path: root/lib/skyline.py

# -*- coding: utf-8 -*-

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"""
Manage outlines on the sky.

This module provides support for working with footprints
on the sky. Primary use case would use the following
generalized steps::

    #. Initialize `SkyLine` objects for each input image.
       This object would be the union of all the input
       image's individual chips WCS footprints.

    #. Determine overlap between all images. The
       determination would employ a recursive operation
       to return the extended list of all overlap values
       computed as [img1 vs [img2,img3,...,imgN],img2 vs
       [img3,...,imgN],...]

    #. Select the pair with the largest overlap, or the
       pair which produces the largest overlap with the
       first input image. This defines the initial
       reference `SkyLine` object.

    #. Perform some operation on the 2 images: for example,
       match sky in intersecting regions, or aligning
       second image with the first (reference) image.

    #. Update the second image, either apply the sky value
       or correct the WCS, then generate a new `SkyLine`
       object for that image.

    #. Create a new reference `SkyLine` object as the union
       of the initial reference object and the newly
       updated `SkyLine` object.

    #. Repeat Steps 2-6 for all remaining input images.

This process will work reasonably fast as most operations
are performed using the `SkyLine` objects and WCS information
solely, not image data itself.

.. note:: Requires Python 2.7 or later.

:Authors: Pey Lian Lim, Warren Hack, Michael Droettboom

:Organization: Space Telescope Science Institute

:History:
    * 2012-05-25 PLL started coding. Original class
      structure by WJH. Parent class by MD.

"""
from __future__ import division, print_function, absolute_import

# STDLIB
from copy import copy, deepcopy

# THIRD-PARTY
import pyfits
from stwcs import wcsutil

# LOCAL
from .polygon import SphericalPolygon

__all__ = ['SkyLine']
__version__ = '0.2a'
__vdate__ = '12-Jun-2012'

class SkyLineMember(object):

    def __init__(self, fname, ext):
        """
        Container for `SkyLine` members.

        Given FITS image and extension, will store its
        `SphericalPolygon` instance from WCS under
        `polygon`.

        Parameters
        ----------
        self: obj
            SkyLineMember instance.

        fname: str
            FITS image.

        ext: int
            Image extension.

        """
        self._fname = fname
        self._ext = ext
        self._polygon = SphericalPolygon.from_wcs(
            wcsutil.HSTWCS(fname, ext=ext))

    def __repr__(self):
        return 'SkyLineMember(%r, %r, %r)' % (self.fname, self.ext,
                                              self.polygon)

    @property
    def fname(self):
        return self._fname

    @property
    def ext(self):
        return self._ext

    @property
    def polygon(self):
        return self._polygon

class SkyLine(object):

    def __init__(self, fname, extname='SCI'):
        """
        Initialize `SkyLine` object instance.

        Parameters
        ----------
        self: obj
            `SkyLine` instance.

        fname: str
            FITS image. `None` to create empty `SkyLine`.

        extname: str
            EXTNAME to use. SCI is recommended for normal
            HST images. PRIMARY if image is single ext.

        """
        # Convert SCI data to SkyLineMember
        if fname is not None:
            with pyfits.open(fname) as pf:
                self.members = [SkyLineMember(fname, i)
                                for i,ext in enumerate(pf)
                                if extname in ext.name.upper()]
        else:
            self.members = []

        # Put mosaic of all the chips in SkyLine
        if len(self.members) > 0:
            self.polygon = SphericalPolygon.multi_union([m.polygon for m in self.members])
        else:
            self.polygon = SphericalPolygon([])

    def __getattr__(self, what):
        return getattr(self.polygon, what)

    def __copy__(self):
        return deepcopy(self)
    
    def __repr__(self):
        return 'SkyLine(%r, %r)' % (self.polygon, self.members)

    @property
    def polygon(self):
        """`SphericalPolygon` portion of `SkyLine`."""
        return self._polygon

    @polygon.setter
    def polygon(self, value):
        """Deep copy a `SphericalPolygon`."""
        assert isinstance(value, SphericalPolygon)
        self._polygon = copy(value)

    @property
    def members(self):
        """List of `SkyLineMember` objects."""
        return self._members

    @members.setter
    def members(self, values):
        """Make sure `SkyLineMember` entries are unique."""
        self._members = []

        # Not using set to preserve order
        for v in values:
            # Report corrupted members list instead of skipping
            assert isinstance(v, SkyLineMember)

            if v not in self._members:
                self._members.append(v)

    def _find_members(self, given_members):
        """
        Find `SkyLineMember` in *given_members* that is in
        *self*. This is used for intersection.

        Parameters
        ----------
        self: obj
            `SkyLine` instance.

        given_members: list
            List of `SkyLineMember` to consider.

        Returns
        -------
        new_members: list
            List of `SkyLineMember` belonging to *self*.

        """
        if len(self.points) > 0:
            out_mem = [m for m in given_members if
                       self.intersects_poly(m.polygon)]
        else:
            out_mem = []
        return out_mem

    def add_image(self, other):
        """
        Return a new `SkyLine` that is the union of *self*
        and *other*.

        .. warning:: `SkyLine.union` only returns `polygon`
            without `members`.

        Examples
        --------
        >>> s1 = SkyLine('image1.fits')
        >>> s2 = SkyLine('image2.fits')
        >>> s3 = s1.add_image(s2)

        """
        newcls = self.__class__(None)
        newcls.polygon = self.union(other)
        newcls.members = self.members + other.members
        return newcls

    def find_intersection(self, other):
        """
        Return a new `SkyLine` that is the intersection of
        *self* and *other*.

        .. warning:: `SkyLine.intersection` only returns
            `polygon` without `members`.

        Examples
        --------
        >>> s1 = SkyLine('image1.fits')
        >>> s2 = SkyLine('image2.fits')
        >>> s3 = s1.find_intersection(s2)

        """
        newcls = self.__class__(None)
        newcls.polygon = self.intersection(other)
        newcls.members = newcls._find_members(self.members + other.members)
        return newcls