Examining the Valve/HTC Vive Ecosystem: Basic Lighthouse Operation

Introduction

If you’re reading this article, you’re probably already aware of the Valve/HTC partnership where HTC will manufacture the Vive, a virtual reality head mounted display, powered by Valve’s SteamVR platform.

As part of the reveal, one new piece of technology was introduced to the public: the Lighthouse. This is a brand-new-to-VR technology which will be used as part of a system to track the position and orientation of a user’s head mounted display and controllers throughout an entire room.

With Lighthouse, instead of using VR in a chair or standing in place, its room-scale VR feature allows you to use the space of an entire room as a stage to physically walk around in a virtual environment.

Valve Lighthouse

Image Source: Valve Lighthouse Slide from “Advanced VR Rendering” at GDC 2015

Disclaimer

This article is based on publicly available information. Be aware that we are trying to explain a system that is unreleased, subject to change, and has very little publicly available information. Some elements of this article may prove inaccurate at a later date.

With any complex system, there are many rules, details, and exceptions to explore. This first article is just going to cover the tech basics (but will still be plenty meaty for many). We’ll consider more detailed issues in later articles.

A Basic Operational Review

The purpose of this first article is to clear up some of the common misconceptions concerning the Lighthouse technology. It will also serve as a starting place for additional articles on Lighthouse and on the various aspects of the HTC/Valve partnership.

By understanding how this one component works, we can understand much more about what HTC and Vive are trying to deliver to consumers. They’re not just cranking out randomly incremental or independent technological solutions here; Valve is running a very deep and highly integrated game plan.

So… we’ve all seen the kind of hand scanner used to read the UPC codes off of the sides of boxes. They send a glowing red line out into space which strikes the surface of the box. If we were able to see infrared light, what Lighthouse does to a room would be similar in appearance. It sends a line of laser light out into space, and lands on the objects and walls inside.

The Lighthouse units have been referred to as a “dumb” device, which is partially true. They are not able to see or interpret what they are scanning. By themselves, they are unable to “read” a room. They serve only as a high-tech flashlight, providing a pattern of predictable illumination.

The Lighthouse units are not conventionally networked. They stand alone and they do not plug into your computer. Each unit only has a single wire for a power connection. Still, in a later article, we’ll learn that they’re far more intelligent than you might first believe.

Twenty-five times a second, each lighthouse unit sweeps the room with two infrared laser beams which are invisible to the naked eye. See the illustration below.

This image is technically inaccurate, but still demonstrates the concept of room scanning. A Valve Lighthouse unit will only scan one axis at a time.

This depiction is technically inaccurate, but still demonstrates the concept of room sweeping. A default Lighthouse unit is expected to sweep only one axis at a time, not two at once. Image Source: Reddit user rubixcube6

Different from the animation above, the Lighthouse does not currently sweep the room with both beams at the same time. It also isn’t this slow. Even if our eyes were capable of seeing the infrared laser beam, it sweeps the room so quickly that the eye cannot track it.

The system has been stated to sweep the room 100 times a second. In 10 milliseconds, a single Lighthouse unit will sweep a first beam horizontally across the room. In the next 10 milliseconds, it will sweep a second beam vertically across the room. Finally, it will rest for another 20 milliseconds.  That’s a total of 50 sweeps per second.

EDIT 3/23/2015: Timings corrected thanks to MadExecutioner.

Because the Lighthouse system consists of two Lighthouse units, a second unit (across the room) is believed to be sweeping while the other unit is resting, and combined, they reach a total of 100 sweeps per second. Some surfaces in the room are swept once, others are swept twice, depending on which Lighthouse can see them.

The video, below, shows the operation of the Lighthouse in slow-motion. If you observe carefully, you may notice the pause after every pair of sweeps.

Aside from potentially being able to achieve higher steady refresh rate, why use two Lighthouses instead of one? With a conventional tracking approach that uses a single camera, if you put a controller behind your back, the computer loses sight of it and is unable to determine exactly where it is. The object you are holding in the virtual world goes dead or disappears from the game.

If you look at the cartoon image at the beginning of this article, you will see the two Lighthouse units are placed high and in the corners of the room. By placing them in opposite corners, it gives them an opportunity to completely surround a person or an object in laser light, making it far more difficult (but certainly not impossible) to foul up the tracking.

Modes

The Lighthouse is expected to be capable of several different modes of operation. What we have described in this article is only one way the Lighthouse might behave, and is based on the behavior of the pre-release units. It is possible that a Lighthouse will ship to you with only a single mode enabled, but the Lighthouse units are user reprogrammable. We can expect other modes to be available for more specific applications, and this topic will be part of another upcoming article.

Coverage

When asked about how much space the Lighthouse covers, the initial answer was 15 feet x 15 feet. This very specific answer caused a lot of unnecessary alarm and confusion. What if I have a smaller room? What if I have a bigger room? What if I can’t dedicate a whole room and I want to sit in a swivel chair at my desk*, or to stand in the middle of my living room?

In response, Valve’s Chet Faliszek clarified this issue at a presentation at EGX Rezzed. “We say 15 feet, which is what a lot of people have heard. That isn’t required; that’s just one version of it. You can be seated, you can be standing, you can have a small room or big room. We like having those options.” He wasn’t walking it back; Valve is offering all those possibilities.

* – It is worth noting that if you intend to use the Vive at a desk, you should place your Lighthouse units where they will have an unobstructed view of your head and arms.

The minimum space for a Lighthouse appears to be enough so that you can sit or stand in place, and freely move your arms about you. Perhaps 6 feet by 4 feet. The maximum space for two Lighthouse units have not yet been defined, but is expected to be greater than the 15’x15′ figure given.

Down the road, they expect to provide the ability to concatenate multiple spaces together with additional Lighthouse units. That is another feature that might work out really well for a specific application.

For in-game tracking, an inspection of the current SteamVR Beta API reveals support for two different methods of positional tracking. The traditional system provides a relative position while seated in a chair. The new system provides absolute position while standing in a room. Developers can use one or both tracking systems as needed.

Other Hardware Manufacturers

As mentioned in the previous article, Competitors with Different Goals: Valve vs Oculus, Valve plans to make the Lighthouse technology freely available for any hardware manufacturers to integrate.

You may not think that this offer is very significant, and based on anything that I’ve read so far, I don’t blame you. Perhaps you only thought of a company which wants to sell you a new controller or a competing head-mounted display?

The more we understand about Lighthouse, the better that we can answer the question of why any other kind of company would want to integrate this technology. We’ll work our way back towards answering that specific question.

Upcoming

For you hardcore geeks and pharophiliacs (also known as lighthouse lovers), yes, we’ll get to the good stuff. We have to lay down some more foundation first. The next article will discuss the other half of the tracking system, which includes the sensors that use the predictable patterns from the Lighthouse to compute your absolute position inside of a room.


This series continues with the next article, “Examining the Valve/HTC Vive Ecosystem: Basic Sensors and Processing“.


 

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7 responses to “Examining the Valve/HTC Vive Ecosystem: Basic Lighthouse Operation”

  1. Rubixcube6 says :

    I was the one who posted that picture of the room sweeping lasers. Source: http://www.reddit.com/r/oculus/comments/2ym0m7/is_this_how_the_lighthouse_base_station_would/

  2. Duncan says :

    Cant wait for part 2. Very interested to hear whether stock IR sensors or even photodiodes could be used as sensors for custom devices!

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