diff --git a/media/libheadtracking/QuaternionUtil.h b/media/libheadtracking/QuaternionUtil.h
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+++ b/media/libheadtracking/QuaternionUtil.h
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+/*
+ * Copyright (C) 2021 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.
+ */
+#pragma once
+
+#include <Eigen/Geometry>
+
+namespace android {
+namespace media {
+
+/**
+ * Converts a rotation vector to an equivalent quaternion.
+ * The rotation vector is given as a 3-vector whose direction represents the rotation axis and its
+ * magnitude the rotation angle (in radians) around that axis.
+ */
+Eigen::Quaternionf rotationVectorToQuaternion(const Eigen::Vector3f& rotationVector);
+
+/**
+ * Converts a quaternion to an equivalent rotation vector.
+ * The rotation vector is given as a 3-vector whose direction represents the rotation axis and its
+ * magnitude the rotation angle (in radians) around that axis.
+ */
+Eigen::Vector3f quaternionToRotationVector(const Eigen::Quaternionf& quaternion);
+
+/**
+ * Returns a quaternion representing a rotation around the X-axis with the given amount (in
+ * radians).
+ */
+Eigen::Quaternionf rotateX(float angle);
+
+/**
+ * Returns a quaternion representing a rotation around the Y-axis with the given amount (in
+ * radians).
+ */
+Eigen::Quaternionf rotateY(float angle);
+
+/**
+ * Returns a quaternion representing a rotation around the Z-axis with the given amount (in
+ * radians).
+ */
+Eigen::Quaternionf rotateZ(float angle);
+
+}  // namespace media
+}  // namespace android