Source code for jwst.skymatch.skyimage

"""
The ``skyimage`` module contains algorithms that are used by
``skymatch`` to manage all of the information for footprints (image outlines)
on the sky as well as perform useful operations on these outlines such as
computing intersections and statistics in the overlap regions.

:Authors: Mihai Cara (contact: help@stsci.edu)


"""

# STDLIB
import numpy as np

# THIRD-PARTY
from spherical_geometry.polygon import SphericalPolygon

# LOCAL
from . skystatistics import SkyStats
from . import region


__all__ = ['SkyImage', 'SkyGroup']


[docs]class SkyImage: """ Container that holds information about properties of a *single* image such as: * image data; * WCS of the chip image; * bounding spherical polygon; * id; * pixel area; * sky background value; * sky statistics parameters; * mask associated image data indicating "good" (1) data. """ def __init__(self, image, wcs_fwd, wcs_inv, pix_area=1.0, convf=1.0, mask=None, id=None, skystat=None, stepsize=None, meta=None): """ Initializes the SkyImage object. Parameters ---------- image : numpy.ndarray A 2D array of image data. wcs_fwd : function "forward" pixel-to-world transformation function. wcs_inv : function "inverse" world-to-pixel transformation function. pix_area : float, optional Average pixel's sky area. convf : float, optional Conversion factor that when multiplied to `image` data converts the data to "uniform" (across multiple images) surface brightness units. .. note:: The functionality to support this conversion is not yet implemented and at this moment `convf` is ignored. mask : numpy.ndarray A 2D array that indicates what pixels in the input `image` should be used for sky computations (``1``) and which pixels should **not** be used for sky computations (``0``). id : anything The value of this parameter is simple stored within the `SkyImage` object. While it can be of any type, it is prefereble that `id` be of a type with nice string representation. skystat : callable, None, optional A callable object that takes a either a 2D image (2D `numpy.ndarray`) or a list of pixel values (a Nx1 array) and returns a tuple of two values: some statistics (e.g., mean, median, etc.) and number of pixels/values from the input image used in computing that statistics. When `skystat` is not set, `SkyImage` will use :py:class:`~jwst_pipeline.skymatch.skystatistics.SkyStats` object to perform sky statistics on image data. stepsize : int, None, optional Spacing between vertices of the image's bounding polygon. Default value of `None` creates bounding polygons with four vertices corresponding to the corners of the image. meta : dict, None, optional A dictionary of various items to be stored within the `SkyImage` object. """ self.image = image self.convf = convf self.meta = meta self._id = id self._pix_area = pix_area # WCS self.wcs_fwd = wcs_fwd self.wcs_inv = wcs_inv # initial sky value: self._sky = 0.0 self._sky_is_valid = False # check that mask has the same shape as image: if mask is None: self.mask = None else: if image is None: raise ValueError("'mask' must be None when 'image' is None") self.mask = np.asanyarray(mask, dtype=bool) if self.mask.shape != image.shape: raise ValueError("'mask' must have the same shape as 'image'.") # create spherical polygon bounding the image if image is None or wcs_fwd is None or wcs_inv is None: self._radec = [(np.array([]), np.array([]))] self._polygon = SphericalPolygon([]) self._poly_area = 0.0 else: self.calc_bounding_polygon(stepsize) # set sky statistics function (NOTE: it must return statistics and # the number of pixels used after clipping) if skystat is None: self.set_builtin_skystat() else: self.skystat = skystat @property def id(self): """ Set or get `SkyImage`'s `id`. While `id` can be of any type, it is prefereble that `id` be of a type with nice string representation. """ return self._id @id.setter def id(self, id): self._id = id @property def pix_area(self): """ Set or get mean pixel area. """ return self._pix_area @pix_area.setter def pix_area(self, pix_area): self._pix_area = pix_area @property def poly_area(self): """ Get bounding polygon area in srad units. """ return self._poly_area @property def sky(self): """ Sky background value. See `calc_sky` for more details. """ return self._sky @sky.setter def sky(self, sky): self._sky = sky @property def is_sky_valid(self): """ Indicates whether sky value was successfully computed. Must be set externally. """ return self._sky_is_valid @is_sky_valid.setter def is_sky_valid(self, valid): self._sky_is_valid = valid @property def radec(self): """ Get RA and DEC of the verteces of the bounding polygon as a `~numpy.ndarray` of shape (N, 2) where N is the number of verteces + 1. """ return self._radec @property def polygon(self): """ Get image's bounding polygon. """ return self._polygon
[docs] def intersection(self, skyimage): """ Compute intersection of this `SkyImage` object and another `SkyImage`, `SkyGroup`, or :py:class:`~spherical_geometry.polygon.SphericalPolygon` object. Parameters ---------- skyimage : SkyImage, SkyGroup, SphericalPolygon Another object that should be intersected with this `SkyImage`. Returns ------- polygon : SphericalPolygon A :py:class:`~spherical_geometry.polygon.SphericalPolygon` that is the intersection of this `SkyImage` and `skyimage`. """ if isinstance(skyimage, (SkyImage, SkyGroup)): return self._polygon.intersection(skyimage.polygon) else: return self._polygon.intersection(skyimage)
[docs] def calc_bounding_polygon(self, stepsize=None): """ Compute image's bounding polygon. Parameters ---------- stepsize : int, None, optional Indicates the maximum separation between two adjacent vertices of the bounding polygon along each side of the image. Corners of the image are included automatically. If `stepsize` is `None`, bounding polygon will contain only vertices of the image. """ ny, nx = self.image.shape if stepsize is None: nintx = 2 ninty = 2 else: nintx = max(2, int(np.ceil((nx + 1.0) / stepsize))) ninty = max(2, int(np.ceil((ny + 1.0) / stepsize))) xs = np.linspace(-0.5, nx - 0.5, nintx, dtype=float) ys = np.linspace(-0.5, ny - 0.5, ninty, dtype=float)[1:-1] nptx = xs.size npty = ys.size npts = 2 * (nptx + npty) borderx = np.empty((npts + 1,), dtype=float) bordery = np.empty((npts + 1,), dtype=float) # "bottom" points: borderx[:nptx] = xs bordery[:nptx] = -0.5 # "right" sl = np.s_[nptx:nptx + npty] borderx[sl] = nx - 0.5 bordery[sl] = ys # "top" sl = np.s_[nptx + npty:2 * nptx + npty] borderx[sl] = xs[::-1] bordery[sl] = ny - 0.5 # "left" sl = np.s_[2 * nptx + npty:-1] borderx[sl] = -0.5 bordery[sl] = ys[::-1] # close polygon: borderx[-1] = borderx[0] bordery[-1] = bordery[0] ra, dec = self.wcs_fwd(borderx, bordery, with_bounding_box=False) # TODO: for strange reasons, occasionally ra[0] != ra[-1] and/or # dec[0] != dec[-1] (even though we close the polygon in the # previous two lines). Then SphericalPolygon fails because # points are not closed. Threfore we force it to be closed: ra[-1] = ra[0] dec[-1] = dec[0] self._radec = [(ra, dec)] self._polygon = SphericalPolygon.from_radec(ra, dec) self._poly_area = np.fabs(self._polygon.area())
@property def skystat(self): """ Stores/retrieves a callable object that takes a either a 2D image (2D `numpy.ndarray`) or a list of pixel values (a Nx1 array) and returns a tuple of two values: some statistics (e.g., mean, median, etc.) and number of pixels/values from the input image used in computing that statistics. When `skystat` is not set, `SkyImage` will use :py:class:`~jwst_pipeline.skymatch.skystatistics.SkyStats` object to perform sky statistics on image data. """ return self._skystat @skystat.setter def skystat(self, skystat): self._skystat = skystat
[docs] def set_builtin_skystat(self, skystat='median', lower=None, upper=None, nclip=5, lsigma=4.0, usigma=4.0, binwidth=0.1): """ Replace already set `skystat` with a "built-in" version of a statistics callable object used to measure sky background. See :py:class:`~jwst_pipeline.skymatch.skystatistics.SkyStats` for the parameter description. """ self._skystat = SkyStats( skystat=skystat, lower=lower, upper=upper, nclip=nclip, lsig=lsigma, usig=usigma, binwidth=binwidth )
# TODO: due to a bug in the sphere package, see # https://github.com/spacetelescope/sphere/issues/74 # intersections with polygons formed as union does not work. # For this reason I re-implement 'calc_sky' below with # a workaround for the bug. # The original implementation (now called ``_calc_sky_orig`` # should replace current 'calc_sky' once the bug is fixed. #
[docs] def calc_sky(self, overlap=None, delta=True): """ Compute sky background value. Parameters ---------- overlap : SkyImage, SkyGroup, SphericalPolygon, list of tuples, \ None, optional Another `SkyImage`, `SkyGroup`, :py:class:`spherical_geometry.polygons.SphericalPolygon`, or a list of tuples of (RA, DEC) of vertices of a spherical polygon. This parameter is used to indicate that sky statistics should computed only in the region of intersection of *this* image with the polygon indicated by `overlap`. When `overlap` is `None`, sky statistics will be computed over the entire image. delta : bool, optional Should this function return absolute sky value or the difference between the computed value and the value of the sky stored in the `sky` property. Returns ------- skyval : float, None Computed sky value (absolute or relative to the `sky` attribute). If there are no valid data to perform this computations (e.g., because this image does not overlap with the image indicated by `overlap`), `skyval` will be set to `None`. npix : int Number of pixels used to compute sky statistics. polyarea : float Area (in srad) of the polygon that bounds data used to compute sky statistics. """ if overlap is None: if self.mask is None: data = self.image else: data = self.image[self.mask] polyarea = self.poly_area else: fill_mask = np.zeros(self.image.shape, dtype=bool) if isinstance(overlap, SkyImage): intersection = self.intersection(overlap) polyarea = np.fabs(intersection.area()) radec = list(intersection.to_radec()) elif isinstance(overlap, SkyGroup): radec = [] polyarea = 0.0 for im in overlap: intersection = self.intersection(im) polyarea1 = np.fabs(intersection.area()) if polyarea1 == 0.0: continue polyarea += polyarea1 radec += list(intersection.to_radec()) elif isinstance(overlap, SphericalPolygon): radec = [] polyarea = 0.0 for p in overlap._polygons: intersection = self.intersection(SphericalPolygon([p])) polyarea1 = np.fabs(intersection.area()) if polyarea1 == 0.0: continue polyarea += polyarea1 radec += list(intersection.to_radec()) else: # assume a list of (ra, dec) tuples: radec = [] polyarea = 0.0 for r, d in overlap: poly = SphericalPolygon.from_radec(r, d) polyarea1 = np.fabs(poly.area()) if polyarea1 == 0.0 or len(r) < 4: continue polyarea += polyarea1 radec.append(self.intersection(poly).to_radec()) if polyarea == 0.0: return (None, 0, 0.0) for ra, dec in radec: if len(ra) < 4: continue # set pixels in 'fill_mask' that are inside a polygon to True: x, y = self.wcs_inv(ra, dec) poly_vert = list(zip(*[x, y])) polygon = region.Polygon(True, poly_vert) fill_mask = polygon.scan(fill_mask) if self.mask is not None: fill_mask &= self.mask data = self.image[fill_mask] if data.size < 1: return (None, 0, 0.0) # Calculate sky try: skyval, npix = self._skystat(data) except ValueError: return (None, 0, 0.0) if not np.isfinite(skyval): return (None, 0, 0.0) if delta: skyval -= self._sky return skyval, npix, polyarea
def _calc_sky_orig(self, overlap=None, delta=True): """ Compute sky background value. Parameters ---------- overlap : SkyImage, SkyGroup, SphericalPolygon, list of tuples, \ None, optional Another `SkyImage`, `SkyGroup`, :py:class:`spherical_geometry.polygons.SphericalPolygon`, or a list of tuples of (RA, DEC) of vertices of a spherical polygon. This parameter is used to indicate that sky statistics should computed only in the region of intersection of *this* image with the polygon indicated by `overlap`. When `overlap` is `None`, sky statistics will be computed over the entire image. delta : bool, optional Should this function return absolute sky value or the difference between the computed value and the value of the sky stored in the `sky` property. Returns ------- skyval : float, None Computed sky value (absolute or relative to the `sky` attribute). If there are no valid data to perform this computations (e.g., because this image does not overlap with the image indicated by `overlap`), `skyval` will be set to `None`. npix : int Number of pixels used to compute sky statistics. polyarea : float Area (in srad) of the polygon that bounds data used to compute sky statistics. """ if overlap is None: if self.mask is None: data = self.image else: data = self.image[self.mask] polyarea = self.poly_area else: fill_mask = np.zeros(self.image.shape, dtype=bool) if isinstance(overlap, (SkyImage, SkyGroup, SphericalPolygon)): intersection = self.intersection(overlap) polyarea = np.fabs(intersection.area()) radec = intersection.to_radec() else: # assume a list of (ra, dec) tuples: radec = [] polyarea = 0.0 for r, d in overlap: poly = SphericalPolygon.from_radec(r, d) polyarea1 = np.fabs(poly.area()) if polyarea1 == 0.0 or len(r) < 4: continue polyarea += polyarea1 radec.append(self.intersection(poly).to_radec()) if polyarea == 0.0: return (None, 0, 0.0) for ra, dec in radec: if len(ra) < 4: continue # set pixels in 'fill_mask' that are inside a polygon to True: x, y = self.wcs_inv(ra, dec) poly_vert = list(zip(*[x, y])) polygon = region.Polygon(True, poly_vert) fill_mask = polygon.scan(fill_mask) if self.mask is not None: fill_mask &= self.mask data = self.image[fill_mask] if data.size < 1: return (None, 0, 0.0) # Calculate sky try: skyval, npix = self._skystat(data) except ValueError: return (None, 0, 0.0) if delta: skyval -= self._sky return skyval, npix, polyarea
[docs] def copy(self): """ Return a shallow copy of the `SkyImage` object. """ si = SkyImage( image=None, wcs_fwd=self.wcs_fwd, wcs_inv=self.wcs_inv, pix_area=self.pix_area, convf=self.convf, mask=None, id=self.id, stepsize=None, meta=self.meta ) si.image = self.image si.mask = self.mask si._radec = self._radec si._polygon = self._polygon si._poly_area = self._poly_area si.sky = self.sky return si
[docs]class SkyGroup: """ Holds multiple :py:class:`SkyImage` objects whose sky background values must be adjusted together. `SkyGroup` provides methods for obtaining bounding polygon of the group of :py:class:`SkyImage` objects and to compute sky value of the group. """ def __init__(self, images, id=None, sky=0.0): if isinstance(images, SkyImage): self._images = [images] elif hasattr(images, '__iter__'): self._images = [] for im in images: if not isinstance(im, SkyImage): raise TypeError("Each element of the 'images' parameter " "must be an 'SkyImage' object.") self._images.append(im) else: raise TypeError("Parameter 'images' must be either a single " "'SkyImage' object or a list of 'SkyImage' objects") self._id = id self._update_bounding_polygon() self._sky = sky for im in self._images: im.sky += sky @property def id(self): """ Set or get `SkyImage`'s `id`. While `id` can be of any type, it is prefereble that `id` be of a type with nice string representation. """ return self._id @id.setter def id(self, id): self._id = id @property def sky(self): """ Sky background value. See `calc_sky` for more details. """ return self._sky @sky.setter def sky(self, sky): delta_sky = sky - self._sky self._sky = sky for im in self._images: im.sky += delta_sky @property def radec(self): """ Get RA and DEC of the verteces of the bounding polygon as a `~numpy.ndarray` of shape (N, 2) where N is the number of verteces + 1. """ return self._radec @property def polygon(self): """ Get image's bounding polygon. """ return self._polygon
[docs] def intersection(self, skyimage): """ Compute intersection of this `SkyImage` object and another `SkyImage`, `SkyGroup`, or :py:class:`~spherical_geometry.polygon.SphericalPolygon` object. Parameters ---------- skyimage : SkyImage, SkyGroup, SphericalPolygon Another object that should be intersected with this `SkyImage`. Returns ------- intersect_poly : SphericalPolygon A :py:class:`~spherical_geometry.polygon.SphericalPolygon` that is the intersection of this `SkyImage` and `skyimage`. """ if isinstance(skyimage, (SkyImage, SkyGroup)): other = skyimage.polygon else: other = skyimage pts1 = np.sort(list(self._polygon.points)[0], axis=0) pts2 = np.sort(list(other.points)[0], axis=0) if np.allclose(pts1, pts2, rtol=0, atol=5e-9): intersect_poly = self._polygon.copy() else: intersect_poly = self._polygon.intersection(other) return intersect_poly
def _update_bounding_polygon(self): polygons = [im.polygon for im in self._images] if len(polygons) == 0: self._polygon = SphericalPolygon([]) self._radec = [] else: self._polygon = SphericalPolygon.multi_union(polygons) self._radec = list(self._polygon.to_radec()) def __len__(self): return len(self._images) def __getitem__(self, idx): return self._images[idx] def __setitem__(self, idx, value): if not isinstance(value, SkyImage): raise TypeError("Item must be of 'SkyImage' type") value.sky += self._sky self._images[idx] = value self._update_bounding_polygon() def __delitem__(self, idx): del self._images[idx] if len(self._images) == 0: self._sky = 0.0 self._id = None self._update_bounding_polygon() def __iter__(self): for image in self._images: yield image
[docs] def insert(self, idx, value): """Inserts a `SkyImage` into the group. """ if not isinstance(value, SkyImage): raise TypeError("Item must be of 'SkyImage' type") value.sky += self._sky self._images.insert(idx, value) self._update_bounding_polygon()
[docs] def append(self, value): """Appends a `SkyImage` to the group. """ if not isinstance(value, SkyImage): raise TypeError("Item must be of 'SkyImage' type") value.sky += self._sky self._images.append(value) self._update_bounding_polygon()
[docs] def calc_sky(self, overlap=None, delta=True): """ Compute sky background value. Parameters ---------- overlap : SkyImage, SkyGroup, SphericalPolygon, list of tuples, \ None, optional Another `SkyImage`, `SkyGroup`, :py:class:`spherical_geometry.polygons.SphericalPolygon`, or a list of tuples of (RA, DEC) of vertices of a spherical polygon. This parameter is used to indicate that sky statistics should computed only in the region of intersection of *this* image with the polygon indicated by `overlap`. When `overlap` is `None`, sky statistics will be computed over the entire image. delta : bool, optional Should this function return absolute sky value or the difference between the computed value and the value of the sky stored in the `sky` property. Returns ------- skyval : float, None Computed sky value (absolute or relative to the `sky` attribute). If there are no valid data to perform this computations (e.g., because this image does not overlap with the image indicated by `overlap`), `skyval` will be set to `None`. npix : int Number of pixels used to compute sky statistics. polyarea : float Area (in srad) of the polygon that bounds data used to compute sky statistics. """ if len(self._images) == 0: return (None, 0, 0.0) wght = 0 area = 0.0 if overlap is None: # compute minimum sky across all images in the group: wsky = None for image in self._images: # make sure all images have the same background: image.background = self._sky sky, npix, imarea = image.calc_sky(overlap=None, delta=delta) if sky is None: continue if wsky is None or wsky > sky: wsky = sky wght = npix area = imarea return (wsky, wght, area) # compute weighted sky in various overlaps: wsky = 0.0 for image in self._images: # make sure all images have the same background: image.background = self._sky sky, npix, area1 = image.calc_sky(overlap=overlap, delta=delta) area += area1 if sky is not None and npix > 0: pix_area = npix * image.pix_area wsky += sky * pix_area wght += pix_area if wght == 0.0 or area == 0.0: return (None, wght, area) else: return (wsky / wght, wght, area)