find max nr of radar() results: tweak bbox algorithm ✅

follow-up of b06c567
follow-up of 98f042d
related: #12

lib/find-max-radar-results.js

@@ -1,6 +1,6 @@
 'use strict'
 
-const debug = require('debug')('hafas-monitor-trips:find-max-radar-results')
+const createDebug = require('debug')
 const distance = require('@turf/distance').default
 const dest = require('@turf/destination').default
 const {ok} = require('assert')
@@ -18,7 +18,10 @@ const CACHE_TTL = 7 * 24 * 60 * 60 // 1 week
 // Therefore, we introduce a minimum to make this case less likely.
 const MIN_NR_OF_MOVEMENTS = 100
 
-const findMaxRadarResults = async (hafas, initialBbox, onReqTime, onMovement) => {
+const debug = createDebug('hafas-monitor-trips:find-max-radar-results')
+const debugBbox = createDebug('hafas-monitor-trips:find-max-radar-results:bbox')
+
+const expandingBoundingBoxes = function* (initialBbox) {
 	// this is accurate enough for our use case
 	const center = {
 		type: 'Point',
@@ -38,20 +41,37 @@ const findMaxRadarResults = async (hafas, initialBbox, onReqTime, onMovement) =>
 	debug('initial bbox', initialBbox)
 	debug('center', center.coordinates, 'width', w, 'height', h)
 
-	let prevResults = -Infinity, prevPrevResults = -Infinity
-	for (let it = 0, distFactor = .1; it < MAX_ITERATIONS; it++, distFactor *= 2) {
+	// this creates wrong bounding boxes when "crossing" the antimeridian or the poles
+	// todo: find a way to deal with this, but allow *initial* legitimate bounding boxes across them?
+	for (let it = 0; it < MAX_ITERATIONS; it++) {
+		const distFactor = .1 * Math.pow(1.5, it)
+		debugBbox(
+			'it', it,
+			'distFactor', distFactor.toFixed(2),
+			'width', (distFactor * w).toFixed(2),
+			'height', (distFactor * h).toFixed(2),
+		)
+
 		const _north = dest(center, distFactor * h / 2,   0).geometry.coordinates[1]
 		const _west = dest(center, distFactor * w / 2,  270).geometry.coordinates[0]
 		const _south = dest(center, distFactor * h / 2, 180).geometry.coordinates[1]
 		const _east = dest(center, distFactor * w / 2,   90).geometry.coordinates[0]
-		const bbox = {
+		yield {
 			north: Math.round(_north * 10000) / 10000,
 			west: Math.round(_west * 10000) / 10000,
 			south: Math.round(_south * 10000) / 10000,
 			east: Math.round(_east * 10000) / 10000,
 		}
+	}
+}
 
-		debug('calling radar()', 'iteration', it, 'bbox', bbox)
+const findMaxRadarResults = async (hafas, initialBbox, onReqTime, onMovement) => {
+	debug('initial bbox', initialBbox)
+
+	let it = 0
+	let prevResults = -Infinity, prevPrevResults = -Infinity
+	for (const bbox of expandingBoundingBoxes(initialBbox)) {
+		debug('calling radar()', 'iteration', it++, 'bbox', bbox)
 		const t0 = Date.now()
 		const movements = await hafas.radar(bbox, {
 			results: ENOUGH_RESULTS,
@@ -92,4 +112,6 @@ const cachedFindMaxRadarResults = async (hafas, bbox, redis, onReqTime, onMoveme
 	return maxResults
 }
 
+// todo [breaking]: export object
+cachedFindMaxRadarResults.expandingBoundingBoxes = expandingBoundingBoxes
 module.exports = cachedFindMaxRadarResults

test.js

@@ -4,8 +4,33 @@ const createHafas = require('vbb-hafas')
 const a = require('assert')
 const {Registry} = require('prom-client')
 const createMonitor = require('.')
+const {expandingBoundingBoxes} = require('./lib/find-max-radar-results')
 const fetchTrips = require('./fetch-trips')
 
+a.deepStrictEqual(
+	Array.from(expandingBoundingBoxes({
+		north: 54.52,
+		west: 6.54,
+		south: 51.29,
+		east: 6.65,
+	}))
+	.map(({north, west, south, east}, i) => [north, west, south, east]),
+	[
+		[53.0665,6.5895,52.7435,6.6005],
+		[53.1473,6.5868,52.6628,6.6032],
+		[53.2684,6.5826,52.5416,6.6074],
+		[53.4501,6.5764,52.3599,6.6136],
+		[53.7226,6.5672,52.0874,6.6228],
+		[54.1314,6.5532,51.6786,6.6368],
+		[54.7446,6.5324,51.0654,6.6576],
+		[55.6644,6.501, 50.1456,6.689 ],
+		[57.0441,6.454, 48.7659,6.736 ],
+		[59.1136,6.3836,46.6964,6.8064],
+		[62.2179,6.2778,43.5921,6.9122],
+		[66.8744,6.1193,38.9356,7.0707],
+	],
+)
+
 const METRICS = [
 	'hafas_reqs_total',
 	'hafas_errors_total',