Tracking Methodologies
There are various methods headsets, controllers, and body trackers use to know their location in their environment. This page discusses the classes devices tend to fall under, and the various pros and cons you would expect a device of a class to likely inherit.
IMU Tracking
Short for Inertial Measurement Unit, measures the strength and direction of linear and rotational forces using accelerometers, gyroscopes, and in some chips magnetometers. Technically all VR tracked devices use IMUs to some extent, but some use IMUs exclusively. Common examples of IMU trackers include SlimeVR trackers.
- IMU Tracking tends to be cheaper
- IMU Tracking does not require external base stations of any type
- IMU Tracking is not affected by a visually noisy environment / lack of light
- IMU Tracking works under blankets
- IMU Tracked Devices tend to be light with a long battery life
- One of the most common implementations of IMU tracking, Slime Tracking, is open source
- IMU Only Tracking will inevitably drift, and needs occasional recalibration during use
- Since essentially no 6DOF headset uses IMU only tracking, you will need some solution to keep the IMU trackers from drifting from your headset, which also requires occasional recalibration
- IMU Tracking quality tends to be worse than SteamVR and vSLAM tracking
How does IMU Tracking Work?
IMUs are composed of accelerometers (devices that measure linear acceleration in XYZ directions), and gyroscopes (device that measure angular acceleration). Some may also use magnetometers (which help keep a rotation frame of reference, but may also induce their own issues at times). These accelerations are integrated to find the linear and rotation velocities, and integrated again to deduce their permissions.
Since there is always small amount of error in measuring accelerations, and no external frame of reference, the errors in acceleration measurement compound over time during the integration step, inevitably leading to drift.
SteamVR Tracking
SteamVR Lighthouse Tracking was originally designed by valve and hardware produced by HTC with the release of the Vive in 2016, and now has become a common standard for VR tracking setups, particularly with users interested in full body tracking. It has gone through 2 main backwards-compatible revisions, commonly denoted by the 2 different generations of base stations used (1.0 vs 2.0).
- Overall best quality tracking, with essentially no drift over time, highest precision, and fastest temporal response
- Tend to be simple, which results in lighter and more battery efficient parts
- Tends to be plug and play with SteamVR itself, without the need for additional software (Some headsets break this rule)
- Works in the dark
- Overall more first-time set up is required
- Requires at least 2 base stations to be installed in a room, making it rather non-portable
- Expensive if you do not already have base stations
- Easily affected by reflective surfaces from the environment
- Cannot be used under blankets, trackers need line of sight with the base stations
- Essentially locked to PC VR
- Additional Trackers require additional watchmen USB dongles that have a high bandwidth requirement (more reading below)
- Base Stations contain moving parts, so they will eventually fail
- You cannot mix 1.0 and 2.0 base stations
SteamVR 1.0 Base Stations vs SteamVR 2.0 Base Stations
1.0 Base Stations
2.0 Base Stations
Tracked devices such as controllers and headsets can that are SteamVR 2.0 can use SteamVR 1.0 and 2.0 base stations, while SteamVR 1.0 devices are limited only to SteamVR 1.0 base stations. You cannot mix base station versions together in the same space.
Reasons to buy SteamVR 2.0 base stations:
- Slightly wider FOV on the base stations, and further distance reached
- The ability to have more than 2 base stations
- This is really only useful for full body tracking, where some users report better tracking by adding a third base station, though adding a fourth rarely helps further. Most people do just fine with 2 base stations though.
Reasons to buy SteamVR 1.0 base stations:
- Backwards Compatibility with older SteamVR hardware
- Cheaper
In general, there is never a need to downgrade from 2.0 base stations to 1.0 if you already have SteamVR 2.0 base stations (except in the case of using old SteamVR tracked hardware that only supports 1.0 stations). However, if you are trying to save money and need to purchase base stations, 1.0 base stations are often perfectly viable. Just be wary of warranty limitations and that you cannot exceed 2 SteamVR 1.0 base stations.
Revisions in 1.0 Base Stations
There are some revisions (hardware differences) between 1.0 base stations. The most notable difference you will be able to see is the arrangement of the IR LEDs.
The launch 1.0 base station at launch has a grid of LEDs
The revised 1.0 base stations (sometimes called 1.1) has a offset pattern to their LEDs.
Generally there's no difference for you the user, though I have heard anecdotal evidence from several people that the original base stations are overall longer lasting. However all base stations of this generation are out of warranty, so ultimately you are running them on borrowed time anyways. Only buy these if you can get them on a good deal!
How does SteamVR Tracking Work?
In principal, SteamVR tracking is quite simple. The base stations emit sweeping infrared laser beams across the room. Each SteamVR tracker / controller / headset is covered in infrared sensors that receive these beams, and given the timing of when these beams hit the sensor, can work out their location.
SteamVR is often incorrectly called Outside-In tracking, due to the incorrect assumption that the base stations themselves are handling the tracking. They do not, they act as "lighthouses" (hence the name) that trackers use to calculate their position. Ergo, technically SteamVR is Inside-Out tracking, just like vSLAM headsets.
For further details, including technical differences between 1.0 and 2.0 SteamVR tracking, read here.