Implement VTEC event polygon parsing

lib/nexrad/vtec.py

@@ -55,13 +55,33 @@ RE_HYDRO = re.compile(r'''
     /$
 ''', re.X)
 
-RE_POLY = re.compile(r'^LAT\.\.\.LON(?P<coords> \d{4})+')
+RE_POLY = re.compile(r'^LAT\.\.\.LON (?P<coords>\d{4}(?: \d{4})+)')
 
 def parse_timestamp(text: str, post_2016_05_11: bool):
     return datetime.datetime.strptime(
         text, '%y%m%dT%H%M%SZ'
     ).astimezone(datetime.UTC)
 
+def parse_lon(text: str):
+    return 0 - float(text[0:2]) + (float(text[3:4]) / 100)
+
+def parse_lat(text: str):
+    return float(text[0:2]) + (float(text[3:4]) / 100)
+
+def parse_shape(text: str):
+    points = list()
+    coords = text.split(' ')
+
+    for i in range(0, len(coords), 2):
+        lat = coords[i]
+        lon = coords[i+1]
+
+        points.append([parse_lon(lon), parse_lat(lat)])
+
+    points.append([parse_lon(coords[0]), parse_lat(coords[1])])
+
+    return shapely.Polygon(points)
+
 class VTECEventType(enum.StrEnum):
     OPERATIONAL       = 'O'
     TEST              = 'T'
@@ -120,9 +140,6 @@ class VTECEvent(DatabaseTable):
     forecaster:       str
     poly:             shapely.Geometry
 
-    def parse_shape(self, coords: str):
-        pass
-
     @staticmethod
     def parse(text: str):
         event = VTECEvent()
@@ -185,7 +202,7 @@ class VTECEvent(DatabaseTable):
                 match = RE_POLY.match(line)
 
                 if match is not None:
-                    event.parse_shape(match['coords'])
+                    event.poly = parse_shape(match['coords'])
                 elif line == '$$':
                     state = VTECEventParserState.FOOTER
                 else: