gnss: handle longitude <=-180 or >=360 (#1290)

+ `utils.utils0.py`: add `standardize_longitude()` to handle the longitude data range
   - ensure longitude is within (-180, 360)
   - could specify the data range format, in either [0, 360) or (-180, 180] via `lon_range` arg

+ `objects.gnss.py`: call `ut.standardize_longitude()` in all the child class of GNSS

This error occurs for the GNSS_UNR sites in Japan, where the longitude of G073 can be -229. In the old code, this results in a NaN value for inc/az_angle extraction from the geometry file.

src/mintpy/objects/gnss.py

@@ -71,7 +71,8 @@ def search_gnss(SNWE, start_date=None, end_date=None, source='UNR', site_list_fi
 
     # ensure that site data formatting is consistent
     sites['site'] = np.array([site.upper() for site in sites['site']])
-    sites['lon'][sites['lon'] > 180] -= 360         # ensure lon values in (-180, 180]
+    # ensure longitude values in (-180, 180]
+    sites['lon'] = ut.standardize_longitude(sites['lon'], limit='-180to180')
     vprint(f'load {len(sites["site"]):d} GNSS sites with fields: {" ".join(sites.keys())}')
 
     # limit in space
@@ -867,6 +868,9 @@ def get_site_lat_lon(self, print_msg=False) -> (float, float):
 
         data = np.loadtxt(self.file, dtype=bytes, skiprows=1, max_rows=10)
         self.site_lat, self.site_lon = data[0, 20:22].astype(float)
+        # ensure longitude in the range of (-180, 180]
+        self.site_lon = ut.standardize_longitude(self.site_lon, limit='-180to180')
+
         return self.site_lat, self.site_lon
 
 
@@ -987,8 +991,9 @@ def get_site_lat_lon(self, print_msg=False) -> (float, float):
             # longitude
             lon_line = [x for x in lines if x.startswith('# East Longitude')][0].strip('\n')
             self.site_lon = float(lon_line.split()[-1])
-            # ensure longitude in the range of (-180, 180]
-            self.site_lon -= 0 if self.site_lon <= 180 else 360
+
+        # ensure longitude in the range of (-180, 180]
+        self.site_lon = ut.standardize_longitude(self.site_lon, limit='-180to180')
 
         return self.site_lat, self.site_lon
 
@@ -1094,6 +1099,8 @@ def get_site_lat_lon(self, print_msg=False) -> (float, float):
         # format
         self.site_lat = float(site_lat)
         self.site_lon = float(site_lon)
+        # ensure longitude in the range of (-180, 180]
+        self.site_lon = ut.standardize_longitude(self.site_lon, limit='-180to180')
 
         if print_msg == True:
             print(f'\t{self.site_lat:f}, {self.site_lon:f}')
@@ -1185,7 +1192,11 @@ def get_site_lat_lon(self, print_msg=False) -> (str, str):
         """
         sites = read_GENERIC_site_list('GenericList.txt')
         ind = sites['site'].tolist().index(self.site)
-        return sites['lat'][ind], sites['lon'][ind]
+        site_lat, site_lon = sites['lat'][ind], sites['lon'][ind]
+        # ensure longitude in the range of (-180, 180]
+        site_lon = ut.standardize_longitude(site_lon, limit='-180to180')
+
+        return site_lat, site_lon
 
 
     def read_displacement(self, start_date=None, end_date=None, print_msg=True, display=False):

src/mintpy/utils/utils0.py

@@ -267,6 +267,30 @@ def touch(fname_list, times=None):
 
 
 ################################## Coordinate ##########################################
+def standardize_longitude(lon, limit='-180to180'):
+    """Normalize the longitude value range into (-180, 180] or [0, 360).
+
+    Parameters: lon   - float / np.ndarray, longitude in degree
+                limit - str, -180to180 or 0to360
+    Returns:    lon   - float / np.ndarray, longitude in degree
+    """
+    lon = np.asarray(lon)
+
+    # ensure data within (-180, 360)
+    lon = np.where(lon >= 360, lon - 360, lon)
+    lon = np.where(lon <= -180, lon + 360, lon)
+
+    # range option 1: ensure data within (-180, 180]
+    if limit == '-180to180':
+        lon = np.where(lon > 180, lon - 360, lon)
+
+    # range option 2: ensure data within [0, 360)
+    elif limit == '0to360' and np.nanmin(lon) < 0:
+        lon = np.where(lon < 0, lon + 360, lon)
+
+    return float(lon) if np.isscalar(lon) else lon
+
+
 def utm_zone2epsg_code(utm_zone):
     """Convert UTM Zone string to EPSG code.