NonFixedTarget

astroplan/core.py

@@ -1681,7 +1681,10 @@ def ra(self):
         """
         if isinstance(self, FixedTarget):
             return self.coord.ra
-        raise NotImplementedError()
+        if isinstance(self. NonFixedTarget):
+            raise ValueError("NonFixedTarget objects require a time and/or "
+                             "other specifications to calculate a position. "
+                             "Did you mean to do NonFixedTarget.at(args).ra?")
 
     @property
     def dec(self):
@@ -1690,8 +1693,10 @@ def dec(self):
         """
         if isinstance(self, FixedTarget):
             return self.coord.dec
-        raise NotImplementedError()
-
+        if isinstance(self. NonFixedTarget):
+            raise ValueError("NonFixedTarget objects require a time and/or "
+                             "other specifications to calculate a position. "
+                             "Did you mean to do NonFixedTarget.at(args).dec?")
 
 class FixedTarget(Target):
     """
@@ -1802,8 +1807,59 @@ def _fixed_target_from_name_mock(cls, name):
 
 class NonFixedTarget(Target):
     """
-    Placeholder for future function.
+    An object that is not "fixed" with respect to the celestial sphere.
+
+    A NonFixedTarget object holds a function that computes the coordinates
+    of the object at various points in time.
+
+    NonFixedTarget objects can at present be initialized only by the
+    ``NonFixedTarget.from_name`` class method.
     """
+    def __init__(self, coord_function=None, name=None, constant_kwargs=None):
+        """
+        TODO: Docstring.
+        """
+        self.name = name.lower() if name is not None else name
+        self.coord_function = coord_function
+        self.constant_kwargs = constant_kwargs
+
+    @classmethod
+    def from_function(cls, coord_function, name=None):
+        """
+        Initialize a `~astropy.NonFixedTarget` by passing in a function that
+        computes a `~astropy.coordinates.SkyCoord` for the target object.
+
+        Parameters
+        ----------
+        coord_function : function
+            This function takes some input parameters and outputs a
+            `~astropy.coordinates.SkyCoord` for the object at one instance
+            in time
+
+        name : str (optional)
+            Name of the object
+        """
+        return cls(coord_function=coord_function, name=name)
+
+    def at(self, *args, **kwargs):
+        """
+        Get a `~astropy.coordinates.SkyCoord` object for the
+        `~astroplan.NonFixedTarget` at a given time, and/or other parameters.
+
+        Parameters
+        ----------
+        All arguments and keyword arguments passed to already-specified
+        ``self.coord_function``.
+
+        Returns
+        -------
+        `~astropy.coordinates.SkyCoord`
+            Specified by passing the arguments to ``self.coord_function``.
+        """
+        if self.constant_kwargs is not None:
+            for key in self.constant_kwargs:
+                kwargs[key] = self.constant_kwargs[key]
+        return self.coord_function(*args, **kwargs)
 
 class Constraint(object):
     """

astroplan/tests/test_core.py

@@ -2,10 +2,10 @@
                         unicode_literals)
 
 from astropy.coordinates import (EarthLocation, Latitude, Longitude, SkyCoord,
-                                 AltAz)
+                                 AltAz, get_sun)
 import astropy.units as u
 from astropy.time import Time
-from astropy.tests.helper import remote_data
+from astropy.tests.helper import remote_data, assert_quantity_allclose
 import numpy as np
 from numpy.testing import assert_allclose
 import pytz
@@ -14,7 +14,8 @@
 
 from ..sites import get_site
 from ..core import (FixedTarget, Observer, list_FixedTarget_to_SkyCoord,
-                    MAGIC_TIME)
+                    MAGIC_TIME, NonFixedTarget)
+from ..moon import get_moon
 from ..exceptions import TargetAlwaysUpWarning, TargetNeverUpWarning
 
 try:
@@ -70,6 +71,31 @@ def test_FixedTarget_from_name():
     # Make sure separation is small
     assert polaris_from_name.coord.separation(polaris_from_SIMBAD) < 1*u.arcsec
 
+def test_NonFixedTarget_sun():
+    time = Time("1995-08-31 02:03:04")
+    sun = NonFixedTarget(coord_function=get_sun, name="Sun")
+    sun_skycoord_nft = sun.at(time)
+
+    sun_skycoord_getsun = get_sun(time)
+    tolerance = 0.1*u.arcsec
+    assert_quantity_allclose(sun_skycoord_nft.ra, sun_skycoord_getsun.ra,
+                             atol=tolerance)
+    assert_quantity_allclose(sun_skycoord_nft.dec, sun_skycoord_getsun.dec,
+                             atol=tolerance)
+
+def test_NonFixedTarget_moon():
+    time = Time("1995-08-31 02:03:04")
+    location = get_site("Subaru")
+    pressure = 0*u.bar
+    moon = NonFixedTarget(coord_function=get_moon, name="Moon")
+    moon_skycoord_nft = moon.at(time, location, pressure)
+
+    moon_skycoord_getmoon = get_moon(time, location, pressure)
+    tolerance = 0.1*u.arcsec
+    assert_quantity_allclose(moon_skycoord_nft.alt, moon_skycoord_getmoon.alt,
+                             atol=tolerance)
+    assert_quantity_allclose(moon_skycoord_nft.az, moon_skycoord_getmoon.az,
+                             atol=tolerance)
 
 def test_Observer_altaz():
     """