Network analysis

The plugin uses the pgRouting extension to find paths on the drinking water network (AEP). See pgRouting to install the extension.

The sanitation network (ASS) is walked without pgRouting, by following the direction of the pipes: see the actions Upstream and Downstream.

Routing graph

The pgRouting functions do not use the StaR'Eau tables directly, but a routing graph stored in two tables of the schema stareau:

Table	Content
aep_vertex	The vertices: the AEP network nodes, with the same identifier as the node (id = fid of the node), and the missing nodes of the AEP network, with fictif = True
aep_edge	The edges: the AEP pipes, with the same identifier as the pipe (id = fid of the pipe), their source and target vertices, and their length as cost and reverse_cost

The water can flow in both directions in the graph: the direction of the pipes is not used.

The graph is built by the algorithm Fill AEP vertices and edges. It is not updated automatically: run this algorithm again after each modification of the drinking water network, otherwise the results of the analysis can be wrong, or an error can occur.

graph LR A[StaR'Eau tables<br>noeud_reseau, canalisation] -->|Fill AEP vertices and edges| B[Routing graph<br>aep_vertex, aep_edge] B --> C[Actions<br>Chercher traitement, reservoir, captage] B --> D[Algorithms<br>Water intake points to nearest treatment<br>Treatments to nearest reservoir] B --> E[SQL functions<br>aep_pgr_*]

Path to the nearest target

From a node of the drinking water network, the function stareau.aep_pgr_path_to_nearest_target returns the pipes of the shortest path to the nearest target:

1. the 10 targets closest to the node (as the crow flies) are selected in the target table, e.g. aep_reservoir,
2. the shortest paths to these targets are calculated on the graph (bidirectional Dijkstra),
3. the shortest path is kept, and its pipes are returned.

The variant stareau.aep_pgr_path_to_nearest_target_avoiding_closed_valves does the same, but the closed valves (etat_ouverture = 'fermee') cannot be crossed.

This calculation is used by:

• the layer actions Chercher traitement, Chercher reservoir and Chercher captage, see Path to the nearest target,
• the algorithms Water intake points to nearest treatment and Treatments to nearest reservoir, which run it for each water intake or for each treatment plant.

Nearest valves

From a point located on a drinking water pipe, the function stareau.aep_pgr_nearest_vannes returns the valves to close to isolate this point: the first valves met in each direction when walking the network from the point. The valves are dead ends: the walk stops at the first valve.

The variant stareau.aep_pgr_nearest_closed_vannes only considers the closed valves: the open valves are crossed, and the walk stops at the first closed valves. It helps to find the closed valves which isolate a part of the network.

These functions are used by the action Nearest valves.

See Useful functions for the parameters of these functions.