From 0ea2cf7adec04a52c725b113b8a4d9bd9dcba225 Mon Sep 17 00:00:00 2001
From: Richard Janssen <richard@aerlabs.com>
Date: Tue, 3 Sep 2019 12:15:34 +0200
Subject: [PATCH] Fix surface positions for negative longitude

---
 .gitignore                   | 10 ++++++++++
 pyModeS/decoder/bds/bds06.py |  3 +++
 tests/test_bds_inference.py  | 15 +++++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/.gitignore b/.gitignore
index 68d6eaa..ddc0d0a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -58,3 +58,13 @@ target/
 
 # PyCharm
 .idea/
+
+# Environments
+.env
+.venv
+.virtualenvs
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
diff --git a/pyModeS/decoder/bds/bds06.py b/pyModeS/decoder/bds/bds06.py
index 2c6c346..a31fe64 100644
--- a/pyModeS/decoder/bds/bds06.py
+++ b/pyModeS/decoder/bds/bds06.py
@@ -89,6 +89,9 @@ def surface_position(msg0, msg1, t0, t1, lat_ref, lon_ref):
     # four possible longitude solutions
     lons = [lon, lon + 90.0, lon + 180.0, lon + 270.0]
 
+    # make sure lons are between -180 and 180
+    lons = [(l + 180) % 360 - 180 for l in lons]
+
     # the closest solution to receiver is the correct one
     dls = [abs(lon_ref - l) for l in lons]
     imin = min(range(4), key=dls.__getitem__)
diff --git a/tests/test_bds_inference.py b/tests/test_bds_inference.py
index f7b8f2f..a6e6ca4 100644
--- a/tests/test_bds_inference.py
+++ b/tests/test_bds_inference.py
@@ -18,3 +18,18 @@ def test_bds_is50or60():
     assert bds.is50or60("A0001838201584F23468207CDFA5", 0, 0, 0) == None
     assert bds.is50or60("A0000000FFDA9517000464000000", 182, 237, 1250) == 'BDS50'
     assert bds.is50or60("A0000000919A5927E23444000000", 413, 54, 18700) == 'BDS60'
+
+
+def test_surface_position():
+    msg0 = "8FE48C033A9FA184B934E744C6FD"
+    msg1 = "8FE48C033A9FA68F7C3D39B1C2F0"
+
+    t0 = 1565608663102
+    t1 = 1565608666214
+
+    lat_ref = -23.4265448
+    lon_ref = -46.4816258
+
+    lat, lon = bds.bds06.surface_position(msg0, msg1, t0, t1, lat_ref, lon_ref)
+
+    assert abs(lon_ref - lon) < 0.05