Public
Edited
Nov 7, 2023
6 forks
Importers
13 stars
edgeSpeedsMPH = {
const edgeSpeeds = new Map();
for (const {seg: coordinates, mph} of roadSpeeds) {
for (let i = 0; i < coordinates.length - 1; i++) {
const [lng1, lat1] = coordinates[i];
const [lng2, lat2] = coordinates[i + 1];
const start = h3.geoToH3(lat1, lng1, h3Resolution);
const end = h3.geoToH3(lat2, lng2, h3Resolution);
if (start !== end) {
const cells = h3.h3Line(start, end);
for (let j = 0; j < cells.length - 1; j++) {
const edge = h3.getH3UnidirectionalEdge(cells[j], cells[j + 1]);
if (!edgeSpeeds.has(edge) || mph > edgeSpeeds.get(edge)) {
edgeSpeeds.set(edge, mph);
}
}
}
}
}
return edgeSpeeds;
}
cellTravelTimes = {
let interCellDist = null;
const {point} = map;
const origin = h3.geoToH3(point.lat, point.lng, h3Resolution);
// Use a priority queue to track the current set of cells to evaluate
const queue = new Heapify(1028, [], [], Array);
queue.push(origin, 0);
// init output map
const output = new Map([[origin, 0]]);
while (queue.length > 0) {
const cell = queue.pop();
const edges = h3.getH3UnidirectionalEdgesFromHexagon(cell);
for (const edge of edges) {
if (edgeSpeedsMPH.has(edge)) {
const dest = h3.getDestinationH3IndexFromUnidirectionalEdge(edge);
// lazy calculation of inter-cell distance
if (interCellDist === null) {
const coord1 = h3.h3ToGeo(cell);
const coord2 = h3.h3ToGeo(dest);
// transform km -> miles
interCellDist = h3.pointDist(coord1, coord2, h3.UNITS.km) * 0.621371;
}
// travel time between current cells
const minutes = (interCellDist / edgeSpeedsMPH.get(edge)) * 60;
// cumulative travel time
const travelTime = output.get(cell) + minutes;
if (!output.has(dest) || travelTime < output.get(dest)) {
output.set(dest, travelTime);
queue.push(dest, travelTime);
}
}
}
}
return output;
}
isochrone = {
const set = [];
for (const [h3Index, minutes] of cellTravelTimes) {
if (minutes < isochroneThreshold) {
set.push(h3Index);
}
}
return {
type: 'Feature',
geometry: {
type: 'MultiPolygon',
coordinates: h3.h3SetToMultiPolygon(set, true)
}
}
}
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