Fix jsts empty (Multi)Polygon error @turf/difference (#725)

* Update fixtures from #644 * Fix jsts empty (Multi)Polygon error - Major refactoring to `index.js` & `test.js` - Update JSDocs & Typescript definition to support MultiPolygon #721
Turfjs · May 10, 2017 · 60b2ee0 · 60b2ee0
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diff --git a/packages/turf-difference/README.md b/packages/turf-difference/README.md
@@ -2,20 +2,22 @@
 
 # difference
 
-Finds the difference between two [polygons](http://geojson.org/geojson-spec.html#polygon) by clipping the second
-polygon from the first.
+Finds the difference between two [polygons](http://geojson.org/geojson-spec.html#polygon) by clipping the second polygon from the first.
 
 **Parameters**
 
--   `p1` **[Feature](http://geojson.org/geojson-spec.html#feature-objects)&lt;[Polygon](http://geojson.org/geojson-spec.html#polygon)>** input Polygon feature
--   `p2` **[Feature](http://geojson.org/geojson-spec.html#feature-objects)&lt;[Polygon](http://geojson.org/geojson-spec.html#polygon)>** Polygon feature to difference from `p1`
+-   `polygon1` **[Feature](http://geojson.org/geojson-spec.html#feature-objects)&lt;([Polygon](http://geojson.org/geojson-spec.html#polygon) \| [MultiPolygon](http://geojson.org/geojson-spec.html#multipolygon))>** input Polygon feature
+-   `polygon2` **[Feature](http://geojson.org/geojson-spec.html#feature-objects)&lt;([Polygon](http://geojson.org/geojson-spec.html#polygon) \| [MultiPolygon](http://geojson.org/geojson-spec.html#multipolygon))>** Polygon feature to difference from polygon1
 
 **Examples**
 
 ```javascript
-var poly1 = {
+var polygon1 = {
   "type": "Feature",
-  "properties": {},
+  "properties": {
+    "fill": "#F00",
+    "fill-opacity": 0.1
+  },
   "geometry": {
     "type": "Polygon",
     "coordinates": [[
@@ -27,31 +29,35 @@ var poly1 = {
     ]]
   }
 };
-var poly2 = {
+var polygon2 = {
   "type": "Feature",
-  "properties": {},
+  "properties": {
+    "fill": "#00F",
+    "fill-opacity": 0.1
+  },
   "geometry": {
     "type": "Polygon",
-    "coordinates": [[
-      [-46.650009, -23.631314],
-      [-46.650009, -23.5237],
-      [-46.509246, -23.5237],
-      [-46.509246, -23.631314],
-      [-46.650009, -23.631314]
-    ]]
+    "coordinates": [[[126, -28], [140, -28], [140, -20], [126, -20], [126, -28]]]
   }
 };
 
-var difference = turf.difference(poly1, poly2);
+var difference = turf.difference(polygon1, polygon2);
 
 //addToMap
-poly1.properties.fill = '#0f0';
-poly2.properties.fill = '#00f';
-difference.properties.fill = '#f00';
-var addToMap = [poly1, poly2, difference];
+var addToMap = [polygon1, polygon2, difference];
 ```
 
-Returns **[Feature](http://geojson.org/geojson-spec.html#feature-objects)&lt;([Polygon](http://geojson.org/geojson-spec.html#polygon) \| [MultiPolygon](http://geojson.org/geojson-spec.html#multipolygon))>** a Polygon or MultiPolygon feature showing the area of `p1` excluding the area of `p2`
+Returns **([Feature](http://geojson.org/geojson-spec.html#feature-objects)&lt;([Polygon](http://geojson.org/geojson-spec.html#polygon) \| [MultiPolygon](http://geojson.org/geojson-spec.html#multipolygon))> | [undefined](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined))** a Polygon or MultiPolygon feature showing the area of `polygon1` excluding the area of `polygon2` (if empty returns `undefined`)
+
+# removeEmptyPolygon
+
+Detect Empty Polygon
+
+**Parameters**
+
+-   `geom` **[Geometry](http://geojson.org/geojson-spec.html#geometry)&lt;([Polygon](http://geojson.org/geojson-spec.html#polygon) \| [MultiPolygon](http://geojson.org/geojson-spec.html#multipolygon))>** Geometry Object
+
+Returns **([Geometry](http://geojson.org/geojson-spec.html#geometry)&lt;([Polygon](http://geojson.org/geojson-spec.html#polygon) \| [MultiPolygon](http://geojson.org/geojson-spec.html#multipolygon))> | [undefined](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined))** removed any polygons with no areas
 
 <!-- This file is automatically generated. Please don't edit it directly:
 if you find an error, edit the source file (likely index.js), and re-run

diff --git a/packages/turf-difference/bench.js b/packages/turf-difference/bench.js
@@ -1,22 +1,38 @@
-var difference = require('./');
-var Benchmark = require('benchmark');
-var fs = require('fs');
+const fs = require('fs');
+const path = require('path');
+const load = require('load-json-file');
+const Benchmark = require('benchmark');
+const difference = require('./');
 
-var clip = JSON.parse(fs.readFileSync(__dirname+'/test/fixtures/in/differencedHole.geojson'));
-var hole = JSON.parse(fs.readFileSync(__dirname+'/test/fixtures/in/differencedFC.geojson'));
+const directory = path.join(__dirname, 'test', 'in') + path.sep;
+let fixtures = fs.readdirSync(directory).map(filename => {
+    return {
+        filename,
+        name: path.parse(filename).name,
+        geojson: load.sync(directory + filename)
+    };
+});
+// fixtures = fixtures.filter(({name}) => name === 'issue-#721');
+
+/**
+ * Benchmark Results
+ *
+ * ==using jsts==
+ * clip-polygons x 2,512 ops/sec ±30.29% (71 runs sampled)
+ * completely-overlapped x 6,777 ops/sec ±4.08% (78 runs sampled)
+ * create-hole x 5,451 ops/sec ±9.92% (75 runs sampled)
+ * issue-#721-inverse x 434,372 ops/sec ±3.40% (85 runs sampled)
+ * issue-#721 x 421,194 ops/sec ±4.35% (80 runs sampled)
+ * multi-polygon-input x 1,904 ops/sec ±5.16% (79 runs sampled)
+ * multi-polygon-target x 1,240 ops/sec ±5.44% (79 runs sampled)
+ * split-polygon x 2,468 ops/sec ±4.75% (82 runs sampled)
+ */
+const suite = new Benchmark.Suite('turf-difference');
+for (const {name, geojson} of fixtures) {
+    suite.add(name, () => difference(geojson.features[0], geojson.features[1]));
+}
 
-var suite = new Benchmark.Suite('turf-difference');
 suite
-  .add('turf-difference#clip',function () {
-    difference(clip[0], clip[1]);
-  })
-  .add('turf-difference#hole',function () {
-    difference(hole[0], hole[1]);
-  })
-  .on('cycle', function (event) {
-    console.log(String(event.target));
-  })
-  .on('complete', function () {
-
-  })
-  .run();
+    .on('cycle', e => console.log(String(e.target)))
+    .on('complete', () => {})
+    .run();
diff --git a/packages/turf-difference/index.d.ts b/packages/turf-difference/index.d.ts
@@ -1,11 +1,13 @@
 /// <reference types="geojson" />
 
-type Polygon = GeoJSON.Feature<GeoJSON.Polygon>;
-type MultiPolygon = GeoJSON.Feature<GeoJSON.MultiPolygon>;
+import {Polygon, MultiPolygon, Feature} from '@turf/meta'
+
+type Input = Feature<Polygon|MultiPolygon> | Polygon | MultiPolygon;
+type Output = Feature<Polygon|MultiPolygon> | undefined;
 
 /**
  * http://turfjs.org/docs/#difference
  */
-declare function difference(poly1: Polygon, poly2: Polygon): Polygon|MultiPolygon;
+declare function difference(polygon1: Input, polygon2: Input): Output;
 declare namespace difference { }
 export = difference;
diff --git a/packages/turf-difference/index.js b/packages/turf-difference/index.js
@@ -1,18 +1,24 @@
 // depend on jsts for now https://github.com/bjornharrtell/jsts/blob/master/examples/overlay.html
 var jsts = require('jsts');
+var area = require('@turf/area');
+var feature = require('@turf/helpers').feature;
+var getGeom = require('@turf/invariant').getGeom;
+var flattenEach = require('@turf/meta').flattenEach;
 
 /**
- * Finds the difference between two {@link Polygon|polygons} by clipping the second
- * polygon from the first.
+ * Finds the difference between two {@link Polygon|polygons} by clipping the second polygon from the first.
  *
  * @name difference
- * @param {Feature<Polygon>} p1 input Polygon feature
- * @param {Feature<Polygon>} p2 Polygon feature to difference from `p1`
- * @return {Feature<(Polygon|MultiPolygon)>} a Polygon or MultiPolygon feature showing the area of `p1` excluding the area of `p2`
+ * @param {Feature<Polygon|MultiPolygon>} polygon1 input Polygon feature
+ * @param {Feature<Polygon|MultiPolygon>} polygon2 Polygon feature to difference from polygon1
+ * @returns {Feature<Polygon|MultiPolygon>|undefined} a Polygon or MultiPolygon feature showing the area of `polygon1` excluding the area of `polygon2` (if empty returns `undefined`)
  * @example
- * var poly1 = {
+ * var polygon1 = {
  *   "type": "Feature",
- *   "properties": {},
+ *   "properties": {
+ *     "fill": "#F00",
+ *     "fill-opacity": 0.1
+ *   },
  *   "geometry": {
  *     "type": "Polygon",
  *     "coordinates": [[
@@ -24,63 +30,62 @@ var jsts = require('jsts');
  *     ]]
  *   }
  * };
- * var poly2 = {
+ * var polygon2 = {
  *   "type": "Feature",
- *   "properties": {},
+ *   "properties": {
+ *     "fill": "#00F",
+ *     "fill-opacity": 0.1
+ *   },
  *   "geometry": {
  *     "type": "Polygon",
- *     "coordinates": [[
- *       [-46.650009, -23.631314],
- *       [-46.650009, -23.5237],
- *       [-46.509246, -23.5237],
- *       [-46.509246, -23.631314],
- *       [-46.650009, -23.631314]
- *     ]]
+ *     "coordinates": [[[126, -28], [140, -28], [140, -20], [126, -20], [126, -28]]]
  *   }
  * };
  *
- * var difference = turf.difference(poly1, poly2);
+ * var difference = turf.difference(polygon1, polygon2);
  *
  * //addToMap
- * poly1.properties.fill = '#0f0';
- * poly2.properties.fill = '#00f';
- * difference.properties.fill = '#f00';
- * var addToMap = [poly1, poly2, difference];
+ * var addToMap = [polygon1, polygon2, difference];
  */
+module.exports = function (polygon1, polygon2) {
+    var geom1 = getGeom(polygon1);
+    var geom2 = getGeom(polygon2);
+    var properties = polygon1.properties || {};
 
-module.exports = function (p1, p2) {
-    var poly1 = JSON.parse(JSON.stringify(p1));
-    var poly2 = JSON.parse(JSON.stringify(p2));
-    if (poly1.type !== 'Feature') {
-        poly1 = {
-            type: 'Feature',
-            properties: {},
-            geometry: poly1
-        };
-    }
-    if (poly2.type !== 'Feature') {
-        poly2 = {
-            type: 'Feature',
-            properties: {},
-            geometry: poly2
-        };
-    }
+    // Issue #721 - JSTS can't handle empty polygons
+    geom1 = removeEmptyPolygon(geom1);
+    geom2 = removeEmptyPolygon(geom2);
+    if (!geom1) return undefined;
+    if (!geom2) return feature(geom1, properties);
 
+    // JSTS difference operation
     var reader = new jsts.io.GeoJSONReader();
-    var a = reader.read(JSON.stringify(poly1.geometry));
-    var b = reader.read(JSON.stringify(poly2.geometry));
+    var a = reader.read(geom1);
+    var b = reader.read(geom2);
     var differenced = a.difference(b);
-
     if (differenced.isEmpty()) return undefined;
-
     var writer = new jsts.io.GeoJSONWriter();
-    var geojsonGeometry = writer.write(differenced);
+    var geom = writer.write(differenced);
 
-    poly1.geometry = differenced;
-
-    return {
-        type: 'Feature',
-        properties: poly1.properties,
-        geometry: geojsonGeometry
-    };
+    return feature(geom, properties);
 };
+
+/**
+ * Detect Empty Polygon
+ *
+ * @param {Geometry<Polygon|MultiPolygon>} geom Geometry Object
+ * @returns {Geometry<Polygon|MultiPolygon>|undefined} removed any polygons with no areas
+ */
+function removeEmptyPolygon(geom) {
+    switch (geom.type) {
+    case 'Polygon':
+        if (area(geom) > 1) return geom;
+        return undefined;
+    case 'MultiPolygon':
+        var coordinates = [];
+        flattenEach(geom, function (feature) {
+            if (area(feature) > 1) coordinates.push(feature.geometry.coordinates);
+        });
+        if (coordinates.length) return {type: 'MultiPolygon', coordinates: coordinates};
+    }
+}
diff --git a/packages/turf-difference/package.json b/packages/turf-difference/package.json
@@ -27,12 +27,17 @@
   },
   "homepage": "https://github.com/Turfjs/turf",
   "devDependencies": {
-    "benchmark": "^1.0.0",
+    "benchmark": "^2.1.4",
     "glob": "~5.0.5",
-    "tape": "~4.0.0"
+    "load-json-file": "^2.0.0",
+    "tape": "^4.6.3",
+    "write-json-file": "^2.0.0"
   },
   "dependencies": {
-    "jsts": "1.3.0",
-    "@turf/helpers": "^4.2.0"
+    "@turf/area": "^4.2.0",
+    "@turf/helpers": "^4.2.0",
+    "@turf/invariant": "^4.2.0",
+    "@turf/meta": "^4.2.0",
+    "jsts": "^1.4.0"
   }
 }