2. Requirements

The following is an exhaustive list of the hardware and software the Geowall requires.

2.1 Hardware

2.1.1 Computer: Any standard PC with a powerful graphics card can be used for the Geowall. The machine may run on Windows, Linux or Macintosh OSX. The only unique component is the video card : it should support 'Twinview' or in other words the video card should have two outputs. You will connect a projector (and/or a monitor) to each head of the card.

Fig 2.1- A Geowall PC with two monitors.


Pentium III/IV 1 GHz
The faster the better. A dual CPU is not necessary, but if you can afford it go ahead and get two CPUs.

Minimum 512 MB RAM

20 GB hard disk space

The more the RAM the better the performance. Most Geowalls out there have 2 GB RAM. Hard disk depends on your requirements. The largest known configuration of a Geowall was 3.5 GB RAM/ 500 GB hard disk
Graphics card

Nvidia GeForce4 Ti 4600 or

Nvidia Quadro4 900 XGL

Your graphics card must support Twinview i.e. it must have 2 video outputs. You can also use one of graphics cards from other vendors like ATI (Radeon cards).

Between the GeForce4 and the Quadro4, you should do a cost-benefit analysis. The Quadro4 has more capabilities (it can do quad-buffered stereo) and is more expensive. It is advisable to insert the graphics card in the AGP slot if available in the PC.

LCD/CRT - 2 nos.
Keep your computer plugged into at least one monitor, so that you can use the machine as a regular desktop too.

Next make sure your computer has the following system software:

Operating System
Windows 2000/XP, RedHat Linux 7.3/8.0, Mac OS X
If you order a PC from a vendor, it will probably have Microsoft Windows XP Professional (or Home) already installed; so it is ready for use. Geowall users typically install Linux on the machine and make it dual boot. 'MacGeowalls' (Apple's Macintosh computers) also exist; but the Windows/Linux dual boot combo is most common. Most Geowall application software run on all three platforms.
Drivers for graphics card

Windows: download the unified drivers. Quite straightforward.

Linux:download 2 files - a GLX driver file and a kernel driver file. Run the NVchooser.sh utility that Nvidia provides to find out exactly which drivers are required for your system.

Get the latest drivers from the NVIDIA web site http://www.nvidia.com or the vendor whose cards you are using.
Application software

Immersaview, Walkabout, Wallview, Viewer

These are all described here. You can do this after your Geowall has been set up.

Miscellaneous Hardware/Software

Treat the Geowall machine as a regular desktop PC i.e. if you need sound install a sound card and speakers;put it on the network etc.

2.1.2 Signal Splitter.

It is useful to connect two monitors to the Geowall PC alongwith the two projectors. This means that you need four video signals from the dual headed graphics card. This can be achieved with a 'Signal Splitter'. Extron makes these.

This is optional as the projectors have data backs that provide an output to the monitor. But if your projectors are turned off then, the monitors will not receive a signal. With the splitters, you can use your Geowall PC as a regular workstation when you do not need the projectors to be lit.

Fig 2.2 A Signal splitter


2.1.3 DVI-VGA converter

The graphics cards may have two Digital video Interface (DVI) ports or a 15 PIN VGA and a DVI port. VGA cables are more commonly available and CRT monitors usually have only VGA connections (LCD monitors come with both type of connections). A DVI-VGA converter will allow you to run VGA cables between a projector and the graphics card output.
Fig 2.3 A DVI-VGA Convertor

The Quadro4 card has only DVI outputs, so if you use VGA cables you will need two such converters. Technically, the connections should be DVI since signal conversion may degrade the video quality. The degradation is very minor, so using VGA connections on your system is recommended.

2.1.4 Projectors

Use two Infocus LP530 DLP projectors for your Geowall. They are stacked on top of each other so that the images overlap. When the Geowall project started out we used the Infocus LP350 projectors, but the 530s are much brighter and the reconditioned ones are cheaper too.

Fig 2.4.1 - Table Mounted
Fig 2.4.2 - Ceiling Mounted

The light emitted by DLP projectors is not polarized and so the Geowall was designed with DLP projectors instead of LCD projectors. The latter are typically pre-polarized, so you cannot control the polarization with filters.

2.1.6 Projector Screen


The projection screen is coated with a special polarization preserving material. Not just any screen will work with polarized light. For a front projection system, the screen is a 'Da Lite silver surface screen' or just a 'silver screen'. Chances are that you don't have a silver screen unless you have an AV closet that hasn't been cleaned in 30 years. Front projection screens also come with a stand and a carrying handle; so they are handy when you want to travel with a Geowall.

Rear projection screens that preserve polarization are also available. These are custom made and coated with 'Disney black film'. These are costlier and used only there is space available for rear projection. The contrast on these screens is much better than the front projection screens.

Fig 2.5 - Front projection Screen

In general EVL recommends rear projection unless budget or room constraints prevent you from doing so.

2.1.7 Polarizers

The light which is projected on to the screen needs to be polarized. You have to attach filters in front of the bulbs on the projectors. This section describes the types of polarization available and where you can get them.

Linear Polarization
Circular Polarization
Light is polarized in either the horizontal or the vertical direction.
Light is polarized in the clockwise or the anticlockwise direction.
Cheaper. But you lose stereo when you tilt your head.

More expensive. Stereo is maintained even when viewers tilt their heads.

EVL recommends the use of circular polarization.

TIP:Polarization filters remove 62% of the light and that energy has to go somewhere. Some of it is reflected away but most is dispersed though heat. If the filters are too close to the projector and the light is concentrated in a small area the filters will begin to depolarize and melt. The way around this is to move the filters as far away from the light source as possible

Fig 2.6 a - Circular Polarizers components
Fig 2.6 b. Polarizers with holders.

The setup procedure is described here

2.1.8. Stereo glasses

All viewers of the GeoWall wear glasses to see stereo. Glasses are available as disposable paper versions, reusable plastic and aviator
style. The type of polarization (linear or circular) has to match the type of polarization used on the projector.The polarized stereo glasses cost much less than the LCD shutters used in active stereo.
Fig 2.8 - Stereo glasses.


2.1.9. Stand.

This is required in case of the front projection systems and the two projectors are placed in front of the screen on the stand and then aligned.
Fig 2.9 Stand for projectors.


2.2 Vendors

Contact Information
Stewart and DaLite
Linear Polarization Glasses
Circular Polarization Glasses
American Polarizer
Projector Stackers
Reason Computers

Sales at Reason Computers