- See also: tracking systems
Constellation is a optical-based outside-in positional tracking system developed by Oculus VR for the Oculus Rift devices. Similar to Lighthouse, Constellation is able to track both the HMD and Oculus Touch controllers. Unlike Lighthouse, Constellation utilizes optical sensors that detect the IR LED markers on the tracked devices. It features 360 degrees tracking and is suitable for both seated and standing VR experiences.
Constellation is an open platform that allows third-party hardware manufactures to create their own controllers that utilize the tracking system. These manufactures will be able to use the Constellation API to create their own positionally tracked accessories for the Rift.
Oculus Rift CV1
- See also: Oculus Rift CV1
The first iteration of the system will be released with Oculus Rift CV1 in Q1 2015. The Rift will utilize an Oculus Sensor that sits on top of a thin and malleable pole about a foot in length. The entire setup can be placed on a desk similar to a lamp. The sensor and its mount is black in color. It is small, sleek and looks like a small desk lamp.
IR LED markers are placed on the HMD and Oculus Touch controllers so they can be tracked by the sensor(s).
Oculus Touch will require an additional camera sensor.
Constellation has similar tracking volume as Lighthouse. It is able to deliver a room-scale VR experience. Multiple optical sensors can be employed to track the HMD and controllers in order to reduce occlusion and increase tracking volume. While technically capable, Oculus is not currently focusing on a room-scale VR experience. Palmer Luckey mentioned that developers wanted a larger demographic of users. Requiring users to not only have powerful computers for the Rift, but also an entire room dedicated to VR, is too much.
How Does It Work?
- See also: Sensor fusion
Oculus Rift uses the IMUs as the primary positional tracking system. It responds extremely quickly and updates at several hundred Hz (1000Hz sampling, 500Hz reporting). However, IMUs drift due to double-integration of error. The drift is on the order of meters per second. So Constellation do is squelch that error 60 times per second (both have a 60Hz global position update rate) using their optical sensors to provide an absolute position reference.
For Constellation, high-speed position tracking performance is down ENTIRELY to IMU performance. It wouldn't be possible at all without another absolute reference system (optical, magnetic or otherwise) but it's the IMU that's doing the grunt-work.
Constellation's Oculus Sensor is genlocked; they capture a frame at the same point in time. That means all marker positions are known at the exact same time. As for Constellation having a 'smearing' issue: Commercial optical MCAP systems do not generally use active markers (though some do), but retroreflective markers and an illumination system adjacent to the camera lens. These relative dim markers are still easily discriminable in all but the harshest (e.g. outdoors in direct sunlight) conditions. If you're being clever with your blob tracking, you can even use the blob shape from the smear in order to provide an instantaneous velocity measurement, though it's generally just easier to drop the shutter speed and make your markers brighter.