Update IodGibbs.java

When there's more than a revolution between first and third observation, sometimes this method returned the corrected orbit but percurred in the wrong sense. So I added a control before the return.

src/main/java/org/orekit/estimation/iod/IodGibbs.java

@@ -118,6 +118,26 @@ public class IodGibbs {
         final AbsoluteDate date = date2;
 
         // compute the equivalent Keplerian orbit
-        return new KeplerianOrbit(pv, frame, date, mu);
+        KeplerianOrbit orbit = new KeplerianOrbit(pv, frame, date, mu);
+        
+        
+        //define the reverse orbit
+        final PVCoordinates pv2 = new PVCoordinates(r2, vlEci.scalarMultiply(-1));
+        KeplerianOrbit orbit2 =new KeplerianOrbit(pv2, frame, date, mu);
+        
+        //check which orbit is correct
+        Vector3D estP3 = orbit.shiftedBy(date3.durationFrom(date2)).
+                getPVCoordinates().getPosition();
+        double dist = estP3.subtract(r3).getNorm();
+        Vector3D estP3_2 = orbit2.shiftedBy(date3.durationFrom(date2)).
+                getPVCoordinates().getPosition();
+        double dist2 = estP3_2.subtract(r3).getNorm();
+        
+        
+        if(dist <= dist2){
+            return orbit;
+        } else {
+            return orbit2;
+        }
     }
 }