Improve network extraction and graph simplification + add docs

package-lock.json

@@ -1915,6 +1915,11 @@
       "resolved": "https://registry.npmjs.org/destroy/-/destroy-1.0.4.tgz",
       "integrity": "sha1-l4hXRCxEdJ5CBmE+N5RiBYJqvYA="
     },
+    "dijkstrajs": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/dijkstrajs/-/dijkstrajs-1.0.1.tgz",
+      "integrity": "sha1-082BIh4+pAdCz83lVtTpnpjdxxs="
+    },
     "doctrine": {
       "version": "3.0.0",
       "resolved": "https://registry.npmjs.org/doctrine/-/doctrine-3.0.0.tgz",

package.json

@@ -17,6 +17,7 @@
     "axios": "^0.21.1",
     "color": "^3.1.3",
     "csv-parse": "^4.15.4",
+    "dijkstrajs": "^1.0.1",
     "express": "^4.17.1",
     "ol": "^6.5.0",
     "unzip-stream": "^0.3.1",

script/output-graph.js

@@ -0,0 +1,37 @@
+#!/usr/bin/env -S node --experimental-json-modules
+
+import network from "../src/tam/network.json";
+
+console.log("digraph {");
+console.log("graph[layout=fdp, outputorder=nodesfirst]");
+
+for (const [stopId, stop] of Object.entries(network.stops)) {
+    console.log(`${stopId}[label="${stop.properties.name}"]`);
+}
+
+const junctions = new Set();
+
+for (const [beginId, begin] of Object.entries(network.navigation)) {
+    if (!(beginId in network.stops)) {
+        junctions.add(beginId);
+    }
+
+    for (const endId in begin) {
+        if (!(endId in network.stops)) {
+            junctions.add(endId);
+        }
+    }
+}
+
+for (const junction of junctions) {
+    console.log(`${junction}[label="", shape=point]`);
+}
+
+for (const [beginId, begin] of Object.entries(network.navigation)) {
+    for (const [endId, end] of Object.entries(begin)) {
+        const len = end.properties.length;
+        console.log(`${beginId} -> ${endId}[len=${len}]`);
+    }
+}
+
+console.log("}");

src/tam/courses.js

@@ -45,7 +45,7 @@ const isPenultimateStop = (stop, finalStop) => {
         return true;
     }
 
-    const route = routing.findRoute(stop, finalStop);
+    const route = routing.findPath(stop, finalStop);
 
     // If there is no way to link both stops, it can’t be
     if (route === null) {

src/tam/network.js

@@ -7,8 +7,8 @@
  * Functions in this file also report inconsistencies in OSM data.
  *
  * Because of the static nature of this data, it is cached in a
- * version-controlled file `network.json` next to this file. To update it, use
+ * version-controlled file `network.json` next to this file. To update it,
- * the `script/update-network` script.
+ * run the `script/update-network.js` script.
  */
 
 import * as turfHelpers from "@turf/helpers";
@@ -17,14 +17,91 @@ import * as util from "../util.js";
 import * as osm from "./sources/osm.js";
 
 /**
- * Fetch stops and lines of the network.
+ * Route of a line of a transport network.
- * @param {string[]} lineRefs List of lines to fetch.
+ * @typedef {Object} Route
- * @returns {{stops: Object, lines: Object, segments: Object}} Set of stops,
+ * @property {string} from Name of the starting point of the route.
- * segments and lines.
+ * @property {string} to Name of the ending point of the route.
+ * @property {string?} via Optional name of a major intermediate
+ * stop of the route.
+ * @property {string} name Human-readable name of the line.
  */
-export const fetch = async lineRefs => {
+
-    // Retrieve routes, ways and stops from OpenStreetMap
+/**
-    const rawData = await osm.runQuery(`[out:json];
+ * Line of a transport network.
+ * @typedef {Object} Line
+ * @property {string} color Hexadecimal color code of this line.
+ * @property {Array.<Route>} routes Routes of this line.
+ */
+
+/**
+ * Stop in a transport network (as a GeoJSON feature point).
+ * @typedef {Object} Stop
+ * @property {string} type Always equal to "Feature".
+ * @property {string} id Stop identifier (unique in each network.).
+ * @property {Object} properties
+ * @property {string} properties.name Human-readable name of the stop.
+ * @property {string} properties.node Associated node ID in OpenStreetMap.
+ * @property {Array.<Array.[string,number]>} properties.routes
+ * List of transport lines using this stop (as pairs of
+ * line and route identifiers).
+ * @property {Object} geometry
+ * @property {string} geometry.type Always equal to "Point"
+ * @property {Array.<number>} geometry.coordinates
+ * Longitude and latitude of the stop point.
+ */
+
+/**
+ * Planned segment routing between two stops of a transport network
+ * (as a GeoJSON feature line string).
+ * @typedef {Object} Segment
+ * @property {string} type Always equal to "Feature".
+ * @property {string} id Segment identifier (format: `{begin}-{end}`).
+ * @property {Object} properties
+ * @property {string} properties.begin ID of the stop at the beginning.
+ * @property {string} properties.end ID of the stop at the end.
+ * @property {number} properties.length Length of this segment (meters).
+ * @property {Array.<Array.[string,number]>} properties.routes
+ * List of transport lines using this segment (as pairs of
+ * line identifiers and line direction numbers).
+ * @property {Object} geometry
+ * @property {string} geometry.type Always equal to "LineString".
+ * @property {Array.<Array.<number>>} geometry.coordinates
+ * Sequence of points forming this segment (as longitude/latitude pairs).
+ */
+
+/**
+ * Edge of the graph for out-of-route navigation between stops.
+ * @typedef {Object} NavigationEdge
+ * @property {string} type Always equal to "Feature".
+ * @property {Object} properties
+ * @property {string} properties.begin ID of the stop or node at the beginning.
+ * @property {string} properties.end ID of the stop or node at the end.
+ * @property {number} properties.length Length of this edge (meters).
+ * @property {Object} geometry
+ * @property {string} geometry.type Always equal to "LineString".
+ * @property {Array.<Array.<number>>} geometry.coordinates
+ * Sequence of points forming this edge (as longitude/latitude pairs).
+ */
+
+/**
+ * Information about a public transport network.
+ * @typedef {Object} Network
+ * @property {Object.<string,Stop>} stops List of stops.
+ * @property {Object.<string,Line>} lines List of lines.
+ * @property {Object.<string,Segment>} segments List of segments.
+ * @property {Object.<string,Object.<string,NavigationEdge>>} navigation
+ * Graph for out-of-route navigation between stops.
+ */
+
+/**
+ * Retrieve raw routes, ways and stops from OpenStreetMap for the given
+ * transport lines.
+ * @param {Array.<string>} lineRefs List of lines to fetch.
+ * @return {Array.<Object>} List of objects returned by OSM.
+ */
+// Retrieve routes, ways and stops from OpenStreetMap
+const queryLines = async lineRefs => {
+    return (await osm.runQuery(`[out:json];
 
 // Find the public transport lines bearing the requested references
 relation[network="TaM"][type="route_master"][ref~"^(${lineRefs.join("|")})$"];
@@ -43,35 +120,23 @@ relation[network="TaM"][type="route_master"][ref~"^(${lineRefs.join("|")})$"];
 );
 
 out body qt;
-`);
+`)).elements;
+};
 
-    // List of retrieved objects
+/**
-    const elementsList = rawData.elements;
+ * Assemble information about lines, stops and segments from the raw
-
+ * OpenStreetMap data.
-    // List of retrieved lines
+ * @param {Array.<Object>} elementsList List of nodes retrieved from OSM.
-    const routeMasters = elementsList.filter(osm.isTransportLine);
+ * @param {Object.<string,Object>} elementsById OSM nodes indexed by their ID.
-
+ * @return {Object} Assembled information about lines, stops and segments.
-    // Retrieved objects indexed by ID
+ */
-    const elements = elementsList.reduce((prev, elt) => {
+const processRoutes = (elementsList, elementsById) => {
-        prev[elt.id] = elt;
-        return prev;
-    }, {});
-
-    // Graph for out-of-route navigation
-    const navigation = {};
-
-    // Stops in the network indexed by reference
-    const stops = {};
-
-    // Stops indexed by OSM identifier
-    const stopsReverse = {};
-
-    // Transport lines of the network indexed by name
     const lines = {};
-
+    const stops = {};
-    // Segments leading from stop to stop in the planned route for each line
     const segments = {};
 
+    const routeMasters = elementsList.filter(osm.isTransportLine);
+
     // Extract lines, associated stops and planned routes
     for (const routeMaster of routeMasters) {
         const lineRef = routeMaster.tags.ref;
@@ -80,14 +145,14 @@ out body qt;
 
         for (const [routeRef, data] of routeMaster.members.entries()) {
             const routeId = data.ref;
-            const route = elements[routeId];
+            const route = elementsById[routeId];
             const { from, via, to, name } = route.tags;
             const state = route.tags.state || "normal";
 
             // Add missing stops to the global stops object
             for (const { ref, role } of route.members) {
                 if (role === "stop") {
-                    const stop = elements[ref];
+                    const stop = elementsById[ref];
 
                     if (!("ref" in stop.tags)) {
                         throw new Error(`Stop ${stop.id}
@@ -101,10 +166,11 @@ a “ref” tag`);
                             stop.lat
                         ], {
                             name: stop.tags.name,
+                            node: ref.toString(),
                             routes: [[lineRef, routeRef]],
+                        }, {
+                            id: stop.tags.ref,
                         });
-
-                        stopsReverse[ref] = stop.tags.ref;
                     } else {
                         stops[stop.tags.ref].properties.routes.push([
                             lineRef,
@@ -151,7 +217,7 @@ of ${name}`);
             let currentNode = lineStops[0];
 
             for (let wayIndex = 0; wayIndex < ways.length; wayIndex += 1) {
-                const way = elements[ways[wayIndex]];
+                const way = elementsById[ways[wayIndex]];
                 const { nodes: wayNodes } = way;
                 const wayNodesSet = new Set(wayNodes);
 
@@ -163,7 +229,7 @@ of ${name}`);
                 let nextNodeIndex = null;
 
                 if (wayIndex + 1 < ways.length) {
-                    const nextNodeCandidates = elements[ways[wayIndex + 1]]
+                    const nextNodeCandidates = elementsById[ways[wayIndex + 1]]
                         .nodes.filter(node => wayNodesSet.has(node));
 
                     if (nextNodeCandidates.length !== 1) {
@@ -201,9 +267,9 @@ ${name} is one-way and cannot be used in reverse.`);
 
             // Split the path into segments between stops
             for (let stopIdx = 0; stopIdx + 1 < lineStops.length; ++stopIdx) {
-                const begin = elements[lineStops[stopIdx]].tags.ref;
+                const begin = elementsById[lineStops[stopIdx]].tags.ref;
                 const beginIdx = path.indexOf(lineStops[stopIdx]);
-                const end = elements[lineStops[stopIdx + 1]].tags.ref;
+                const end = elementsById[lineStops[stopIdx + 1]].tags.ref;
                 const endIdx = path.indexOf(
                     lineStops[stopIdx + 1],
                     beginIdx
@@ -225,15 +291,17 @@ different sequence of nodes in two or more lines.`);
                 } else {
                     segments[id] = turfHelpers.lineString(nodesIds.map(
                         nodeId => [
-                            elements[nodeId].lon,
+                            elementsById[nodeId].lon,
-                            elements[nodeId].lat
+                            elementsById[nodeId].lat
                         ]
                     ), {
                         // Keep track of the original sequence of nodes to
                         // compare with duplicates
                         nodesIds,
-                        routes: [[lineRef, routeRef]]
+                        routes: [[lineRef, routeRef]],
-                    });
+                        begin: begin,
+                        end: end,
+                    }, { id });
 
                     segments[id].properties.length = (
                         1000 * turfLength(segments[id]));
@@ -260,47 +328,240 @@ different sequence of nodes in two or more lines.`);
         delete segment.properties.nodesIds;
     }
 
-    // Create out-of-route navigation graph
+    return { lines, stops, segments };
-    const navigationId = objId => (
+};
+
+/**
+ * Create a graph for navigating between stops outside of
+ * regular planned routes.
+ * @property {Object.<string,Stop>} stops List of stops.
+ * @param {Array.<Object>} elementsList List of nodes retrieved from OSM.
+ * @param {Object.<string,Object>} elementsById OSM nodes indexed by their ID.
+ * @return {Object.<string,Object.<string,NavigationEdge>} Resulting graph.
+ */
+const createNavigationGraph = (stops, elementsList, elementsById) => {
+    // Graph of network stops and junctions
+    const navigation = {};
+
+    // Predecessors of each graph node
+    const navigationReverse = {};
+
+    // Stops indexed by their OSM ID instead of their network ID
+    const stopsReverse = Object.fromEntries(
+        Object.entries(stops).map(([id, stop]) => [stop.properties.node, id])
+    );
+
+    // Get the ID of a node in the navigation graph
+    // (its network ID if it is a network object, otherwise its OSM id)
+    const getNavigationId = objId => (
         objId in stopsReverse
         ? stopsReverse[objId]
         : objId.toString()
     );
 
+    // Get the OSM ID of a navigation object
+    const getOSMId = navId => (
+        navId in stops
+        ? stops[navId].properties.node
+        : navId
+    );
+
+    // Create graph nodes from OSM nodes
     for (const obj of elementsList) {
         if (obj.type === "node") {
-            const id = navigationId(obj.id);
+            navigation[getNavigationId(obj.id)] = {};
-
+            navigationReverse[getNavigationId(obj.id)] = {};
-            navigation[id] = {
-                // Position of this node
-                lon: obj.lon,
-                lat: obj.lat,
-
-                // List of other nodes that can be accessed from this node
-                successors: [],
-            };
         }
     }
 
+    // Link up graph edges with OSM ways
     for (const obj of elementsList) {
         if (obj.type === "way") {
             const oneWay = osm.isOneWay(obj);
             const pairs = obj.nodes.slice(0, -1).map(
                 (node, i) => [
-                    navigationId(node),
+                    getNavigationId(node),
-                    navigationId(obj.nodes[i + 1]),
+                    getNavigationId(obj.nodes[i + 1]),
                 ]
             );
 
             for (const [from, to] of pairs) {
-                navigation[from].successors.push(to);
+                navigation[from][to] = [from, to];
+                navigationReverse[to][from] = true;
 
                 if (!oneWay) {
-                    navigation[to].successors.push(from);
+                    navigation[to][from] = [to, from];
+                    navigationReverse[from][to] = true;
                 }
             }
         }
     }
 
-    return { navigation, stops, lines, segments };
+    // Mark nodes of the graph to be kept
+    const nodesToKeep = {};
+
+    for (const nodeId in navigation) {
+        if (nodeId in stops) {
+            // Keep stop nodes
+            nodesToKeep[nodeId] = true;
+            continue;
+        }
+
+        const entries = new Set(Object.keys(navigationReverse[nodeId]));
+        const exits = new Set(Object.keys(navigation[nodeId]));
+
+        // Keep split nodes, i.e. nodes with at least two exit nodes
+        // and one entry node that are all distinct from each other
+        if (entries.size >= 1) {
+            if (exits.size >= 3) {
+                nodesToKeep[nodeId] = true;
+                continue;
+            }
+
+            if (exits.size === 2) {
+                for (const entry of entries) {
+                    if (!exits.has(entry)) {
+                        nodesToKeep[nodeId] = true;
+                        continue;
+                    }
+                }
+            }
+        }
+
+        // Keep junction nodes, i.e. nodes with at least two entry nodes
+        // and one exit node that are all distinct from each other
+        if (exits.size >= 1) {
+            if (entries.size >= 3) {
+                nodesToKeep[nodeId] = true;
+                continue;
+            }
+
+            if (entries.size === 2) {
+                for (const exit of exits) {
+                    if (!entries.has(exit)) {
+                        nodesToKeep[nodeId] = true;
+                        continue;
+                    }
+                }
+            }
+        }
+    }
+
+    // Compress edges between nodes of interest
+    for (const beginId in nodesToKeep) {
+        const begin = navigation[beginId];
+        const stack = [];
+        const parent = {[beginId]: beginId};
+
+        for (const succId in begin) {
+            stack.push(succId);
+            parent[succId] = beginId;
+        }
+
+        while (stack.length > 0) {
+            const endId = stack.pop();
+            const end = navigation[endId];
+
+            if (endId in nodesToKeep) {
+                if (endId in begin) {
+                    continue;
+                }
+
+                const reversePath = [endId];
+                let trackback = parent[endId];
+                let oneWay = !(trackback in end);
+
+                while (trackback !== beginId) {
+                    reversePath.push(trackback);
+                    oneWay = oneWay || !(parent[trackback] in navigation[trackback]);
+
+                    delete navigation[trackback];
+                    trackback = parent[trackback];
+                }
+
+                reversePath.push(beginId);
+                const forwardPath = [...reversePath];
+                forwardPath.reverse();
+
+                delete begin[forwardPath[1]];
+
+                if (!(endId in begin)) {
+                    begin[endId] = forwardPath;
+                }
+
+                if (!oneWay) {
+                    delete end[reversePath[1]];
+
+                    if (!(beginId in end)) {
+                        end[beginId] = reversePath;
+                    }
+                }
+            } else {
+                let isFirst = true;
+
+                for (const succId in end) {
+                    if (succId !== parent[endId]) {
+                        if (isFirst) {
+                            parent[succId] = endId;
+                            stack.push(succId);
+                            isFirst = false;
+                        } else {
+                            throw new Error(`Multiple successors in \
+non-junction node ${endId}`);
+                        }
+                    }
+                }
+
+                if (isFirst) {
+                    // Reached a dead-end: remove the path
+                    let trackback = endId;
+
+                    while (parent[trackback] !== beginId) {
+                        delete navigation[trackback];
+                        trackback = parent[trackback];
+                    }
+
+                    delete navigation[trackback];
+                    delete begin[trackback];
+                }
+            }
+        }
+    }
+
+    // Convert graph edges to GeoJSON line strings
+    for (const [beginId, begin] of Object.entries(navigation)) {
+        for (const endId in begin) {
+            begin[endId] = turfHelpers.lineString(begin[endId].map(
+                nodeId => [
+                    elementsById[getOSMId(nodeId)].lon,
+                    elementsById[getOSMId(nodeId)].lat
+                ]
+            ), {
+                begin: beginId,
+                end: endId,
+            });
+
+            begin[endId].properties.length = 1000 * turfLength(begin[endId]);
+        }
+    }
+
+    return navigation;
+};
+
+/**
+ * Fetch information about the network.
+ * @param {Array.<string>} lineRefs List of lines to fetch.
+ * @returns {Network} Network metadata extracted from OSM.
+ */
+export const fetch = async lineRefs => {
+    const elementsList = await queryLines(lineRefs);
+    const elementsById = elementsList.reduce((prev, elt) => {
+        prev[elt.id] = elt;
+        return prev;
+    }, {});
+
+    const { lines, stops, segments } = processRoutes(elementsList, elementsById);
+    const navigation = createNavigationGraph(stops, elementsList, elementsById);
+
+    return { navigation, lines, stops, segments };
 };

src/tam/routing.js

@@ -1,40 +1,58 @@
+import * as turfHelpers from "@turf/helpers";
+import dijkstra from "dijkstrajs";
 import network from "./network.json";
 
-/**
+// Transform the navigation graph to be in the format expected by dijkstrajs
- * Find a route linking two nodes or stops.
+const graph = {};
- * @param {string} from ID of the starting stop or node.
- * @param {string} to ID of the ending stop or node.
- * @return {lineString?} If it exists, a segment linking the two nodes that has
- * the least number of nodes possible.
- */
-export const findRoute = (from, to) => {
-    const queue = [from];
-    const parent = {from: from};
 
-    while (queue.length > 0 && !(to in parent)) {
+for (const [beginId, begin] of Object.entries(network.navigation)) {
-        const current = queue.shift();
+    const neighbors = {};
 
-        for (const successor of network.navigation[current].successors) {
+    for (const [endId, end] of Object.entries(begin)) {
-            if (!(successor in parent)) {
+        neighbors[endId] = end.properties.length;
-                queue.push(successor);
-                parent[successor] = current;
-            }
-        }
     }
 
-    if (!(to in parent)) {
+    graph[beginId] = neighbors;
+}
+
+/**
+ * Find the shortest path of nodes linking two nodes or stops.
+ * @param {string} from ID of the starting stop or node.
+ * @param {string} to ID of the ending stop or node.
+ * @return {Array.<string>} If possible, list of nodes joining `from` to `to`.
+ */
+export const findPath = (from, to) => {
+    try {
+        return dijkstra.find_path(graph, from, to);
+    } catch (err) {
+        return null;
+    }
+};
+
+/**
+ * Find the shortest segment linking two nodes or stops.
+ * @param {string} from ID of the starting stop or node.
+ * @param {string} to ID of the ending stop or node.
+ * @return {LineString?} If it exists, a segment linking the two nodes.
+ */
+export const findSegment = (from, to) => {
+    const path = findPath(from, to);
+
+    if (path === null) {
         return null;
     }
 
-    const path = [];
+    const initial = network.navigation[path[0]][path[1]];
-    let current = to;
+    let points = [...initial.geometry.coordinates];
+    let length = initial.properties.length;
 
-    while (current !== from) {
+    for (let i = 1; i + 1 < path.length; ++i) {
-        path.push(current);
+        const current = network.navigation[path[i]][path[i + 1]];
-        current = parent[current];
+        points = points.concat(current.geometry.coordinates.slice(1));
+        length += current.properties.length;
     }
 
-    path.push(from);
+    const route = turfHelpers.lineString(points);
-    path.reverse();
+    route.properties.length = length;
-    return path;
+    return route;
 };

src/tam/simulation.js

@@ -1,7 +1,5 @@
 import axios from "axios";
 import turfAlong from "@turf/along";
-import turfLength from "@turf/length";
-import * as turfHelpers from "@turf/helpers";
 import * as turfProjection from "@turf/projection";
 import * as routing from "./routing.js";
 import network from "./network.json";
@@ -100,20 +98,12 @@ class Course {
         }
 
         // Compute a custom route between two stops
-        const route = routing.findRoute(this.departureStop, this.arrivalStop);
+        this.segment = routing.findSegment(this.departureStop, this.arrivalStop);
 
-        if (route === null) {
+        if (this.segment === null) {
             console.warn(`No route from ${this.departureStop} \
 to ${this.arrivalStop}`);
         }
-
-        this.segment = turfHelpers.lineString(
-            route.map(node => [
-                network.navigation[node].lon,
-                network.navigation[node].lat,
-            ])
-        );
-        this.segment.properties.length = 1000 * turfLength(this.segment);
     }
 
     /** Merge passings data received from the server. */