Photogrammetry: if a picture is worth a thousand words, what are 40,000 worth?

18/04/2024

UKAHT is undertaking a programme of digital data capture across its Historic Sites and Monuments. Our XR Producer Lesley Johnston tells us about her latest work at Detaille.

On a small island inside the Antarctic Circle, one dedicated conservation camera was working overtime, all the time! Over one month, three buildings and twenty-three rooms, this camera captured thousands of photographs per room or building! 

In total, I captured just shy of 40,000 photographs which take up 1.35 terabytes (TB) of hard drive space. If I printed all of my photographs and laid them out end-to-end, they would stretch ​​4.6 miles (7.4km) and take up 36.25 sq km – an area roughly the size of the city of Cambridge where our UK office is based. 

Photographing inside Detaille (Credit: UKAHT/Lesley Johnston) 

This year, photogrammetry was an important component of the conservation programme at Base W, Detaille Island. Photogrammetry is the process of taking many, many, many overlapping photographs of a subject – an object, structure or space – and then running those pictures through specialist software that stitches the photographs together like a big three-dimensional jigsaw, creating a digital 3D model, a spatial model if you prefer the more technical lingo.

Spot the difference (Credit: UKAHT/Lesley Johnston) 

Is a 3D model worth 40,000 pictures?

There are many reasons to undertake photogrammetry. For starters, it’s fun and anyone can do it but that's not what motivates us here at UKAHT. Our sites are, generally, inaccessible, often even to the UKAHT team. It also costs a lot for us to get to our sites and, as we are a charity and rely on the generosity of our supporters, when we do visit, we like to get our money’s worth. Doing photogrammetry on site means: 

• We have lots of reference images for future years. 
• We have spatial, 3D models that can be scaled and measured to support our conservation team’s planning of future works.
• We can share our sites and our work with you! 

A 3D model of Base E, Stonington Island (Credit: UKAHT/Lesley Johnston)

We could just share normal photographs with you or splash out on a 360 camera I hear you say, well, we took images using traditional and 360 techniques too! But you can’t change perspective in a 2D photograph or walk through a 360 image. With photogrammetry, we might make a virtual tour, or a historic Detaille VR experience embellished with sound and artefacts, but before we dash into the future, let me tell you about photogrammetry ‘in the field’ via some questions that might have popped through your mind.

So… you only need a camera to make the photographs to make a 3D model? 

Sometimes, you definitely need the photographs, but you also need a subject that plays nice. Photogrammetry doesn’t like surfaces that are too shiny, like the glossy paint that our buildings are often coated with. And you can’t take photographs in the dark, Detaille has a loft and dark room that are, well, dark! So sometimes you need something to stop the light coming in the window and other times you need to add light. Getting creative on how to resolve these issues is part of the challenge of a task that is part art and part science. 

Lesley at work at Detaille (Credit: UKAHT/Lesley Johnston)

It's easy though, right? They’re just photographs.

They are just photographs but to get a good quality model out, you need to put good data in, and as much good data as possible! That means no motion blur and the highest possible depth of field (your best friend is your tripod!). You can’t underexpose or overexpose and once you’ve taken that perfect picture, you must take one step to the side and start again!

Lesley at work at Detaille (Credit: UKAHT/Ruth Mullett)

Do you only need one person for photogrammetry?

I was the only photogrammetrist this season but I didn’t work alone. Everything in Antarctica is challenging and needs teamwork. I couldn’t have done my job without coordinating daily with the conservators and carpenters on where we’d all be working to give each other enough space and time to work. 

Working together: before and after the bunk room was cleared (Credit: UKAHT/Lesley Johnston)

Photogrammetry also captures the room like a snapshot and you need space to move. The capture wouldn’t have been possible without the entire operations and field team clearing our conservation equipment and food out of the way to get each room looking as spick and span as possible! 

Lesley is UKAHT's XR Producer (Credit: UKAHT/Ruth Mullett)

– Lesley Johnston, XR Producer