Review of the Antikythera Mechanism, 2D and 3D artefacts; a potential for an Augmented Reality project with a discussion about collection of dimensions for training in the making of a simple AR.

Reviewed by Isabel Garbayo and Michael Martin, edited by Krzysztof Bahrynowski.

27^th March 2013.

Have you ever heard about the Antikythera Mechanism? It’s an astronomical calendar which was built by the Greeks more than 2000 years ago. It’s thought to be one of the world´s oldest geared mechanisms! There has been much collection of its data of its dimensions that the Antikythera Mechanism has potential for an Augmented Reality modelling project. This would be an ambitious project but it would become interesting material for history and engineering classes.

In 1900 a Greek diver, Elias Stadiatos, found a shipwreck off the Greek island of Antikythera. Two years later archaeologist Valerios Stais discovered the Antikythera mechanism inside the ship! Initially he thought it was a rock with a gear wheel, but after closer examination it was found that it was a mechanism that was encrusted and corroded. After years of inspection, a science historian, Derek J. de Solla Price, developed the theory that it had been used to calculate the motions of the stars and planets. Two videos show how the data was captured from Antikythera Mechanism to make a 3D model. At first a special Hewlett Packard fixed camera was used to photograph with multiple flash guns at different angles to produce many photographs which were collated to give a photograph with depth. This allowed scientists to read more information in the mechanism.

Photograph of Hewlet Packard Camera used to collect data of the Antikythera Mechanism

 

In 2006 high-resolution X-ray tomography revealed the device’s true purpose: predicting celestial events and eclipses with exceptional precision!

The way that X-ray tomography technique works is by putting a fragment on a turntable, rotate the fragment in front of the detector and take it over 3000 different X-ray projections. Then the computer software will put it all together so you have 3D pictures!  From these images it can be seen that all the gears are packed together in layers, almost touching each other. They found 27 gears but probably in the complete mechanism there were 50 or 60 gears.

An X-ray camera took photographs as the mechanism rotates 360 degrees. From this data a 3D diagram was produced. The BBC video explains in greater detail the data capture. http://www.bbc.co.uk/news/science-environment-17989915 X-ray camera.

http://www.nature.com/nature/videoarchive/antikythera/ HP camera and X-ray camera. Discussion.

 

In 2010 a fully functional replica of the Antikythera Mechanism was built out of Lego. There were used 1500 Lego technical parts, 110 gears and it took 30 days to design, and build the model. This is the way the mechanism works:

A middle drive chain transfers power into two “wings”, each performing the same calculations as the original Mechanism. Each wing contains four gearboxes that perform one mathematical operation. The front set multiplies each turn of the crank by 47 and connects to a rear set, which multiplies again by 5/19ths. Using twice as many gears as the original Mechanism the math is easier to follow if we turn the gears backwards. These gears multiply by five and the set multiplies by three and divides by five. The differential gear combines the other two sets together making -19/5ths. Turning the gears forward again it becomes 5/19ths, which is a crucial figure for calculating the cycle of eclipses. Each gearbox does one bit of arithmetic and passes the calculation to the next box in line which eventually turns the needles on the front dials. And when the needles line up correctly they predict the time and date of a future eclipse: 8^th April 2024 16.30 hrs GMT http://www.youtube.com/watch?feature=player_embedded&v=RLPVCJjTNgk Lego video.

The archaeology scientists have produced beautiful animations and wish to produce a working model. The Lego animation on the video is 3D on a 2D screen.

Scientists hope to reproduce a full working replica with all the mathematical data available. It is hoped that the museum produces an Augmented Reality model that could be used by teachers and students to learn about ancient gear systems and this ancient calendar. It is remarkable that 1400 years passed before a similar working instrument was produced by Wallington.

With other mechanisms we envisage, with the help of scanned photographs, that it should be possible to use the cursor to measure details against a reference point (x,y,z).

 2D diagram obtained from visible and X-ray data.

 If the reference point in every scanned photograph is the same, in the future we should be able to produce individual gears, axles and mountings and assemble them in an Augmented Reality setting to learn how the Antikythera mechanism can be assembled and other geared systems. All we need is data about the thickness of the gears and length of the axles. This schematic could be used to make an AR model.

 

 

It seems that what we’ve thought about technology in ancient times is wrong. They did have the knowledge about how to predict celestial events and eclipses but for some reason the information was lost, say the scientists. It’s a real mystery how this information has been hidden for such a long time. Maybe 2000 years ago only a small amount of privileged people were able to access to this information and there were interests in not allowing others to do so. Possibly they kept it a secret so that when they died the secret went with them.

If you want to take a look to the Antikythera Mechanism and a reconstruction of it you must visit the National Archaeological Museum of Athens, 44 Patission Street, Athens 10682. There is a reconstructed model at the American Computer Museum in Montana as well.

In Joanna Pinewood Education we wondered about how measurements can be taken accurately from many photographs to make an AR model.  In 2012, inspiration came during photography of this simple Roman shape.

How to measure distances with only one known size?

 

Michael used the photo of ‘Maria’ on an obelisk taken from about 3 metres away.  The photo is then used to assess the size of the obelisk using ratios of the know height of ‘Maria’ at 1.73 metres.

 

Graphic programs like

‘Paint Shop Pro’,

Adobe ‘Photoshop’,

GIMP (an Open Source, free software, ‘Graphic Image Manipulation Program’) have rulers along the top and side of the ‘photo area’. 

By drawing lines against ‘Maria’s’ height we get the ratio of her size (metres) to the pixels (or centimetres or inches) of the photo.

 

GIMP has a ‘Measure’ facility, so one can draw the line and the program gives you the pixel value.

 

With our photo (top), ‘Maria’ was 381 pixels tall, the obelisk was 544 pixels.  The base or plinth was 417 pixels wide.  The capping stone (top) was 284 pixels wide.

 

‘Maria’s’ real height is 1.73 metres.

 

The ratio to get the obelisk height is ‘Maria’s’ real height, 1.73, divided by her pixel height (the only common measure) 381, multiplied by the obelisk pixel height, 544, which gives 2.47 metres.

 

 

 

Similarly, the base or plinth width is 1.73 divided by 381, multiplied by 417, giving 1.89 metres width.

 

The top capping stone width is similarly 1.73 divided by 381, multiplied by 284, giving 1.29 metres width.

 

This seems to be a simple way of obtaining fairly accurate width and height dimensions when only one measure can be easily obtained, ‘Maria’s’ height.

 

Engineers love accuracy and measure in mm.  Scientists measure in microns, nanometres and picometres.  

All adult learners need to be reminded that errors can be introduced with blunt HB pencils. A sharp H pencil is the tool best suited but few learners of school geometry are aware of this and introduce errors of + or – one mm with an HB pencil. Use of the measure facility in graphic programs would encourage better detail and disadvantaged learners who have motor neurone disorders would find this tool to gather measurements more fun.