From 4cfca57cfbacaaced36aaad356013aa25925efcc Mon Sep 17 00:00:00 2001
From: Sameh Khamis <sameh@halfpixel.ai>
Date: Thu, 1 Oct 2026 16:19:28 -0700
Subject: [PATCH] fix: bound large boxes by their farthest point on the sphere

A box's radius was the distance to its farthest corner, which falls short for
large boxes: a whole-world box measured about 10,000 km, so bike-share and
transit selection never considered systems beyond it. The radius now checks
whether the box holds the point opposite its center and otherwise samples
every edge.
---
 src/tools/area.js                   | 40 +++++++++++++++++++++++------
 src/tools/area.test.mjs             | 17 ++++++++++++
 src/tools/queries/mobility.test.mjs | 15 +++++++++++
 3 files changed, 64 insertions(+), 8 deletions(-)

diff --git a/src/tools/area.js b/src/tools/area.js
index dbd3aabb6..4af62a03c 100644
--- a/src/tools/area.js
+++ b/src/tools/area.js
@@ -142,14 +142,38 @@ export async function resolvePoint(point, { services, signal } = {}) {
 export function areaRadiusKm(area) {
   if (area.center) return area.center.radiusKm;
   const center = areaCenter(area);
-  return Math.max(
-    ...[
-      { lat: area.north, lon: area.west },
-      { lat: area.north, lon: area.east },
-      { lat: area.south, lon: area.west },
-      { lat: area.south, lon: area.east },
-    ].map((corner) => distanceKm(center, corner)),
-  );
+  // A box holding the point opposite its center reaches half the globe.
+  const antipode = {
+    lat: -center.lat,
+    lon: center.lon > 0 ? center.lon - 180 : center.lon + 180,
+  };
+  if (areaContains(area, antipode)) return Math.PI * EARTH_RADIUS_KM;
+  // Otherwise the farthest point is on the boundary: sample each edge, and
+  // include where each parallel edge comes nearest the antipode's longitude.
+  const width =
+    area.west <= area.east
+      ? area.east - area.west
+      : 360 - (area.west - area.east);
+  const lonAt = (t) => area.west + width * t;
+  const steps = 64;
+  const points = [];
+  for (let step = 0; step <= steps; step += 1) {
+    const t = step / steps;
+    const lat = area.south + (area.north - area.south) * t;
+    points.push(
+      { lat, lon: area.west },
+      { lat, lon: area.east },
+      { lat: area.north, lon: lonAt(t) },
+      { lat: area.south, lon: lonAt(t) },
+    );
+  }
+  const offset = (((antipode.lon - area.west) % 360) + 360) % 360;
+  if (offset <= width)
+    points.push(
+      { lat: area.north, lon: antipode.lon },
+      { lat: area.south, lon: antipode.lon },
+    );
+  return Math.max(...points.map((point) => distanceKm(center, point)));
 }
 
 /** Great-circle distance in kilometers. */
diff --git a/src/tools/area.test.mjs b/src/tools/area.test.mjs
index d901813b5..7ec551aae 100644
--- a/src/tools/area.test.mjs
+++ b/src/tools/area.test.mjs
@@ -3,6 +3,7 @@ import test from 'node:test';
 import {
   areaCenter,
   areaContains,
+  areaRadiusKm,
   distanceKm,
   lineTouchesArea,
   polygonsTouchArea,
@@ -245,3 +246,19 @@ test('polygons touch an area by vertex, crossing edge or enclosing it', async ()
   const circle = await resolveArea({ lat: 0, lon: 0, radius_km: 20 });
   assert.ok(polygonsTouchArea([square(5)], circle));
 });
+
+test('a box radius reaches every point of the box, however large', async () => {
+  const world = await resolveArea({ bbox: [-180, -90, 180, 90] });
+  assert.ok(Math.abs(areaRadiusKm(world) - Math.PI * 6371.0088) < 1);
+  const wide = await resolveArea({ bbox: [-60, -70, 100, 60] });
+  const radius = areaRadiusKm(wide);
+  const center = areaCenter(wide);
+  for (let lat = -70; lat <= 60; lat += 2.5)
+    for (let lon = -60; lon <= 100; lon += 2.5)
+      assert.ok(
+        distanceKm(center, { lat, lon }) <= radius + 0.5,
+        `${lat},${lon}`,
+      );
+  const small = await resolveArea({ bbox: [-97.94, 30.1, -97.56, 30.52] });
+  assert.ok(areaRadiusKm(small) < 30);
+});
diff --git a/src/tools/queries/mobility.test.mjs b/src/tools/queries/mobility.test.mjs
index 1d3212ff7..af8142305 100644
--- a/src/tools/queries/mobility.test.mjs
+++ b/src/tools/queries/mobility.test.mjs
@@ -481,3 +481,18 @@ test('traffic counts only roads inside a radius area and reports missing tiles',
   assert.equal(partial.data.partial, true);
   assert.match(partial.summary, /Some map tiles did not load/);
 });
+
+test('a whole-world bike-share search names every system it skipped', async () => {
+  const empty = { data: { stations: [] } };
+  const result = await composeCatalog({
+    tools: coreTools,
+    services: {
+      bikeshare: {
+        systems: GBFS_CITY_REGISTRY,
+        getStations: async () => empty,
+      },
+    },
+  }).call('get_bike_share', { area: { bbox: [-180, -90, 180, 90] } });
+  const named = [...result.data.systems, ...result.data.systems_not_searched];
+  assert.equal(named.length, GBFS_CITY_REGISTRY.length);
+});