The 5x4 display wall
From Greenspace
The visualisation cluster/display wall consists of six computers linked together. One of these (10.195.253.37) is the master node hereafter referred to as "viz". The 5 slave nodes each power 4 Dell displays. This diagram shows the basic layout:
The cluster runs ROCKS 5.3 with the viz roll on top of a fairly standard CentOS Linux distribution.
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Bezels and Resolution
More info about the physical geometry (bezels and the like) is available here.
Running commands
External clients can only log in to the master node, viz. The slave nodes can all be accessed from viz, however.
Viz is configured to allow access via SSH and also via a VNC viewer. It is necessary to use the VNC viewer for configuring some of the graphical applications.
SSH is configured on all the slave nodes such that it is possible to run commands on them from viz (as root). E.g.
viz% ssh tile-0-0 uptime
will return the uptime for the slave node tile-0-0. The same thing can be done with non-root users, if they set up ssh keyfile authentication.
Creating new users
If you create new users on viz, you should run rocks sync users afterwards. This makes sure the user exists on all the slave nodes. It also makes sure that the user's home directory is placed under /home on the NFS mount (meaning it is visible in the same place across all nodes). This is a Good Thing.
Wall Modes
The wall can be run in two graphical modes: simple and meta.
Simple Mode
Simple mode means that each monitor is individually addressed by the ROCKS system. To make the cluster operate in this mode, run this command from viz:
viz% rocks sync tile mode=simple
Simple mode is not currently used much.
Meta Mode
Meta mode means that each slave node conglomerates its four monitors into one virtual one (the resolutions are summed). Enter meta mode by using the following command:
viz% rocks sync tile mode=meta
Both SAGE and Chromium use meta mode in our configurations (although Chromium originally required simple mode). The standard (multi-coloured) ROCKS screensaver will tell you which mode the cluster is currently operating in.
Engage Meta mode - the Greenspace Way
The rocks sync mode=meta command does not work very well for our setup, so we created our own script to turn the wall from simple to meta mode. See how to do this.
SAGE and Chromium
At the time of writing we have two different ways of displaying content on the wall: SAGE and Chromium. These operate the display wall in different ways and for different reasons: SAGE provides several utilities (most notably an ImageViewer, a video player and a VNC client) together with a GUI for running them; Chromium allows almost any OpenGL app's data to be displayed on the wall (most notably Google Earth). A third way of using the wall, cglX, used to be installed but is not now used. Archived information about it is however still available.
SAGE
SAGE is often used to run up virtual VNC sessions across the whole or parts of the wall.
More details (and some random jottings) about using SAGE are contained in the SAGE page.
Chromium
Info on how we got Chromium to work with Google Earth, and how to make it work for you in two easy steps...
Google Earth Case Study: Lewis Windspeeds
Read more about a proof-of-concept overlay created for use with the wall.
Other Visualisation Tools
Some other tools we can use with the wall also exist. These often involve Chromium, but may not.
Paraview
Paraview, an advanced data-visualisation application, runs on the cluster.
Applications
There are applications that we have designed and developed to work specifically with the wall.
Data charts
Data Charts was created in order for charts to be displayed on the wall.
Viz Client PC
The Viz wall has a client Windows PC permanently connected to it.
- Running Google Earth on the wall with one (double) click from the client PC.
