From 60828ba200c0d35d3e1eae261eaee7f6af49e776 Mon Sep 17 00:00:00 2001
From: Christian Wygoda <christian.wygoda@satellitevu.com>
Date: Thu, 30 Jan 2025 09:32:05 +0100
Subject: [PATCH] fix: footprint was calculated on wrong side of orbit

---
 tle_sat/satellite.py      |  8 ++++----
 tle_sat/satellite_test.py | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/tle_sat/satellite.py b/tle_sat/satellite.py
index 3711fbd..954acb9 100644
--- a/tle_sat/satellite.py
+++ b/tle_sat/satellite.py
@@ -165,22 +165,22 @@ def footprint(
         try:
             fr = self.los(
                 t,
-                -view_angles.across - 0.5 * fov.x,
+                view_angles.across + 0.5 * fov.x,
                 view_angles.along + 0.5 * fov.y,
             )
             fl = self.los(
                 t,
-                -view_angles.across + 0.5 * fov.x,
+                view_angles.across - 0.5 * fov.x,
                 view_angles.along + 0.5 * fov.y,
             )
             rl = self.los(
                 t,
-                -view_angles.across + 0.5 * fov.x,
+                view_angles.across - 0.5 * fov.x,
                 view_angles.along - 0.5 * fov.y,
             )
             rr = self.los(
                 t,
-                -view_angles.across - 0.5 * fov.x,
+                view_angles.across + 0.5 * fov.x,
                 view_angles.along - 0.5 * fov.y,
             )
         except OverflowError as exc:
diff --git a/tle_sat/satellite_test.py b/tle_sat/satellite_test.py
index 867c4fe..3026181 100644
--- a/tle_sat/satellite_test.py
+++ b/tle_sat/satellite_test.py
@@ -134,6 +134,40 @@ def test_footprint(polar_tle, t, v, f, expectation):
             assert all(not is_ccw(interior) for interior in e.interiors)
 
 
+@mark.parametrize(
+    "target,t,footprint",
+    (
+        (
+            Point(13, 53, 0),
+            datetime(2024, 4, 19, 21, 39, 59, tzinfo=timezone.utc),
+            Polygon(
+                (
+                    (13.20496447259038, 52.87415752284107),
+                    (12.758567800131482, 52.90986652401911),
+                    (12.799711072078717, 53.12031287404936),
+                    (13.249444062185855, 53.090245713914435),
+                    (13.20496447259038, 52.87415752284107),
+                )
+            ),
+        ),
+    ),
+)
+def test_pass_footprint(polar_tle, target: Point, t: datetime, footprint: Polygon):
+    sat = Satellite(polar_tle)
+
+    passes = sat.passes(
+        TimeOfInterest(t - timedelta(minutes=15), t + timedelta(minutes=15)), target
+    )
+    assert len(passes) == 1
+    p = passes[0]
+
+    actual_footprint = sat.footprint(t=p.t, view_angles=p.view_angles)
+
+    assert _precision(footprint, 8).equals(_precision(actual_footprint, 8))
+    assert actual_footprint.contains(target)
+    assert _precision(footprint.centroid, 2).equals(_precision(target, 2))
+
+
 @mark.parametrize(
     "t,target,passes",
     (