Add radec_to_desiname function

py/desiutil/names.py

@@ -0,0 +1,62 @@
+# Licensed under a 3-clause BSD style license - see LICENSE.rst
+# -*- coding: utf-8 -*-
+"""
+============
+desiutil.names
+============
+
+This package contains functions for naming 'things' in DESI
+or decoding those names
+"""
+import numpy as np
+
+
+def radec_to_desiname(target_ra, target_dec):
+    """Convert the right ascension and declination of a DESI target
+    into the corresponding "DESI name" for reference in publications.
+    Length of target_ra and target_dec must be the same if providing an
+    array or list.
+
+    Parameters
+    ----------
+    target_ra: array of :class:`float64`
+        Right ascension in degrees of target object(s). Can be float, double,
+         or array/list of floats or doubles
+    target_dec: array of :class:`float64`
+        Declination in degrees of target object(s). Can be float, double,
+         or array/list of floats or doubles
+
+    Returns
+    -------
+    array of :class:`str`
+        The DESI names referring to the input target RA and DEC's. Array is
+        the same length as the input arrays.
+
+    """
+    # Convert to numpy array in case inputs are scalars or lists
+    target_ra, target_dec = np.atleast_1d(target_ra), np.atleast_1d(target_dec)
+
+    # Number of decimal places in final naming convention
+    precision = 4
+
+    # Truncate decimals to the given precision
+    ratrunc = np.trunc((10 ** precision) * target_ra).astype(int).astype(str)
+    dectrunc = np.trunc((10 ** precision) * target_dec).astype(int).astype(str)
+
+    # Loop over input values and create DESINAME as: DESI JXXX.XXXX+/-YY.YYYY
+    # Here J refers to J2000, which isn't strictly correct but is the closest
+    #   IAU compliant term
+    desinames = []
+    for ra, dec in zip(ratrunc, dectrunc):
+        desiname = 'DESI J' + ra[:-precision].zfill(3) + '.' + ra[-precision:]
+        # Positive numbers need an explicit "+" while negative numbers
+        #   already have a "-".
+        # zfill works properly with '-' but counts it in number of characters
+        #   so need one more
+        if dec.startswith('-'):
+            desiname += dec[:-precision].zfill(3) + '.' + dec[-precision:]
+        else:
+            desiname += '+' + dec[:-precision].zfill(2) + '.' + dec[-precision:]
+        desinames.append(desiname)
+
+    return np.array(desinames)

py/desiutil/test/test_names.py

@@ -0,0 +1,46 @@
+# Licensed under a 3-clause BSD style license - see LICENSE.rst
+# -*- coding: utf-8 -*-
+"""Test desiutil.names.
+"""
+import unittest
+import numpy as np
+
+
+class TestNames(unittest.TestCase):
+    """Test desiutil.names
+    """
+
+    @classmethod
+    def setUpClass(cls):
+        pass
+
+    @classmethod
+    def tearDownClass(cls):
+        pass
+
+    def test_radec_to_desiname(self):
+        """Test MaskedArrayWithLimits
+        """
+        from ..names import radec_to_desiname
+        ras = [6.2457354547234, 23.914121939862518, 36.23454570972834,
+               235.25235223446, 99.9999999999999]
+        decs = [29.974787585945496, -42.945872347904356, -0.9968423456,
+                8.45677345352345, 89.234958294953]
+        correct_names = np.array(['DESI J006.2457+29.9747',
+                                  'DESI J023.9141-42.9458',
+                                  'DESI J036.2345-00.9968',
+                                  'DESI J235.2523+08.4567',
+                                  'DESI J099.9999+89.2349'])
+        # Test scalar conversion
+        for ra, dec, correct_name in zip(ras, decs, correct_names):
+            outname = radec_to_desiname(ra, dec)
+            self.assertEqual(outname, correct_name)
+
+        # Test list conversion
+        outnames = radec_to_desiname(ras, decs)
+        self.assertTrue(np.alltrue(outnames == correct_names))
+
+        # Test array conversion
+        outnames = radec_to_desiname(np.array(ras),
+                                     np.array(decs))
+        self.assertTrue(np.alltrue(outnames == correct_names))