update airborne_position(), allow swapping the odd and even messages

pyModeS/decoder/bds/bds05.py

@@ -24,6 +24,7 @@
 from __future__ import absolute_import, print_function, division
 from pyModeS.decoder import common
 
+
 def airborne_position(msg0, msg1, t0, t1):
     """Decode airborn position from a pair of even and odd position message
 
@@ -40,6 +41,16 @@ def airborne_position(msg0, msg1, t0, t1):
     mb0 = common.hex2bin(msg0)[32:]
     mb1 = common.hex2bin(msg1)[32:]
 
+    oe0 = int(mb0[21])
+    oe1 = int(mb1[21])
+    if oe0 == 0 and oe1 == 1:
+        pass
+    elif oe0 == 1 and oe1 == 0:
+        mb0, mb1 = mb1, mb0
+        t0, t1 = t1, t0
+    else:
+        raise RuntimeError("Both even and odd CPR frames are required.")
+
     # 131072 is 2^17, since CPR lat and lon are 17 bits each.
     cprlat_even = common.bin2int(mb0[22:39]) / 131072.0
     cprlon_even = common.bin2int(mb0[39:56]) / 131072.0
@@ -66,7 +77,7 @@ def airborne_position(msg0, msg1, t0, t1):
         return None
 
     # compute ni, longitude index m, and longitude
-    if (t0 > t1):
+    if t0 > t1:
         lat = lat_even
         nl = common.cprNL(lat)
         ni = max(common.cprNL(lat) - 0, 1)
@@ -100,7 +111,6 @@ def airborne_position_with_ref(msg, lat_ref, lon_ref):
         (float, float): (latitude, longitude) of the aircraft
     """
 
-
     mb = common.hex2bin(msg)[32:]
 
     cprlat = common.bin2int(mb[22:39]) / 131072.0
@@ -109,8 +119,9 @@ def airborne_position_with_ref(msg, lat_ref, lon_ref):
     i = int(mb[21])
     d_lat = 360.0 / 59 if i else 360.0 / 60
 
-    j = common.floor(lat_ref / d_lat) \
-        + common.floor(0.5 + ((lat_ref % d_lat) / d_lat) - cprlat)
+    j = common.floor(lat_ref / d_lat) + common.floor(
+        0.5 + ((lat_ref % d_lat) / d_lat) - cprlat
+    )
 
     lat = d_lat * (j + cprlat)
 
@@ -121,8 +132,9 @@ def airborne_position_with_ref(msg, lat_ref, lon_ref):
     else:
         d_lon = 360.0
 
-    m = common.floor(lon_ref / d_lon) \
-        + common.floor(0.5 + ((lon_ref % d_lon) / d_lon) - cprlon)
+    m = common.floor(lon_ref / d_lon) + common.floor(
+        0.5 + ((lon_ref % d_lon) / d_lon) - cprlon
+    )
 
     lon = d_lon * (m + cprlon)
 

tests/test_adsb.py

@@ -25,6 +25,16 @@ def test_adsb_position():
     assert pos == (49.81755, 6.08442)
 
 
+def test_adsb_position_swap_odd_even():
+    pos = adsb.position(
+        "8D40058B58C904A87F402D3B8C59",
+        "8D40058B58C901375147EFD09357",
+        1446332405,
+        1446332400,
+    )
+    assert pos == (49.81755, 6.08442)
+
+
 def test_adsb_position_with_ref():
     pos = adsb.position_with_ref("8D40058B58C901375147EFD09357", 49.0, 6.0)
     assert pos == (49.82410, 6.06785)
@@ -33,20 +43,14 @@ def test_adsb_position_with_ref():
 
 
 def test_adsb_airborne_position_with_ref():
-    pos = adsb.airborne_position_with_ref(
-        "8D40058B58C901375147EFD09357", 49.0, 6.0
-    )
+    pos = adsb.airborne_position_with_ref("8D40058B58C901375147EFD09357", 49.0, 6.0)
     assert pos == (49.82410, 6.06785)
-    pos = adsb.airborne_position_with_ref(
-        "8D40058B58C904A87F402D3B8C59", 49.0, 6.0
-    )
+    pos = adsb.airborne_position_with_ref("8D40058B58C904A87F402D3B8C59", 49.0, 6.0)
     assert pos == (49.81755, 6.08442)
 
 
 def test_adsb_surface_position_with_ref():
-    pos = adsb.surface_position_with_ref(
-        "8FC8200A3AB8F5F893096B000000", -43.5, 172.5
-    )
+    pos = adsb.surface_position_with_ref("8FC8200A3AB8F5F893096B000000", -43.5, 172.5)
     assert pos == (-43.48564, 172.53942)