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

u'''(INTERNAL) Ellipsoidal base classes C{CartesianEllipsoidalBase} and
C{LatLonEllipsoidalBase}.

Pure Python implementation of geodesy tools for ellipsoidal earth models,
transcribed in part from JavaScript originals by I{(C) Chris Veness 2005-2016}
and published under the same MIT Licence**, see for example U{latlon-ellipsoidal
<https://www.Movable-Type.co.UK/scripts/geodesy/docs/latlon-ellipsoidal.js.html>}.

@newfield example: Example, Examples
'''

from pygeodesy.basics import EPS, PI, property_doc_, property_RO, \
                            _xinstanceof, _xkwds
from pygeodesy.cartesianBase import CartesianBase
from pygeodesy.datum import Datum, Datums
from pygeodesy.ecef import EcefVeness
from pygeodesy.errors import _AssertionError, _incompatible, IntersectionError, \
                             _IsnotError, _ValueError, _xellipsoidal
from pygeodesy.fmath import favg, fsum_
from pygeodesy.interns import _COMMA_, _datum_, _ellipsoidal_, \
                              _exceed_PI_radians_, _Missing, _N_, \
                              _near_concentric_, NN, _no_convergence_, \
                              _no_conversion_, _too_distant_fmt_  # PYCHOK used!
from pygeodesy.latlonBase import LatLonBase
from pygeodesy.lazily import _ALL_DOCS
from pygeodesy.named import LatLon4Tuple, Vector3Tuple, _xnamed
from pygeodesy.trf import _2epoch, RefFrame, TRFError, _reframeTransforms
from pygeodesy.units import Radius_

__all__ = ()
__version__ = '20.08.02'

_TOL_M = 1e-3  # 1 millimeter, in .ellipsoidKarney, -Vincenty
_TRIPS = 16    # intersect2 interations, 4 sufficient


class CartesianEllipsoidalBase(CartesianBase):
    '''(INTERNAL) Base class for ellipsoidal C{Cartesian}s.
    '''
    _datum = Datums.WGS84  #: (INTERNAL) L{Datum}.
    _Ecef  = EcefVeness    #: (INTERNAL) Preferred C{Ecef...} class, backward compatible.

    def convertRefFrame(self, reframe2, reframe, epoch=None):
        '''Convert this cartesian point from one to an other reference frame.

           @arg reframe2: Reference frame to convert I{to} (L{RefFrame}).
           @arg reframe: Reference frame to convert I{from} (L{RefFrame}).
           @kwarg epoch: Optional epoch to observe for B{C{reframe}}, a
                         fractional calendar year (C{scalar}).

           @return: The converted point (C{Cartesian}) or this point if
                    conversion is C{nil}.

           @raise TRFError: No conversion available from B{C{reframe}}
                            to B{C{reframe2}}.

           @raise TypeError: B{C{reframe2}} or B{C{reframe}} not a
                             L{RefFrame} or B{C{epoch}} not C{scalar}.
        '''
        _xinstanceof(RefFrame, reframe2=reframe2, reframe=reframe)

        c, d = self, self.datum
        for t in _reframeTransforms(reframe2, reframe, reframe.epoch if
                                    epoch is None else _2epoch(epoch)):
            c = c._applyHelmert(t, False, datum=d)
        return c


class LatLonEllipsoidalBase(LatLonBase):
    '''(INTERNAL) Base class for ellipsoidal C{LatLon}s.
    '''
    _convergence  = None  #: (INTERNAL) UTM/UPS meridian convergence (C{degrees}).
    _datum        = Datums.WGS84  #: (INTERNAL) Datum (L{Datum}).
    _elevation2   = ()    #: (INTERNAL) Cached C{elevation2} result.
    _epoch        = None  #: (INTERNAL) overriding .reframe.epoch (C{float}).
    _etm          = None  #: (INTERNAL) Cached toEtm (L{Etm}).
    _geoidHeight2 = ()    #: (INTERNAL) Cached C{geoidHeight2} result.
    _lcc          = None  #: (INTERNAL) Cached toLcc (C{Lcc}).
    _osgr         = None  #: (INTERNAL) Cached toOsgr (C{Osgr}).
    _reframe      = None  #: (INTERNAL) reference frame (L{RefFrame}).
    _scale        = None  #: (INTERNAL) UTM/UPS scale factor (C{float}).
    _ups          = None  #: (INTERNAL) Cached toUps (L{Ups}).
    _utm          = None  #: (INTERNAL) Cached toUtm (L{Utm}).
    _wm           = None  #: (INTERNAL) Cached toWm (webmercator.Wm instance).

    def __init__(self, lat, lon, height=0, datum=None, reframe=None,
                                           epoch=None, name=NN):
        '''Create an ellipsoidal C{LatLon} point frome the given
           lat-, longitude and height on the given datum and with
           the given reference frame and epoch.

           @arg lat: Latitude (C{degrees} or DMS C{[N|S]}).
           @arg lon: Longitude (C{degrees} or DMS C{str[E|W]}).
           @kwarg height: Optional elevation (C{meter}, the same units
                          as the datum's half-axes).
           @kwarg datum: Optional, ellipsoidal datum to use (L{Datum}).
           @kwarg reframe: Optional reference frame (L{RefFrame}).
           @kwarg epoch: Optional epoch to observe for B{C{reframe}}
                         (C{scalar}), a non-zero, fractional calendar year.
           @kwarg name: Optional name (string).

           @raise TypeError: B{C{datum}} is not a L{datum}, B{C{reframe}}
                             is not a L{RefFrame} or B{C{epoch}} is not
                             C{scalar} non-zero.

           @example:

           >>> p = LatLon(51.4778, -0.0016)  # height=0, datum=Datums.WGS84
        '''
        LatLonBase.__init__(self, lat, lon, height=height, name=name)
        if datum and datum != self._datum:
            self.datum = datum
        if reframe:
            self.reframe = reframe
            self.epoch = epoch

    def _Radjust2(self, adjust, datum, meter_text2):
        '''(INTERNAL) Adjust elevation or geoidHeight with difference
           in Gaussian radii of curvature of given datum and NAD83.

           @note: This is an arbitrary, possibly incorrect adjustment.
        '''
        if adjust:  # Elevation2Tuple or GeoidHeight2Tuple
            m, t = meter_text2
            if isinstance(m, float):
                n = Datums.NAD83.ellipsoid.rocGauss(self.lat)
                if min(abs(m), n) > EPS:
                    # use ratio, datum and NAD83 units may differ
                    e = self.ellipsoid(datum).rocGauss(self.lat)
                    if min(abs(e - n), e) > EPS:
                        m *= e / n
                        meter_text2 = meter_text2.classof(m, t)
        return self._xnamed(meter_text2)

    def _update(self, updated, *attrs):
        '''(INTERNAL) Zap cached attributes if updated.
        '''
        if updated:
            LatLonBase._update(self, updated, '_etm', '_lcc', '_osgr',
                                      '_ups', '_utm', '_wm', *attrs)
            if self._elevation2:
                self._elevation2 = ()
            if self._geoidHeight2:
                self._geoidHeight2 = ()

    def antipode(self, height=None):
        '''Return the antipode, the point diametrically opposite
           to this point.

           @kwarg height: Optional height of the antipode, height
                          of this point otherwise (C{meter}).

           @return: The antipodal point (C{LatLon}).
        '''
        lla = LatLonBase.antipode(self, height=height)
        if lla.datum != self.datum:
            lla.datum = self.datum
        return lla

    @property_RO
    def convergence(self):
        '''Get this point's UTM or UPS meridian convergence (C{degrees})
           or C{None} if not converted from L{Utm} or L{Ups}.
        '''
        return self._convergence

    def convertDatum(self, datum2):
        '''Convert this point to an other datum.

           @arg datum2: Datum to convert I{to} (L{Datum}).

           @return: The converted point (ellipsoidal C{LatLon}).

           @raise TypeError: The B{C{datum2}} is not a L{Datum}.

           @example:

           >>> p = LatLon(51.4778, -0.0016)  # default Datums.WGS84
           >>> p.convertDatum(Datums.OSGB36)  # 51.477284°N, 000.00002°E
        '''
        if self.datum == datum2:
            return self.copy()

        c = self.toCartesian().convertDatum(datum2)
        return c.toLatLon(datum=datum2, LatLon=self.classof)

    def convertRefFrame(self, reframe2):
        '''Convert this point to an other reference frame.

           @arg reframe2: Reference frame to convert I{to} (L{RefFrame}).

           @return: The converted point (ellipsoidal C{LatLon}) or
                    this point if conversion is C{nil}.

           @raise TRFError: No B{C{.reframe}} or no conversion
                            available from B{C{.reframe}} to
                            B{C{reframe2}}.

           @raise TypeError: The B{C{reframe2}} is not a L{RefFrame}.

           @example:

           >>> p = LatLon(51.4778, -0.0016, reframe=RefFrames.ETRF2000)  # default Datums.WGS84
           >>> p.convertRefFrame(RefFrames.ITRF2014)  # 51.477803°N, 000.001597°W, +0.01m
        '''
        _xinstanceof(RefFrame, reframe2=reframe2)

        if not self.reframe:
            raise TRFError(_no_conversion_, txt='%r.reframe %s' % (self, _Missing))

        ts = _reframeTransforms(reframe2, self.reframe, self.epoch)
        if ts:
            c = self.toCartesian()
            for t in ts:
                c = c._applyHelmert(t, False)
            ll = c.toLatLon(datum=self.datum, LatLon=self.classof,
                            epoch=self.epoch, reframe=reframe2)
            # ll.reframe, ll.epoch = reframe2, self.epoch
        else:
            ll = self
        return ll

    @property_doc_(''' this points's datum (L{Datum}).''')
    def datum(self):
        '''Get this point's datum (L{Datum}).
        '''
        return self._datum

    @datum.setter  # PYCHOK setter!
    def datum(self, datum):
        '''Set this point's datum I{without conversion}.

           @arg datum: New datum (L{Datum}).

           @raise TypeError: The B{C{datum}} is not a L{Datum}
                             or not ellipsoidal.
        '''
        _xinstanceof(Datum, datum=datum)
        if not datum.isEllipsoidal:
            raise _IsnotError(_ellipsoidal_, datum=datum)
        self._update(datum != self._datum)
        self._datum = datum

    def distanceTo2(self, other):
        '''Approximate the distance and (initial) bearing between this
           and an other (ellipsoidal) point based on the radii of curvature.

           Suitable only for short distances up to a few hundred Km
           or Miles and only between non-near-polar points.

           @arg other: The other point (C{LatLon}).

           @return: An L{Distance2Tuple}C{(distance, initial)}.

           @raise TypeError: The B{C{other}} point is not C{LatLon}.

           @raise ValueError: Incompatible datum ellipsoids.

           @see: Method L{Ellipsoid.distance2} and U{Local, flat earth
                 approximation<https://www.EdWilliams.org/avform.htm#flat>}.
        '''
        return self.ellipsoids(other).distance2(self.lat,  self.lon,
                                               other.lat, other.lon)

    def elevation2(self, adjust=True, datum=Datums.WGS84, timeout=2):
        '''Return elevation of this point for its or the given datum.

           @kwarg adjust: Adjust the elevation for a B{C{datum}} other
                          than C{NAD83} (C{bool}).
           @kwarg datum: Optional datum (L{Datum}).
           @kwarg timeout: Optional query timeout (C{seconds}).

           @return: An L{Elevation2Tuple}C{(elevation, data_source)}
                    or C{(None, error)} in case of errors.

           @note: The adjustment applied is the difference in geocentric
                  earth radius between the B{C{datum}} and C{NAV83}
                  upon which the L{elevations.elevation2} is based.

           @note: NED elevation is only available for locations within
                  the U{Conterminous US (CONUS)
                  <https://WikiPedia.org/wiki/Contiguous_United_States>}.

           @see: Function L{elevations.elevation2} and method
                 L{Ellipsoid.Rgeocentric} for further details and
                 possible C{error}s.
        '''
        if not self._elevation2:  # get elevation and data source
            from pygeodesy.elevations import elevation2
            self._elevation2 = elevation2(self.lat, self.lon,
                                          timeout=timeout)
        return self._Radjust2(adjust, datum, self._elevation2)

    def ellipsoid(self, datum=Datums.WGS84):
        '''Return the ellipsoid of this point's datum or the given datum.

           @kwarg datum: Default datum (L{Datum}).

           @return: The ellipsoid (L{Ellipsoid}).
        '''
        return getattr(self, _datum_, datum).ellipsoid

    def ellipsoids(self, other):
        '''Check the type and ellipsoid of this and an other point's datum.

           @arg other: The other point (C{LatLon}).

           @return: This point's datum ellipsoid (L{Ellipsoid}).

           @raise TypeError: The B{C{other}} point is not C{LatLon}.

           @raise ValueError: Incompatible datum ellipsoids.
        '''
        self.others(other, up=2)  # ellipsoids' caller

        E = self.ellipsoid()
        try:  # other may be Sphere, etc.
            e = other.ellipsoid()
        except AttributeError:  # PYCHOK no cover
            try:  # no ellipsoid method, try datum
                e = other.datum.ellipsoid
            except AttributeError:
                e = E  # no datum, XXX assume equivalent?
        if e != E:
            raise _ValueError(e.named2, txt=_incompatible(E.named2))
        return E

    @property_doc_(''' this point's observed epoch (C{float}).''')
    def epoch(self):
        '''Get this point's observed epoch (C{float}) or C{None}.
        '''
        return self._epoch or (self.reframe.epoch if self.reframe else None)

    @epoch.setter  # PYCHOK setter!
    def epoch(self, epoch):
        '''Set or clear this point's observed epoch.

           @arg epoch: Observed epoch, a fractional calendar year
                       (C{scalar}) or C{None}.

           @raise TypeError: The B{C{epoch}} is not C{scalar}.
        '''
        self._epoch = None if epoch is None else _2epoch(epoch)

    def geoidHeight2(self, adjust=False, datum=Datums.WGS84, timeout=2):
        '''Return geoid height of this point for its or the given datum.

           @kwarg adjust: Adjust the geoid height for a B{C{datum}}
                          other than C{NAD83/NADV88} (C{bool}).
           @kwarg datum: Optional datum (L{Datum}).
           @kwarg timeout: Optional query timeout (C{seconds}).

           @return: An L{GeoidHeight2Tuple}C{(height, model_name)} or
                    C{(None, error)} in case of errors.

           @note: The adjustment applied is the difference in geocentric
                  earth radius between the B{C{datum}} and C{NAV83/NADV88}
                  upon which the L{elevations.geoidHeight2} is based.

           @note: The geoid height is only available for locations within
                  the U{Conterminous US (CONUS)
                  <https://WikiPedia.org/wiki/Contiguous_United_States>}.

           @see: Function L{elevations.geoidHeight2} and method
                 L{Ellipsoid.Rgeocentric} for further details and
                 possible C{error}s.
        '''
        if not self._geoidHeight2:  # get elevation and data source
            from pygeodesy.elevations import geoidHeight2
            self._geoidHeight2 = geoidHeight2(self.lat, self.lon,
                                              model=0, timeout=timeout)
        return self._Radjust2(adjust, datum, self._geoidHeight2)

    def intersections2(self, rad1, other, rad2, height=None, wrap=False,
                                            equidistant=None, tol=_TOL_M):
        '''Compute the intersection points of two circles each defined
           by a center point and radius.

           @arg rad1: Radius of the this circle (C{meter}).
           @arg other: Center of the other circle (C{LatLon}).
           @arg rad2: Radius of the other circle (C{meter}).
           @kwarg height: Optional height for the intersection points,
                          overriding the mean height (C{meter}).
           @kwarg wrap: Wrap and unroll longitudes (C{bool}).
           @kwarg equidistant: An azimuthal equidistant projection class
                               (L{Equidistant} or L{EquidistantKarney}),
                               function L{azimuthal.equidistant} will be
                               invoked if left unspecified.
           @kwarg tol: Convergence tolerance (C{meter}).

           @return: 2-Tuple of the intersection points, each a C{LatLon}
                    instance.  For abutting circles, the intersection
                    points are the same instance.

           @raise IntersectionError: Concentric, antipodal, invalid or
                                     non-intersecting circles or no
                                     convergence for B{C{tol}}.

           @raise TypeError: If B{C{other}} is not C{LatLon}.

           @raise ValueError: Invalid B{C{rad1}}, B{C{rad2}} or B{C{height}}.
        '''
        self.others(other)
        return _intersect2(self, rad1, other, rad2, height=height, wrap=wrap,
                               equidistant=equidistant, tol=tol, LatLon=self.classof)

    @property_RO
    def iteration(self):
        '''Get the iteration number (C{int} or C{None} if not available/applicable).
        '''
        return None

    def parse(self, strll, height=0, datum=None, sep=_COMMA_):
        '''Parse a string representing this C{LatLon} point.

           The lat- and longitude must be separated by a sep[arator]
           character.  If height is present it must follow and be
           separated by another sep[arator].  Lat- and longitude
           may be swapped, provided at least one ends with the
           proper compass direction.

           For more details, see functions L{parse3llh} and L{parseDMS}
           in sub-module L{dms}.

           @arg strll: Lat, lon [, height] (string).
           @kwarg height: Optional, default height (C{meter} or C{None}).
           @kwarg datum: Optional, default datum (L{Datum}).
           @kwarg sep: Optional separator (string).

           @return: The point (L{LatLonEllipsoidalBase}).

           @raise ParseError: Invalid B{C{strll}}.
        '''
        from pygeodesy.dms import parse3llh
        a, b, h = parse3llh(strll, height=height, sep=sep)
        return self.classof(a, b, height=h, datum=datum or self.datum)

    @property_doc_(''' this point's reference frame (L{RefFrame}).''')
    def reframe(self):
        '''Get this point's reference frame (L{RefFrame}) or C{None}.
        '''
        return self._reframe

    @reframe.setter  # PYCHOK setter!
    def reframe(self, reframe):
        '''Set or clear this point's reference frame.

           @arg reframe: Reference frame (L{RefFrame}) or C{None}.

           @raise TypeError: The B{C{reframe}} is not a L{RefFrame}.
        '''
        if reframe is not None:
            _xinstanceof(RefFrame, reframe=reframe)
            self._reframe = reframe
        elif self.reframe is not None:
            self._reframe = None

    @property_RO
    def scale(self):
        '''Get this point's UTM grid or UPS point scale factor (C{float})
           or C{None} if not converted from L{Utm} or L{Ups}.
        '''
        return self._scale

    def to3xyz(self):  # PYCHOK no cover
        '''DEPRECATED, use method C{toEcef}.

           @return: A L{Vector3Tuple}C{(x, y, z)}.

           @note: Overloads C{LatLonBase.to3xyz}
        '''
        r = self.toEcef()
        return self._xnamed(Vector3Tuple(r.x, r.y, r.z))

    def toEtm(self):
        '''Convert this C{LatLon} point to an ETM coordinate.

           @return: The ETM coordinate (L{Etm}).

           @see: Function L{toEtm8}.
        '''
        if self._etm is None:
            from pygeodesy.etm import toEtm8, Etm  # PYCHOK recursive import
            self._etm = toEtm8(self, datum=self.datum, Etm=Etm)
        return self._etm

    def toLcc(self):
        '''Convert this C{LatLon} point to a Lambert location.

           @see: Function L{toLcc} in module L{lcc}.

           @return: The Lambert location (L{Lcc}).
        '''
        if self._lcc is None:
            from pygeodesy.lcc import Lcc, toLcc  # PYCHOK recursive import
            self._lcc = toLcc(self, height=self.height, Lcc=Lcc,
                                                        name=self.name)
        return self._lcc

    def toOsgr(self):
        '''Convert this C{LatLon} point to an OSGR coordinate.

           @see: Function L{toOsgr} in module L{osgr}.

           @return: The OSGR coordinate (L{Osgr}).
        '''
        if self._osgr is None:
            from pygeodesy.osgr import Osgr, toOsgr  # PYCHOK recursive import
            self._osgr = toOsgr(self, datum=self.datum, Osgr=Osgr,
                                                        name=self.name)
        return self._osgr

    def toUps(self, pole=_N_, falsed=True):
        '''Convert this C{LatLon} point to a UPS coordinate.

           @kwarg pole: Optional top/center of (stereographic)
                        projection (C{str}, 'N[orth]' or 'S[outh]').
           @kwarg falsed: False easting and northing (C{bool}).

           @return: The UPS coordinate (L{Ups}).

           @see: Function L{toUps8}.
        '''
        if self._ups is None:
            from pygeodesy.ups import toUps8, Ups  # PYCHOK recursive import
            self._ups = toUps8(self, datum=self.datum, Ups=Ups,
                                     pole=pole, falsed=falsed)
        return self._ups

    def toUtm(self):
        '''Convert this C{LatLon} point to a UTM coordinate.

           @return: The UTM coordinate (L{Utm}).

           @see: Function L{toUtm8}.
        '''
        if self._utm is None:
            from pygeodesy.utm import toUtm8, Utm  # PYCHOK recursive import
            self._utm = toUtm8(self, datum=self.datum, Utm=Utm)
        return self._utm

    def toUtmUps(self, pole=NN):
        '''Convert this C{LatLon} point to a UTM or UPS coordinate.

           @kwarg pole: Optional top/center of UPS (stereographic)
                        projection (C{str}, 'N[orth]' or 'S[outh]').

           @return: The UTM or UPS coordinate (L{Utm} or L{Ups}).

           @raise TypeError: Result in L{Utm} or L{Ups}.

           @see: Function L{toUtmUps}.
        '''
        if self._utm:
            u = self._utm
        elif self._ups and (self._ups.pole == pole or not pole):
            u = self._ups
        else:
            from pygeodesy.utmups import toUtmUps8, Utm, Ups  # PYCHOK recursive import
            u = toUtmUps8(self, datum=self.datum, Utm=Utm, Ups=Ups, pole=pole)
            if isinstance(u, Utm):
                self._utm = u
            elif isinstance(u, Ups):
                self._ups = u
            else:
                _xinstanceof(Utm, Ups, toUtmUps8=u)
        return u

    def toWm(self):
        '''Convert this C{LatLon} point to a WM coordinate.

           @see: Function L{toWm} in module L{webmercator}.

           @return: The WM coordinate (L{Wm}).
        '''
        if self._wm is None:
            from pygeodesy.webmercator import toWm  # PYCHOK recursive import
            self._wm = toWm(self)
        return self._wm


# (INTERNAL) C{_intersect2} imported by .ellipsoidalKarney and -Vincenty
def _intersections2(center1, rad1, center2, rad2, height=None, wrap=False,
                    equidistant=None, tol=_TOL_M, LatLon=None, **LatLon_kwds):
    '''Iteratively compute the intersection points of two circles each defined
       by an (ellipsoidal) center point and a radius.

       @arg center1: Center of the first circle (ellipsoidal C{LatLon}).
       @arg rad1: Radius of the first circle (C{meter}).
       @arg center2: Center of the second circle (ellipsoidal C{LatLon}).
       @arg rad2: Radius of the second circle (C{meter}).
       @kwarg height: Optional height for the intersection points,
                      overriding the "radical height" at the "radical
                      line" between both centers (C{meter}).
       @kwarg wrap: Wrap and unroll longitudes (C{bool}).
       @kwarg equidistant: An azimuthal equidistant projection class
                           (L{Equidistant} or L{EquidistantKarney}) or
                           C{None} for function L{azimuthal.equidistant}.
       @kwarg tol: Convergence tolerance (C{meter}).
       @kwarg LatLon: Optional class to return the intersection points
                     (ellipsoidal C{LatLon}) or C{None}.
       @kwarg LatLon_kwds: Optional, additional B{C{LatLon}} keyword
                           arguments, ignored if B{C{LatLon=None}}.

       @return: 2-Tuple of the intersection points, each a B{C{LatLon}}
                instance or L{LatLon4Tuple}C{(lat, lon, height, datum)}
                if B{C{LatLon}} is C{None}.  For abutting circles, the
                intersection points are the same instance.

       @raise ImportError: If B{C{equidistant}} is L{EquidistantKarney})
                           and package U{geographiclib
                           <https://PyPI.org/project/geographiclib>}
                           not installed or not found.

       @raise IntersectionError: Concentric, antipodal, invalid or
                                 non-intersecting circles or no
                                 convergence for B{C{tol}}.

       @raise TypeError: If B{C{center1}} or B{C{center2}} not ellipsoidal.

       @raise UnitError: Invalid B{C{rad1}}, B{C{rad2}} or B{C{height}}.

       @see: U{The B{ellipsoidal} case<https://GIS.StackExchange.com/questions/48937/
             calculating-intersection-of-two-circles>}, U{Karney's paper
             <https://arxiv.org/pdf/1102.1215.pdf>}, pp 20-21, section 14 I{Maritime Boundaries},
             U{circle-circle<https://MathWorld.Wolfram.com/Circle-CircleIntersection.html>} and
             U{sphere-sphere<https://MathWorld.Wolfram.com/Sphere-SphereIntersection.html>}
             intersections.
    '''

    c1 = _xellipsoidal(center1=center1)
    c2 = c1.others(center2)

    r1 = Radius_(rad1, name='rad1')
    r2 = Radius_(rad2, name='rad2')

    try:
        return _intersect2(c1, r1, c2, r2, height=height, wrap=wrap,
                                      equidistant=equidistant, tol=tol,
                                           LatLon=LatLon, **LatLon_kwds)
    except (TypeError, ValueError) as x:
        raise IntersectionError(center1=center1, rad1=rad1,
                                center2=center2, rad2=rad2, txt=str(x))


def _intersect2(c1, r1, c2, r2, height=None, wrap=False,  # MCCABE 15
                equidistant=None, tol=_TOL_M, LatLon=None, **LatLon_kwds):
    # (INTERNAL) Intersect of two spherical circles, see L{_intersections2}
    # above, separated to allow callers to embellish any exceptions

    from pygeodesy.formy import _euclidean
    from pygeodesy.sphericalTrigonometry import _intersect2 as _si2, LatLon as _LLS
    from pygeodesy.utily import m2degrees
    from pygeodesy.vector3d import _intersect2 as _vi2, _radical2

    def _latlon4(t, h, n):
        if LatLon is None:
            r = LatLon4Tuple(t.lat, t.lon, h, t.datum)
        else:
            kwds = _xkwds(LatLon_kwds, datum=t.datum, height=h)
            r = LatLon(t.lat, t.lon, **kwds)
        return _xnamed(r, n)

    if r1 < r2:
        c1, c2 = c2, c1
        r1, r2 = r2, r1

    E = c1.ellipsoids(c2)
    if r1 > (E.b * PI):
        raise ValueError(_exceed_PI_radians_)

    # distance between centers and radii are
    # measured along the ellipsoid's surface
    m = c1.distanceTo(c2, wrap=wrap)  # meter
    if m < max(r1 - r2, EPS):
        raise ValueError(_near_concentric_)
    if fsum_(r1, r2, -m) < 0:
        raise ValueError(_too_distant_fmt_ % (m,))

    f, _ = _radical2(m, r1, r2)  # "radical ratio"
    r = E.rocMean(favg(c1.lat, c2.lat, f=f))
    e = max(m2degrees(tol, radius=r), EPS)

    # gu-/estimate initial intersections, spherically
    t1, t2 = _si2(_LLS(c1.lat, c1.lon, height=c1.height), r1,
                  _LLS(c2.lat, c2.lon, height=c2.height), r2,
                   radius=r, height=height, wrap=wrap, too_d=m)
    h, n = t1.height, t1.name

    # get the azimuthal equidistant projection
    if equidistant is None:
        from pygeodesy.azimuthal import equidistant as A
    else:
        A = equidistant
    A = A(0, 0, datum=c1.datum)

    # for each gu-/estimate, iterate like Karney
    # suggests to find tri-points of median lines
    ts, ta = [], None
    for t in ((t1,) if t1 is t2 else (t1, t2)):
        p = None  # force d == p False
        for _ in range(_TRIPS):
            A.reset(t.lat, t.lon)  # gu-/estimate as origin
            # convert centers to projection space
            t1 = A.forward(c1.lat, c1.lon)
            t2 = A.forward(c2.lat, c2.lon)
            # compute intersections in projection space
            v1, v2 = _vi2(t1, r1,  # XXX * t1.scale?,
                          t2, r2,  # XXX * t2.scale?,
                          sphere=False, too_d=m)
            # convert intersections back to geodetic
            t1 = A.reverse(v1.x, v1.y)
            t2 = A.reverse(v2.x, v2.y)
            # consider only the closer intersection
            d1 = _euclidean(t1.lat - t.lat, t1.lon - t.lon)
            d2 = _euclidean(t2.lat - t.lat, t2.lon - t.lon)
            # break if below tolerance or if unchanged
            t, d = (t1, d1) if d1 < d2 else (t2, d2)
            if d < e or d == p:
                ts.append(t)
                if v1 is v2:  # abutting
                    ta = t
                break
            p = d
        else:
            raise ValueError('%s (%g)' % (_no_convergence_, tol))

    if ta:  # abutting circles
        r = _latlon4(ta, h, n)
    elif len(ts) == 2:
        return _latlon4(ts[0], h, n), _latlon4(ts[1], h, n)
    elif len(ts) == 1:  # XXX assume abutting
        r = _latlon4(ts[0], h, n)
    else:
        raise _AssertionError(ts=ts)
    return r, r


__all__ += _ALL_DOCS(CartesianEllipsoidalBase, LatLonEllipsoidalBase)

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