create and update rtree spatial index only when needed

mesa_geo/geospace.py

@@ -91,6 +91,12 @@
         """
         Return the bounds of the GeoSpace in [min_x, min_y, max_x, max_y] format.
         """
+        if self._total_bounds is None:
+            if len(self.agents) > 0:
+                self._update_bounds(self._agent_layer.total_bounds)
+            if len(self.layers) > 0:
+                for layer in self.layers:
+                    self._update_bounds(layer.total_bounds)
         return self._total_bounds
 
     def _update_bounds(self, new_bounds: np.ndarray) -> None:
@@ -128,7 +134,7 @@
                     "to `False` to suppress this warning message."
                 )
             layer.to_crs(self.crs, inplace=True)
-        self._update_bounds(layer.total_bounds)
+        self._total_bounds = None
         self._static_layers.append(layer)
 
     def _check_agent(self, agent):
@@ -161,7 +167,7 @@
             for agent in agents:
                 self._check_agent(agent)
         self._agent_layer.add_agents(agents)
-        self._update_bounds(new_bounds=self._agent_layer.total_bounds)
+        self._total_bounds = None
 
     def _recreate_rtree(self, new_agents=None):
         """Create a new rtree index from agents geometries."""
@@ -170,6 +176,7 @@
     def remove_agent(self, agent):
         """Remove an agent from the GeoSpace."""
         self._agent_layer.remove_agent(agent)
+        self._total_bounds = None
 
     def get_relation(self, agent, relation):
         """Return a list of related agents.
@@ -231,34 +238,50 @@
     """
 
     def __init__(self):
+        # neighborhood graph for touching neighbors
         self._neighborhood = None
-
-        # Set up rtree index
-        self.idx = index.Index()
-        self.idx.agents = {}
+        # rtree index for spatial indexing (e.g., neighbors within distance, agents at pos, etc.)
+        self._idx = None
+        self._id_to_agent = {}
+        # bounds of the layer in [min_x, min_y, max_x, max_y] format
+        # While it is possible to calculate the bounds from rtree index,
+        # total_bounds is almost always needed (e.g., for plotting), while rtree index is not.
+        # Hence we compute total_bounds separately from rtree index.
+        self._total_bounds = None
 
     @property
     def agents(self):
         """
         Return a list of all agents in the layer.
         """
 
-        return list(self.idx.agents.values())
+        return list(self._id_to_agent.values())
 
     @property
     def total_bounds(self):
         """
         Return the bounds of the layer in [min_x, min_y, max_x, max_y] format.
         """
 
-        return self.idx.get_bounds(coordinate_interleaved=True)
+        if self._total_bounds is None and len(self.agents) > 0:
+            bounds = np.array([agent.geometry.bounds for agent in self.agents])
+            min_x, min_y = np.min(bounds[:, :2], axis=0)
+            max_x, max_y = np.max(bounds[:, 2:], axis=0)
+            self._total_bounds = np.array([min_x, min_y, max_x, max_y])
+        return self._total_bounds
 
     def _get_rtree_intersections(self, geometry):
         """
         Calculate rtree intersections for candidate agents.
         """
 
-        return (self.idx.agents[i] for i in self.idx.intersection(geometry.bounds))
+        self._ensure_index()
+        if self._idx is None:
+            return []
+        else:
+            return [
+                self._id_to_agent[i] for i in self._idx.intersection(geometry.bounds)
+            ]
 
     def _create_neighborhood(self):
         """
@@ -273,21 +296,27 @@
         for agent, key in zip(agents, self._neighborhood.neighbors.keys()):
             self._neighborhood.idx[agent] = key
 
+    def _ensure_index(self):
+        """
+        Ensure that the rtree index is created.
+        """
+
+        if self._idx is None:
+            self._recreate_rtree()
+
     def _recreate_rtree(self, new_agents=None):
         """
         Create a new rtree index from agents geometries.
         """
 
         if new_agents is None:
             new_agents = []
-        old_agents = list(self.agents)
-        agents = old_agents + new_agents
-
-        # Bulk insert agents
-        index_data = ((id(agent), agent.geometry.bounds, None) for agent in agents)
+        agents = list(self.agents) + new_agents
 
-        self.idx = index.Index(index_data)
-        self.idx.agents = {id(agent): agent for agent in agents}
+        if len(agents) > 0:
+            # Bulk insert agents
+            index_data = ((id(agent), agent.geometry.bounds, None) for agent in agents)
+            self._idx = index.Index(index_data)
 
     def add_agents(self, agents):
         """
@@ -303,18 +332,25 @@
 
         if isinstance(agents, GeoAgent):
             agent = agents
-            self.idx.insert(id(agent), agent.geometry.bounds, None)
-            self.idx.agents[id(agent)] = agent
+            self._id_to_agent[id(agent)] = agent
+            if self._idx:
+                self._idx.insert(id(agent), agent.geometry.bounds, None)
         else:
-            self._recreate_rtree(agents)
+            for agent in agents:
+                self._id_to_agent[id(agent)] = agent
+            if self._idx:
+                self._recreate_rtree(agents)
+        self._total_bounds = None
 
     def remove_agent(self, agent):
         """
         Remove an agent from the layer.
         """
 
-        self.idx.delete(id(agent), agent.geometry.bounds)
-        del self.idx.agents[id(agent)]
+        del self._id_to_agent[id(agent)]
+        if self._idx:
+            self._idx.delete(id(agent), agent.geometry.bounds)
+        self._total_bounds = None
 
     def get_relation(self, agent, relation):
         """Return a list of related agents.
@@ -327,6 +363,7 @@
                 Omit to compare against all other agents of the layer.
         """
 
+        self._ensure_index()
         possible_agents = self._get_rtree_intersections(agent.geometry)
         for other_agent in possible_agents:
             if (
@@ -336,6 +373,7 @@
                 yield other_agent
 
     def get_intersecting_agents(self, agent):
+        self._ensure_index()
         intersecting_agents = self.get_relation(agent, "intersects")
         return intersecting_agents
 
@@ -347,7 +385,7 @@
         Distance is measured as a buffer around the agent's geometry,
         set center=True to calculate distance from center.
         """
-
+        self._ensure_index()
         if center:
             geometry = agent.geometry.centroid.buffer(distance)
         else:
@@ -363,6 +401,7 @@
         Return a generator of agents at given pos.
         """
 
+        self._ensure_index()
         if not isinstance(pos, Point):
             pos = Point(pos)
 
@@ -386,10 +425,13 @@
         if not self._neighborhood or self._neighborhood.agents != self.agents:
             self._create_neighborhood()
 
-        idx = self._neighborhood.idx[agent]
-        neighbors_idx = self._neighborhood.neighbors[idx]
-        neighbors = [self.agents[i] for i in neighbors_idx]
-        return neighbors
+        if self._neighborhood is None:
+            return []
+        else:
+            idx = self._neighborhood.idx[agent]
+            neighbors_idx = self._neighborhood.neighbors[idx]
+            neighbors = [self.agents[i] for i in neighbors_idx]
+            return neighbors
 
     def get_agents_as_GeoDataFrame(self, agent_cls=GeoAgent) -> gpd.GeoDataFrame:
         """

tests/test_GeoSpace.py

@@ -265,3 +265,13 @@ def test_agents_at(self):
             agent.unique_id for agent in self.geo_space.agents_at((1, 1))
         }
         self.assertEqual(agents_id_found, agents_id)
+
+    def test_get_neighbors(self):
+        self.geo_space.add_agents(self.polygon_agent)
+        self.assertEqual(len(self.geo_space.get_neighbors(self.polygon_agent)), 0)
+        self.geo_space.add_agents(self.touching_agent)
+        self.assertEqual(len(self.geo_space.get_neighbors(self.polygon_agent)), 1)
+        self.assertEqual(
+            self.geo_space.get_neighbors(self.polygon_agent)[0].unique_id,
+            self.touching_agent.unique_id,
+        )