From f9cce2c52e7275ed45557b3289a35800d15be676 Mon Sep 17 00:00:00 2001
From: Laura Sandoval <46567335+laspsandoval@users.noreply.github.com>
Date: Wed, 14 Aug 2024 10:33:09 -0600
Subject: [PATCH] Calculate the path length for L1b Ultra (#749)

* Calculate the path length for L1b Ultra
---
 .../ultra/unit/test_ultra_l1b_extended.py     | 39 ++++++++++++++-----
 .../ultra/l1b/ultra_l1b_extended.py           | 27 +++++++++++++
 2 files changed, 56 insertions(+), 10 deletions(-)

diff --git a/imap_processing/tests/ultra/unit/test_ultra_l1b_extended.py b/imap_processing/tests/ultra/unit/test_ultra_l1b_extended.py
index 88989edd5..b48c62afe 100644
--- a/imap_processing/tests/ultra/unit/test_ultra_l1b_extended.py
+++ b/imap_processing/tests/ultra/unit/test_ultra_l1b_extended.py
@@ -6,9 +6,23 @@
 from imap_processing.ultra.l1b.ultra_l1b_extended import (
     get_front_x_position,
     get_front_y_position,
+    get_path_length,
 )
 
 
+@pytest.fixture()
+def yf_fixture(de_dataset, events_fsw_comparison_theta_0):
+    """Fixture to compute and return yf and related data."""
+    df = pd.read_csv(events_fsw_comparison_theta_0)
+    df_filt = df[df["StartType"] != -1]
+
+    d, yf = get_front_y_position(
+        de_dataset["START_TYPE"].data, df_filt.Yb.values.astype("float")
+    )
+
+    return df_filt, d, yf
+
+
 def test_get_front_x_position(
     de_dataset,
     events_fsw_comparison_theta_0,
@@ -26,17 +40,22 @@ def test_get_front_x_position(
     assert xf == pytest.approx(df_filt["Xf"].astype("float"), 1e-5)
 
 
-def test_get_front_y_position(
-    de_dataset,
-    events_fsw_comparison_theta_0,
-):
+def test_get_front_y_position(yf_fixture):
     """Tests get_front_y_position function."""
+    df_filt, d, yf = yf_fixture
 
-    df = pd.read_csv(events_fsw_comparison_theta_0)
-    df_filt = df[df["StartType"] != -1]
+    assert yf == pytest.approx(df_filt["Yf"].astype("float"), abs=1e-5)
 
-    d, yf = get_front_y_position(
-        de_dataset["START_TYPE"].data, df_filt.Yb.values.astype("float")
-    )
 
-    assert yf == pytest.approx(df_filt["Yf"].astype("float"), abs=1e-5)
+def test_get_path_length(de_dataset, yf_fixture):
+    """Tests get_path_length function."""
+
+    df_filt, d, yf = yf_fixture
+
+    test_xf = df_filt["Xf"].astype("float").values
+    test_yf = df_filt["Yf"].astype("float").values
+
+    test_xb = df_filt["Xb"].astype("float").values
+    test_yb = df_filt["Yb"].astype("float").values
+    r = get_path_length((test_xf, test_yf), (test_xb, test_yb), d)
+    assert r == pytest.approx(df_filt["r"].astype("float"), abs=1e-5)
diff --git a/imap_processing/ultra/l1b/ultra_l1b_extended.py b/imap_processing/ultra/l1b/ultra_l1b_extended.py
index 52e3a42dc..c977981fb 100644
--- a/imap_processing/ultra/l1b/ultra_l1b_extended.py
+++ b/imap_processing/ultra/l1b/ultra_l1b_extended.py
@@ -109,3 +109,30 @@ def get_front_y_position(start_type: ndarray, yb: ndarray) -> tuple[ndarray, nda
     d[index_right] = (SLIT_Z - distance_adjust_right) * 100
 
     return np.array(d), np.array(yf)
+
+
+def get_path_length(front_position: tuple, back_position: tuple, d: float) -> float:
+    """
+    Calculate the path length.
+
+    Parameters
+    ----------
+    front_position : tuple of floats
+        Front position (xf,yf) (hundredths of a millimeter).
+    back_position : tuple of floats
+        Back position (xb,yb) (hundredths of a millimeter).
+    d : float
+        Distance from slit to foil (hundredths of a millimeter).
+
+    Returns
+    -------
+    r : float
+        Path length (hundredths of a millimeter).
+    """
+    r: float = np.sqrt(
+        (front_position[0] - back_position[0]) ** 2
+        + (front_position[1] - back_position[1]) ** 2
+        + (d) ** 2
+    )
+
+    return r