From dd8ba562d29906306eaac3cce7cfa92bceaafff9 Mon Sep 17 00:00:00 2001
From: Sameh Khamis <sameh@halfpixel.ai>
Date: Thu, 1 Oct 2026 15:18:55 -0700
Subject: [PATCH] fix: find fire perimeters that overlap an area

Fire perimeters were placed at their average vertex, so a fire enclosing the
whole requested area was missed. Polygons now count when a vertex is inside
the area, an edge crosses it, or the polygon contains it outside any hole.
---
 src/tools/area.js                      | 35 ++++++++++++++++++++++++++
 src/tools/area.test.mjs                | 21 ++++++++++++++++
 src/tools/queries/environment.js       |  4 ++-
 src/tools/queries/environment.test.mjs | 29 +++++++++++++++++++++
 4 files changed, 88 insertions(+), 1 deletion(-)

diff --git a/src/tools/area.js b/src/tools/area.js
index b8eef612b..dbd3aabb6 100644
--- a/src/tools/area.js
+++ b/src/tools/area.js
@@ -296,3 +296,38 @@ export function lineTouchesArea(coords, area) {
   }
   return false;
 }
+
+/** Whether a point lies inside a ring of `[lon, lat]` vertices (ray casting). */
+function ringContains(ring, point) {
+  let inside = false;
+  for (let i = 0, j = ring.length - 1; i < ring.length; j = i, i += 1) {
+    const [xi, yi] = ring[i];
+    const [xj, yj] = ring[j];
+    if (
+      yi > point.lat !== yj > point.lat &&
+      point.lon < ((xj - xi) * (point.lat - yi)) / (yj - yi) + xi
+    )
+      inside = !inside;
+  }
+  return inside;
+}
+
+/**
+ * Whether polygons (each a list of `[lon, lat]` rings, outer ring first)
+ * overlap an area: a vertex inside it, an edge crossing it, or the area's
+ * center inside a polygon and outside its holes.
+ */
+export function polygonsTouchArea(polygons, area) {
+  const center = areaCenter(area);
+  return (polygons || []).some((rings) => {
+    if (!Array.isArray(rings) || !rings.length) return false;
+    const closed = rings.map((ring) =>
+      ring.length && ring[0] !== ring.at(-1) ? [...ring, ring[0]] : ring,
+    );
+    if (closed.some((ring) => lineTouchesArea(ring, area))) return true;
+    return (
+      ringContains(rings[0], center) &&
+      !rings.slice(1).some((hole) => ringContains(hole, center))
+    );
+  });
+}
diff --git a/src/tools/area.test.mjs b/src/tools/area.test.mjs
index dee34f402..d901813b5 100644
--- a/src/tools/area.test.mjs
+++ b/src/tools/area.test.mjs
@@ -5,6 +5,7 @@ import {
   areaContains,
   distanceKm,
   lineTouchesArea,
+  polygonsTouchArea,
   resolveArea,
 } from './area.js';
 import { placeFromGeocodeResult } from './places.js';
@@ -224,3 +225,23 @@ test('lines touch an area when a segment crosses it with no vertex inside', asyn
     ),
   );
 });
+
+test('polygons touch an area by vertex, crossing edge or enclosing it', async () => {
+  const box = await resolveArea({ bbox: [-1, -1, 1, 1] });
+  const square = (half, x = 0) => [
+    [
+      [x - half, -half],
+      [x + half, -half],
+      [x + half, half],
+      [x - half, half],
+    ],
+  ];
+  assert.ok(polygonsTouchArea([square(5)], box), 'encloses the area');
+  assert.ok(polygonsTouchArea([square(0.5)], box), 'inside the area');
+  assert.ok(polygonsTouchArea([square(1, 1.5)], box), 'overlaps an edge');
+  assert.ok(!polygonsTouchArea([square(0.5, 5)], box), 'elsewhere');
+  const ring = [...square(5), ...square(3)];
+  assert.ok(!polygonsTouchArea([ring], box), 'the area sits in a hole');
+  const circle = await resolveArea({ lat: 0, lon: 0, radius_km: 20 });
+  assert.ok(polygonsTouchArea([square(5)], circle));
+});
diff --git a/src/tools/queries/environment.js b/src/tools/queries/environment.js
index 7def1f87d..141a8e70c 100644
--- a/src/tools/queries/environment.js
+++ b/src/tools/queries/environment.js
@@ -10,6 +10,7 @@ import {
   areaCenter,
   areaContains,
   distanceKm,
+  polygonsTouchArea,
   resolveArea,
   resolvePoint,
 } from '../area.js';
@@ -237,8 +238,9 @@ export const getFirePerimeters = defineTool({
   async run(args, { services, signal }) {
     const area = await resolveArea(args.area, { services, signal });
     const rows = (await services.perimeters.getSnapshot({ signal }))
+      .filter((fire) => polygonsTouchArea(fire.polygons, area))
       .map((fire) => ({ fire, point: polygonCenter(fire.polygons) }))
-      .filter(({ point }) => point && areaContains(area, point))
+      .filter(({ point }) => point)
       .map(({ fire, point }) => ({
         id: fire.stableId,
         name: fire.name,
diff --git a/src/tools/queries/environment.test.mjs b/src/tools/queries/environment.test.mjs
index 2a7a82982..b26c615bf 100644
--- a/src/tools/queries/environment.test.mjs
+++ b/src/tools/queries/environment.test.mjs
@@ -665,3 +665,32 @@ test('brief sections use a named place at its own point', async () => {
   assert.deepEqual(queries[0], { latitude: 35.6769, longitude: 139.7639 });
   assert.match(result.data.sections.aircraft.summary, /in Tokyo, Japan\.$/);
 });
+
+test('a fire perimeter enclosing the whole area is found', async () => {
+  const perimeters = {
+    getSnapshot: async () => [
+      {
+        stableId: 'big',
+        name: 'Big Fire',
+        acres: 250000,
+        polygons: [
+          [
+            [
+              [-122, 38],
+              [-120, 38],
+              [-120, 40],
+              [-122, 40],
+            ],
+          ],
+        ],
+      },
+    ],
+  };
+  const result = await catalogWith({ perimeters }).call('get_fire_perimeters', {
+    area: { bbox: [-121.2, 38.9, -120.8, 39.1] },
+  });
+  assert.deepEqual(
+    result.data.rows.map((row) => row.id),
+    ['big'],
+  );
+});