Change allowed_rolldev to use chandra_models

ska_sun/sun.py

@@ -3,7 +3,6 @@
 Utility for calculating sun position, pitch angle and values related to roll.
 """
 from math import acos, asin, atan2, cos, degrees, pi, radians, sin
-from pathlib import Path
 
 import numpy as np
 import Ska.quatutil
@@ -12,14 +11,20 @@
 from chandra_aca.transform import radec_to_eci
 from Quaternion import Quat
 from ska_helpers.utils import LazyVal
+from ska_helpers import chandra_models
+
+
+CHANDRA_MODELS_PITCH_ROLL_FILE = "chandra_models/pitch_roll/pitch_roll_constraint.csv"
 
 
 def load_roll_table():
-    dat = Table.read(Path(__file__).parent / "data" / "pitch_roll.fits.gz")
+    """Load the pitch/roll table from the chandra_models repo."""
+    dat = chandra_models.get_data(
+        CHANDRA_MODELS_PITCH_ROLL_FILE, read_func=Table.read
+    )
+    # Sanity check that the pitch values are monotonically increasing.
+    assert np.all(np.diff(dat["pitch"]) > 0)
 
-    # Add a terminating row to the data such that for pitch at or greater
-    # than 180 the allowed roll deviation is defined as 0.
-    dat.add_row({"pitch": 180, "rolldev": 0})
     return dat
 
 
@@ -28,17 +33,24 @@ def load_roll_table():
 
 def allowed_rolldev(pitch):
     """Get allowed roll deviation (off-nominal roll) for the given ``pitch``.
-    :param pitch: Sun pitch angle (deg)
-    :returns: Roll deviation (deg)
+
+    This performs a linear interpolation of the values in the pitch/roll table in
+    the chandra_models repo in ``chandra_models/pitch_roll/pitch_roll_constraint.csv``.
+
+    For pitch values outside the range of the table the returned rolldev is 0.
+
+    :param pitch: float, ndarray
+        Sun pitch angle (deg)
+    :returns: float, ndarray
+        Roll deviation (deg)
     """
-    idx1 = np.searchsorted(ROLL_TABLE.val["pitch"], pitch, side="right")
-    idx0 = idx1 - 1
-    idx_max = len(ROLL_TABLE.val) - 1
-    idx0 = np.clip(idx0, 0, idx_max)
-    idx1 = np.clip(idx1, 0, idx_max)
-    val0 = ROLL_TABLE.val["rolldev"][idx0]
-    val1 = ROLL_TABLE.val["rolldev"][idx1]
-    out = np.minimum(val0, val1)  # works even for a vector input for `pitch`
+    out = np.interp(
+        x=pitch,
+        xp=ROLL_TABLE.val["pitch"],
+        fp=ROLL_TABLE.val["off_nom_roll"],
+        left=0,
+        right=0,
+    )
     return out
 
 

ska_sun/tests/test_sun.py

@@ -1,6 +1,7 @@
 # Licensed under a 3-clause BSD style license - see LICENSE.rst
 
 import numpy as np
+import pytest
 from Quaternion import Quat
 
 from ..sun import (
@@ -13,30 +14,35 @@
 from ..sun import pitch as sun_pitch
 from ..sun import position
 
-
-def test_allowed_rolldev():
-
-    # Test array of pitchs and allowed roll dev
-    testarr = [
-        [135, 13.979],
-        [138, 14.516],
+# Expected pitch, rolldev pairs
+exp_pitch_rolldev = np.array(
+    [
         [0, 0],
         [40, 0],
-        [179.9, 18.748772],
-        [179.997, 0],
+        [56.0, 0],
+        [85.49229, 4.95597],
+        [85.52, 4.9560848],
+        [124.99, 12.23652],
+        [125, 12.2380],
+        [135, 13.979],
+        [138, 14.516],
+        [179.9, 18.749],
+        [179.997, 18.749],
         [180, 0],
         [181, 0],
-        [85.49229, 13.677669],
-        [85.52, 18.756727],
-        [124.99, 18.748772],
-        [125, 17.0],
     ]
-    for pitch, rolldev in testarr:
-        assert np.isclose(allowed_rolldev(pitch), rolldev)
+)
+
+@pytest.mark.parametrize("pitch, rolldev", exp_pitch_rolldev)
+def test_allowed_rolldev(pitch, rolldev):
+
+    # Test array of pitchs and allowed roll dev
+    assert np.isclose(allowed_rolldev(pitch), rolldev)
+
 
-    # Also test with pitch as vector
+def test_allowed_rolldev_vector():
     assert np.allclose(
-        allowed_rolldev(np.array(testarr)[:, 0]), np.array(testarr)[:, 1]
+        allowed_rolldev(exp_pitch_rolldev[:, 0]), exp_pitch_rolldev[:, 1]
     )