reimplement distance calculation in routeguide

6 files changed, 45 insertions, 53 deletions

diff --git a/examples/cpp/route_guide/route_guide_server.cc b/examples/cpp/route_guide/route_guide_server.cc
index 24a4184a56..5867c16712 100644
--- a/examples/cpp/route_guide/route_guide_server.cc
+++ b/examples/cpp/route_guide/route_guide_server.cc
@@ -51,6 +51,7 @@ float ConvertToRadians(float num) {
   return num * 3.1415926 /180;
 }
 
+// The formula is based on http://mathforum.org/library/drmath/view/51879.html
 float GetDistance(const Point& start, const Point& end) {
   const float kCoordFactor = 10000000.0;
   float lat_1 = start.latitude() / kCoordFactor;
diff --git a/examples/csharp/route_guide/RouteGuide/RouteGuideUtil.cs b/examples/csharp/route_guide/RouteGuide/RouteGuideUtil.cs
index 66c4a94573..f9af190888 100644
--- a/examples/csharp/route_guide/RouteGuide/RouteGuideUtil.cs
+++ b/examples/csharp/route_guide/RouteGuide/RouteGuideUtil.cs
@@ -52,26 +52,23 @@ namespace Routeguide
 
         /// <summary>
         /// Calculate the distance between two points using the "haversine" formula.
-        /// This code was taken from http://www.movable-type.co.uk/scripts/latlong.html.
+        /// The formula is based on http://mathforum.org/library/drmath/view/51879.html
         /// </summary>
         /// <param name="start">the starting point</param>
         /// <param name="end">the end point</param>
         /// <returns>the distance between the points in meters</returns>
         public static double GetDistance(this Point start, Point end)
         {
-            double lat1 = start.GetLatitude();
-            double lat2 = end.GetLatitude();
-            double lon1 = start.GetLongitude();
-            double lon2 = end.GetLongitude();
-            int r = 6371000; // metres
-            double phi1 = ToRadians(lat1);
-            double phi2 = ToRadians(lat2);
-            double deltaPhi = ToRadians(lat2 - lat1);
-            double deltaLambda = ToRadians(lon2 - lon1);
+            int r = 6371000;  // earth radius in metres
+            double lat1 = ToRadians(start.GetLatitude());
+            double lat2 = ToRadians(end.GetLatitude());
+            double lon1 = ToRadians(start.GetLongitude());
+            double lon2 = ToRadians(end.GetLongitude());
+            double deltalat = lat2 - lat1;
+            double deltalon = lon2 - lon1;
 
-            double a = Math.Sin(deltaPhi / 2) * Math.Sin(deltaPhi / 2) + Math.Cos(phi1) * Math.Cos(phi2) * Math.Sin(deltaLambda / 2) * Math.Sin(deltaLambda / 2);
+            double a = Math.Sin(deltalat / 2) * Math.Sin(deltalat / 2) + Math.Cos(lat1) * Math.Cos(lat2) * Math.Sin(deltalon / 2) * Math.Sin(deltalon / 2);
             double c = 2 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1 - a));
-
             return r * c;
         }
 
diff --git a/examples/node/dynamic_codegen/route_guide/route_guide_server.js b/examples/node/dynamic_codegen/route_guide/route_guide_server.js
index ab537ff401..f9028e860d 100644
--- a/examples/node/dynamic_codegen/route_guide/route_guide_server.js
+++ b/examples/node/dynamic_codegen/route_guide/route_guide_server.js
@@ -103,7 +103,7 @@ function listFeatures(call) {
 
 /**
  * Calculate the distance between two points using the "haversine" formula.
- * This code was taken from http://www.movable-type.co.uk/scripts/latlong.html.
+ * The formula is based on http://mathforum.org/library/drmath/view/51879.html.
  * @param start The starting point
  * @param end The end point
  * @return The distance between the points in meters
@@ -112,21 +112,18 @@ function getDistance(start, end) {
   function toRadians(num) {
     return num * Math.PI / 180;
   }
-  var lat1 = start.latitude / COORD_FACTOR;
-  var lat2 = end.latitude / COORD_FACTOR;
-  var lon1 = start.longitude / COORD_FACTOR;
-  var lon2 = end.longitude / COORD_FACTOR;
-  var R = 6371000; // metres
-  var φ1 = toRadians(lat1);
-  var φ2 = toRadians(lat2);
-  var Δφ = toRadians(lat2-lat1);
-  var Δλ = toRadians(lon2-lon1);
-
-  var a = Math.sin(Δφ/2) * Math.sin(Δφ/2) +
-      Math.cos(φ1) * Math.cos(φ2) *
-      Math.sin(Δλ/2) * Math.sin(Δλ/2);
+  var R = 6371000;  // earth radius in metres
+  var lat1 = toRadians(start.latitude / COORD_FACTOR);
+  var lat2 = toRadians(end.latitude / COORD_FACTOR);
+  var lon1 = toRadians(start.longitude / COORD_FACTOR);
+  var lon2 = toRadians(end.longitude / COORD_FACTOR);
+
+  var deltalat = lat2-lat1;
+  var deltalon = lon2-lon1;
+  var a = Math.sin(deltalat/2) * Math.sin(deltalat/2) +
+      Math.cos(lat1) * Math.cos(lat2) *
+      Math.sin(dlon/2) * Math.sin(dlon/2);
   var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
-
   return R * c;
 }
 
diff --git a/examples/node/static_codegen/route_guide/route_guide_server.js b/examples/node/static_codegen/route_guide/route_guide_server.js
index ef00bbbdfb..eecac62354 100644
--- a/examples/node/static_codegen/route_guide/route_guide_server.js
+++ b/examples/node/static_codegen/route_guide/route_guide_server.js
@@ -102,7 +102,7 @@ function listFeatures(call) {
 
 /**
  * Calculate the distance between two points using the "haversine" formula.
- * This code was taken from http://www.movable-type.co.uk/scripts/latlong.html.
+ * The formula is based on http://mathforum.org/library/drmath/view/51879.html.
  * @param start The starting point
  * @param end The end point
  * @return The distance between the points in meters
@@ -111,21 +111,18 @@ function getDistance(start, end) {
   function toRadians(num) {
     return num * Math.PI / 180;
   }
-  var lat1 = start.getLatitude() / COORD_FACTOR;
-  var lat2 = end.getLatitude() / COORD_FACTOR;
-  var lon1 = start.getLongitude() / COORD_FACTOR;
-  var lon2 = end.getLongitude() / COORD_FACTOR;
-  var R = 6371000; // metres
-  var φ1 = toRadians(lat1);
-  var φ2 = toRadians(lat2);
-  var Δφ = toRadians(lat2-lat1);
-  var Δλ = toRadians(lon2-lon1);
-
-  var a = Math.sin(Δφ/2) * Math.sin(Δφ/2) +
-      Math.cos(φ1) * Math.cos(φ2) *
-      Math.sin(Δλ/2) * Math.sin(Δλ/2);
+  var R = 6371000;  // earth radius in metres
+  var lat1 = toRadians(start.getLatitude() / COORD_FACTOR);
+  var lat2 = toRadians(end.getLatitude() / COORD_FACTOR);
+  var lon1 = toRadians(start.getLongitude() / COORD_FACTOR);
+  var lon2 = toRadians(end.getLongitude() / COORD_FACTOR);
+
+  var deltalat = lat2-lat1;
+  var deltalon = lon2-lon1;
+  var a = Math.sin(deltalat/2) * Math.sin(deltalat/2) +
+      Math.cos(lat1) * Math.cos(lat2) *
+      Math.sin(deltalon/2) * Math.sin(deltalon/2);
   var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
-
   return R * c;
 }
 
diff --git a/examples/python/route_guide/route_guide_server.py b/examples/python/route_guide/route_guide_server.py
index f10008fdec..1969fdd378 100644
--- a/examples/python/route_guide/route_guide_server.py
+++ b/examples/python/route_guide/route_guide_server.py
@@ -46,6 +46,7 @@ def get_distance(start, end):
     delta_lat_rad = math.radians(lat_2 - lat_1)
     delta_lon_rad = math.radians(lon_2 - lon_1)
 
+    # Formula is based on http://mathforum.org/library/drmath/view/51879.html
     a = (pow(math.sin(delta_lat_rad / 2), 2) +
          (math.cos(lat_rad_1) * math.cos(lat_rad_2) * pow(
              math.sin(delta_lon_rad / 2), 2)))
diff --git a/examples/ruby/route_guide/route_guide_server.rb b/examples/ruby/route_guide/route_guide_server.rb
index 8ea07a21c5..5eb268b533 100755
--- a/examples/ruby/route_guide/route_guide_server.rb
+++ b/examples/ruby/route_guide/route_guide_server.rb
@@ -32,19 +32,18 @@ COORD_FACTOR = 1e7
 RADIUS = 637_100
 
 # Determines the distance between two points.
+# The formula is based on http://mathforum.org/library/drmath/view/51879.html.
 def calculate_distance(point_a, point_b)
   to_radians = proc { |x| x * Math::PI / 180 }
-  lat_a = point_a.latitude / COORD_FACTOR
-  lat_b = point_b.latitude / COORD_FACTOR
-  long_a = point_a.longitude / COORD_FACTOR
-  long_b = point_b.longitude / COORD_FACTOR
-  φ1 = to_radians.call(lat_a)
-  φ2 = to_radians.call(lat_b)
-  Δφ = to_radians.call(lat_a - lat_b)
-  Δλ = to_radians.call(long_a - long_b)
-  a = Math.sin(Δφ / 2)**2 +
-      Math.cos(φ1) * Math.cos(φ2) +
-      Math.sin(Δλ / 2)**2
+  lat_a = to_radians.call(point_a.latitude / COORD_FACTOR)
+  lat_b = to_radians.call(point_b.latitude / COORD_FACTOR)
+  lon_a = to_radians.call(point_a.longitude / COORD_FACTOR)
+  lon_b = to_radians.call(point_b.longitude / COORD_FACTOR)
+  delta_lat = lat_a - lat_b
+  delta_lon = lon_a - lon_b
+  a = Math.sin(delta_lat / 2)**2 +
+      Math.cos(lat_a) * Math.cos(lat_b) +
+      Math.sin(delta_lon / 2)**2
   (2 * RADIUS *  Math.atan2(Math.sqrt(a), Math.sqrt(1 - a))).to_i
 end