Detect and remove disconnected roads upfront

README.md

@@ -83,8 +83,8 @@ tool):
 
 ```
 function json_diff {
-  cat $1 | jq > /tmp/before.json
-  git show HEAD^:./$1 | jq > /tmp/after.json
+  cat $1 | jq > /tmp/after.json
+  git show HEAD^:./$1 | jq > /tmp/before.json
   meld /tmp/before.json /tmp/after.json
 }
 

backend/Cargo.toml

@@ -32,6 +32,7 @@ utils = { git = "https://github.com/a-b-street/utils", features = ["serde"] }
 wasm-bindgen = "0.2.87"
 web-sys = { version = "0.3.64", features = ["console"] }
 web-time = "1.0.0"
+petgraph = "0.7.1"
 
 # For local development, build dependencies in release mode once, but otherwise
 # use dev profile and avoid wasm-opt.

backend/src/create.rs

@@ -3,8 +3,12 @@ use std::collections::{BTreeMap, BTreeSet, HashMap};
 use anyhow::Result;
 use geo::{Coord, LineInterpolatePoint, LineString, Polygon};
 use osm_reader::{Element, NodeID};
+use petgraph::graphmap::UnGraphMap;
 use rstar::{primitives::GeomWithData, RTree};
-use utils::Tags;
+use utils::{
+    osm2graph::{EdgeID, Graph},
+    Tags,
+};
 
 use crate::{
     impact::Impact, Direction, FilterKind, Intersection, IntersectionID, MapModel, Road, RoadID,
@@ -98,7 +102,8 @@ pub fn create_from_osm(
     })?;
 
     info!("Splitting {} ways into edges", highways.len());
-    let mut graph = utils::osm2graph::Graph::from_scraped_osm(node_mapping, highways);
+    let mut graph = Graph::from_scraped_osm(node_mapping, highways);
+    remove_disconnected_components(&mut graph);
     graph.compact_ids();
 
     // Copy all the fields
@@ -321,3 +326,37 @@ fn parse_maxspeed_mph(tags: &Tags) -> Option<f64> {
     }
     None
 }
+
+// TODO Consider upstreaming to osm2graph
+fn remove_disconnected_components(graph: &mut Graph) {
+    let mut scc_graph: UnGraphMap<utils::osm2graph::IntersectionID, EdgeID> = UnGraphMap::new();
+    for edge in graph.edges.values() {
+        scc_graph.add_edge(edge.src, edge.dst, edge.id);
+    }
+
+    let mut components: Vec<BTreeSet<EdgeID>> = Vec::new();
+    for nodes in petgraph::algo::kosaraju_scc(&scc_graph) {
+        components.push(nodes_to_edges(graph, nodes));
+    }
+    components.sort_by_key(|scc| scc.len());
+    components.reverse();
+
+    let mut remove_edges = BTreeSet::new();
+    // Keep only the largest component
+    for scc in components.into_iter().skip(1) {
+        info!("Removing component with only {} roads", scc.len());
+        remove_edges.extend(scc);
+    }
+
+    info!("Removing {} disconnected roads", remove_edges.len());
+    graph.remove_edges(remove_edges);
+}
+
+// Note this only works for connected components of nodes!
+fn nodes_to_edges(graph: &Graph, nodes: Vec<utils::osm2graph::IntersectionID>) -> BTreeSet<EdgeID> {
+    let mut edges = BTreeSet::new();
+    for i in nodes {
+        edges.extend(graph.intersections[&i].edges.clone());
+    }
+    edges
+}