A telescope at London Open City

Seeing Is Deceiving

By Stephen Jayna, 15^th May 2009

Tim Simpson's coin-operated tourist telescopes allow you to peer through and see, well, not quite what you may have expected. As you pan and tilt each telescope you in fact explore a film of his devising and not the veranda you were perhaps hoping for. You can watch one such film here.

Background

The exhibition London Open City, shows the 'tug-of-war' nature of London life that is only exaggerated by the city’s fast pace: order versus chaos, interaction versus privacy, heritage versus change. Tim Simpson presents three telescopes in collaboration with Richard Wentworth.

How It Was Done: In Brief

The telescope looks for all intents and purposes like the sort you'd find at any good tourist spot. The sort that ask for 20 pence in return for a minute or two of spectacular views. In this case — rather than charge viewers — a mere twist of the telescope's knob is enough for the viewing to commence.

As you look through the telescope's eye-piece you're actually watching a small video screen; you can see the back of it in the photo below. Using a mirror system its output is reflected back to the viewer.

The film is being played from a Mac mini tucked away in the base of the telescope. As you twist and tilt the telescope the area of the film you're watching changes accordingly giving the impression of a real viewing experience.

A telescope's inner workings

How It Was Done: Not So Brief

Gentoo Linux on the Mac Mini

My first foray into the world of Apple Mac was short lived. It involved putting Gentoo Linux onto a seperate partition on a Mac mini. The reason is two-fold:

• Firstly, as with all interactive installations it was desirable for it to be super-low maintenance. By that I mean the only burden it could place on the exhibition staff was to have them plug it in and turn it on. What's more it had to work for weeks on end without interruption. Linux is good at that, you can rely on it not to need rebooting, not to perform software updates in your absence, and for it to generally have all the properties of an energizer bunny.
• Secondly all my experience — at the time — was centered around Linux. Given the amount of control it affords to a programmer it seemed like the obvious choice to produce something quite so bespoke.

Rather than use Boot Camp to install Linux on the Mac I chose rEFIt instead. It's free. And permits you to install Windows, Linux or both in addition to OS X on your Mac.

It should have been a breeze but I spent days rebuilding kernels and worrying about SATA drivers trying to get Gentoo to boot before I realised I simply had to press 'sync partition tables' in rEFIt. At the time I swear this wasn't common knowledge given how hard I googled for the answer!! Sometimes you just have to work things out for yourself it would seem.

Something I didn't work out for myself was how to have the Mac mini — under Linux — turn itself back on in the event of a power failure. Given the mini was inside the base of the telescope, behind a metal plate and four screws, pressing the 'on' button would have been tricky. Mythic Beasts had this handy hint:

setpci -s 0:1f.0 0xa4.b=0

The Precision Joystick Controller: BU0836

The BU0836 exposed

With a platform on which to play our film from we now needed a way to relay the telescope's pitch and yaw (thankfully no roll) to the Mac mini. It was obvious that the telescope mimicked a traditional joystick and so almost immediately came across the BU0386. By Leo Bodnar it's a USB joystick controller that allows you to control 8 axes, 32 buttons and a hat switch. My, my. In the event we only needed 2 axes plus a switch to trigger the telescope into life. Although it's not mentioned on Leo's site I managed to get the controller working on Gentoo Linux with very little trouble. It appeared as /dev/input/js0 as you might expect, you expected that right?

Panning around the film with XLib and MPlayer

To achieve the actual panning effect Tim made a film that can only be described as super-widescreen. Three or four times wider than the display you could only see perhaps a quarter of it at any given moment.

To move the video around in sync with the telescope a rather crude method was employed. Using XLib — a library that allows you to manipulate windows on a Linux desktop — the video's position on the screen was dictated by the input from the BU0386. It was as if you were dragging the window using a mouse. Crude, but very effective. Computationally cheap too.

And To Sum Up

A testament to the versatility of a Mac mini and what you can do when you connect it to a physical interface. With a controller as simple as the BU0386 it becomes very easy to control a computer by switches, toggles and variable resistors.