fix choropleth hover over Antarctica

- ++ cleaner hover polygon logic - no mutation when offsetting RUS and FJI longitudes - do not offset RUS and FJI polygons that do not need modification for hover!
plotly · etpinard · Sep 28, 2017 · Sep 21, 2017 · Sep 21, 2017 · Sep 21, 2017
commit 190c7338b3f2a6271d54bf90129129374e5596f8
diff --git a/src/traces/choropleth/plot.js b/src/traces/choropleth/plot.js
@@ -55,9 +55,8 @@ function calcGeoJSON(calcTrace, topojson) {
     var trace = calcTrace[0].trace;
     var len = calcTrace.length;
     var features = getTopojsonFeatures(trace, topojson);
-    var i, j, k, m;
 
-    for(i = 0; i < len; i++) {
+    for(var i = 0; i < len; i++) {
         var calcPt = calcTrace[i];
         var feature = locationToFeature(trace.locationmode, calcPt.loc, features);
 
@@ -66,48 +65,116 @@ function calcGeoJSON(calcTrace, topojson) {
             continue;
         }
 
+
         calcPt.geojson = feature;
         calcPt.ct = feature.properties.ct;
         calcPt.index = i;
+        calcPt._polygons = feature2polygons(feature);
+    }
+}
 
-        var geometry = feature.geometry;
-        var coords = geometry.coordinates;
-        calcPt._polygons = [];
+function feature2polygons(feature) {
+    var geometry = feature.geometry;
+    var coords = geometry.coordinates;
+    var loc = feature.id;
+
+    var polygons = [];
+    var appendPolygon, j, k, m;
+
+    function doesCrossAntiMerdian(pts) {
+        for(var l = 0; l < pts.length - 1; l++) {
+            if(pts[l][0] > 0 && pts[l + 1][0] < 0) return l;
+        }
+        return null;
+    }
 
+    if(loc === 'RUS' || loc === 'FJI') {
         // Russia and Fiji have landmasses that cross the antimeridian,
         // we need to add +360 to their longitude coordinates, so that
         // polygon 'contains' doesn't get confused when crossing the antimeridian.
         //
         // Note that other countries have polygons on either side of the antimeridian
         // (e.g. some Aleutian island for the USA), but those don't confuse
         // the 'contains' method; these are skipped here.
-        if(calcPt.loc === 'RUS' || calcPt.loc === 'FJI') {
-            for(j = 0; j < coords.length; j++) {
-                for(k = 0; k < coords[j].length; k++) {
-                    for(m = 0; m < coords[j][k].length; m++) {
-                        if(coords[j][k][m][0] < 0) {
-                            coords[j][k][m][0] += 360;
-                        }
-                    }
+        appendPolygon = function(_pts) {
+            var pts;
+
+            if(doesCrossAntiMerdian(_pts) === null) {
+                pts = _pts;
+            } else {
+                pts = new Array(_pts.length);
+                for(m = 0; m < _pts.length; m++) {
+                    // do nut mutate calcdata[i][j].geojson !!
+                    pts[m] = [
+                        _pts[m][0] < 0 ? _pts[m][0] + 360 : _pts[m][0],
+                        _pts[m][1]
+                    ];
                 }
             }
-        }
 
-        switch(geometry.type) {
-            case 'MultiPolygon':
-                for(j = 0; j < coords.length; j++) {
-                    for(k = 0; k < coords[j].length; k++) {
-                        calcPt._polygons.push(polygon.tester(coords[j][k]));
-                    }
+            polygons.push(polygon.tester(pts));
+        };
+    } else if(loc === 'ATA') {
+        // Antarctica has a landmass that wraps around every longitudes which
+        // confuses the 'contains' methods.
+        appendPolygon = function(pts) {
+            var crossAntiMeridianIndex = doesCrossAntiMerdian(pts);
+
+            // polygon that do not cross anti-meridian need no special handling
+            if(crossAntiMeridianIndex === null) {
+                return polygons.push(polygon.tester(pts));
+            }
+
+            // stitch polygon by adding pt over South Pole,
+            // so that it covers the projected region covers all latitudes
+            //
+            // Note that the algorithm below only works for polygons that
+            // start and end on longitude -180 (like the ones built by
+            // https://github.com/etpinard/sane-topojson).
+            var stitch = new Array(pts.length + 1);
+            var si = 0;
+
+            for(m = 0; m < pts.length; m++) {
+                if(m > crossAntiMeridianIndex) {
+                    stitch[si++] = [pts[m][0] + 360, pts[m][1]];
+                } else if(m === crossAntiMeridianIndex) {
+                    stitch[si++] = pts[m];
+                    stitch[si++] = [pts[m][0], -90];
+                } else {
+                    stitch[si++] = pts[m];
                 }
-                break;
-            case 'Polygon':
-                for(j = 0; j < coords.length; j++) {
-                    calcPt._polygons.push(polygon.tester(coords[j]));
+            }
+
+            // polygon.tester by default appends pt[0] to the points list,
+            // we must remove it here, to avoid a jump in longitude from 180 to -180,
+            // that would confuse the 'contains' method
+            var tester = polygon.tester(stitch);
+            tester.pts.pop();
+            polygons.push(tester);
+        };
+    } else {
+        // otherwise using same array ref is fine
+        appendPolygon = function(pts) {
+            polygons.push(polygon.tester(pts));
+        };
+    }
+
+    switch(geometry.type) {
+        case 'MultiPolygon':
+            for(j = 0; j < coords.length; j++) {
+                for(k = 0; k < coords[j].length; k++) {
+                    appendPolygon(coords[j][k]);
                 }
-                break;
-        }
+            }
+            break;
+        case 'Polygon':
+            for(j = 0; j < coords.length; j++) {
+                appendPolygon(coords[j]);
+            }
+            break;
     }
+
+    return polygons;
 }
 
 function style(geo) {

diff --git a/test/jasmine/tests/geo_test.js b/test/jasmine/tests/geo_test.js
@@ -1306,8 +1306,8 @@ describe('Test geo interactions', function() {
 
         Plotly.newPlot(gd, [{
             type: 'choropleth',
-            locations: ['RUS', 'FJI'],
-            z: [0, 1]
+            locations: ['RUS', 'FJI', 'ATA'],
+            z: [0, 1, 2]
         }])
         .then(function() {
             check([81, 66], 1, 'spot in north-central Russia that polygon.contains gets wrong before +360 shift');
@@ -1326,6 +1326,17 @@ describe('Test geo interactions', function() {
         .then(function() {
             check([179, -16.6], 1, 'spot on Fiji island that cross antimeridian west of antimeridian');
             check([-179.9, -16.2], 1, 'spot on Fiji island that cross antimeridian east of antimeridian');
+
+            return Plotly.relayout(gd, {
+                'geo.center.lat': null,
+                'geo.projection': {
+                    type: 'orthographic',
+                    rotation: {lat: -90}
+                }
+            });
+        })
+        .then(function() {
+            check([-150, -89], 1, 'spot in Antarctica that requires *stitching*');
         })
         .catch(fail)
         .then(done);