support custom projections / tile bounds

README.md

@@ -101,4 +101,4 @@ An object that contains the data for a single feature.
 - **loadGeometry()** — parses feature geometry and returns an array of
   [Point](https://github.com/mapbox/point-geometry) arrays (with each point having `x` and `y` properties)
 - **bbox()** — calculates and returns the bounding box of the feature in the form `[x1, y1, x2, y2]`
-- **toGeoJSON(x, y, z)** — returns a GeoJSON representation of the feature. (`x`, `y`, and `z` refer to the containing tile's index.)
+- **toGeoJSON(x, y, z, project)** — returns a GeoJSON representation of the feature. `x`, `y`, and `z` refer to the containing tile's index. An optional project function can be used if the projection is not EPSG:3857, it will receive coordinates in the form `[x, y]` with `x` from 0.0 to 1.0 and `y` depending on the projection used, and it must return `[x, y]` in EPSG:4326.

lib/vectortilefeature.js

@@ -126,21 +126,28 @@ VectorTileFeature.prototype.bbox = function() {
     return [x1, y1, x2, y2];
 };
 
-VectorTileFeature.prototype.toGeoJSON = function(x, y, z) {
+VectorTileFeature.prototype.toGeoJSON = function(x, y, z, project) {
     var size = this.extent * Math.pow(2, z),
         x0 = this.extent * x,
         y0 = this.extent * y,
         coords = this.loadGeometry(),
         type = VectorTileFeature.types[this.type],
-        i, j;
+        i, j,
+        projectPoint = project || projectMercator;
+
+    function projectMercator(point) {
+        return [
+            point[0] * 360 - 180,
+            360 / Math.PI * Math.atan(Math.exp((180 - point[1] * 360) * Math.PI / 180)) - 90
+        ];
+    }
 
-    function project(line) {
+    function projectLine(line) {
         for (var j = 0; j < line.length; j++) {
-            var p = line[j], y2 = 180 - (p.y + y0) * 360 / size;
-            line[j] = [
-                (p.x + x0) * 360 / size - 180,
-                360 / Math.PI * Math.atan(Math.exp(y2 * Math.PI / 180)) - 90
-            ];
+            line[j] = projectPoint([
+                (line[j].x + x0) / size,
+                (line[j].y + y0) / size
+            ]);
         }
     }
 
@@ -151,20 +158,20 @@ VectorTileFeature.prototype.toGeoJSON = function(x, y, z) {
             points[i] = coords[i][0];
         }
         coords = points;
-        project(coords);
+        projectLine(coords);
         break;
 
     case 2:
         for (i = 0; i < coords.length; i++) {
-            project(coords[i]);
+            projectLine(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]);
+                projectLine(coords[i][j]);
             }
         }
         break;

test/parse.test.js

@@ -138,6 +138,64 @@ test('parsing vector tiles', function(t) {
             }
         }));
 
+        function projectMercator(point) {
+            return [
+                point[0] * 360 - 180,
+                360 / Math.PI * Math.atan(Math.exp((180 - point[1] * 360) * Math.PI / 180)) - 90
+            ];
+        }
+
+        t.ok(approximateDeepEqual(tile.layers.poi_label.feature(11).toGeoJSON(8801, 5371, 14, projectMercator), {
+            type: 'Feature',
+            id: 3000003150561,
+            properties: {
+                localrank: 1,
+                maki: 'park',
+                name: 'Mauerpark',
+                name_de: 'Mauerpark',
+                name_en: 'Mauerpark',
+                name_es: 'Mauerpark',
+                name_fr: 'Mauerpark',
+                osm_id: 3000003150561,
+                ref: '',
+                scalerank: 2,
+                type: 'Park'
+            },
+            geometry: {
+                type: 'Point',
+                coordinates: [13.402258157730103, 52.54398925380624]
+            }
+        }));
+
+        t.ok(approximateDeepEqual(tile.layers.bridge.feature(0).toGeoJSON(8801, 5371, 14, projectMercator), {
+            type: 'Feature',
+            id: 238162948,
+            properties: {
+                class: 'service',
+                oneway: 0,
+                osm_id: 238162948,
+                type: 'service'
+            },
+            geometry: {
+                type: 'LineString',
+                coordinates: [[13.399457931518555, 52.546334844036416], [13.399441838264465, 52.546504478525016]]
+            }
+        }));
+
+        t.ok(approximateDeepEqual(tile.layers.building.feature(0).toGeoJSON(8801, 5371, 14, projectMercator), {
+            type: 'Feature',
+            id: 1000267229912,
+            properties: {
+                osm_id: 1000267229912
+            },
+            geometry: {
+                type: 'Polygon',
+                coordinates: [[[13.392285704612732, 52.54974045706258], [13.392264246940613, 52.549737195107554],
+                [13.392248153686523, 52.549737195107554], [13.392248153686523, 52.54974045706258],
+                [13.392285704612732, 52.54974045706258]]]
+            }
+        }));
+
         function geoJSONFromFixture(name) {
             var tile = new VectorTile(new Protobuf(fs.readFileSync(__dirname + '/fixtures/' + name + '.pbf')));
             return tile.layers.geojson.feature(0).toGeoJSON(0, 0, 0);