docs/attachments/LUCENE-4550/LUCENE-4550__fix_SpatialArgs_calcDistanceFromErrPct.patch

Index: lucene/spatial/src/test/org/apache/lucene/spatial/SpatialArgsTest.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- lucene/spatial/src/test/org/apache/lucene/spatial/SpatialArgsTest.java	(revision )
+++ lucene/spatial/src/test/org/apache/lucene/spatial/SpatialArgsTest.java	(revision )
@@ -0,0 +1,51 @@
+package org.apache.lucene.spatial;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import com.spatial4j.core.context.SpatialContext;
+import com.spatial4j.core.shape.Shape;
+import org.apache.lucene.spatial.query.SpatialArgs;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class SpatialArgsTest {
+
+  @Test
+  public void calcDistanceFromErrPct() {
+    final SpatialContext ctx = SpatialContext.GEO;
+    final double DEP = 0.5;//distErrPct
+
+    //the result is the diagonal distance from the center to the closest corner,
+    // times distErrPct
+
+    Shape superwide = ctx.makeRectangle(-180, 180, 0, 0);
+    //0 distErrPct means 0 distance always
+    assertEquals(0, SpatialArgs.calcDistanceFromErrPct(superwide, 0, ctx), 0);
+    assertEquals(180 * DEP, SpatialArgs.calcDistanceFromErrPct(superwide, DEP, ctx), 0);
+
+    Shape supertall = ctx.makeRectangle(0, 0, -90, 90);
+    assertEquals(90 * DEP, SpatialArgs.calcDistanceFromErrPct(supertall, DEP, ctx), 0);
+
+    Shape upperhalf = ctx.makeRectangle(-180, 180, 0, 90);
+    assertEquals(45 * DEP, SpatialArgs.calcDistanceFromErrPct(upperhalf, DEP, ctx), 0.0001);
+
+    Shape midCircle = ctx.makeCircle(0, 0, 45);
+    assertEquals(60 * DEP, SpatialArgs.calcDistanceFromErrPct(midCircle, DEP, ctx), 0.0001);
+  }
+}
Index: lucene/spatial/src/java/org/apache/lucene/spatial/query/SpatialArgs.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- lucene/spatial/src/java/org/apache/lucene/spatial/query/SpatialArgs.java	(revision 1437032)
+++ lucene/spatial/src/java/org/apache/lucene/spatial/query/SpatialArgs.java	(revision )
@@ -47,7 +47,7 @@
   /**
    * Computes the distance given a shape and the {@code distErrPct}.  The
    * algorithm is the fraction of the distance from the center of the query
-   * shape to its furthest bounding box corner.
+   * shape to its closest bounding box corner.
    *
    * @param shape Mandatory.
    * @param distErrPct 0 to 0.5
@@ -62,11 +62,13 @@
       return 0;
     }
     Rectangle bbox = shape.getBoundingBox();
-    //The diagonal distance should be the same computed from any opposite corner,
-    // and this is the longest distance that might be occurring within the shape.
-    double diagonalDist = ctx.getDistCalc().distance(
-        ctx.makePoint(bbox.getMinX(), bbox.getMinY()), bbox.getMaxX(), bbox.getMaxY());
-    return diagonalDist * 0.5 * distErrPct;
+    //Compute the distance from the center to a corner.  Because the distance
+    // to a bottom corner vs a top corner can vary in a geospatial scenario,
+    // take the closest one (greater precision).
+    Point ctr = bbox.getCenter();
+    double y = (ctr.getY() >= 0 ? bbox.getMaxY() : bbox.getMinY());
+    double diagonalDist = ctx.getDistCalc().distance(ctr, bbox.getMaxX(), y);
+    return diagonalDist * distErrPct;
   }
 
   /**