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
- 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. Some solutions (such as SlimeVR) employ a skeletal model of the person to try to minimize this effect, but drift will still occur eventually.
What do I need for a good experience?
- Good quality IMUs
- Cheaper IMU sensors can give good results
- Occasional calibration to correct drifts
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
- Trackers tend to be lighter and have longer battery lives
- 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 (mirrors, occasionally TVs)
- 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 here)
- Base Stations contain moving parts, so they will eventually fail
- You cannot mix 1.0 and 2.0 base stations
All about Base Stations
Base Stations, also called LightHouses, spin IR lasers throughout your playspace that are used by SteamVR tracked devices in order for them to locate their position. Since they are IR, they emit no visible light, and SteamVR tracked devices themselves only use the base stations, meaning you can play VR in a dark room if you wish.
There are 2 major revisions of 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.
Common Questions about Base Stations
Do I really need at least 2 Base Stations?
Technically you can get basic tracking working with even 1 base station, however it is extremely easy for your trackers / controllers / headset to lose tracking, so its not recommended
Do Base Stations 2.0 track better than 1.0?
Not Really. The benefit of 2.0 base stations is mainly the fact that you can have up to 4 base stations to produce a larger play-space, and to lower the odds of occlusion which can help with Full-Body tracking in some situations.
Is 4 the maximum number of 2.0 Base Stations allowed?
Technically no. You can add more base stations, however a individual SteamVR tracked device can only utilize up to 4 base stations at any one time. Keep in mind there may be a tracking stutter if a tracked device has to hop between base stations. Realistically speaking, some users report better full body tracking performance (when using vive trackers) with 3 base stations, but essentially no change when they had 4. However most people do fine with 2 base stations, regardless if they are 1.0 or 2.0.
Should I leave my base stations powered on all the time?
It depends but probably not. Base stations produce a little bit of noise which may be annoying for some users. However, a bigger concern is wear, as base stations contain moving parts, they will eventually fail. That being said, a base station running constantly generally doesn't produce much wear, its the boot-up process that's actually the heaviest. In other words, if you use your VR system once a week, its probably a good idea to turn off your base stations (SteamVR has a setting to do this automatically over bluetooth). However, if you go in and out of VR multiple times per day, it may be best just to leave your base stations running.
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!
All about Dongles
SteamVR receivers (also referred to as watchmen receivers) are wireless receivers that each can talk to one SteamVR tracked device over the 2.4 GHz wireless band, and typically come in the form of a USB 2.0 dongle. The plastic shells of these dongles do vary by manufacturer, as do the specific wireless chip used (more on this later). SteamVR 1.0 tracking and SteamVR 2.0 tracking are irrelevant here, all wireless trackers use the same watchmen receivers.
Tundra and Vive trackers (excluding the ultimate inside-out tracker) use these dongles, as well as controllers such such as the Vive wands or the index controllers. Essentially anything you can pair with SteamVR's pairing menu.
There are more unique dongles out there, such as the tundra super dongle, which have multiple watchmen receivers in them so you can connect multiple tracked devices to a single USB dongle.
HTC sells something called the "Vive Ultimate Dongle" alongside their watchmen dongles for SteamVR tracked devices. Be wary because this dongle is NOT for SteamVR devices but actually intended for their "Vive Ultimate Tracker," which uses a separate vSLAM tracking system instead of base stations!
It is also important to note that most SteamVR headsets (such as the index, bigscreen beyond, and vive) contain 2 watchmen receivers built in, intended for a right and left controller (though technically can be paired to any SteamVR device). Non-SteamVR headsets, like the Quest, do not have any watchmen receivers.
As an example, if you had an index headset, and wanted to use your 2 index controllers and 3 Vive trackers for full body tracking, you would need 3 additional dongles (the controllers can connect to the 2 watchmen receivers in the headset, and you get one dongle per Vive tracker). If you were using a quest headset but wanted to use the index controllers and 3 Vive trackers, you would need to use 5 dongles. If you had an index headset and only wanted to pair your 2 index controllers (no steamVR tracked FBT trackers at all), you wouldn't need any additional dongles!
Steam Controller Dongles?
The Steam Controller also shipped with its own 2.4 ghz dongle, and actually is capable of acting as a SteamVR dongle, if you flash it with the appropriate firmware. Be cautious as this can be destructive and do research before attempting if you wish to go down this path. You can read more here
One thing to note about these dongles is they use a lot of USB 2.0 bandwidth, meaning they may have issues on some USB hubs. Since the dongles operate under USB 2.0, additional USB 3.0 throughput (IE USB 3.0, 3.1, 3.2, etc) is meaningless (this is because USB 2.0 and 3.0 communication occurs on different wires in a USB cable). This is important to understand under the context of using USB hubs, since they can cause connectivity issues. More explained here.
In addition, dongles should be placed out in the open (IE not behind your desk) for best connectivity to your VR devices, and should also be each kept some distance away from other 2.4 GHz signal devices (routers, or other dongles)
"Super" Dongles and other multi-watchmen receiver dongles
There are some dongles that are sold that contain multiple watchmen receivers, which sounds convenient since you don't need to worry about hubs and other things with them. These super dongles can work but may also have issues, so do you research and read reviews. A notable failure was EOZ's 7 watchmen-receiver mega dongle, which suffered massive overheating issues, and thus was discontinued.
A common one floating around is a white box hub that contains 7 receivers, that you can find on Aliexpress (This is not an endorsement).
These are not rated for testing, however they generally have good reviews at time of writing. Of course be wary of generic, unbranded products like this.
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.
What do I need for a good experience?
- 2 (or more) Base Stations mounted high on opposite corners of your play space
- Ensure that the base stations are mounted in a stable manner
- In a vast majority of cases, 2 base stations are good enough for even full body tracking
- The room should be free of reflective surfaces
- Some TV's / big monitors can cause issues
- The same number of watchmen / SteamVR dongles as you have SteamVR controllers / trackers, and USB ports to plug them into
- Remember most SteamVR native headsets contain 2 dongles (1 per controller). but if you are using something like a quest, you will need separate dongles for SteamVR tracked controllers
- The dongles need to be connected to a good USB port without bandwidth constraints
- The dongles should be away from other 2.4 GHz producing devices (particularly routers)
- Make sure the dongles are NOT next to each other as they can interfere with one and another
- If using a USB hub, try getting short USB extension cables to be able to spread out the dongles
- Make sure the dongles are NOT next to each other as they can interfere with one and another
- The dongles should have a general line of sight with your playspace
vSLAM (Inside-Out) Camera Tracking
vSlam, or camera tracking, makes use of cameras to observe the environment to note how the device is moving through it. These cameras may be IR or standard color. This is a relatively common form of tracking done on many headsets, and pretty much on all standalone headsets.
- Very accessible, very little setup required
- Does not required base stations of any type
- Often opens the door to other capabilities, such as camera based hand tracking
- Needs a well lit room to work (however in the case of IR camera vSLAM, IR lights may be enough)
- If a lot of things are in your room moving, there may be tracking issues
- if controllers are being tracked externally via cameras (typically by the headset), bringing them behind you may result in lost tracking. In addition, very fast controller movements tend to lose accuracy