4-Projector Display under Ubuntu 11.04

For my tabletop interaction research project, I need to create a large extended display with 4 projectors in a 2x2 configuration. I could not make all 4 projectors to display at the same time with the original 2 Nvidia GeForce 8600GT graphics cards. Turns out it is especially hard to do this, if not impossible. Also, the Nvidia cards are kind of old, so I switched to a new graphics card, ATI Radeon HD 6870 with two DVI ports, 2 Mini DisplayPorts and 1 HDMI port.

After connecting the projectors to the 2 DVI ports and 2 Mini DisplayPorts, all 4 projectors can display now, however the displayed areas are not well-aligned as before. Specifically, the two displays from the projectors connected to the DVI ports are smaller with black area around them.

The problem is with underscan. The Catalyst Control Center does have the underscan and overscan option for HDMI but it doesn't always show up. It is supposed to be under "Display Manager" -> <a particular projector/monitor> -> Adjustment, but the "Adjustment" tab does not always appear. For me, it appears for one projector and I changed the scaling to 0% underscan. This did expand the displayed area for that projector. But I couldn't do the same for the other projector.

Finally, what worked is using the command line to disable underscan:

sudo aticonfig --set-pcs-val=MCIL,DigitalHDTVDefaultUnderscan,0