+#if HAS_GYRO
+static void
+ao_sample_rotate(void)
+{
+#ifdef AO_FLIGHT_TEST
+ float dt = (ao_sample_tick - ao_sample_prev_tick) / 100.0;
+#else
+ static const float dt = 1/100.0;
+#endif
+ float x = ao_mpu6000_gyro((float) ((ao_sample_pitch << 9) - ao_ground_pitch) / 512.0f) * dt;
+ float y = ao_mpu6000_gyro((float) ((ao_sample_yaw << 9) - ao_ground_yaw) / 512.0f) * dt;
+ float z = ao_mpu6000_gyro((float) ((ao_sample_roll << 9) - ao_ground_roll) / 512.0f) * dt;
+ struct ao_quaternion rot;
+ struct ao_quaternion point;
+
+ /* The amount of rotation is just the length of the vector. Now,
+ * here's the trick -- assume that the rotation amount is small. In this case,
+ * sin(x) ≃ x, so we can just make this the sin.
+ */
+
+ n_2 = x*x + y*y + z*z;
+ n = sqrtf(n_2);
+ s = n / 2;
+ if (s > 1)
+ s = 1;
+ c = sqrtf(1 - s*s);
+
+ /* Make unit vector */
+ if (n > 0) {
+ x /= n;
+ y /= n;
+ z /= n;
+ }
+
+ /* Now compute the unified rotation quaternion */
+
+ ao_quaternion_init_rotation(&rot,
+ x, y, z,
+ s, c);
+
+ /* Integrate with the previous rotation amount */
+ ao_quaternion_multiply(&ao_rotation, &ao_rotation, &rot);
+
+ /* And normalize to make sure it remains a unit vector */
+ ao_quaternion_normalize(&ao_rotation, &ao_rotation);
+
+ /* Compute pitch angle from vertical by taking the pad
+ * orientation vector and rotating it by the current total
+ * rotation value. That will be a unit vector pointing along
+ * the airframe axis. The Z value will be the cosine of the
+ * change in the angle from vertical since boost.
+ *
+ * rot = ao_rotation * vertical * ao_rotation°
+ * rot = ao_rotation * (0,0,0,1) * ao_rotation°
+ * = ((a.z, a.y, -a.x, a.r) * (a.r, -a.x, -a.y, -a.z)) .z
+ *
+ * = (-a.z * -a.z) + (a.y * -a.y) - (-a.x * -a.x) + (a.r * a.r)
+ * = a.z² - a.y² - a.x² + a.r²
+ *
+ * rot = ao_rotation * (0, 0, 0, -1) * ao_rotation°
+ * = ((-a.z, -a.y, a.x, -a.r) * (a.r, -a.x, -a.y, -a.z)) .z
+ *
+ * = (a.z * -a.z) + (-a.y * -a.y) - (a.x * -a.x) + (-a.r * a.r)
+ * = -a.z² + a.y² + a.x² - a.r²
+ */
+
+ float rotz;
+ rotz = ao_rotation.z * ao_rotation.z - ao_rotation.y * ao_rotation.y - ao_rotation.x * ao_rotation.x + ao_rotation.r * ao_rotation.r;
+
+ ao_sample_orient = acosf(rotz) * (float) (180.0/M_PI);
+}
+#endif
+