Classify polygon rings to distinguish inner polygon rings and multipolygons

Author: jfirebaugh

fixtures.js

@@ -2,7 +2,7 @@ var mapnik = require('mapnik');
 var path = require('path');
 var fs = require('fs');
 
-mapnik.register_datasource(path.join(mapnik.settings.paths.input_plugins,'geojson.input'));
+mapnik.register_datasource(path.join(mapnik.settings.paths.input_plugins, 'geojson.input'));
 
 var fixtures = {
     "zero-point": {
@@ -31,6 +31,19 @@ var fixtures = {
             }
         ]
     },
+    "zero-polygon": {
+        "type": "FeatureCollection",
+        "features": [
+            {
+                "type": "Feature",
+                "geometry": {
+                    "type": "MultiPolygon",
+                    "coordinates": []
+                },
+                "properties": {}
+            }
+        ]
+    },
     "singleton-multi-point": {
         "type": "FeatureCollection",
         "features": [
@@ -57,6 +70,19 @@ var fixtures = {
             }
         ]
     },
+    "singleton-multi-polygon": {
+        "type": "FeatureCollection",
+        "features": [
+            {
+                "type": "Feature",
+                "geometry": {
+                    "type": "MultiPolygon",
+                    "coordinates": [[[[0, 0], [1, 0], [1, 1], [0, 0]]]]
+                },
+                "properties": {}
+            }
+        ]
+    },
     "multi-point": {
         "type": "FeatureCollection",
         "features": [
@@ -82,11 +108,50 @@ var fixtures = {
                 "properties": {}
             }
         ]
+    },
+    "multi-polygon": {
+        "type": "FeatureCollection",
+        "features": [
+            {
+                "type": "Feature",
+                "geometry": {
+                    "type": "MultiPolygon",
+                    "coordinates": [[[[0, 0], [1, 0], [1, 1], [0, 0]]], [[[0, 0], [-1, 0], [-1, -1], [0, 0]]]]
+                },
+                "properties": {}
+            }
+        ]
+    },
+    "polygon-with-inner": {
+        "type": "FeatureCollection",
+        "features": [
+            {
+                "type": "Feature",
+                "geometry": {
+                    "type": "Polygon",
+                    "coordinates": [[[-2, 2], [2, 2], [2, -2], [-2, -2], [-2, 2]], [[-1, 1], [1, 1], [1, -1], [-1, -1], [-1, 1]]]
+                },
+                "properties": {}
+            }
+        ]
+    },
+    "stacked-multipolygon": {
+        "type": "FeatureCollection",
+        "features": [
+            {
+                "type": "Feature",
+                "geometry": {
+                    "type": "MultiPolygon",
+                    "coordinates": [[[[-2, 2], [2, 2], [2, -2], [-2, -2], [-2, 2]]], [[[-1, 1], [1, 1], [1, -1], [-1, -1], [-1, 1]]]]
+                },
+                "properties": {}
+            }
+        ]
     }
 }
 
 for (var fixture in fixtures) {
-    var vtile = new mapnik.VectorTile(0,0,0);
+    var vtile = new mapnik.VectorTile(0, 0, 0);
     vtile.addGeoJSON(JSON.stringify(fixtures[fixture]), "geojson");
     fs.writeFileSync('./test/fixtures/' + fixture + '.pbf', vtile.getData());
 }

lib/vectortilefeature.js

@@ -131,10 +131,10 @@ VectorTileFeature.prototype.toGeoJSON = function(x, y, z) {
         x0 = this.extent * x,
         y0 = this.extent * y,
         coords = this.loadGeometry(),
-        type = VectorTileFeature.types[this.type];
+        type = VectorTileFeature.types[this.type],
+        i, j;
 
-    for (var i = 0; i < coords.length; i++) {
-        var line = coords[i];
+    function project(line) {
         for (var j = 0; j < line.length; j++) {
             var p = line[j], y2 = 180 - (p.y + y0) * 360 / size;
             line[j] = [
@@ -144,15 +144,36 @@ VectorTileFeature.prototype.toGeoJSON = function(x, y, z) {
         }
     }
 
-    if (type === 'Point' && coords.length === 1) {
-        coords = coords[0][0];
-    } else if (type === 'Point') {
-        coords = coords.map(function (c) { return c[0]; });
-        type = 'MultiPoint';
-    } else if (type === 'LineString' && coords.length === 1) {
+    switch (this.type) {
+    case 1:
+        var points = [];
+        for (i = 0; i < coords.length; i++) {
+            points[i] = coords[i][0];
+        }
+        coords = points;
+        project(coords);
+        break;
+
+    case 2:
+        for (i = 0; i < coords.length; i++) {
+            project(coords[i]);
+        }
+        break;
+
+    case 3:
+        coords = classifyRings(coords);
+        for (i = 0; i < coords.length; i++) {
+            for (j = 0; j < coords[i].length; j++) {
+                project(coords[i][j]);
+            }
+        }
+        break;
+    }
+
+    if (coords.length === 1) {
         coords = coords[0];
-    } else if (type === 'LineString') {
-        type = 'MultiLineString';
+    } else {
+        type = 'Multi' + type;
     }
 
     var result = {
@@ -170,3 +191,43 @@ VectorTileFeature.prototype.toGeoJSON = function(x, y, z) {
 
     return result;
 };
+
+// classifies an array of rings into polygons with outer rings and holes
+
+function classifyRings(rings) {
+    var len = rings.length;
+
+    if (len <= 1) return [rings];
+
+    var polygons = [],
+        polygon,
+        ccw;
+
+    for (var i = 0; i < len; i++) {
+        var area = signedArea(rings[i]);
+        if (area === 0) continue;
+
+        if (ccw === undefined) ccw = area < 0;
+
+        if (ccw === area < 0) {
+            if (polygon) polygons.push(polygon);
+            polygon = [rings[i]];
+
+        } else {
+            polygon.push(rings[i]);
+        }
+    }
+    if (polygon) polygons.push(polygon);
+
+    return polygons;
+}
+
+function signedArea(ring) {
+    var sum = 0;
+    for (var i = 0, len = ring.length, j = len - 1, p1, p2; i < len; j = i++) {
+        p1 = ring[i];
+        p2 = ring[j];
+        sum += (p2.x - p1.x) * (p1.y + p2.y);
+    }
+    return sum;
+}

package.json

@@ -12,7 +12,7 @@
     "benchmark": "^1.0.0",
     "coveralls": "~2.11.2",
     "istanbul": "~0.3.6",
-    "mapnik": "^3.1.6",
+    "mapnik": "^3.5.13",
     "jshint": "^2.6.3",
     "pbf": "^1.3.2",
     "tape": "~3.5.0",

test/fixtures/multi-line.pbf

@@ -1,4 +1,4 @@
-$
-geojson
"	� �
+$x
+geojson(� "	� �
 .-	.+
-.-(� x

+.-

test/fixtures/multi-point.pbf

@@ -1,2 +1,2 @@
-
-geojson

"	� �	.-(� x

+x
+geojson(� 
"� �.-

test/fixtures/multi-polygon.pbf

@@ -1,3 +1,3 @@
-
-geojson
"	� �
-.-(� x

+x
+geojson(� "	� �
+.-

test/fixtures/multipolygon.pbf

@@ -1,2 +1,2 @@
-
-geojson

"	� �(� x

+x
+geojson(� 
"	� �