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diff --git a/gps/src/main/java/org/wamblee/gps/geometry/SphericalCoordinateSystem.java b/gps/src/main/java/org/wamblee/gps/geometry/SphericalCoordinateSystem.java
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+++ b/gps/src/main/java/org/wamblee/gps/geometry/SphericalCoordinateSystem.java
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+/*
+ * Copyright 2006 the original author or authors.
+ * 
+ * Licensed 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.
+ */ 
+
+package org.wamblee.gps.geometry;
+
+import static java.lang.Math.PI;
+import static java.lang.Math.cos;
+import static java.lang.Math.sin;
+
+
+/**
+ * Represents the coordinate system for a GPS measurement identified by
+ * <ul>
+ *   <li> x1: latitude in degrees </li>
+ *   <li> x2: longitude in degrees </li>
+ *   <li> x3: elevation in meters </li>
+ * </ul>
+ * This coordinate system models the earth as a sphere of a specific radius. 
+ */
+public class SphericalCoordinateSystem implements CoordinateSystem {
+    /**
+     * Earth radius in meters. 
+     */
+    private static final double EARTH_RADIUS = 6371000; 
+
+ 
+    /* (non-Javadoc)
+     * @see org.wamblee.gpx.CoordinateSystem#toReferenceSystem(org.wamblee.gpx.Coordinates)
+     */
+    public Coordinates toReferenceSystem(Coordinates aCoordinates) {
+        double latrad = radians(aCoordinates.getX1()); 
+        double lonrad = radians(aCoordinates.getX2());
+        double coslat = cos(latrad); 
+        double sinlat = sin(latrad);
+        double coslon = cos(lonrad);
+        double sinlon = sin(lonrad); 
+        
+        double trueElevation = EARTH_RADIUS + aCoordinates.getX3(); 
+        return new Coordinates(trueElevation*coslat*coslon,
+                               trueElevation*coslat*sinlon,
+                               trueElevation*sinlat); 
+        
+    }
+    
+    private double radians(double aDegrees) { 
+        return aDegrees/180.0*PI; 
+    }
+}