2 Requirements
The following is an exhaustive list of the hardware and software the geo wall requires.

2.1 Hardware

2.1.1 Computer: Any standard PC with a powerful graphics card canbe 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.

TODO: Image of a Geowall PC.

Next make sure your computer has the following system software:

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. The exact specification is : TODO - exact name of splitter.

TODO : Image of a splitter.

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.

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.

TODO : IMAGE of a DVI-VGA converter.

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 DLPl 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.


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.

TODO : Whom to contact for projectors?

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.

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

TODO : Whom to contact for a screen ?

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.

EVL recommends the use of circular polarization.

TODO: Vendor information.

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

fig4.1 fig4.2

The setup procedure is described in the next section TODO : give link.

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.

2.1.9. Stand.
This is required in case of the front ptojection systems and the two projectors are placed in front of the screen on the stand and then aligned.

fig6