Tuesday 23 April 2013

The Photogrammetrical Palaeontologist

I don't get out into the field anywhere as much as I would like to, and when I am out there I want to be sure I can record as much data as possible, as accurately as I can. In the past this has meant using tracings, drawings, field notes, measurements and photographs to record tracks*, the location of a specimen or if excavating a specimen, the site itself. All good techniques and methods no palaeontologist worth their salt is likely to abandon in the foreseeable future, but what if you could record field localities in a way that you meant you could analyse, share with colleagues and present them back at your workstation, with sub-millimetre accuracy and all the detail visible in the field? What if you could have a scaled-down, physical section of a partially excavated skeleton from your quarry to help plan the next field season? In fact, you could be sharing not just data from the field, but specimens from collections or that you're working on right now. In the past the tools for acquiring high-quality 3D data have often been expensive and not available to all workers; we can't all afford a luggable Lidar unit to record our quarries or outcrops. As the shiny digital future becomes everyday reality a number of imaging techniques are now being used to analyse 3D data from specimens and field locations on equipment we all have, such as laptops and mobile devices.

A large ornithopod footprint in the back garden of a collector on the Isle of Wight.
Not so easy to share with your colleagues across the world? You can with photogrammetry!

Photogrammetry is one of these techniques. Most palaeontologists and amateurs will already have the tools to practice photogrammetry in their field kit: a camera and a laptop. In fact, your mobile phone and an internet connection will enable you to produce reasonable quality 3D data very little time using free software, downloadable right now.

So what is photogrammetry? It's the technique of generating a 3D point cloud from a series of overlapping photographs and at it's most basic a mesh can be generated from a stereo pair, but in most cases more images are better. It is capable of sub-millimetre accuracy and can capture virtually any subject, including outcrops and objects in the round. Photogrammetry has several advantages over traditional techniques. As mentioned earlier most of us having the equipment needed as part of our regular field kit and  vitally photogrammetry is totally non-destructive and this is important when recording delicate fossils as well as tracks and traces as often a traditional technique (for example creating a mould) will cause some damage to the fossil as part of the process. The software used to generate the 3D data is free, multi-platform, open-source or relatively cheap and capable of excellent results.

Chirotherium footprint, textured 3D mesh.

One example of a photogrammetry workflow is as follows:

  1. Take overlapping photographs.
  2. Load into photogrammetry application.
  3. Generate a point cloud (the software looks for points on the various photos and these are assigned a point in 3D virtual space).
  4. Generate mesh and texture (if required).
  5. Output, analyse and share.

The 3D data has one huge advantage over traditional data: it's very easy to share. You could record a specimen in the field, generate a point cloud and the a mesh, save it into any one of a variety of formats read by a variety of apps. This data could then be emailed, uploaded and shared with colleagues across the world, all from your position in the field (provided you have internet access).

Another Isle of Wight footprint, this time a theropod track which some gooner has
tried to remove with a rocksaw. I recorded it using photogrammetry and did no damage at all.
An untextured 3D mesh.

This data has a wide variety of uses. The point cloud and mesh generated from it can be used for morphological analysis, measurements, false colour and contour analysis and light sources etc can be manipulated to aid interpretation. The meshes can also be 3D printed to bring the specimen back into the physical realm; want to have a scaled 3D version of that Allosaurus skull you excavated last field season on your desk? Use your photogrammetry data!

PG data also has potential as uses when publishing research, as stills in a paper and animations and meshes supplied as part of the supplementary data of papers. 3D works particularly well for outreach too, with animations and 3D video particularly useful for encouraging engagement.

So how to start in photogrammetry? Watch this space!

*You might notice this post is ichnology-centric. For that, I make no apology at all.

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