Head mounted displays
There are three important considerations when
choosing a head-mounted display (HMD):
1)
Field-of-view:
Across the board, the field-of-view of HMDs is disappointingly small and the
task of choosing an HMD is one of finding the most acceptable compromise. Unlike the over 180 deg horizontal
field-of-view of the human visual system, HMDs available today offer 50 deg
horizontal or less field-of-view.
2)
Stereo
vision: Even if you do not explicitly require stereoscopic depth perception
for your particular application, the use of stereoscopic imagery is extremely
valuable for the ways in which it adds to the sense of realism and
immersion. All of the HMDs listed below
are stereoscopic.
3) Resolution: The standard resolution for VR applications has been 640 x 480 pixels (horizontal x vertical) or 800 x 600 (in the frame-sequential models). Lower resolution devices (TV quality or worse) are available but not listed below and are sufficient when the intended application does not require discriminating visual detail. Very recently, high-resolution HMDs providing up to 1280 x 1024 resolution have become available. Bear in mind that there is a general resolution/performance tradeoff, so unless you need the extra resolution you may want to increase performance instead (only the latest nVidia FX and ATI Radeon chipsets can work at high-resolution and maintain frame-rates).
Given those considerations, here are the HMDs that offer the best balance. There are others available but these are my favorites.
|
Product |
|
Resolution |
3D stereo |
Price USD |
|
V8
|
50 |
640 x 480 |
Dual VGA frame-parallel |
12,000 |
|
V1280
|
50 |
1280 x 1024 |
Dual VGA frame-parallel |
16,000 |
|
nVisor SX
|
50 |
1280 x 1024 |
Dual VGA frame-parallel |
24,000 |
|
ProviewXL50
|
40 |
1024 x 768 |
Dual VGA frame-parallel |
16,000 |
|
HMD 800
|
28 |
800x600 |
Stereo frame-sequential |
5,000 |
|
|
28-32 |
800x600 |
Stereo frame-sequential |
2,000 |
Bottom line: It’s been tough to beat the V8 for quality, FOV, and resolution. Recently, nVisInc has started shipping a high-resolution HMD. Virtual Research will soon follow suit.
Tracking devices
Tracking systems are designed to detect user motion
and relay this information back to the graphics computer so that the virtual environment
can be properly updated and rendered to the display device in real-time. While technical capabilities of tracking
system are typically measured in terms of resolution, accuracy, and latency,
most systems worth considering are reasonably comparable for most
applications. The more important
considerations are often the following:
1)
Range: You
need to decide how important it is that your users be able to move over a large
range. Large range means more than about
1.5 meters in every direction but is generally still less than 10-30 meters.
2)
Achille’s
heel: Every tracking system that exists today is susceptible to loss of
signal by interfering with the means which it detects user motion. Optical systems are susceptible to
line-of-sight occlusions between the user and the optical sensor. Electromagnetic systems are susceptible to
magnetic interference from many metallic and electric devices prevalent in
industrial architecture. Inertial
systems (only available for orientation) rely on the Earth magnetic fields and
therefore have some susceptibility similar to the electromagnetic systems. Ultrasonic systems are mildly susceptible to
line-of-sight occlusions, but are moderately sensitive to certain types of
ambient noise (e.g., white noise generators such of electric motors). Mechanical systems require a hard linkage
between the device and the user and severely limit mobility.
|
Product |
Range |
Technology |
Degrees of freedom |
Price USD |
|
|
10 x 10 meters |
Optical |
3 + 3 |
9.9K |
|
Flock of Birds
|
1.5 meters |
Electromagnetic |
6 |
3K |
|
Fastrack
|
1.5 meters |
Electromagnetic |
6 |
3K |
|
InertiaCube2
|
N/A |
Inertial |
3 – orientation only |
1.5K |
|
IS-600
|
3 x 3 meters tile-able |
Acoustic/Inertial |
6 |
10K |
|
HiBall
|
10 x 10 meters |
Optical |
6 |
100K (30K for 4 x 4 m) |
|
A.R.T. |
6 x 6
meters |
Optical |
6 |
30K |
|
Northern Digital |
3 x 3
meters |
Optical |
6 |
30K |
|
|
8 x 8 meters |
Optical |
6 |
50-100K |
Bottom line: This is a much harder decision to make. If you don't need to translate at all and
just want to have a participant sit in a chair and look around, then one of the
orientation sensors by Intersense is the no-brainer (likely the Inertia-cube2).
If you
need translation, then you need to decide how much. Do you need few feet or a dozen feet? If you don't think you're ever going to want
to do wide-area tracking, then you can get by with a $3-4K device from either www.polhemus.com
or www.ascension-tech.com. The downside of these devices is they only
have a range of about 3-5 foot radius and are somewhat susceptible to magnetic
interference (from metal or electronic objects in the immediate vicinity). The
advantage is that these devices are an all-in-one 6 degree of freedom solution
(orientation and position).
RECVEB/UCSB uses a hybrid tracker that gets
orientation information from an inertial system (made by www.isense.com)
and position information from the optical originally developed at UCSB. The former costs about between $US 1.5K to
$US 3.5K and the latter has recently been commercialized by startup company
(with which I'm associated), www.worldviz.com,
for $10K . Alternative optical position
trackers are available from www.3rdtech.com
and www.northerndigital.com
(they offer many advantages over the Worldviz technology but are about 3-4
times the cost). Of course, all optical systems have strict line-of-sight
requirements.
To maximize the performance to cost ratio, we
recommend a hybrid solution which combines an inertial orientation tracking
system (Intersense InertiaCube2) with an optical position tracking system.
Software
Right up front you need to decide how you want to
handle running the real-time side of your immersive worlds. How you build your content is an entirely
different matter and will basically boil down to using one of several
commercially available 3D modelers (e.g., 3D Studio MAX) and image manipulators
like Adobe Photoshop. For rendering
& simulating your worlds, however, you can choose between developing
your own applications written in C/C++ with the aid of specialty libraries to
interface to hardware and import objects, or using a higher-level platform that
let's your either script of graphically create interactive worlds. The chart below presents the platforms that I
think are worth considering. I'm
involved in one of these (Vizard).
|
Software |
Programming treatment |
Rough price USD |
|
Scripting/graphical |
$3,250 |
|
|
Virtools
VR |
Graphical based |
$10,000 (dev) + $5,000 (VR) |
|
Eon Reality
|
Scripting/graphical |
$13,000 |
|
|
C/C++ tools |
$10-20,000 |
|
Quest3D |
Graphical
based |
$750 |
Graphics cards
nVidia (www.nvidia.com) based cards are recommended. nVidia just makes chips but go to their website and find vendors selling cards (www.nvidia.com).
For stereo applications with high-end HMDs (field-parallel) you need a graphics card with dual pipe output (two VGA or digital output connectors). Most high-end cards provide this but you should verify this before ordering. Frame-sequential based HMDs use a single output and alternate between left and right eye images so only one output is used.