d3.geo.area: return positive areas.

d3.js

@@ -5519,7 +5519,7 @@
       λ0 = λ, φ0 = φ;
       cosφ0 = cosφ, sinφ0 = sinφ;
     }
-    return area > 2 * π && area <= 4 * π ? 4 * π - area : area <= -2 * π && area > -4 * π ? area + 4 * π : area;
+    return Math.abs(area < -ε ? 4 * π + area : area);
   }
   var d3_geo_azimuthalEqualArea = d3_geo_azimuthal(function(cosλcosφ) {
     return Math.sqrt(2 / (1 + cosλcosφ));

src/geo/area.js

@@ -13,7 +13,7 @@ var d3_geo_areaType = d3_geo_type({
   Feature: function(feature) { return d3_geo_areaType.geometry(feature.geometry); },
   FeatureCollection: function(collection) { return d3.sum(collection.features, d3_geo_areaType.Feature); },
   GeometryCollection: function(collection) { return d3.sum(collection.geometries, d3_geo_areaType.geometry); },
-  geometry: function(geometry) { return d3_geo_areaType[geometry.type](geometry); } // TODO add 3rd argument to d3.sum?
+  geometry: function(geometry) { return d3_geo_areaType[geometry.type](geometry); }
 });
 
 function d3_geo_areaPolygon(polygon) {
@@ -58,7 +58,5 @@ function d3_geo_areaRing(ring) {
     λ0 = λ, φ0 = φ;
     cosφ0 = cosφ, sinφ0 = sinφ;
   }
-  return area > 2 * π && area <= 4 * π ? 4 * π - area
-      : area <= -2 * π && area > -4 * π ? area + 4 * π
-      : area;
+  return Math.abs(area < -ε ? 4 * π + area : area);
 }

test/geo/area-test.js

@@ -55,6 +55,32 @@ suite.addBatch({
         "semilune": function(area) {
           assert.inDelta(area(d3.geo.graticule().extent([[0, 0], [90, 90]]).outline()), π / 2, 1e-5);
         }
+      },
+      "circles": {
+        "hemisphere": function(area) {
+          assert.inDelta(area(d3.geo.circle().angle(90)()), 2 * π, 1e-5);
+        },
+        "45°": function(area) {
+          assert.inDelta(area(d3.geo.circle().angle(45).precision(.1)()), π * (2 - Math.SQRT2), 1e-5);
+        },
+        "45° North": function(area) {
+          assert.inDelta(area(d3.geo.circle().angle(45).precision(.1).origin([0, 90])()), π * (2 - Math.SQRT2), 1e-5);
+        },
+        "45° South": function(area) {
+          assert.inDelta(area(d3.geo.circle().angle(45).precision(.1).origin([0, -90])()), π * (2 - Math.SQRT2), 1e-5);
+        },
+        "135°": function(area) {
+          assert.inDelta(area(d3.geo.circle().angle(135).precision(.1)()), π * (2 + Math.SQRT2), 1e-5);
+        },
+        "135° North": function(area) {
+          assert.inDelta(area(d3.geo.circle().angle(135).precision(.1).origin([0, 90])()), π * (2 + Math.SQRT2), 1e-5);
+        },
+        "135° South": function(area) {
+          assert.inDelta(area(d3.geo.circle().angle(135).precision(.1).origin([0, -90])()), π * (2 + Math.SQRT2), 1e-5);
+        },
+        "tiny": function(area) {
+          assert.inDelta(area(d3.geo.circle().angle(1e-6)()), 0, 1e-6);
+        }
       }
     },
     "MultiPolygon": {