Merge pull request #3549 from anacmontoya/wpc-bulletin-coords

fixes issue #3535

src/metpy/io/text.py

@@ -42,15 +42,22 @@ def _decode_coords(coordinates):
     (-119.3, 47.3)
 
     """
+    # Define latitude orientation
+    flip = 1
+
+    if coordinates[0] == '-':
+        coordinates = coordinates[1:]
+        # Flip latitude to Southern Hemisphere
+        flip = -1
+
     # Based on the number of digits, find the correct place to split between lat and lon
     # Hires bulletins provide 7 digits for coordinates; regular bulletins provide 4 or 5 digits
     split_pos = int(len(coordinates) / 2)
     lat, lon = coordinates[:split_pos], coordinates[split_pos:]
 
     # Insert decimal point at the correct place and convert to float
-    lat = float(f'{lat[:2]}.{lat[2:]}')
+    lat = float(f'{lat[:2]}.{lat[2:]}') * flip
     lon = -float(f'{lon[:3]}.{lon[3:]}')
-
     return lon, lat
 
 

tests/io/test_text.py

@@ -61,3 +61,40 @@ def test_parse_wpc_surface_bulletin():
                                                 [-102, 32], [-103, 31]])
 
     assert all(df.valid == datetime(2021, 6, 28, 18, 0, 0))
+
+
+@needs_module('shapely')
+def test_negative_lat_highres():
+    """Test decoding of high res coordinates with negative latitude."""
+    from io import BytesIO
+
+    import shapely.geometry as sgeom
+
+    sample = BytesIO(b"""
+178
+ASUS02 KWBC 281800
+CODSUS
+
+CODED SURFACE FRONTAL POSITIONS
+NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
+342 PM EDT MON JUN 28 2021
+
+VALID 062818Z
+HIGHS 1022 -3961069 1020 -3851069 1026 3750773 1022 4430845 1019 5520728 1018
+""")
+    df = parse_wpc_surface_bulletin(sample)
+    assert df.geometry[0] == sgeom.Point([-106.9, -39.6])
+
+
+@needs_module('shapely')
+def test_negative_lat():
+    """Test decoding of coordinates with negative latitude."""
+    from io import BytesIO
+
+    import shapely.geometry as sgeom
+
+    sample = BytesIO(b"""12HR PROG VALID xxxxxxZ
+HIGHS -351 -3985 -4046 -38117 -7510
+ """)
+    df = parse_wpc_surface_bulletin(sample)
+    assert df.geometry[0] == sgeom.Point([-51, -3])