add files and folders

webgis-spbu/osm_to_geojson_draft.js

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+const fs = require('fs');
+
+const data = JSON.parse(fs.readFileSync('osm_pontianak.json', 'utf8'));
+
+const geojson = {
+  type: 'FeatureCollection',
+  features: []
+};
+
+data.elements.forEach(el => {
+  if (el.type === 'relation' && el.tags && el.tags.admin_level === '6') {
+    const name = el.tags.name;
+    // Extract polygons from relation members
+    const coordinates = [];
+    el.members.forEach(member => {
+      if (member.type === 'way' && member.geometry) {
+        const wayCoords = member.geometry.map(pt => [pt.lon, pt.lat]);
+        coordinates.push(wayCoords);
+      }
+    });
+    
+    // Assemble into MultiPolygon or Polygon (simplistic)
+    if (coordinates.length > 0) {
+      geojson.features.push({
+        type: 'Feature',
+        properties: {
+          kecamatan: name,
+          ...el.tags
+        },
+        geometry: {
+          type: 'Polygon',
+          coordinates: coordinates
+        }
+      });
+    }
+  }
+});
+
+// Since OSM returns fragments of outer and inner rings in relations, a naive conversion might have topological issues in Leaflet (like crossing lines if not ordered).
+// We should use an existing library like osmtogeojson. Let's install it and use it.