='TAN', sip_degree=None): """ Given two matching sets of coordinates on detector and sky, compute the WCS. Fits a WCS object to matched set of input detector and sky coordinates. Optionally, a SIP can be fit to account for geometric distortion. Returns an `~astropy.wcs.WCS` object with the best fit parameters for mapping between input pixel and sky coordinates. The projection type (default 'TAN') can passed in as a string, one of the valid three-letter projection codes - or as a WCS object with projection keywords already set. Note that if an input WCS has any non-polynomial distortion, this will be applied and reflected in the fit terms and coefficients. Passing in a WCS object in this way essentially allows it to be refit based on the matched input coordinates and projection point, but take care when using this option as non-projection related keywords in the input might cause unexpected behavior. Notes ------ - The fiducial point for the spherical projection can be set to 'center' to use the mean position of input sky coordinates, or as an `~astropy.coordinates.SkyCoord` object. - Units in all output WCS objects will always be in degrees. - If the coordinate frame differs between `~astropy.coordinates.SkyCoord` objects passed in for ``world_coords`` and ``proj_point``, the frame for ``world_coords`` will override as the frame for the output WCS. - If a WCS object is passed in to ``projection`` the CD/PC matrix will be used as an initial guess for the fit. If this is known to be significantly off and may throw off the fit, set to the identity matrix (for example, by doing wcs.wcs.pc = [(1., 0.,), (0., 1.)]) Parameters ---------- xy : tuple of two `numpy.ndarray` x & y pixel coordinates. world_coords : `~astropy.coordinates.SkyCoord` Skycoord object with world coordinates. proj_point : 'center' or ~astropy.coordinates.SkyCoord` Defaults to 'center', in which the geometric center of input world coordinates will be used as the projection point. To specify an exact point for the projection, a Skycoord object with a coordinate pair can be passed in. For consistency, the units and frame of these coordinates will be transformed to match ``world_coords`` if they don't. projection : str or `~astropy.wcs.WCS` Three letter projection code, of any of standard projections defined in the FITS WCS standard. Optionally, a WCS object with projection keywords set may be passed in. sip_degree : None or int If set to a non-zero integer value, will fit SIP of degree ``sip_degree`` to model geometric distortion. Defaults to None, meaning no distortion corrections will be fit. Returns ------- wcs : `~astropy.wcs.WCS` The best-fit WCS to the points given. """ from astropy.coordinates import SkyCoord # here to avoid circular import import astropy.units as u from .wcs import Sip from scipy.optimize import least_squares try: xp, yp = xy lon, lat = world_coords.data.lon.deg, world_coords.data.lat.deg except AttributeError: unit_sph = world_coords.unit_spherical lon, lat = unit_sph.lon.deg, unit_sph.lat.deg # verify input if (proj_point != 'center') and (type(proj_point) != type(world_coords)): raise ValueError("proj_point must be set to 'center', or an" + "`~astropy.coordinates.SkyCoord` object with " + "a pair of points.") if proj_point != 'center': assert proj_point.size == 1 proj_codes = [ 'AZP', 'SZP', 'TAN', 'STG', 'SIN', 'ARC', 'ZEA', 'AIR', 'CYP', 'CEA', 'CAR', 'MER', 'SFL', 'PAR', 'MOL', 'AIT', 'COP', 'COE', 'COD', 'COO', 'BON', 'PCO', 'TSC', 'CSC', 'QSC', 'HPX', 'XPH' ] if type(projection) == str: if projection not in proj_codes: raise ValueError("Must specify valid projection code from list of " + "supported types: ", ', '.join(proj_codes)) # empty wcs to fill in with fit values wcs = celestial_frame_to_wcs(frame=world_coords.frame, projection=projection) else: #if projection is not string, should be wcs object. use as template. wcs = copy.deepcopy(projection) wcs.cdelt = (1., 1.) # make sure cdelt is 1 wcs.sip = None # Change PC to CD, since cdelt will be set to 1 if wcs.wcs.has_pc(): wcs.wcs.cd = wcs.wcs.pc wcs.wcs.__delattr__('pc') if (type(sip_degree) != type(None)) and (type(sip_degree) != int): raise ValueError("sip_degree must be None, or integer.") # set pixel_shape to span of input points wcs.pixel_shape = (xp.max()-xp.min(), yp.max()-yp.min()) # determine CRVAL from input close = lambda l, p: p[np.argmin(np.abs(l))] if str(proj_point) == 'center': # use center of input points sc1 = SkyCoord(lon.min()*u.deg, lat.max()*u.deg) sc2 = SkyCoord(lon.max()*u.deg, lat.min()*u.deg) pa = sc1.position_angle(sc2) sep = sc1.separation(sc2) midpoint_sc = sc1.directional_offset_by(pa, sep/2) wcs.wcs.crval = ((midpoint_sc.data.lon.deg, midpoint_sc.data.lat.deg)) wcs.wcs.crpix = ((xp.max()+xp.min())/2., (yp.max()+yp.min())/2.) elif proj_point is not None: # convert units, initial guess for crpix proj_point.transform_to(world_coords) wcs.wcs.crval = (proj_point.data.lon.deg, proj_point.data.lat.deg) wcs.wcs.crpix = (close(lon-wcs.wcs.crval[0], xp), close(lon-wcs.wcs.crval[1], yp)) # fit linear terms, assign to wcs # use (1, 0, 0, 1) as initial guess, in case input wcs was passed in # and cd terms are way off. p0 = np.concatenate([wcs.wcs.cd.flatten(), wcs.wcs.crpix.flatten()]) fit = least_squares(_linear_wcs_fit, p0, args=(lon, lat, xp, yp, wcs)) wcs.wcs.crpix = np.array(fit.x[4:6]) wcs.wcs.cd = np.array(fit.x[0:4].reshape((2, 2))) # fit SIP, if specified. Only fit forward coefficients if sip_degree: degree = sip_degree if '-SIP' not in wcs.wcs.ctype[0]: wcs.wcs.ctype = [x + '-SIP' for x in wcs.wcs.ctype] coef_names = ['{0}_{1}'.format(i, j) for i in range(degree+1) for j in range(degree+1) if (i+j) < (degree+1) and (i+j) > 1] p0 = np.concatenate((np.array(wcs.wcs.crpix), wcs.wcs.cd.flatten(), np.zeros(2*len(coef_names)))) fit = least_squares(_sip_fit, p0, args=(lon, lat, xp, yp, wcs, degree, coef_names)) coef_fit = (list(fit.x[6:6+len(coef_names)]), list(fit.x[6+len(coef_names):])) # put fit values in wcs wcs.wcs.cd = fit.x[2:6].reshape((2, 2)) wcs.wcs.crpix = fit.x[0:2] a_vals = np.zeros((degree+1, degree+1)) b_vals = np.zeros((degree+1, degree+1)) for coef_name in coef_names: a_vals[int(coef_name[0])][int(coef_name[2])] = coef_fit[0].pop(0) b_vals[int(coef_name[0])][int(coef_name[2])] = coef_fit[1].pop(0) wcs.sip = Sip(a_vals, b_vals, np.zeros((degree+1, degree+1)), np.zeros((degree+1, degree+1)), wcs.wcs.crpix) return wcs