From 2337f4687fb29a576723c99d464da2c1a88e09f5 Mon Sep 17 00:00:00 2001
From: "Chris M. Hostetter" <hossman@apache.org>
Date: Tue, 29 Nov 2011 22:38:08 +0000
Subject: [PATCH] LUCENE-3599: Fix DistanceUtils.haversine() javadocs -- were
 incorrectly stating the expected order of the arguments

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1208118 13f79535-47bb-0310-9956-ffa450edef68
---
 lucene/contrib/CHANGES.txt                    |  5 +++++
 .../apache/lucene/spatial/DistanceUtils.java  | 14 ++++++------
 .../function/distance/HaversineFunction.java  | 22 +++++++++----------
 3 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/lucene/contrib/CHANGES.txt b/lucene/contrib/CHANGES.txt
index 193d812fe69..5690a63c7d0 100644
--- a/lucene/contrib/CHANGES.txt
+++ b/lucene/contrib/CHANGES.txt
@@ -92,6 +92,11 @@ Bug Fixes
    assert if such a parent doc was the first doc in the segment).
    (Shay Banon, Mike McCandless)
 
+Documentation
+
+ * LUCENE-3599: Javadocs for DistanceUtils.haversine() were incorrectly 
+   stating the expected order of the arguments (David Smiley via hossman)
+
 ======================= Lucene 3.5.0 ================
 
 Changes in backwards compatibility policy
diff --git a/lucene/contrib/spatial/src/java/org/apache/lucene/spatial/DistanceUtils.java b/lucene/contrib/spatial/src/java/org/apache/lucene/spatial/DistanceUtils.java
index e9769850aa0..9ba4ba86690 100644
--- a/lucene/contrib/spatial/src/java/org/apache/lucene/spatial/DistanceUtils.java
+++ b/lucene/contrib/spatial/src/java/org/apache/lucene/spatial/DistanceUtils.java
@@ -312,15 +312,15 @@ public class DistanceUtils {
   }
 
   /**
-   * @param x1     The x coordinate of the first point, in radians
+   * Computes the haversine distance between two points. The arguments are in radians and provided in lat,lon order.
    * @param y1     The y coordinate of the first point, in radians
-   * @param x2     The x coordinate of the second point, in radians
+   * @param x1     The x coordinate of the first point, in radians
    * @param y2     The y coordinate of the second point, in radians
+   * @param x2     The x coordinate of the second point, in radians
    * @param radius The radius of the sphere
-   * @return The distance between the two points, as determined by the Haversine formula.
-
+   * @return The distance between the two points, as determined by the haversine formula.
    */
-  public static double haversine(double x1, double y1, double x2, double y2, double radius) {
+  public static double haversine(double y1, double x1, double y2, double x2, double radius) {
     double result = 0;
     //make sure they aren't all the same, as then we can just return 0
     if ((x1 != x2) || (y1 != y2)) {
@@ -328,8 +328,8 @@ public class DistanceUtils {
       double diffY = y1 - y2;
       double hsinX = Math.sin(diffX * 0.5);
       double hsinY = Math.sin(diffY * 0.5);
-      double h = hsinX * hsinX +
-              (Math.cos(x1) * Math.cos(x2) * hsinY * hsinY);
+      double h = hsinY * hsinY +
+          (Math.cos(y1) * Math.cos(y2) * hsinX * hsinX);
       result = (radius * 2 * Math.atan2(Math.sqrt(h), Math.sqrt(1 - h)));
     }
     return result;
diff --git a/solr/core/src/java/org/apache/solr/search/function/distance/HaversineFunction.java b/solr/core/src/java/org/apache/solr/search/function/distance/HaversineFunction.java
index 1febdaf19f1..fa0074406c1 100644
--- a/solr/core/src/java/org/apache/solr/search/function/distance/HaversineFunction.java
+++ b/solr/core/src/java/org/apache/solr/search/function/distance/HaversineFunction.java
@@ -76,22 +76,22 @@ public class HaversineFunction extends ValueSource {
     double[] p2D = new double[2];
     p1DV.doubleVal(doc, p1D);
     p2DV.doubleVal(doc, p2D);
-    double x1;
     double y1;
-    double x2;
+    double x1;
     double y2;
+    double x2;
     if (convertToRadians) {
-      x1 = p1D[0] * DistanceUtils.DEGREES_TO_RADIANS;
-      y1 = p1D[1] * DistanceUtils.DEGREES_TO_RADIANS;
-      x2 = p2D[0] * DistanceUtils.DEGREES_TO_RADIANS;
-      y2 = p2D[1] * DistanceUtils.DEGREES_TO_RADIANS;
+      y1 = p1D[0] * DistanceUtils.DEGREES_TO_RADIANS;
+      x1 = p1D[1] * DistanceUtils.DEGREES_TO_RADIANS;
+      y2 = p2D[0] * DistanceUtils.DEGREES_TO_RADIANS;
+      x2 = p2D[1] * DistanceUtils.DEGREES_TO_RADIANS;
     } else {
-      x1 = p1D[0];
-      y1 = p1D[1];
-      x2 = p2D[0];
-      y2 = p2D[1];
+      y1 = p1D[0];
+      x1 = p1D[1];
+      y2 = p2D[0];
+      x2 = p2D[1];
     }
-    return DistanceUtils.haversine(x1, y1, x2, y2, radius);
+    return DistanceUtils.haversine(y1, x1, y2, x2, radius);
   }