Mapsforge: heuristic determine if a map element is an area, closes #35

vtm/src/org/oscim/tiling/source/mapfile/MapDatabase.java

@@ -591,7 +591,7 @@ public class MapDatabase implements ITileDataSource {
 			int len = numWayNodes * 2;
 
 			wayLengths[coordinateBlock] = decodeWayNodes(doubleDeltaEncoding,
-			                                             e, len, isLine);;
+			                                             e, len, isLine);
 		}
 
 		return true;
@@ -813,14 +813,7 @@ public class MapDatabase implements ITileDataSource {
 			}
 
 			/* some guessing if feature is a line or a polygon */
-			boolean linearFeature = e.tags.containsKey("highway") ||
-			        e.tags.containsKey("boundary") ||
-			        e.tags.containsKey("railway");
-			if (linearFeature) {
-				Tag areaTag = e.tags.get("area");
-				if (areaTag != null && areaTag.value == Tag.VALUE_YES)
-					linearFeature = false;
-			}
+			boolean linearFeature = !OSMUtils.isArea(e);
 
 			for (int wayDataBlock = 0; wayDataBlock < wayDataBlocks; wayDataBlock++) {
 				e.clear();

vtm/src/org/oscim/tiling/source/mapfile/OSMUtils.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright 2016 devemux86
+ *
+ * This program is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License along with
+ * this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.oscim.tiling.source.mapfile;
+
+import org.oscim.core.MapElement;
+import org.oscim.core.Tag;
+
+import java.util.Locale;
+
+public final class OSMUtils {
+
+    /**
+     * Heuristic to determine from attributes if a map element is likely to be an area.
+     * Precondition for this call is that the first and last node of a map element are the
+     * same, so that this method should only return false if it is known that the
+     * feature should not be an area even if the geometry is a polygon.
+     * <p/>
+     * Determining what is an area is neigh impossible in OSM, this method inspects tag elements
+     * to give a likely answer. See http://wiki.openstreetmap.org/wiki/The_Future_of_Areas and
+     * http://wiki.openstreetmap.org/wiki/Way
+     *
+     * @param mapElement the map element (which is assumed to be closed and have enough nodes to be an area)
+     * @return true if tags indicate this is an area, otherwise false.
+     */
+    public static boolean isArea(MapElement mapElement) {
+        boolean result = true;
+        for (int i = 0; i < mapElement.tags.numTags; i++) {
+            Tag tag = mapElement.tags.tags[i];
+            String key = tag.key.toLowerCase(Locale.ENGLISH);
+            String value = tag.value.toLowerCase(Locale.ENGLISH);
+            if ("area".equals(key)) {
+                // obvious result
+                if (("yes").equals(value) || ("y").equals(value) || ("true").equals(value)) {
+                    return true;
+                }
+                if (("no").equals(value) || ("n").equals(value) || ("false").equals(value)) {
+                    return false;
+                }
+            }
+            // as specified by http://wiki.openstreetmap.org/wiki/Key:area
+            if ("aeroway".equals(key) || "building".equals(key) || "landuse".equals(key) || "leisure".equals(key) || "natural".equals(key)) {
+                return true;
+            }
+            if ("highway".equals(key) || "barrier".equals(key)) {
+                // false unless something else overrides this.
+                result = false;
+            }
+            if ("railway".equals(key)) {
+                // there is more to the railway tag then just rails, this excludes the
+                // most common railway lines from being detected as areas if they are closed.
+                // Since this method is only called if the first and last node are the same
+                // this should be safe
+                if ("rail".equals(value) || "tram".equals(value) || "subway".equals(value)
+                        || "monorail".equals(value) || "narrow_gauge".equals(value) || "preserved".equals(value)
+                        || "light_rail".equals(value) || "construction".equals(value)) {
+                    result = false;
+                }
+            }
+        }
+        return result;
+    }
+
+    private OSMUtils() {
+    }
+}