Structure from motion

Welcome to my blog. From the start of my PhD I was frustrated by three things. Firstly, there was a serious lack of high quality digital elevation models for most parts of the world, especially the places I was interested in such as mountain ranges. Digital elevation models are an excellent way of studying the land surface because they can help you map features like glacial landforms by identifying small details of the land’s surface. Secondly, it was impossible to capture the depth of a complicated object in a photo, such as the shape of a boulder or striations on a surface. Lastly, sketching geological sections in my notebook seemed to be a time-consuming and inaccurate chore. Later I’d have to digitise the sketch and hope my photos turned out well enough that I’d be able to remember what I sketched. It was like we hadn’t moved on from the 19th century when Darwin used notebooks on the Beagle.

Over time, technology has emerged which has gone a long way to solving my frustrations. Instead of waiting with crossed fingers while my photos were developed, we now have digital cameras that can record images in far greater detail. It is possible to take 50 photos from every angle of an object in only minutes. Increases in computing power mean my phone has more processing power than my PhD desktop computer had and my camera has hundreds of times more digital storage space. Lastly, clever programmers have written algorithms which make it possible to create a representation of a 3D object very quickly. This is done much the same way as the brain can interpret an object in three dimensions when it moves, giving it structure from motion. Software now exists that can take your 50 2D photos of an object and stitch them together to restore the 3 dimensions, as if you were still looking around the object in the field. The advantages of such an approach are obvious. Digital elevation models of landscapes can be made from any aerial photography, complex objects in the field can be recorded and distortion-corrected photos of geological sections can be generated. All of these approaches save a great deal of time and money whilst also making our observations more accurate. Structure from motion is reinvigorating the old science of geomorphology.

Most of my career has been spent working in the fourth dimension, not living a bad episode of Doctor Who, but trying to work out when something occurred in time or at what rate it occurred. For example, when in the past did glaciers form in the world’s mountains or how long does it take to weather a metre of rock off an outcrop surface? Combining the science of dating (geochrononology) with the science of studying the Earth’s surface (geomorphology) is a logical step. With these four dimensions you have a complete view of the evolution of the Earth’s surface. Structure from motion allows us to combine these disciplines in novel ways.

In this blog I will take you on a journey through my field sites, or places I’d like to visit, and show you what I’ve learnt, or what there still is to find out. I’ll usually post a 3D model from the site with its location and provide some commentary on its context. I’ll only go briefly into technical detail because there is a wealth of excellent papers and web resources devoted to those elements. I hope to introduce experts and novices alike to this fascinating world.

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