Tag Archives: Prosthetic

Experiments in Photogrammetry

Recently we experimented with producing a set of 3D models of items from the collection using a process called photogrammetry. Rose Attu, a Digital Humanities MA Student from UCL, who’s currently on placement at the BPMA, talks us through the process.

To create a 3D model a series of overlapping photographs of a single object are taken from different positions, and then a piece of software is used to triangulate the coordinates of each image and align them, reconstructing the whole object in 3D. With each shot, the digital camera also records metadata including the focal distance between the lens and the object; this enables the software to recreate the position the camera was in when each photo was taken.

Curator Emma Harper holding the stamp snake

Curator Emma Harper holding the stamp snake

The objects we chose were the prosthetic Postman’s Hand and the Stamp Snake. An object covered in a repeating pattern, or one without any distinguishing features at all, will affect the software’s ability to rebuild the depth of an object. Both these objects have plenty of distinctive features, so the software could detect the details from photo to photo and build accurate models without distortions.

Postman's prosthetic hand being photographed

Postman’s prosthetic hand being photographed

Our first object was the Postman’s Hand. Once it was in frame and in focus, and evenly lit to avoid shadows, we could begin the capture process. To capture our objects from multiple angles we used a turntable to rotate them through 360°. The turntable was also covered in a distinctive image, which gave the software more common points to identify. The turntable was edited out at a later stage, so that our final models were just of the hand and the stamp snake.

Stamp snake being photographed

Stamp snake being photographed

On average it took 30 photos to complete one rotation, after which the camera was raised for a second sequence capturing the object from a higher angle. For more consistent results we kept the camera settings the same until a rotation was complete, and used a tripod and remote shutter release to keep the camera static. We output the raw image data as a set of TIFFs and corrected the white balance, and then our images were ready to be transformed.

Based on the estimated camera positions and the details in the images, the software built a point cloud, which is essentially a 3D model made up of dots. It then added a more detailed polygonal mesh layer representing the object surface. The final step was to add the textures; because we photographed our objects in high resolution, even the tiniest details were visible on the final models.

Snapshot of the 3D model of the stamp snake. Manipulate the model on Sketchfab.

Snapshot of the 3D model of the stamp snake. Manipulate the model on Sketchfab!

We were surprised with how little effort and technology it took, and the results were fantastic!  For our set-up we used:

  • Lazy Susan turntable with a nonrepeating pattern on it
  • Digital SLR camera and tripod
  • Light box or tent
  • Studio lights or some source to help get rid of shadows
  • Photogrammetry software – we used Agisoft which was great and you get a 30 day free trial

Have a go yourself– we would love to see your models!

– Rose Attu

My Favourite Object: Prosthetic Hand

Asking a Curator to choose their favourite object is like putting a kid in a sweet shop and then telling them they can only have one! In fact, some of you may remember that I shared my favourite object with you last year, a truncheon issued to Post Office employees before the Chartist riots of 1848. Today however my favourite object is a recent acquisition of a Postman’s Hand, which is not quite as sinister as it sounds, I promise!

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Prosthetic hand with letter

 

Besides all the pun based opportunities this object has provided (for the last few weeks I have been constantly asking my colleagues if they need a hand with anything…) it is actually a very important addition to the BPMA’s collection, as it reveals an often hidden aspect of history.

The hand in question is not a real one but is made of wood covered with leather and has an adaptor to fit it into the wrist unit of a prosthetic arm. Some of the earliest prosthetics in history were also made of wood and leather but this hand fits into the advanced development of prosthetic limbs that occurred after the Second World War to aid rehabilitation of the many soldiers who had limbs amputated as a result of the conflict.

Postman's hand on adaptor to fit a prosthetic arm.

Postman’s hand on adaptor to fit a prosthetic arm.

The Post Office as an employer has always made a concerted effort to advance employment opportunities for disabled people, including veterans, as has been shown in previous posts and this was particularly so after the Second World War. Hands like this were in use from the 1950s through to the 1970s – this example bears its date on it ‘4/11/64’ – and were designed to hold letters. What is particularly revolutionary about this object though is that it has a roller, or wheel, under the thumb which allowed one letter to be removed while still keeping grasp of the others. This enabled disabled employees to sort letters with greater ease and efficiency than with the previous, more basic, prosthetics. Feeling the hand it is quite heavy and it has made me think what it would have been like to use.

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Profile of hand

 

This object was kindly donated to us from the Limb Fitting Centre at the Queen Mary’s Hospital in Roehampton, which was founded to care for soldiers wounded in the First World War, and has since become renowned as a limb fitting and amputee rehabilitation centre. They were able to tell us that the hand had been developed by Hugh Steeper Ltd, major manufacturers of prosthetics at the time. This was the only remaining postman’s hand at Roehampton and it was returned to them by a retiring postman in the early 1970s.

As you can see the BPMA’s collection is constantly developing and this object adds to our knowledge of an important part of our history which is relatively under-represented. It is fascinating objects such as this that will form the bedrock of the new Postal Museum but they are nothing without the stories of the people who used them. If you have a story to share please email us at peoplespost@postalheritage.org.uk and help us achieve our ambition of filling our brand new museum with the voices of real people. Thank you!

-Emma Harper, Curator