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Improve navigation graph compression

This commit is contained in:
Mattéo Delabre 2021-05-23 00:45:09 +02:00
parent 474fc94a06
commit a51a80a4b3
Signed by: matteo
GPG Key ID: AE3FBD02DC583ABB
3 changed files with 17396 additions and 27223 deletions
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302
src/tam/network.js
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@ -70,7 +70,7 @@ import * as osm from "./sources/osm.js";
*/
/**
* Edge of the graph for out-of-route navigation between stops.
* Edge of the graph for navigating between stops.
* @typedef {Object} NavigationEdge
* @property {string} type Always equal to "Feature".
* @property {Object} properties
@ -83,13 +83,18 @@ import * as osm from "./sources/osm.js";
* Sequence of points forming this edge (as longitude/latitude pairs).
*/
/**
* Graph for navigating between stops.
* @typedef {Object.<string,Object.<string,NavigationEdge>>} Navigation
*/
/**
* 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
* @property {Navigation} navigation
* Graph for out-of-route navigation between stops.
*/
@ -332,45 +337,20 @@ different sequence of nodes in two or more lines.`);
};
/**
* Create a graph for navigating between stops outside of
* regular planned routes.
* @property {Object.<string,Stop>} stops List of stops.
* Create a graph for navigating between 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 createNavigationGraph = (elementsList, elementsById) => {
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") {
navigation[getNavigationId(obj.id)] = {};
navigationReverse[getNavigationId(obj.id)] = {};
navigation[obj.id] = {};
navigationReverse[obj.id] = {};
}
}
@ -378,95 +358,202 @@ const createNavigationGraph = (stops, elementsList, elementsById) => {
for (const obj of elementsList) {
if (obj.type === "way") {
const oneWay = osm.isOneWay(obj);
const pairs = obj.nodes.slice(0, -1).map(
(node, i) => [
getNavigationId(node),
getNavigationId(obj.nodes[i + 1]),
]
);
for (const [from, to] of pairs) {
navigation[from][to] = [from, to];
for (let i = 0; i + 1 < obj.nodes.length; ++i) {
const from = obj.nodes[i];
let to = obj.nodes[i + 1];
let path = [from.toString(), to.toString()];
// Make sure we can’t jump between rails at railway crossings
if (i + 2 < obj.nodes.length
&& osm.isRailwayCrossing(elementsById[to])) {
const next = obj.nodes[i + 2];
path = [from.toString(), to.toString(), next.toString()];
to = next;
i += 1;
}
navigation[from][to] = path;
navigationReverse[to][from] = true;
if (!oneWay) {
navigation[to][from] = [to, from];
const reversePath = [...path];
reversePath.reverse();
navigation[to][from] = reversePath;
navigationReverse[from][to] = true;
}
}
}
}
// Mark nodes of the graph to be kept
const nodesToKeep = {};
return { navigation, navigationReverse };
};
for (const nodeId in navigation) {
if (nodeId in stops) {
// Keep stop nodes
nodesToKeep[nodeId] = true;
continue;
}
/**
* Remove and relink nodes that connect only two nodes or less.
* @param {Object.<string,Stop>} stops List of stops.
* @param {Navigation} navigation Input navigation graph.
* @param {Object.<string,Object.<string,boolean>>} navigationReverse
* Backward edges of the navigation graph.
*/
const compressNavigationGraph = (stops, navigation, navigationReverse) => {
const stopsReverse = Object.fromEntries(
Object.entries(stops).map(([id, stop]) => [stop.properties.node, id])
);
const entries = new Set(Object.keys(navigationReverse[nodeId]));
const exits = new Set(Object.keys(navigation[nodeId]));
let removedDeadEnds = true;
const nodesToCompress = {};
// 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;
while (removedDeadEnds) {
// Identify nodes to be compressed
for (const nodeId in navigation) {
if (nodeId in stopsReverse) {
// Keep stop nodes
continue;
}
if (exits.size === 2) {
for (const entry of entries) {
if (!exits.has(entry)) {
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) {
continue;
}
let isSplit = false;
if (exits.size === 2) {
for (const entry of entries) {
if (!exits.has(entry)) {
isSplit = true;
break;
}
}
}
if (isSplit) {
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) {
continue;
}
let isJunction = false;
if (entries.size === 2) {
for (const exit of exits) {
if (!entries.has(exit)) {
isJunction = true;
break;
}
}
}
if (isJunction) {
continue;
}
}
// Compress all other nodes
nodesToCompress[nodeId] = true;
}
// Find nodes that cannot be used to directly link up two kept nodes
const usedNodes = {};
for (const beginId in navigation) {
if (beginId in nodesToCompress) {
continue;
}
usedNodes[beginId] = true;
// Start a DFS from each node to be kept
const begin = navigation[beginId];
const stack = [];
const parent = {[beginId]: beginId};
for (const succId in begin) {
if (succId in nodesToCompress) {
stack.push(succId);
parent[succId] = beginId;
}
}
while (stack.length > 0) {
const endId = stack.pop();
const end = navigation[endId];
if (!(endId in nodesToCompress)) {
let trackback = parent[endId];
while (trackback !== beginId) {
usedNodes[trackback] = true;
trackback = parent[trackback];
}
} else {
for (const succId in end) {
if (succId !== parent[endId]) {
parent[succId] = endId;
stack.push(succId);
}
}
}
}
}
// 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;
}
// Remove dead-end nodes
removedDeadEnds = false;
if (entries.size === 2) {
for (const exit of exits) {
if (!entries.has(exit)) {
nodesToKeep[nodeId] = true;
continue;
}
for (const beginId in navigation) {
if (!(beginId in usedNodes)) {
for (const neighborId in navigation[beginId]) {
delete navigationReverse[neighborId][beginId];
}
for (const neighborId in navigationReverse[beginId]) {
delete navigation[neighborId][beginId];
}
delete navigation[beginId];
delete navigationReverse[beginId];
removedDeadEnds = true;
}
}
}
// Compress edges between nodes of interest
for (const beginId in nodesToKeep) {
// Perform node compression
for (const beginId in navigation) {
if (beginId in nodesToCompress) {
continue;
}
// Start a DFS from each node to be kept
const begin = navigation[beginId];
const stack = [];
const parent = {[beginId]: beginId};
for (const succId in begin) {
stack.push(succId);
parent[succId] = beginId;
if (succId in nodesToCompress) {
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;
}
if (!(endId in nodesToCompress)) {
// Found another kept node
// Collect and remove intermediate nodes
const reversePath = [endId];
let trackback = parent[endId];
let oneWay = !(trackback in end);
@ -476,6 +563,7 @@ const createNavigationGraph = (stops, elementsList, elementsById) => {
oneWay = oneWay || !(parent[trackback] in navigation[trackback]);
delete navigation[trackback];
delete navigationReverse[trackback];
trackback = parent[trackback];
}
@ -483,20 +571,24 @@ const createNavigationGraph = (stops, elementsList, elementsById) => {
const forwardPath = [...reversePath];
forwardPath.reverse();
// Create edges to link both nodes directly
delete begin[forwardPath[1]];
delete navigationReverse[endId][reversePath[1]];
delete end[reversePath[1]];
delete navigationReverse[beginId][forwardPath[1]];
if (!(endId in begin)) {
begin[endId] = forwardPath;
navigationReverse[endId][beginId] = true;
}
if (!oneWay) {
delete end[reversePath[1]];
if (!(beginId in end)) {
end[beginId] = reversePath;
}
if (!oneWay && !(beginId in end)) {
end[beginId] = reversePath;
navigationReverse[beginId][endId] = true;
}
} else {
// Continue the traversal down unused nodes
let isFirst = true;
for (const succId in end) {
@ -511,30 +603,23 @@ 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
/**
* Transform navigation graph edges into GeoJSON segments.
* @param {Navigation} navigation Input navigation graph.
* @param {Object.<string,Object>} elementsById OSM nodes indexed by their ID.
*/
const makeNavigationSegments = (navigation, elementsById) => {
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
elementsById[nodeId].lon,
elementsById[nodeId].lat
]
), {
begin: beginId,
@ -544,8 +629,6 @@ non-junction node ${endId}`);
begin[endId].properties.length = 1000 * turfLength(begin[endId]);
}
}
return navigation;
};
/**
@ -561,7 +644,12 @@ export const fetch = async lineRefs => {
}, {});
const { lines, stops, segments } = processRoutes(elementsList, elementsById);
const navigation = createNavigationGraph(stops, elementsList, elementsById);
const { navigation, navigationReverse } = createNavigationGraph(
elementsList, elementsById
);
compressNavigationGraph(stops, navigation, navigationReverse);
makeNavigationSegments(navigation, elementsById);
return { navigation, lines, stops, segments };
};

44304
src/tam/network.json
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13
src/tam/sources/osm.js
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@ -48,6 +48,19 @@ export const isOneWay = obj => (
obj.tags.highway === "motorway")
);
/**
* Determine if a node is a railway crossing or not.
*
* See <https://wiki.osm.org/Tag:railway=railway_crossing> for details.
* @param {Object} obj OSM node object.
* @return {boolean} Whether the node is a railway crossing.
*/
export const isRailwayCrossing = obj => (
obj.type === "node" &&
isObject(obj.tags) &&
(obj.tags.railway === "railway_crossing")
);
/**
* Determine if an OSM object is a public transport line (route master).
*