From ba4c1ef0148c15f8d973daf144349848fda6cb8e Mon Sep 17 00:00:00 2001
From: Quincy Morgan <2046746+quincylvania@users.noreply.github.com>
Date: Thu, 29 Oct 2020 14:28:21 -0400
Subject: [PATCH] Account for instances where d3.geoCentroid returns incorrect
 results

---
 modules/actions/extract.js       | 5 ++++-
 modules/ui/panels/measurement.js | 4 +++-
 package.json                     | 1 +
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/modules/actions/extract.js b/modules/actions/extract.js
index 0db93c174..d283a42fb 100644
--- a/modules/actions/extract.js
+++ b/modules/actions/extract.js
@@ -1,5 +1,7 @@
 
 import { geoCentroid as d3_geoCentroid } from 'd3-geo';
+import geojsonRewind from '@mapbox/geojson-rewind';
+
 import { osmNode } from '../osm/node';
 
 export function actionExtract(entityID) {
@@ -45,7 +47,8 @@ export function actionExtract(entityID) {
         var keysToRetain = ['area'];
         var buildingKeysToRetain = ['architect', 'building', 'height', 'layer'];
 
-        var extractedLoc = d3_geoCentroid(entity.asGeoJSON(graph));
+        // d3_geoCentroid is wrong for counterclockwise-wound polygons, so wind them clockwise
+        var extractedLoc = d3_geoCentroid(geojsonRewind(Object.assign({}, entity.asGeoJSON(graph)), true));
         if (!extractedLoc  || !isFinite(extractedLoc[0]) || !isFinite(extractedLoc[1])) {
             extractedLoc = entity.extent(graph).center();
         }
diff --git a/modules/ui/panels/measurement.js b/modules/ui/panels/measurement.js
index 20be05d66..cf5965290 100644
--- a/modules/ui/panels/measurement.js
+++ b/modules/ui/panels/measurement.js
@@ -2,6 +2,7 @@ import {
     geoLength as d3_geoLength,
     geoCentroid as d3_geoCentroid
 } from 'd3-geo';
+import geojsonRewind from '@mapbox/geojson-rewind';
 
 import { t, localizer } from '../../core/localizer';
 import { displayArea, displayLength, decimalCoordinatePair, dmsCoordinatePair } from '../../util/units';
@@ -78,7 +79,8 @@ export function uiPanelMeasurement(context) {
                         closed = (entity.type === 'relation') || (entity.isClosed() && !entity.isDegenerate());
                         var feature = entity.asGeoJSON(graph);
                         length += radiansToMeters(d3_geoLength(toLineString(feature)));
-                        centroid = d3_geoCentroid(feature);
+                        // d3_geoCentroid is wrong for counterclockwise-wound polygons, so wind them clockwise
+                        centroid = d3_geoCentroid(geojsonRewind(Object.assign({}, feature), true));
                         if (closed) {
                             area += steradiansToSqmeters(entity.area(graph));
                         }
diff --git a/package.json b/package.json
index 901a6ea01..ad1d57fc5 100644
--- a/package.json
+++ b/package.json
@@ -44,6 +44,7 @@
   "dependencies": {
     "@ideditor/country-coder": "^3.2.0",
     "@ideditor/location-conflation": "~0.5.0",
+    "@mapbox/geojson-rewind": "^0.5.0",
     "@mapbox/sexagesimal": "1.2.0",
     "@mapbox/togeojson": "0.16.0",
     "@mapbox/vector-tile": "^1.3.1",