Author Archives: okreylos

About okreylos

I am a research computer scientist at the University of California, Davis. My research areas are scientific visualization, particularly in immersive ("virtual reality") environments, human/computer interaction in immersive environments, and 3D computer graphics. My primary work is software development, from architecture over design to implementation and coding. I am the primary software developer for the UC Davis W.M. Keck Center for Active Visualization in the Earth Sciences (KeckCAVES). Some of my released packages are Vrui (a VR development toolkit), CollaborationInfrastructure (a tele-collaboration plug-in for Vrui), Kinect (a driver suite to capture 3D video from Microsoft Kinect cameras), LiDAR Viewer (a visualization package for very large 3D point clouds), 3D Visualizer (a system for interactive visual analysis of 3D volumetric data), Nanotech Construction Kit (an interactive molecular design program), and SARndbox (an augmented reality sandbox). I also dabble in VR hardware, in the sense that I take existing custom or commodity hardware components (3D TVs, head-mounted displays, projectors, tracking systems, Wiimotes, Kinect cameras, ...) and build fully integrated immersive environments out of them. This includes a fair share of driver development to support hardware that either doesn't have drivers, or whose vendor-supplied drivers are not up to par.

Here we go again with Apple’s holography patent

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I just found an article about my 3D Video Capture with Three Kinects video on Discovery News (which is great!), but then I found Figure 1 in the “Related Gallery.” Oh, and they also had a link to another article titled “Virtual Reality Sex Game Set To Stimulate” right in the middle of my article, but you learn to take that kind of thing in stride.

Figure 1: Image in the “related gallery” on Discovery News. Original caption: “Apple has filed a patent for a holographic phone, a concept that sounds absolutely cool. We can’t wait. But what would it look like? A video created by animator Mike Ko, who has made animations for Google, Nike, Toyota, and NASCAR, gives us an idea. Check it out here”

Nope. Nope nope nope no. Where do I start? No, Apple has not filed a patent for a holographic phone. And even if Apple had, this is not what it would look like. I don’t want to rag on Mike Ko, the animator who created the concept video (watch it here, it’s beautiful). It’s just that this is not how holograms work. See Figure 2 for a very crude Photoshop (well, Gimp) job on what this would look like if such holographic screens really existed, and Figure 4 for an even cruder job of what the thing Apple actually patented would look like, if they were audacious enough to put it into an iPhone. Continue reading →

I think this is what statisticians call an “outlier”

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My web server was close to having a nervous breakdown today, but it held up! Behold:

Figure 1: Total page views on Doc-Ok.org over the last 30 days.

I’m expecting tomorrow will be back to normal. BTW, my previous “Best ever” was around 4,500 views on the day I published my first impressions from the Oculus Rift dev kit, a little more than one year ago.

3D Video Capture with Three Kinects

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I just moved all my Kinects back to my lab after my foray into experimental mixed-reality theater a week ago, and just rebuilt my 3D video capture space / tele-presence site consisting of an Oculus Rift head-mounted display and three Kinects. Now that I have a new extrinsic calibration procedure to align multiple Kinects to each other (more on that soon), and managed to finally get a really nice alignment, I figured it was time to record a short video showing what multi-camera 3D video looks like using current-generation technology (no, I don’t have any Kinects Mark II yet). See Figure 1 for a still from the video, and the whole thing after the jump.

Figure 1: A still frame from the video, showing the user’s real-time “holographic” avatar from the outside, providing a literal kind of out-of-body experience to the user.

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Quikwriting with a Thumbstick

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In my previous post about gaze-directed Quikwriting I mentioned that the method should be well-suited to be mapped to a thumbstick. And indeed it is:

Using Vrui, implementing this was a piece of cake. Instead of modifying the existing Quikwrite tool, I created a new transformation tool that converts a two-axis analog joystick, e.g., a thumbstick on a game controller, to a virtual 6-DOF input device moving inside a flat square. Then, when binding the unmodified Quikwrite tool to that virtual input device, exactly the expected happens: the directions of the thumbstick translate 1:1 to the character selection regions of the Quikwrite square. I’m expecting that this new transformation tool will come in handy for other applications in the future, so that’s another benefit.

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Gaze-directed Text Entry in VR Using Quikwrite

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Text entry in virtual environments is one of those old problems that never seem to get solved. The core issue, of course, is that users in VR either don’t have keyboards (because they are in a CAVE, say), or can’t effectively use the keyboard they do have (because they are wearing an HMD that obstructs their vision). To the latter point: I consider myself a decent touch typist (my main keyboard doesn’t even have key labels), but the moment I put on an HMD, that goes out the window. There’s an interesting research question right there — do typists need to see their keyboards in their peripheral vision to use them, even when they never look at them directly? — but that’s a topic for another post.

Until speech recognition becomes powerful and reliable enough to use as an exclusive method (and even then, imagining having to dictate “for(int i=0;i<numEntries&&entries[i].key!=searchKey;++i)” already gives me a headache), and until brain/computer interfaces are developed and we plug our computers directly into our heads, we’re stuck with other approaches.

Unsurprisingly, the go-to method for developers who don’t want to write a research paper on text entry, but just need text entry in their VR applications right now, and don’t have good middleware to back them up, is a virtual 3D QWERTY keyboard controlled by a 2D or 3D input device (see Figure 1). It’s familiar, straightforward to implement, and it can even be used to enter text.

Figure 1: Guilty as charged — a virtual keyboard in the Vrui toolkit, implemented as a GLMotif pop-up window with rows and columns of buttons.

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Apple Patents Holographic Projector (no, not quite)

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About once a day I check out this blog’s access statistics, and specifically the search terms that brought viewers to it (that’s how I found out that I’m the authority on the Oculus Rift being garbage). It’s often surprising, and often leads to new (new to me, at least) discoveries. Following one such search term, today I learned that Apple was awarded a patent for interactive holographic display technology. Well, OK, strike that. Today I learned that, apparently, reading an article is not a necessary condition for reblogging it — Apple wasn’t awarded a patent, but a patent application that Apple filed 18 months ago was published recently, according to standard procedure.

But that aside, what’s in the patent? The main figure in the application (see Figure 1) should already clue you in, if you read my pair of posts about the thankfully failed Holovision Kickstarter project. It’s a volumetric display of some unspecified sort (maybe a non-linear crystal? Or, if that fails, a rotating 2D display? Or “other 3D display technology?” Sure, why be specific! It’s only a patent! I suggest adding “holomatter” or “mass effect field” to the list, just to be sure.), placed inside a double parabolic mirror to create a real image of the volumetric display floating in air above the display assembly. Or, in other words, Project Vermeer. Now, I’m not a patent lawyer, but how Apple continues to file patents on the patently trivial (rounded corners, anyone?), or some exact thing that was shown by Microsoft in 2011, about a year before Apple’s patent was filed, is beyond me.

Figure 1: Main image from Apple’s patent application, showing the unspecified 3D image source (24) located inside the double-parabolic mirror, and the real 3D image of same (32) floating above the mirror. There is also some unspecified optical sensor (16) that may or may not let the user interact with the real 3D image in some unspecified way.

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Someone at Oculus is Reading my Blog

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I am getting the feeling that Big Brother is watching me. When I released the inital version of the Vrui VR toolkit with native Oculus Rift support, it had magnetic yaw drift correction, which the official Oculus SDK didn’t have at that point (Vrui doesn’t use the Oculus SDK at all to talk to the Rift; it has its own tracking driver that talks to the Rift’s inertial movement unit directly via USB, and does its own sensor fusion, and also does its own projection setup and lens distortion correction). A week or so later, Oculus released an updated SDK with magnetic drift correction.

A little more than a month ago, I wrote a pair of articles investigating and explaining the internals of the Rift’s display, and how small deviations in calibration have a large effect on the perceived size of the virtual world, and the degree of “solidity” (for lack of a better word) of the virtual objects therein. In those posts, I pointed out that a single lens distortion correction formula doesn’t suffice, because lens distortion parameters depend on the position of the viewers’ eyes relative to the lenses, particularly the eye/lens distance, otherwise known as “eye relief.” And guess what: I just got an email via the Oculus developer mailing list announcing the (preview) release of SDK version 0.3.1, which lists eye relief-dependent lens correction as one of its major features.

Maybe I should keep writing articles on the virtues of 3D pupil tracking, and the obvious benefits of adding an inertially/optically tracked 6-DOF input device to the consumer-level Rift’s basic package, and those things will happen as well. 🙂

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New Adventures in Blogging

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Today I learned what happens when an article gets reblogged (is that a word now?) that does not have a picture in it, and apparently an embedded YouTube video does not count as a picture: the blogging software scoops up whatever the first picture below the article headline is, and if that picture happens to be a commenter’s mugshot, so be it. Proof: see Figure 1.

Figure 1: How an article without a picture in the article is represented when reblogged by an artificial “intelligence.”

Note to self: always add a picture. Now I’m curious to see what will happen if this article gets reblogged. After all, it has a picture in it…

How to Measure Your IPD

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Update: There have been complaints that the post below is an overly complicated and confusing explanation of the IPD measurement process. Maybe that’s so. Therefore, here’s the TL;DR version of how the process works. If you want to know why it works, read on below.

  1. Stand in front of a mirror and hold a ruler up to your nose, such that the measuring edge runs directly underneath both your pupils.
  2. Close your right eye and look directly at your left eye. Move the ruler such that the “0” mark appears directly underneath the center of your left pupil. Try to keep the ruler still for the next step.
  3. Close your left eye and look directly at your right eye. The mark directly underneath the center of your right pupil is your inter-pupillary distance.

Here follows the long version:

I’ve recently talked about the importance of calibrating 3D displays, especially head-mounted displays, which have very tight tolerances. An important part of calibration is entering each user’s personal inter-pupillary distance. Even when using the eyeball center as projection focus point (as I describe in the second post linked above), the distance between the eyeballs’ centers is the same as the inter-pupillary distance.

So how do you actually go about determining your IPD? You could go to an optometrist, of course, but it turns out it’s very easy to do it accurately at home. As it so happened, I did go to an optometrist recently (for my annual check-up), and I asked him to measure my IPD as well while he was at it. I was expecting him to pull out some high-end gizmo, but instead he pulled up a ruler. So that got me thinking.

Figure 1: How to precisely measure infinity-converged inter-pupillary distance using only a mirror and a ruler. Focus on the left eye in step one and mark point A; focus on the right eye in step two and mark point B; the distance between points A and B is precisely the infinity-converged inter-pupillary distance (and also the eyeball center distance).

Continue reading →

What is Presence?

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Disclaimer: Presence research is not my area of expertise. I’m basically speaking as an interested layperson, and just writing down some vaguely related observations that have re-occurred to me recently.

So, presence. What is presence, and why should we care? Libraries full of papers have been written about it, and there’s even a long-running journal of that title. I guess one could say that presence is the sensation of bodily being in a place or environment where one knows one is not. And why is it important in the discussion of virtual reality? Because it is often trotted out as the distinguishing feature between the medium of VR (yes, VR is the medium, not the content) and other media, such as film or interactive 3D graphics; in other words, it is often a feature that’s used to sell the idea of VR (not that there’s anything wrong with that).

But how does one actually measure presence, and know that one has achieved it? Some researchers do it by putting users into fMRI machines, but that’s not really something you can do at home. So here are a few things I’ve observed over sixteen years of working in VR, and showing 3D display environments and 3D software to probably more than 1,000 people, both experts and members of the general public: