@dtcv/cities/dist/find-city.js

City metadata and utility functions

import { getMeterZoom, getDistanceScales } from '@math.gl/web-mercator';
// this should probably be moved to separate service later as it bloats the bundle
// at the moment its more for testing that it works
import RBush from 'rbush';
import Queue from 'tinyqueue';
// https://simplemaps.com/data/se-cities
import cityList from './cities.js';
// The knn was copied here due to propblems on the tinyqueue dependency
// https://github.com/mourner/rbush-knn/blob/master/index.js
// Copyright (c) 2016, Vladimir Agafonkin ISC License
export default function knn(tree, x, y, n, predicate, maxDistance) {
    let node = tree.data;
    const result = [];
    const toBBox = tree.toBBox;
    let i;
    let child;
    let dist;
    let candidate;
    const queue = new Queue(undefined, compareDist);
    while (node) {
        for (i = 0; i < node.children.length; i++) {
            child = node.children[i];
            dist = boxDist(x, y, node.leaf ? toBBox(child) : child);
            if (!maxDistance || dist <= maxDistance * maxDistance) {
                queue.push({
                    node: child,
                    isItem: node.leaf,
                    dist: dist,
                });
            }
        }
        while (queue.length && queue.peek().isItem) {
            candidate = queue.pop().node;
            if (!predicate || predicate(candidate))
                result.push(candidate);
            if (n && result.length === n)
                return result;
        }
        node = queue.pop();
        if (node)
            node = node.node;
    }
    return result;
}
function compareDist(a, b) {
    return a.dist - b.dist;
}
function boxDist(x, y, box) {
    const dx = axisDist(x, box.minX, box.maxX), dy = axisDist(y, box.minY, box.maxY);
    return dx * dx + dy * dy;
}
function axisDist(k, min, max) {
    return k < min ? min - k : k <= max ? 0 : k - max;
}
const EARTH_RADIUS = 6371008.8;
const EARTH_CIRC = 2 * Math.PI * EARTH_RADIUS;
const HALF_EARTH_CIRC = EARTH_CIRC / 2;
// todo: this should be moved to some util place, or why not use proj4
// (epsg4326/epsg3857)
function coordinateToMeters(lng, lat) {
    const x = lng * (EARTH_CIRC / 360);
    const y = Math.log(Math.tan(lat * (Math.PI / 360) + Math.PI / 4)) / Math.PI;
    return [x, y * HALF_EARTH_CIRC];
}
// todo: just generate a prepared list and require to give the city metadata on loading the viewer from app side
export const cities = cityList.map(c => {
    const lng = Number(c.lng);
    const lat = Number(c.lat);
    const xy = coordinateToMeters(lng, lat);
    const distanceScale = getDistanceScales({ longitude: lng, latitude: lat });
    const startZoom = getMeterZoom({ latitude: lat });
    const cityRadius = 4096;
    return {
        minX: xy[0] - cityRadius,
        minY: xy[1] - cityRadius,
        maxX: xy[0] + cityRadius,
        maxY: xy[1] + cityRadius,
        x: xy[0],
        y: xy[1],
        id: c.id,
        name: c.city,
        lng,
        lat,
        distanceScale,
        startZoom,
    };
});
const tree = new RBush();
tree.load(cities);
// webmercator, or send boolean for lnglat
export function findCity(x, y, isLngLat) {
    let c1 = x;
    let c2 = y;
    if (isLngLat) {
        const meters = coordinateToMeters(c1, c2);
        c1 = meters[0];
        c2 = meters[1];
    }
    const city = knn(tree, c1, c2, 1)[0];
    return {
        name: city.name,
        x: city.minX,
        y: city.minY,
    };
}
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