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diff --git a/services/sensorservice/Fusion.h b/services/sensorservice/Fusion.h
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+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#ifndef ANDROID_FUSION_H
+#define ANDROID_FUSION_H
+
+#include <utils/Errors.h>
+
+#include "vec.h"
+#include "mat.h"
+
+namespace android {
+
+class Fusion {
+    /*
+     * the state vector is made of two sub-vector containing respectively:
+     * - modified Rodrigues parameters
+     * - the estimated gyro bias
+     */
+    vec<vec3_t, 2> x;
+
+    /*
+     * the predicated covariance matrix is made of 4 3x3 sub-matrices and it
+     * semi-definite positive.
+     *
+     * P = | P00  P10 | = | P00  P10 |
+     *     | P01  P11 |   | P10t  Q1 |
+     *
+     * Since P01 = transpose(P10), the code below never calculates or
+     * stores P01. P11 is always equal to Q1, so we don't store it either.
+     */
+    mat<mat33_t, 2, 2> P;
+
+    /*
+     * the process noise covariance matrix is made of 2 3x3 sub-matrices
+     * Q0 encodes the attitude's noise
+     * Q1 encodes the bias' noise
+     */
+    vec<mat33_t, 2> Q;
+
+    static const float gyroSTDEV = 1.0e-5;  // rad/s (measured 1.2e-5)
+    static const float accSTDEV  = 0.05f;   // m/s^2 (measured 0.08 / CDD 0.05)
+    static const float magSTDEV  = 0.5f;    // uT    (measured 0.7  / CDD 0.5)
+    static const float biasSTDEV = 2e-9;    // rad/s^2 (guessed)
+
+public:
+    Fusion();
+    void init();
+    void handleGyro(const vec3_t& w, float dT);
+    status_t handleAcc(const vec3_t& a);
+    status_t handleMag(const vec3_t& m);
+    vec3_t getAttitude() const;
+    vec3_t getBias() const;
+    mat33_t getRotationMatrix() const;
+    bool hasEstimate() const;
+
+private:
+    vec3_t Ba, Bm;
+    uint32_t mInitState;
+    vec<vec3_t, 3> mData;
+    size_t mCount[3];
+    enum { ACC=0x1, MAG=0x2, GYRO=0x4 };
+    bool checkInitComplete(int, const vec3_t&);
+    bool checkState(const vec3_t& v);
+    void predict(const vec3_t& w);
+    void update(const vec3_t& z, const vec3_t& Bi, float sigma);
+    static mat33_t getF(const vec3_t& p);
+    static mat33_t getdFdp(const vec3_t& p, const vec3_t& we);
+};
+
+}; // namespace android
+
+#endif // ANDROID_FUSION_H