CODEWITHSUNDEEP
androidrotationandroid-sensors
Svj0hn
Svj0hn

Reputation: 454

Does Android's "Game Rotation Vector" sensor ignore rotation around vertical axis?

I'm developing an app that uses Android sensors to help vehicles navigate in an indoor location. As part of my evaluation process of different sensors, I wanted to try the "rotation vector" sensors. For various reasons, magnetic field readings are not very useful for my location, so thus I wanted to try the "Game Rotation Vector" sensor (sensor fusion, available from API level 18 and later). The description states that it is identical to the regular Rotation Vector sensor except no magnetic field information is used to correct for gyroscope drift around the vertical axis.

When looking for information about the Rotation Vector sensors, I came across an example from Google, where they show the Rotation Vector sensor using a 3d cube. It works pretty well, except for being very sensitive to local magnetic fields (and me being far north, even worse, since the horizontal component is very small here).

Since long term drift can be compensated by other reference data (map information), I wanted to use the Game Rotation Vector sensor for my app. However, when changing all references from "TYPE_ROTATION_VECTOR" to "TYPE_GAME_ROTATION_VECTOR" in the example code, the cube no longer reacted to rotations around the vertical axis (eg. me spinning my chair, holding the device in front of me). Tilting the device in the other two directions moved the cube. I also noticed the cube was a lot more "laggy" this time around, reacting very slowly to any movement.

Is this the way the Game Rotation Vector sensor is supposed to work (eg. ignoring any Z axis rotations)? It would kind of make sense, since a gamer playing in the back seat shouldn't be affected by the vehicle turning, but at the same time it differs from the description provided by Google (my first link). From the description I was under the impression that it would drift slowly, not ignore rotation all together.

I would be deeply grateful for any input on this issue.

Best Regards,

John

Upvotes: 4

Views: 3750

Answers (1)

Svj0hn
Svj0hn

Reputation: 454

Ok, just in case anyone happens to find this, here are my findings:

The Game Rotation Vector sensor does detect rotation around the vertical axis. It is quite accurate in most situations.

However, it has a couple of issues... First, while lying still it has accelerating horizontal drift (even when a gyroscope-based orientation has linear drift). For my device, Game Rotation Vector started out good, but accelerated and finally drifted more than 400 degrees over the course of an hour.

Secondly, and even more disturbing, it does not seem to ignore magnetic fields, contrary to the official description (linked in the question). I tried driving around the parking lot with my device fixed on the passenger seat, and the Game Rotation Vector fell behind largely (it was more than 180 degrees off after one full rotation over 40 seconds), while integrated gyroscope data was accurate within a few degrees. It also showed changes in rotation when the gyroscope was hovering around zero, suggesting that it was in fact compensating for a change in (what I presume to be) magnetic field.

I still don't know why it acted wierd in the test app I linked to before, but I have since decided to use a complementary filter to combine accelerometer and gyro data instead.

Upvotes: 5

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