diff --git a/gtsam/navigation/ImuBias.cpp b/gtsam/navigation/ImuBias.cpp
new file mode 100644
index 000000000..0dbc5736f
--- /dev/null
+++ b/gtsam/navigation/ImuBias.cpp
@@ -0,0 +1,82 @@
+/* ----------------------------------------------------------------------------
+
+ * GTSAM Copyright 2010, Georgia Tech Research Corporation,
+ * Atlanta, Georgia 30332-0415
+ * All Rights Reserved
+ * Authors: Frank Dellaert, et al. (see THANKS for the full author list)
+
+ * See LICENSE for the license information
+
+ * -------------------------------------------------------------------------- */
+
+/**
+ * @file ImuBias.cpp
+ * @date  Feb 2, 2012
+ * @author Vadim Indelman, Stephen Williams
+ */
+
+#include "ImuBias.h"
+
+#include <gtsam/geometry/Point3.h>
+#include <iostream>
+
+namespace gtsam {
+
+/// All bias models live in the imuBias namespace
+namespace imuBias {
+
+/*
+ * NOTES:
+ * - Earth-rate correction:
+ *     + Currently the user should supply R_ECEF_to_G, which is the rotation from ECEF to Local-Level system (NED or ENU as defined by the user).
+ *     + R_ECEF_to_G can be calculated by approximated values of latitude and longitude of the system.
+ *     + A relatively small distance is traveled w.r.t. to initial pose is assumed, since R_ECEF_to_G is constant.
+ *        Otherwise, R_ECEF_to_G should be updated each time using the current lat-lon.
+ *
+ *  - Currently, an empty constructed is not enabled so that the user is forced to specify R_ECEF_to_G.
+ */
+//    // H1: Jacobian w.r.t. IMUBias
+//    // H2: Jacobian w.r.t. pose
+//    Vector CorrectGyroWithEarthRotRate(Vector measurement, const Pose3& pose, const Vector& w_earth_rate_G,
+//        boost::optional<Matrix&> H1=boost::none, boost::optional<Matrix&> H2=boost::none) const {
+//
+//      Matrix R_G_to_I( pose.rotation().matrix().transpose() );
+//      Vector w_earth_rate_I = R_G_to_I * w_earth_rate_G;
+//
+//      if (H1){
+//        Matrix zeros3_3(zeros(3,3));
+//        Matrix m_eye3(-eye(3));
+//
+//        *H1 = collect(2, &zeros3_3, &m_eye3);
+//      }
+//
+//      if (H2){
+//        Matrix zeros3_3(zeros(3,3));
+//        Matrix H = -skewSymmetric(w_earth_rate_I);
+//
+//        *H2 = collect(2, &H, &zeros3_3);
+//      }
+//
+//      //TODO: Make sure H2 is correct.
+//
+//      return measurement - biasGyro_ - w_earth_rate_I;
+//
+////      Vector bias_gyro_temp((Vector(3) << -bias_gyro_(0), bias_gyro_(1), bias_gyro_(2)));
+////      return measurement - bias_gyro_temp - R_G_to_I * w_earth_rate_G;
+//    }
+/// ostream operator
+std::ostream& operator<<(std::ostream& os, const ConstantBias& bias) {
+  os << "acc = " << Point3(bias.accelerometer());
+  os << " gyro = " << Point3(bias.gyroscope());
+  return os;
+}
+
+/// print with optional string
+void ConstantBias::print(const std::string& s) const {
+  std::cout << s << *this << std::endl;
+}
+
+} // namespace imuBias
+
+} // namespace gtsam
+
diff --git a/gtsam/navigation/ImuBias.h b/gtsam/navigation/ImuBias.h
index 929b7ac22..11799f310 100644
--- a/gtsam/navigation/ImuBias.h
+++ b/gtsam/navigation/ImuBias.h
@@ -17,22 +17,11 @@
 
 #pragma once
 
-#include <gtsam/base/Matrix.h>
-#include <gtsam/base/Vector.h>
+#include <gtsam/base/OptionalJacobian.h>
 #include <gtsam/base/VectorSpace.h>
+#include <iosfwd>
 #include <boost/serialization/nvp.hpp>
 
-/*
- * NOTES:
- * - Earth-rate correction:
- *     + Currently the user should supply R_ECEF_to_G, which is the rotation from ECEF to Local-Level system (NED or ENU as defined by the user).
- *     + R_ECEF_to_G can be calculated by approximated values of latitude and longitude of the system.
- *     + A relatively small distance is traveled w.r.t. to initial pose is assumed, since R_ECEF_to_G is constant.
- *        Otherwise, R_ECEF_to_G should be updated each time using the current lat-lon.
- *
- *  - Currently, an empty constructed is not enabled so that the user is forced to specify R_ECEF_to_G.
- */
-
 namespace gtsam {
 
 /// All bias models live in the imuBias namespace
@@ -94,50 +83,16 @@ public:
     return measurement - biasGyro_;
   }
 
-//    // H1: Jacobian w.r.t. IMUBias
-//    // H2: Jacobian w.r.t. pose
-//    Vector CorrectGyroWithEarthRotRate(Vector measurement, const Pose3& pose, const Vector& w_earth_rate_G,
-//        boost::optional<Matrix&> H1=boost::none, boost::optional<Matrix&> H2=boost::none) const {
-//
-//      Matrix R_G_to_I( pose.rotation().matrix().transpose() );
-//      Vector w_earth_rate_I = R_G_to_I * w_earth_rate_G;
-//
-//      if (H1){
-//        Matrix zeros3_3(zeros(3,3));
-//        Matrix m_eye3(-eye(3));
-//
-//        *H1 = collect(2, &zeros3_3, &m_eye3);
-//      }
-//
-//      if (H2){
-//        Matrix zeros3_3(zeros(3,3));
-//        Matrix H = -skewSymmetric(w_earth_rate_I);
-//
-//        *H2 = collect(2, &H, &zeros3_3);
-//      }
-//
-//      //TODO: Make sure H2 is correct.
-//
-//      return measurement - biasGyro_ - w_earth_rate_I;
-//
-////      Vector bias_gyro_temp((Vector(3) << -bias_gyro_(0), bias_gyro_(1), bias_gyro_(2)));
-////      return measurement - bias_gyro_temp - R_G_to_I * w_earth_rate_G;
-//    }
-
   /// @}
   /// @name Testable
   /// @{
 
   /// ostream operator
   GTSAM_EXPORT friend std::ostream& operator<<(std::ostream& os,
-                                               const ConstantBias& bias) {
-    os << "acc = " << Point3(bias.accelerometer());
-    os << " gyro = " << Point3(bias.gyroscope());
-    return os;
-  }
+                                               const ConstantBias& bias);
 
   /// print with optional string
-  void print(const std::string& s = "") const { std::cout << s << *this << std::endl; }
+  void print(const std::string& s = "") const;
 
   /** equality up to tolerance */
   inline bool equals(const ConstantBias& expected, double tol = 1e-5) const {