Fixed the signal strength data map to (1) warn the user about the

bounding box limitation and (2) gracefully handle invalid distance
errors from the propagation model.

west/data_map_signal_strength.py

@@ -1,4 +1,5 @@
 from data_map import DataMap2D
+from propagation_model import InvalidDistanceError
 from abc import abstractmethod
 from geopy.distance import vincenty
 
@@ -44,6 +45,13 @@ def add_tv_stations(self, list_of_tv_stations, pathloss_function,
             pl_function = lambda *args, **kwargs: pm.get_pathloss_coefficient(*args, curve_enum=PropagationCurve.curve_50_90, **kwargs)
             my_signal_map.add_tv_stations(my_tv_stations, pathloss_function=pl_function)
 
+        .. warning:: the signal strength will not be calculated outside the \
+        station's bounding box in order to save on computations.
+
+        .. warning:: any InvalidDistanceErrors from the propagation model will \
+        be ignored and the signal strength at that location (for that station) \
+        will be zero.
+
         :param list_of_tv_stations: list of \
         :class:`protected_entity_tv_station.ProtectedEntityTvStation` objects
         :param pathloss_function: the pathloss function to be used when \
@@ -80,11 +88,15 @@ def _get_station_signal_strength(self, location, tv_station,
         tv_location = tv_station.get_location()
         distance_km = vincenty(tv_location, location).kilometers
         freq = tv_station.get_center_frequency()
-        pathloss = pathloss_function(distance_km, frequency=freq,
-                                     tx_height=tv_station.get_haat_meters(),
-                                     rx_height=None, tx_location=tv_location,
-                                     rx_location=location)
-        # TODO: account for rx height?
+        try:
+            pathloss = pathloss_function(distance_km, frequency=freq,
+                                         tx_height=tv_station.get_haat_meters(),
+                                         rx_height=None,
+                                         tx_location=tv_location,
+                                         rx_location=location)
+            # TODO: account for rx height?
+        except InvalidDistanceError:
+            return 0
 
         return tv_station.get_erp_watts() * pathloss
 

west/propagation_model.py

@@ -1,6 +1,11 @@
 from abc import ABCMeta, abstractmethod
 from custom_logging import getModuleLogger
 
+
+class InvalidDistanceError(ValueError):
+    pass
+
+
 class PropagationCurve(object):
     """
     This class is a poor-man's enum because Python 2 does not support the Enum class.

west/propagation_model_fcurves.py

@@ -1,11 +1,10 @@
-from propagation_model import PropagationModel, PropagationCurve
+from propagation_model import PropagationModel, PropagationCurve, InvalidDistanceError
 from configuration import package_directory
 from ctypes import *
 import os.path
 from math import log10
 
 
-
 class PropagationModelFcurves(PropagationModel):
     """The FCC's F-curves model.
 
@@ -192,6 +191,7 @@ def _initialize_error_codes(self):
             "A9": "INVALID 'DISTANCE' VALUE FOR SWITCH = 1.",
             "  ": None
         }
+        self._invalid_distance_errors = ["A2"]
 
         self._warning_codes = {
             "A1": "FREE SPACE EQUATION USED TO FIND REQUESTED ARGUMENT.",
@@ -216,6 +216,10 @@ def _raise_warning_or_error_if_flag_set(self, flag):
 
 
         if flag in self._error_codes:
+            if flag in self._invalid_distance_errors:
+                raise InvalidDistanceError("Invalid distance for propagation "
+                                           "model %r" % self)
+
             error_message = self._error_codes[flag]
 
             if error_message is None: