Roger Bays

Augmented reality (AR) is a technology where users can simultaneously view the real world and virtual content. In the specific case of the Semaphore installation, art viewers wear a head-mounted display (HMD) or headset.

To enable the correct virtual content to be rendered in the correct position, angle, and size, black-and-white augmented reality markers (essentially black-and-white panels) are placed in the real world.

The headset has a built-in camera, which captures the environment. When the camera detects a marker, the computer program uses its exact position and orientation to overlay the virtual content.

Augmented reality markers are, in essence, flags that enable the correct virtual content to be displayed correctly.

Because of the flag like nature of augmented reality markers I began researching flags and discovered that shutter towers, used between the end of the 18th century and the beginning of the 19th century, used mechanical black-and-white shutters as flags to transmit signals across the south of England. The similarity between the mechanical shutters and a typical augmented reality marker was uncanny! And because of this I decided to go with shutter towers as the central idea.

Note: The installation is titled Semaphore. Technically semaphore towers are a different device to shutter towers, but are used for the same purpose. Semaphore towers use mechanical arms rather than rotating  shutters.

The shutter telegraph was used to transmit messages between towns and cities in the south of England. On a clear day, the shutter telegraph was much faster than a relay of riders on horseback, making it an essential military tool. Shutter tower operators could quickly warn the Admiralty, in London, of any impending invasion from the English Channel or the southern region of the North Sea. Day-to-day, the shutter telegraph was used to transmit various messages between towns and cities and also played a vital role in time synchronisation.

Mechanics

Shutter towers are mechanical signalling devices. When combined in a line, they form a visual telegraph system that can convey messages over long distances. Shutter towers were primarily used to transmit information between cities.

Origin

Visual telegraph systems were first developed in France by Claude Chappe and his four brothers. They were soon utilised and adapted by the British into shutter towers that use six black-and-white mechanical panels.

Usage and reach

Shutter towers were used in England during the late 1700s and the early 1800s.

The British Admiralty used shutter towers to communicate between:

• The Admiralty, London, and Sheerness (which opened in 1796).

• The Admiralty, London, and Deal (which opened in 1796).

• The Admiralty, London, and The Glacis, Portsmouth (which opened in 1796).

• The Admiralty, London, and Plymouth Mount Wise (which opened in 1806).

• The Admiralty, London, and Great Yarmouth (which opened in 1808).

The Admiralty's London shutter telegraph system consisted of 63 tower stations. Interestingly, the number of different signals that can be conveyed using a six-panel shutter tower is also 63.

2^6 - 1 = 63

Speed and obsolescence

On a clear day, information could be conveyed at speeds between 3,000 and 7,200 kilometres per hour, depending on the distances between towers. The towers were, at worst, 300 times faster than a relay of riders on horseback. However, the system was very costly to run and was eventually surpassed by semaphore towers (which used arms instead of shutters), and later the electric telegraph.

I drew this map because the historical information was fragmented. The map is based on details from The Old Telegraphs by Geoffrey Wilson, The Semaphore by T. W. Holmes, Military Signals from the South Coast by John Goodwin, and conversations with Paul Taylor (Curator of the Chatley Heath Semaphore Tower, Chatley, England).

The image shows a miniature prototype that acted as a proof of concept. The towers represent the shutter telegraph and the contour maps, situated between the towers, represent the green fields of England.

The image shows a tower prototype.

The image shows floor plan layout.

The image shows floor plan dimensions.

I hoped that each tower would have six identical panels, as per the original design. However, technological constraints of the ARToolKit (the software) meant that each panel needed to be different. To work within this constraint, I added minor marks to the panels. These resemble the arms used in the semaphore telegraph system (the communication method that superseded the shutter telegraph).

The 2D oscillating animation presented unique design complexities. To prevent art viewers from becoming disorientated, nauseous, or dizzy, green stripes were used rather than a large field of oscillating green. This ensured the viewer could maintain orientation by seeing the ground underfoot.

The Semaphore installation has three shutter towers. The art viewer dons an augmented reality (AR) headset, positioned at the central tower, as if they were the ‘Glassman’.

Historically, the Glassman would use a telescope to look up and down the shutter-tower line to see whether a message needed to be relayed to a neighbouring tower. If a message required relaying, the Glassman would tell the ropeman which shutters to operate. Finally, he would double-check that the next tower had received and transmitted the message onwards correctly.

When the art viewer looks at the towers they see 3D animated ones (capsules) and zeros (tori), symbolising packets of binary data in transmission.

When the art viewer looks at the contour maps on the ground they see 2D oscillating green lines representing the green fields of England, viewed from the perspective of photons in transmission.

TV3 covered the story in a news broadcast.

View broadcast here.

See what one viewer saw through the headset

To make the Semaphore installation possible a number of people were involved. I would like to give my many thanks to the following:

• Dr. Mark Billinghurst (Head of HIT Lab NZ, University of Canterbury, New Zealand)

• Dr. Raphael Grasset (HIT Lab NZ, University of Canterbury, New Zealand)

• Hartmut Seichter (HIT Lab NZ, University of Canterbury, New Zealand)

• Professor Tony Brooks (Aalborg University, Denmark)

• Professor Desmond Rochfort (Head of Fine Art, University of Canterbury, New Zealand)

• Paul Taylor (Curator of Chatley Heath Semaphore Tower, England)

• Tim Stankus (Royal Signals Museum, Blandford Camp, Dorset, England)

• Richard Taylor

• Jane Zusters