Week 2

Making it Work - Hardware








There is no one best / correct way to build these systems - choices are made based on use cases, available space, and available $.

Some of the largest displays currently in use


2D 328 MPixel wall (40,960 x 8000) - made from 80 Dell 3007WFP Widescreen LCDs customized to reduce borders
CPU - 40 X 6-core Intel Sandy Bridge 2667W @ 2.9 GHz
RAM - 64GB per node
Disk - 1TB per node
GPU - 1 NVIDIA GTX 680 per node

Lasso - 2D Multitouch 12.4 MPixel (5760x2160) - made from 6 (3 x 2) 46" monitors
Single computer


SUNY Stony Brook

Reality Deck
2D 1,500 MPixel - made from 416 Samsung S27A850D 2560 by 1440 LCD displays
covers four walls of a 33' x 19' x 10' room
CPU - 18 X dual 6-core Intel Xeon
RAM - 48 GB Per Node
Disk -1 TB per node
GPU - 4 AMD Firepro V9800 GPUs (each node can drive up to 24 displays)
building a 24.4 soundsystem


Adler's Grainger Sky Theater

2D 64 MPixel - from 20 Rockwell Collins projectors
71 foot diameter Dome


Its not just about having the biggest display - big displays are great, they push the boundaries and get us closer to a future where any surface could be a display if that's what we want, but they take a lot of space and cost a lot of money to build and maintain. They are often built in visualization centers surrounded by visualization people, but not necessarily surrounded by domain scientists or other potential users.

To be really useful these kinds of displays need to be near their users so those users have regular easy access to them. Users do not want to walk across campus to a visualization center. They don't want to walk to another building. They often don't even want to walk to another floor of the same building. This makes smaller but still high-resolution large-format displays in conference rooms or labs more appealing.

here is a web page showing many of the various smaller displays running the same software the we use during class - sage

There are portable versions of these displays that can be moved around - Optiportables

Projection-based systems



Rear projection systems mount the projectors behind a black screen. Front projection systems mount the projectors on the ceiling in front of the screen. The advantage of rear projection is that the users can get very close to the screen without casting shadows and the noise and heat of the projectors can be hidden. The disadvantage is that the projectors take up a lot of wasted space to have enough throw distance behind the screen, even if the optics are folded with mirrors.

Front projection systems have the advantage of being able to project onto existing surfaces, although projecting onto dedicated front projection screens gives better brightness and contrast, and is required for passive stereo projection. Very large screens are expensive and also have seems.

Front projection screens are best in theatre situations where the users will not get very close to the screen or a very large screen is needed. Rear projection is better when the users need to get close to the screen. Rear projection also creates a cleaner look.

Its important to think about the users' natural distance from screen.

Its also important to think about throughput. Is this a device where people will come and go quickly, say in a museum setting, so it needs a big entryway and ways for people to enter and exit at the same time, or will people be using the display for long periods of time. To achieve the effect of imagery surrounding the users it is usually necessary to have imagery on a door that can be closed, but then it takes longer to get in and get out

Are there chairs and desks in the space? People can only stand comfortably for so long.

Another increasingly important issue with displays and computers is the power cost to operate the system. All of the components are getting more power efficient over time but its important to add up all of the power in use. Our current estimate is that cave2 uses 50 kW, or about 16 times my home electricity usage if the A/C is on at home, or about 200 times my home usage without the A/C on.

Stereo Visuals

Stereo visuals, with each eye seeing a scene from a slightly different point of view, can be very beneficial in certain cases, and not beneficial at all in others. The stereo effect is strongest within a few feet from your head and diminishes with distance. Stereo visuals add a very strong sense of presence to nearby objects, especially when coupled with head tracking. 3d position in space can also be a very strong cue to help disambiguate complex scenes.

With stereo imagery there are a variety of approaches. The most common today are:
Aligning stereo projectors adds in more work, though the human visual system is pretty good at fusing stereo images that are slightly misaligned.

Since passive glasses have no active components they are cheaper, less fragile, and you don't have to replace the batteries regularly

Another important feature with large curved or angled displays is how stereo is computed. In virtual reality systems the viewing position and the stereo visuals are typically computed for the main tracked person - this means there is no stereo separation looking 90 degrees to the right or right of the tracked person and reversed stereo looking behind them since the two images are computed for the tracked person's two eyes. For larger groups in curved or angled displays its better to generate the stereo for each screen assuming the user is looking perpendicular to it so people can see stereo wherever they look.

Stereo visuals are strongest when coupled to head-tracking. At the movie theatre you see through the camera operators eyes. In tracked environments you control the camera with your head motion giving a very natural way to look around objects. Most trackers of this kind have 6 degrees of freedom: motion in X, Y, Z and the ability to sense Roll, Pitch, Yaw.

Tracking in the old CAVE days made use of electromagnetic trackers, then acoustic trackers + gyros, and now camera-based tracking. Electromagnetic had the advantage of not needing line of site between the emitters and the receivers, but was sucessiptible to interference from metal objects and typically required a wired connection between the user and the system. Camera based systems are wireless, so they are more comfortable, but you need to have enough cameras to cover the volume, and cameras can be occluded when there are large numbers of people in the space

There are large displays; there are high-resolution displays; there are large high-resolution displays; there are also small high-resolution displays

The first small form factor ultra high resolution panel was the IBM T220/T221 'big Bertha' that had 3820 x 2400 resolution in a 22" diagonal display at 204 ppi in 2001 for $18,000.

Today an iPad 4's 9.7" diagonal display has 2048 x 1536 resolution at 264 ppi.
Today an HTC One phone's 4.7" diagonal screen has 1920 x 1080 pixels at 468 ppi.
The user is typically a foot away from these screens but could get much closer to look at fine details.

Today a Macbook Pro's 15" diagonal display has 2880 x 1800 resolution at 220 ppi.
Today a google Chromebook Pixel's 13" diagonal display has 2560 x 1700 resolution at 239 ppi.
The user is typically two feet so away from these screens.

We are at the point where our portable displays have more resolution than we can see and the actual resolution numbers will no longer matter. For large displays we sit back and look at we are near that point. For large displays that we want to walk up to and interact with, we are not there yet.

We are going to start thinking about displays in terms of whether they give us 20/20 (6/6 in the rest of the world) at the natural usage point.

The original cave had 8 ppi and you were typically standing 5' from the screens
cave2 has 32 ppi and you are typically standing 8 to 10' from the screens

now getting 4K LCD screens (3840 x 2160)
Sharp 32"
Panasonic 56"
Sony 55" and 65" and 84"
LG 84" $17,000

For single person office-based high-resolution systems it can be difficult to get projectors into that space, though there are some nice small short throw distanace projectors out there now. flat panels work more naturally in that confined space - e.g. the tilings of displays used by the NSA or stock traders. There are similar issues with resolution and border size. These tend to be single user and single interaction device.


We have 100 gigabits coming into the lab and 80 of that going to the cave.


local storage is often a mix of RAM, SSD Drives, traditional drives, network storage

Different applications have different local storage / local network / remote storage / remote network needs that have to e balanced.

Need to be sure there are reliable backups of the data and the applications to be able to rebuild a node quickly if it fails, or replace a drive that fails


Increasing usage of GPUs to speed up and improve rendering - using shaders to render data rather than creation of a large number of polygons

Different GPUs have different abilities in synchronization
GPU capabilities continue to increase at a pleasant rate - still have issues getting data onto the card, but that situation is also improving.

How many screens are driven by a single computer is an important design decision.


Ambient sounds are useful to increase the believability of a space

Sounds are useful as a feedback mechanism

Important in collaborative applications to relay voice between the various participants

Spatialized sound can be useful

Simple audio can be monaural with a single speaker but there are many advantages to having multiple speakers as in a surround sound system to give directional audio where sounds occur form a particular location. As you get close to these sounds they get louder. This can tell you where things have happened, or lead you towards something.

In a surround environment such as cave2 sounds  an alert you to something happening out of your current field of view

ideally want a quiet environment with no fan noise from the computers or displays so the only sounds you hear are those form the application, or from your collaborators to minimize distrations


looking at the imagery
pointing at features / structures in the imagery by hand  / laser pointer / through a pointer on the screen
panning / zooming the imagery
turning elements on and off
changing time steps  / playing / pausing of an animated sequence
changing colour transfer function
changing data and processing upstream

moving closer to the screen to get a better view of details / moving back to get the big picture
with head tracking being able to dynamically change the viewpoint

interaction with other devices - laptops, phones, tablets

We really want people to be 'looking through the display' at the data ... that is the users stop talking about the display hardware and spend their time talking about the content.

Some other papers relevant to our work here in evl:

The CAVE®: Audio Visual Experience Automatic Virtual Environment
Cruz-Neira, C., Sandin, D., DeFanti, T., Kenyon, R., Hart, J.
Communications of the ACM, 06/01/1992

GeoWall: Stereoscopic Visualization for Geoscience Research and Education
Johnson, A., Leigh, J., Morin, P., Van Keken, P.
IEEE Computer Graphics and Applications, 11/01/2006 - 12/31/2006

Scalable resolution display walls

J. Leigh, et. al.
Proceedings of the IEEE 101, no. 1 (2013): 115–129.
CAVE2: A Hybrid Reality Environment for Immersive Simulation and Information Analysis

Febretti, A., et. al.
Proceedings of IS&T/SPIE Electronic Imaging, The Engineering Reality of Virtual Reality 2013, San Francisco, CA, 02/04/2013 - 02/05/2013

For Thursday's Class

If your UIN ends in an odd number you should read this paper from 2000

Building and using a scalable display wall system
Li, K et al
IEEE Computer Graphics and Applications 20.4 July-Aug 2000

If your UIN ends in an even number you should read this paper from 2005

Tools and Applications for Large-Scale Display Walls
Wallace et. al.
IEEE Computer Graphics and Applications, July 2005

Each person should produce a 1 page pdf file critiquing the appropriate paper including your name, the title of the paper, a short paragraph summary of the paper, a  list of things you found interesting in the paper, and then what you think are the positives and negatives about the research.

In class on Thursday everyone will use sage to drag and drop their file onto the wall and a subset of the students will be asked to talk more in depth about what you found in the paper

Coming Next Week

Making it Work - Software

Before next class please read

Ultrascale Collaborative Visualization in Display-Rich Global Cyberinfrastructure
Jeong, B., Leigh, J., Johnson, A., Renambot, L., Jagodic, R., Nam, S., Hur, H.
IEEE Computer Graphics and Applications Vol. 30.3

Again, you should produce a 1 page critique of the paper to put up on the wall Tuesday in class, and a subset of the students will be asked to talk more in depth about the paper.

last modified 9/1/13