# Source code for astroplan.constraints

```
# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""
Specify and constraints to determine which targets are observable for
an observer.
"""
from __future__ import (absolute_import, division, print_function,
unicode_literals)
# Standard library
from abc import ABCMeta, abstractmethod
import datetime
import warnings
# Third-party
from astropy.time import Time
import astropy.units as u
from astropy.coordinates import get_body, get_sun, get_moon, SkyCoord
from astropy import table
import numpy as np
from numpy.lib.stride_tricks import as_strided
# Package
from .moon import moon_illumination
from .utils import time_grid_from_range
from .target import get_skycoord
__all__ = ["AltitudeConstraint", "AirmassConstraint", "AtNightConstraint",
"is_observable", "is_always_observable", "time_grid_from_range",
"SunSeparationConstraint", "MoonSeparationConstraint",
"MoonIlluminationConstraint", "LocalTimeConstraint", "Constraint",
"TimeConstraint", "observability_table", "months_observable",
"max_best_rescale", "min_best_rescale"]
def _make_cache_key(times, targets):
"""
Make a unique key to reference this combination of ``times`` and ``targets``.
Often, we wish to store expensive calculations for a combination of
``targets`` and ``times`` in a cache on an ``observer``` object. This
routine will provide an appropriate, hashable, key to store these
calculations in a dictionary.
Parameters
----------
times : `~astropy.time.Time`
Array of times on which to test the constraint.
targets : `~astropy.coordinates.SkyCoord`
Target or list of targets.
Returns
-------
cache_key : tuple
A hashable tuple for use as a cache key
"""
# make a tuple from times
try:
timekey = tuple(times.jd) + times.shape
except:
# must be scalar
timekey = (times.jd,)
# make hashable thing from targets coords
try:
if hasattr(targets, 'frame'):
# treat as a SkyCoord object. Accessing the longitude
# attribute of the frame data should be unique and is
# quicker than accessing the ra attribute.
targkey = tuple(targets.frame.data.lon.value.ravel()) + targets.shape
else:
# assume targets is a string.
targkey = (targets,)
except:
targkey = (targets.frame.data.lon,)
return timekey + targkey
def _get_altaz(times, observer, targets, force_zero_pressure=False):
"""
Calculate alt/az for ``target`` at times linearly spaced between
the two times in ``time_range`` with grid spacing ``time_resolution``
for ``observer``.
Cache the result on the ``observer`` object.
Parameters
----------
times : `~astropy.time.Time`
Array of times on which to test the constraint.
targets : {list, `~astropy.coordinates.SkyCoord`, `~astroplan.FixedTarget`}
Target or list of targets.
observer : `~astroplan.Observer`
The observer who has constraints ``constraints``.
force_zero_pressure : bool
Forcefully use 0 pressure.
Returns
-------
altaz_dict : dict
Dictionary containing two key-value pairs. (1) 'times' contains the
times for the alt/az computations, (2) 'altaz' contains the
corresponding alt/az coordinates at those times.
"""
if not hasattr(observer, '_altaz_cache'):
observer._altaz_cache = {}
# convert times, targets to tuple for hashing
aakey = _make_cache_key(times, targets)
if aakey not in observer._altaz_cache:
try:
if force_zero_pressure:
observer_old_pressure = observer.pressure
observer.pressure = 0
altaz = observer.altaz(times, targets, grid_times_targets=False)
observer._altaz_cache[aakey] = dict(times=times,
altaz=altaz)
finally:
if force_zero_pressure:
observer.pressure = observer_old_pressure
return observer._altaz_cache[aakey]
def _get_moon_data(times, observer, force_zero_pressure=False):
"""
Calculate moon altitude az and illumination for an array of times for
``observer``.
Cache the result on the ``observer`` object.
Parameters
----------
times : `~astropy.time.Time`
Array of times on which to test the constraint.
observer : `~astroplan.Observer`
The observer who has constraints ``constraints``.
force_zero_pressure : bool
Forcefully use 0 pressure.
Returns
-------
moon_dict : dict
Dictionary containing three key-value pairs. (1) 'times' contains the
times for the computations, (2) 'altaz' contains the
corresponding alt/az coordinates at those times and (3) contains
the moon illumination for those times.
"""
if not hasattr(observer, '_moon_cache'):
observer._moon_cache = {}
# convert times to tuple for hashing
aakey = _make_cache_key(times, 'moon')
if aakey not in observer._moon_cache:
try:
if force_zero_pressure:
observer_old_pressure = observer.pressure
observer.pressure = 0
altaz = observer.moon_altaz(times)
illumination = np.array(moon_illumination(times))
observer._moon_cache[aakey] = dict(times=times,
illum=illumination,
altaz=altaz)
finally:
if force_zero_pressure:
observer.pressure = observer_old_pressure
return observer._moon_cache[aakey]
def _get_meridian_transit_times(times, observer, targets):
"""
Calculate next meridian transit for an array of times for ``targets`` and
``observer``.
Cache the result on the ``observer`` object.
Parameters
----------
times : `~astropy.time.Time`
Array of times on which to test the constraint
observer : `~astroplan.Observer`
The observer who has constraints ``constraints``
targets : {list, `~astropy.coordinates.SkyCoord`, `~astroplan.FixedTarget`}
Target or list of targets
Returns
-------
time_dict : dict
Dictionary containing a key-value pair. 'times' contains the
meridian_transit times.
"""
if not hasattr(observer, '_meridian_transit_cache'):
observer._meridian_transit_cache = {}
# convert times to tuple for hashing
aakey = _make_cache_key(times, targets)
if aakey not in observer._meridian_transit_cache:
meridian_transit_times = observer.target_meridian_transit_time(times, targets)
observer._meridian_transit_cache[aakey] = dict(times=meridian_transit_times)
return observer._meridian_transit_cache[aakey]
@abstractmethod
[docs]class Constraint(object):
"""
Abstract class for objects defining observational constraints.
"""
__metaclass__ = ABCMeta
[docs] def __call__(self, observer, targets, times=None,
time_range=None, time_grid_resolution=0.5*u.hour,
grid_times_targets=False):
"""
Compute the constraint for this class
Parameters
----------
observer : `~astroplan.Observer`
the observation location from which to apply the constraints
targets : sequence of `~astroplan.Target`
The targets on which to apply the constraints.
times : `~astropy.time.Time`
The times to compute the constraint.
WHAT HAPPENS WHEN BOTH TIMES AND TIME_RANGE ARE SET?
time_range : `~astropy.time.Time` (length = 2)
Lower and upper bounds on time sequence.
time_grid_resolution : `~astropy.units.quantity`
Time-grid spacing
grid_times_targets : bool
if True, grids the constraint result with targets along the first
index and times along the second. Otherwise, we rely on broadcasting
the shapes together using standard numpy rules.
Returns
-------
constraint_result : 1D or 2D array of float or bool
The constraints. If 2D with targets along the first index and times along
the second.
"""
if times is None and time_range is not None:
times = time_grid_from_range(time_range,
time_resolution=time_grid_resolution)
if grid_times_targets:
targets = get_skycoord(targets)
# TODO: these broadcasting operations are relatively slow
# but there is potential for huge speedup if the end user
# disables gridding and re-shapes the coords themselves
# prior to evaluating multiple constraints.
if targets.isscalar:
# ensure we have a (1, 1) shape coord
targets = SkyCoord(np.tile(targets, 1))[:, np.newaxis]
else:
targets = targets[..., np.newaxis]
times, targets = observer._preprocess_inputs(times, targets, grid_times_targets=False)
result = self.compute_constraint(times, observer, targets)
# make sure the output has the same shape as would result from
# broadcasting times and targets against each other
if targets is not None:
# broadcasting times v targets is slow due to
# complex nature of these objects. We make
# to simple numpy arrays of the same shape and
# broadcast these to find the correct shape
shp1, shp2 = times.shape, targets.shape
x = np.array([1])
a = as_strided(x, shape=shp1, strides=[0] * len(shp1))
b = as_strided(x, shape=shp2, strides=[0] * len(shp2))
output_shape = np.broadcast(a, b).shape
if output_shape != np.array(result).shape:
result = np.broadcast_to(result, output_shape)
return result
@abstractmethod
[docs] def compute_constraint(self, times, observer, targets):
"""
Actually do the real work of computing the constraint. Subclasses
override this.
Parameters
----------
times : `~astropy.time.Time`
The times to compute the constraint
observer : `~astroplan.Observer`
the observaton location from which to apply the constraints
targets : sequence of `~astroplan.Target`
The targets on which to apply the constraints.
Returns
-------
constraint_result : 2D array of float or bool
The constraints, with targets along the first index and times along
the second.
"""
# Should be implemented on each subclass of Constraint
raise NotImplementedError
[docs]class AltitudeConstraint(Constraint):
"""
Constrain the altitude of the target.
.. note::
This can misbehave if you try to constrain negative altitudes, as
the `~astropy.coordinates.AltAz` frame tends to mishandle negative
Parameters
----------
min : `~astropy.units.Quantity` or `None`
Minimum altitude of the target (inclusive). `None` indicates no limit.
max : `~astropy.units.Quantity` or `None`
Maximum altitude of the target (inclusive). `None` indicates no limit.
boolean_constraint : bool
If True, the constraint is treated as a boolean (True for within the
limits and False for outside). If False, the constraint returns a
float on [0, 1], where 0 is the min altitude and 1 is the max.
"""
def __init__(self, min=None, max=None, boolean_constraint=True):
if min is None:
self.min = -90*u.deg
else:
self.min = min
if max is None:
self.max = 90*u.deg
else:
self.max = max
self.boolean_constraint = boolean_constraint
[docs] def compute_constraint(self, times, observer, targets):
cached_altaz = _get_altaz(times, observer, targets)
alt = cached_altaz['altaz'].alt
if self.boolean_constraint:
lowermask = self.min <= alt
uppermask = alt <= self.max
return lowermask & uppermask
else:
return max_best_rescale(alt, self.min, self.max)
[docs]class AirmassConstraint(AltitudeConstraint):
"""
Constrain the airmass of a target.
In the current implementation the airmass is approximated by the secant of
the zenith angle.
.. note::
The ``max`` and ``min`` arguments appear in the order (max, min)
in this initializer to support the common case for users who care
about the upper limit on the airmass (``max``) and not the lower
limit.
Parameters
----------
max : float or `None`
Maximum airmass of the target. `None` indicates no limit.
min : float or `None`
Minimum airmass of the target. `None` indicates no limit.
boolean_contstraint : bool
Examples
--------
To create a constraint that requires the airmass be "better than 2",
i.e. at a higher altitude than airmass=2::
AirmassConstraint(2)
"""
def __init__(self, max=None, min=1, boolean_constraint=True):
self.min = min
self.max = max
self.boolean_constraint = boolean_constraint
[docs] def compute_constraint(self, times, observer, targets):
cached_altaz = _get_altaz(times, observer, targets)
secz = cached_altaz['altaz'].secz.value
if self.boolean_constraint:
if self.min is None and self.max is not None:
mask = secz <= self.max
elif self.max is None and self.min is not None:
mask = self.min <= secz
elif self.min is not None and self.max is not None:
mask = (self.min <= secz) & (secz <= self.max)
else:
raise ValueError("No max and/or min specified in "
"AirmassConstraint.")
return mask
else:
if self.max is None:
raise ValueError("Cannot have a float AirmassConstraint if max "
"is None")
else:
mx = self.max
mi = 1 if self.min is None else self.min
# values below 1 should be disregarded
return min_best_rescale(secz, mi, mx, less_than_min=0)
[docs]class AtNightConstraint(Constraint):
"""
Constrain the Sun to be below ``horizon``.
"""
@u.quantity_input(horizon=u.deg)
def __init__(self, max_solar_altitude=0*u.deg, force_pressure_zero=True):
"""
Parameters
----------
max_solar_altitude : `~astropy.units.Quantity`
The altitude of the sun below which it is considered to be "night"
(inclusive).
force_pressure_zero : bool (optional)
Force the pressure to zero for solar altitude calculations. This
avoids errors in the altitude of the Sun that can occur when the
Sun is below the horizon and the corrections for atmospheric
refraction return nonsense values.
"""
self.max_solar_altitude = max_solar_altitude
self.force_pressure_zero = force_pressure_zero
@classmethod
[docs] def twilight_civil(cls, **kwargs):
"""
Consider nighttime as time between civil twilights (-6 degrees).
"""
return cls(max_solar_altitude=-6*u.deg, **kwargs)
@classmethod
[docs] def twilight_nautical(cls, **kwargs):
"""
Consider nighttime as time between nautical twilights (-12 degrees).
"""
return cls(max_solar_altitude=-12*u.deg, **kwargs)
@classmethod
[docs] def twilight_astronomical(cls, **kwargs):
"""
Consider nighttime as time between astronomical twilights (-18 degrees).
"""
return cls(max_solar_altitude=-18*u.deg, **kwargs)
def _get_solar_altitudes(self, times, observer, targets):
if not hasattr(observer, '_altaz_cache'):
observer._altaz_cache = {}
aakey = _make_cache_key(times, 'sun')
if aakey not in observer._altaz_cache:
try:
if self.force_pressure_zero:
observer_old_pressure = observer.pressure
observer.pressure = 0
# find solar altitude at these times
altaz = observer.altaz(times, get_sun(times))
altitude = altaz.alt
# cache the altitude
observer._altaz_cache[aakey] = dict(times=times,
altitude=altitude)
finally:
if self.force_pressure_zero:
observer.pressure = observer_old_pressure
else:
altitude = observer._altaz_cache[aakey]['altitude']
return altitude
[docs] def compute_constraint(self, times, observer, targets):
solar_altitude = self._get_solar_altitudes(times, observer, targets)
mask = solar_altitude <= self.max_solar_altitude
return mask
[docs]class SunSeparationConstraint(Constraint):
"""
Constrain the distance between the Sun and some targets.
"""
def __init__(self, min=None, max=None):
"""
Parameters
----------
min : `~astropy.units.Quantity` or `None` (optional)
Minimum acceptable separation between Sun and target (inclusive).
`None` indicates no limit.
max : `~astropy.units.Quantity` or `None` (optional)
Minimum acceptable separation between Sun and target (inclusive).
`None` indicates no limit.
"""
self.min = min
self.max = max
[docs] def compute_constraint(self, times, observer, targets):
# use get_body rather than get sun here, since
# it returns the Sun's coordinates in an observer
# centred frame, so the separation is as-seen
# by the observer.
# 'get_sun' returns ICRS coords.
sun = get_body('sun', times, location=observer.location)
solar_separation = sun.separation(targets)
if self.min is None and self.max is not None:
mask = self.max >= solar_separation
elif self.max is None and self.min is not None:
mask = self.min <= solar_separation
elif self.min is not None and self.max is not None:
mask = ((self.min <= solar_separation) &
(solar_separation <= self.max))
else:
raise ValueError("No max and/or min specified in "
"SunSeparationConstraint.")
return mask
[docs]class MoonSeparationConstraint(Constraint):
"""
Constrain the distance between the Earth's moon and some targets.
"""
def __init__(self, min=None, max=None, ephemeris=None):
"""
Parameters
----------
min : `~astropy.units.Quantity` or `None` (optional)
Minimum acceptable separation between moon and target (inclusive).
`None` indicates no limit.
max : `~astropy.units.Quantity` or `None` (optional)
Maximum acceptable separation between moon and target (inclusive).
`None` indicates no limit.
ephemeris : str, optional
Ephemeris to use. If not given, use the one set with
``astropy.coordinates.solar_system_ephemeris.set`` (which is
set to 'builtin' by default).
"""
self.min = min
self.max = max
self.ephemeris = ephemeris
[docs] def compute_constraint(self, times, observer, targets):
# removed the location argument here, which causes small <1 deg
# innacuracies, but it is needed until astropy PR #5897 is released
# which should be astropy 1.3.2
moon = get_moon(times,
ephemeris=self.ephemeris)
# note to future editors - the order matters here
# moon.separation(targets) is NOT the same as targets.separation(moon)
# the former calculates the separation in the frame of the moon coord
# which is GCRS, and that is what we want.
moon_separation = moon.separation(targets)
if self.min is None and self.max is not None:
mask = self.max >= moon_separation
elif self.max is None and self.min is not None:
mask = self.min <= moon_separation
elif self.min is not None and self.max is not None:
mask = ((self.min <= moon_separation) &
(moon_separation <= self.max))
else:
raise ValueError("No max and/or min specified in "
"MoonSeparationConstraint.")
return mask
[docs]class MoonIlluminationConstraint(Constraint):
"""
Constrain the fractional illumination of the Earth's moon.
Constraint is also satisfied if the Moon has set.
"""
def __init__(self, min=None, max=None, ephemeris=None):
"""
Parameters
----------
min : float or `None` (optional)
Minimum acceptable fractional illumination (inclusive). `None`
indicates no limit.
max : float or `None` (optional)
Maximum acceptable fractional illumination (inclusive). `None`
indicates no limit.
ephemeris : str, optional
Ephemeris to use. If not given, use the one set with
`~astropy.coordinates.solar_system_ephemeris` (which is
set to 'builtin' by default).
"""
self.min = min
self.max = max
self.ephemeris = ephemeris
@classmethod
[docs] def dark(cls, min=None, max=0.25, **kwargs):
"""
initialize a `~astroplan.constraints.MoonIlluminationConstraint`
with defaults of no minimum and a maximum of 0.25
Parameters
----------
min : float or `None` (optional)
Minimum acceptable fractional illumination (inclusive). `None`
indicates no limit.
max : float or `None` (optional)
Maximum acceptable fractional illumination (inclusive). `None`
indicates no limit.
"""
return cls(min, max, **kwargs)
@classmethod
[docs] def grey(cls, min=0.25, max=0.65, **kwargs):
"""
initialize a `~astroplan.constraints.MoonIlluminationConstraint`
with defaults of a minimum of 0.25 and a maximum of 0.65
Parameters
----------
min : float or `None` (optional)
Minimum acceptable fractional illumination (inclusive). `None`
indicates no limit.
max : float or `None` (optional)
Maximum acceptable fractional illumination (inclusive). `None`
indicates no limit.
"""
return cls(min, max, **kwargs)
@classmethod
[docs] def bright(cls, min=0.65, max=None, **kwargs):
"""
initialize a `~astroplan.constraints.MoonIlluminationConstraint`
with defaults of a minimum of 0.65 and no maximum
Parameters
----------
min : float or `None` (optional)
Minimum acceptable fractional illumination (inclusive). `None`
indicates no limit.
max : float or `None` (optional)
Maximum acceptable fractional illumination (inclusive). `None`
indicates no limit.
"""
return cls(min, max, **kwargs)
[docs] def compute_constraint(self, times, observer, targets):
# first is the moon up?
cached_moon = _get_moon_data(times, observer)
moon_alt = cached_moon['altaz'].alt
moon_down_mask = moon_alt < 0
moon_up_mask = moon_alt >= 0
illumination = cached_moon['illum']
if self.min is None and self.max is not None:
mask = (self.max >= illumination) | moon_down_mask
elif self.max is None and self.min is not None:
mask = (self.min <= illumination) & moon_up_mask
elif self.min is not None and self.max is not None:
mask = ((self.min <= illumination) &
(illumination <= self.max)) & moon_up_mask
else:
raise ValueError("No max and/or min specified in "
"MoonSeparationConstraint.")
return mask
[docs]class LocalTimeConstraint(Constraint):
"""
Constrain the observable hours.
"""
def __init__(self, min=None, max=None):
"""
Parameters
----------
min : `~datetime.time`
Earliest local time (inclusive). `None` indicates no limit.
max : `~datetime.time`
Latest local time (inclusive). `None` indicates no limit.
Examples
--------
Constrain the observations to targets that are observable between
23:50 and 04:08 local time:
>>> from astroplan import Observer
>>> from astroplan.constraints import LocalTimeConstraint
>>> import datetime as dt
>>> subaru = Observer.at_site("Subaru", timezone="US/Hawaii")
>>> # bound times between 23:50 and 04:08 local Hawaiian time
>>> constraint = LocalTimeConstraint(min=dt.time(23,50), max=dt.time(4,8))
"""
self.min = min
self.max = max
if self.min is None and self.max is None:
raise ValueError("You must at least supply either a minimum or a maximum time.")
if self.min is not None:
if not isinstance(self.min, datetime.time):
raise TypeError("Time limits must be specified as datetime.time objects.")
if self.max is not None:
if not isinstance(self.max, datetime.time):
raise TypeError("Time limits must be specified as datetime.time objects.")
[docs] def compute_constraint(self, times, observer, targets):
timezone = None
# get timezone from time objects, or from observer
if self.min is not None:
timezone = self.min.tzinfo
elif self.max is not None:
timezone = self.max.tzinfo
if timezone is None:
timezone = observer.timezone
if self.min is not None:
min_time = self.min
else:
min_time = self.min = datetime.time(0, 0, 0)
if self.max is not None:
max_time = self.max
else:
max_time = datetime.time(23, 59, 59)
# If time limits occur on same day:
if self.min < self.max:
try:
mask = np.array([min_time <= t.time() <= max_time for t in times.datetime])
except:
# use np.bool so shape queries don't cause problems
mask = np.bool_(min_time <= times.datetime.time() <= max_time)
# If time boundaries straddle midnight:
else:
try:
mask = np.array([(t.time() >= min_time) or
(t.time() <= max_time) for t in times.datetime])
except:
mask = np.bool_((times.datetime.time() >= min_time) or
(times.datetime.time() <= max_time))
return mask
[docs]class TimeConstraint(Constraint):
"""Constrain the observing time to be within certain time limits.
An example use case for this class would be to associate an acceptable
time range with a specific observing block. This can be useful if not
all observing blocks are valid over the time limits used in calls
to `is_observable` or `is_always_observable`.
"""
def __init__(self, min=None, max=None):
"""
Parameters
----------
min : `~astropy.time.Time`
Earliest time (inclusive). `None` indicates no limit.
max : `~astropy.time.Time`
Latest time (inclusive). `None` indicates no limit.
Examples
--------
Constrain the observations to targets that are observable between
2016-03-28 and 2016-03-30:
>>> from astroplan import Observer
>>> from astropy.time import Time
>>> subaru = Observer.at_site("Subaru")
>>> t1 = Time("2016-03-28T12:00:00")
>>> t2 = Time("2016-03-30T12:00:00")
>>> constraint = TimeConstraint(t1,t2)
"""
self.min = min
self.max = max
if self.min is None and self.max is None:
raise ValueError("You must at least supply either a minimum or a "
"maximum time.")
if self.min is not None:
if not isinstance(self.min, Time):
raise TypeError("Time limits must be specified as "
"astropy.time.Time objects.")
if self.max is not None:
if not isinstance(self.max, Time):
raise TypeError("Time limits must be specified as "
"astropy.time.Time objects.")
[docs] def compute_constraint(self, times, observer, targets):
with warnings.catch_warnings():
warnings.simplefilter('ignore')
min_time = Time("1950-01-01T00:00:00") if self.min is None else self.min
max_time = Time("2120-01-01T00:00:00") if self.max is None else self.max
mask = np.logical_and(times > min_time, times < max_time)
return mask
[docs]def is_always_observable(constraints, observer, targets, times=None,
time_range=None, time_grid_resolution=0.5*u.hour):
"""
A function to determine whether ``targets`` are always observable throughout
``time_range`` given constraints in the ``constraints_list`` for a
particular ``observer``.
Parameters
----------
constraints : list or `~astroplan.constraints.Constraint`
Observational constraint(s)
observer : `~astroplan.Observer`
The observer who has constraints ``constraints``
targets : {list, `~astropy.coordinates.SkyCoord`, `~astroplan.FixedTarget`}
Target or list of targets
times : `~astropy.time.Time` (optional)
Array of times on which to test the constraint
time_range : `~astropy.time.Time` (optional)
Lower and upper bounds on time sequence, with spacing
``time_resolution``. This will be passed as the first argument into
`~astroplan.time_grid_from_range`.
time_grid_resolution : `~astropy.units.Quantity` (optional)
If ``time_range`` is specified, determine whether constraints are met
between test times in ``time_range`` by checking constraint at
linearly-spaced times separated by ``time_resolution``. Default is 0.5
hours.
Returns
-------
ever_observable : list
List of booleans of same length as ``targets`` for whether or not each
target is observable in the time range given the constraints.
"""
if not hasattr(constraints, '__len__'):
constraints = [constraints]
applied_constraints = [constraint(observer, targets, times=times,
time_range=time_range,
time_grid_resolution=time_grid_resolution,
grid_times_targets=True)
for constraint in constraints]
constraint_arr = np.logical_and.reduce(applied_constraints)
return np.all(constraint_arr, axis=1)
[docs]def is_observable(constraints, observer, targets, times=None,
time_range=None, time_grid_resolution=0.5*u.hour):
"""
Determines if the ``targets`` are observable during ``time_range`` given
constraints in ``constraints_list`` for a particular ``observer``.
Parameters
----------
constraints : list or `~astroplan.constraints.Constraint`
Observational constraint(s)
observer : `~astroplan.Observer`
The observer who has constraints ``constraints``
targets : {list, `~astropy.coordinates.SkyCoord`, `~astroplan.FixedTarget`}
Target or list of targets
times : `~astropy.time.Time` (optional)
Array of times on which to test the constraint
time_range : `~astropy.time.Time` (optional)
Lower and upper bounds on time sequence, with spacing
``time_resolution``. This will be passed as the first argument into
`~astroplan.time_grid_from_range`.
time_grid_resolution : `~astropy.units.Quantity` (optional)
If ``time_range`` is specified, determine whether constraints are met
between test times in ``time_range`` by checking constraint at
linearly-spaced times separated by ``time_resolution``. Default is 0.5
hours.
Returns
-------
ever_observable : list
List of booleans of same length as ``targets`` for whether or not each
target is ever observable in the time range given the constraints.
"""
if not hasattr(constraints, '__len__'):
constraints = [constraints]
applied_constraints = [constraint(observer, targets, times=times,
time_range=time_range,
time_grid_resolution=time_grid_resolution,
grid_times_targets=True)
for constraint in constraints]
constraint_arr = np.logical_and.reduce(applied_constraints)
return np.any(constraint_arr, axis=1)
[docs]def months_observable(constraints, observer, targets,
time_grid_resolution=0.5*u.hour):
"""
Determines which month the specified ``targets`` are observable for a
specific ``observer``, given the supplied ``constriants``.
Parameters
----------
constraints : list or `~astroplan.constraints.Constraint`
Observational constraint(s)
observer : `~astroplan.Observer`
The observer who has constraints ``constraints``
targets : {list, `~astropy.coordinates.SkyCoord`, `~astroplan.FixedTarget`}
Target or list of targets
time_grid_resolution : `~astropy.units.Quantity` (optional)
If ``time_range`` is specified, determine whether constraints are met
between test times in ``time_range`` by checking constraint at
linearly-spaced times separated by ``time_resolution``. Default is 0.5
hours.
Returns
-------
observable_months : list
List of sets of unique integers representing each month that a target is
observable, one set per target. These integers are 1-based so that
January maps to 1, February maps to 2, etc.
"""
# TODO: This method could be sped up a lot by dropping to the trigonometric
# altitude calculations.
if not hasattr(constraints, '__len__'):
constraints = [constraints]
# Calculate throughout the year of 2014 so as not to require forward
# extrapolation off of the IERS tables
time_range = Time(['2014-01-01', '2014-12-31'])
times = time_grid_from_range(time_range, time_grid_resolution)
# TODO: This method could be sped up a lot by dropping to the trigonometric
# altitude calculations.
applied_constraints = [constraint(observer, targets,
times=times,
grid_times_targets=True)
for constraint in constraints]
constraint_arr = np.logical_and.reduce(applied_constraints)
months_observable = []
for target, observable in zip(targets, constraint_arr):
s = set([t.datetime.month for t in times[observable]])
months_observable.append(s)
return months_observable
[docs]def observability_table(constraints, observer, targets, times=None,
time_range=None, time_grid_resolution=0.5*u.hour):
"""
Creates a table with information about observability for all the ``targets``
over the requested ``time_range``, given the constraints in
``constraints_list`` for ``observer``.
Parameters
----------
constraints : list or `~astroplan.constraints.Constraint`
Observational constraint(s)
observer : `~astroplan.Observer`
The observer who has constraints ``constraints``
targets : {list, `~astropy.coordinates.SkyCoord`, `~astroplan.FixedTarget`}
Target or list of targets
times : `~astropy.time.Time` (optional)
Array of times on which to test the constraint
time_range : `~astropy.time.Time` (optional)
Lower and upper bounds on time sequence, with spacing
``time_resolution``. This will be passed as the first argument into
`~astroplan.time_grid_from_range`.
time_grid_resolution : `~astropy.units.Quantity` (optional)
If ``time_range`` is specified, determine whether constraints are met
between test times in ``time_range`` by checking constraint at
linearly-spaced times separated by ``time_resolution``. Default is 0.5
hours.
Returns
-------
observability_table : `~astropy.table.Table`
A Table containing the observability information for each of the
``targets``. The table contains four columns with information about the
target and it's observability: ``'target name'``, ``'ever observable'``,
``'always observable'``, and ``'fraction of time observable'``. It also
contains metadata entries ``'times'`` (with an array of all the times),
``'observer'`` (the `~astroplan.Observer` object), and ``'constraints'``
(containing the supplied ``constraints``).
"""
if not hasattr(constraints, '__len__'):
constraints = [constraints]
applied_constraints = [constraint(observer, targets, times=times,
time_range=time_range,
time_grid_resolution=time_grid_resolution,
grid_times_targets=True)
for constraint in constraints]
constraint_arr = np.logical_and.reduce(applied_constraints)
colnames = ['target name', 'ever observable', 'always observable',
'fraction of time observable']
target_names = [target.name for target in targets]
ever_obs = np.any(constraint_arr, axis=1)
always_obs = np.all(constraint_arr, axis=1)
frac_obs = np.sum(constraint_arr, axis=1) / constraint_arr.shape[1]
tab = table.Table(names=colnames, data=[target_names, ever_obs, always_obs,
frac_obs])
if times is None and time_range is not None:
times = time_grid_from_range(time_range,
time_resolution=time_grid_resolution)
tab.meta['times'] = times.datetime
tab.meta['observer'] = observer
tab.meta['constraints'] = constraints
return tab
[docs]def min_best_rescale(vals, min_val, max_val, less_than_min=1):
"""
rescales an input array ``vals`` to be a score (between zero and one),
where the ``min_val`` goes to one, and the ``max_val`` goes to zero.
Parameters
----------
vals : array-like
the values that need to be rescaled to be between 0 and 1
min_val : float
worst acceptable value (rescales to 0)
max_val : float
best value cared about (rescales to 1)
less_than_min : 0 or 1
what is returned for ``vals`` below ``min_val``. (in some cases
anything less than ``min_val`` should also return one,
in some cases it should return zero)
Returns
-------
array of floats between 0 and 1 inclusive rescaled so that
``vals`` equal to ``max_val`` equal 0 and those equal to
``min_val`` equal 1
Examples
--------
rescale airmasses to between 0 and 1, with the best (1)
and worst (2.25). All values outside the range should
return 0.
>>> from astroplan.constraints import min_best_rescale
>>> import numpy as np
>>> airmasses = np.array([1, 1.5, 2, 3, 0])
>>> min_best_rescale(airmasses, 1, 2.25, less_than_min = 0)
array([ 1. , 0.6, 0.2, 0. , 0. ])
"""
rescaled = (vals - max_val) / (min_val - max_val)
below = vals < min_val
above = vals > max_val
rescaled[below] = less_than_min
rescaled[above] = 0
return rescaled
[docs]def max_best_rescale(vals, min_val, max_val, greater_than_max=1):
"""
rescales an input array ``vals`` to be a score (between zero and one),
where the ``max_val`` goes to one, and the ``min_val`` goes to zero.
Parameters
----------
vals : array-like
the values that need to be rescaled to be between 0 and 1
min_val : float
worst acceptable value (rescales to 0)
max_val : float
best value cared about (rescales to 1)
greater_than_max : 0 or 1
what is returned for ``vals`` above ``max_val``. (in some cases
anything higher than ``max_val`` should also return one,
in some cases it should return zero)
Returns
-------
array of floats between 0 and 1 inclusive rescaled so that
``vals`` equal to ``min_val`` equal 0 and those equal to
``max_val`` equal 1
Examples
--------
rescale an array of altitudes to be between 0 and 1,
with the best (60) going to 1 and worst (35) going to
0. For values outside the range, the rescale should
return 0 below 35 and 1 above 60.
>>> from astroplan.constraints import max_best_rescale
>>> import numpy as np
>>> altitudes = np.array([20, 30, 40, 45, 55, 70])
>>> max_best_rescale(altitudes, 35, 60)
array([ 0. , 0. , 0.2, 0.4, 0.8, 1. ])
"""
rescaled = (vals - min_val) / (max_val - min_val)
below = vals < min_val
above = vals > max_val
rescaled[below] = 0
rescaled[above] = greater_than_max
return rescaled
```