Illustration talk slide 9

Illustration talk slide 10

Illustration talk slide 11

Illustration talk slide 12

That link in the first slide will take you here, and the rest of the series is here.

Recently I had the opportunity to give a talk on photographing specimens and preparing illustrations in Jim Parham‘s phylogenetics course at Cal State Fullerton. Jim is having each student (1) write a description of a specimen, (2) run a phylogenetic analysis, and (3) do some kind of calibration on their tree. I think that’s rad.

Anyway, it was fun talk and I wanted to put it up for everyone, but Mike had the idea of posting a batch of slides at a time, to hopefully fire some discussion on different aspects of photography and illustration. So if you’re impatient to see the whole thing, blame him! I will post the whole talk at the end of the post series, and you can find all of the talk posts here.

And now, on with the show.

Illustration talk slide 1

Illustration talk slide 2

Illustration talk slide 3

Illustration talk slide 4

Illustration talk slide 5

Illustration talk slide 6

Illustration talk slide 7

Illustration talk slide 8

Here are two photos of what I infer to be C8 of OMNH 53062, the holotype of Sauroposeidon. The top one was taken by Mike during our visit to the OMNH in 2007. If you’re a regular you may recognize it from several older posts: 1, 2, 3. The bottom one was taken by Mike Callaghan, the former museum photographer at the OMNH, sometime in 1999 or 2000. I used it in Wedel et al. (2000) and Wedel and Cifelli (2005).

Sauroposeidon OMNH 53062 C8 photos compared

You’ll notice that the two photos are far from identical. In both cases, the photographers were up on ladders, as far above the vertebra as they could get, and there are still significant perspective effects. That’s just a fact of life when you’re taking photos of a vertebra that is 1.4 meters long, from anything lower than a helicopter. In Mike Taylor’s shot, the neural spine looms a little too large; in Mike Callaghan’s shot, the prezygapophysis looks a little too small, probably because it was curving off at the edge of the shot. So neither photograph is “right”; both distort the morphology of the specimen in different ways. Here’s how the two images stack up, with the outlines scaled to the same length:

Sauroposeidon OMNH 53062 C8 outlines compared

When I ran a draft of this post past Mike, he wrote (with permission to post):

I think the current draft misses an important point: the warning. We really can’t trust photos, however carefully taken, and however beautifully composited into TNFs*. You’re welcome to quote me as having said I’d have assumed the two C8s were different vertebrae. For that matter, I bet I could have worked up several taxonomically significant characters to distinguish them. Yikes.

* TNF = Taylor Normal Form, i.e., making multi-view photos like the ones here and here.

So the moral is, photos of big specimens almost always involve some distortion. This is clearly not ideal. But I have a plan for fixing it. I am hoping to get back to the OMNH this spring, and the next time I’m there, I’m going to take photos of this vertebra from a zillion angles and make a 3D model through photogrammetry. Happily, Heinrich Mallison has been producing a very helpful series of tutorials on that very topic over at dinosaurpaleo: 1, 2, 3, 4, with more on the way (I’ll update the links here later). Update: Don’t forget to check out Peter Falkingham’s (2012) paper in PE on making photogrammetric models with free software.

Armed with that model, it should be possible to produce a perspective-free lateral view image of the vertebra, to which all of the previous photos can be compared. I can’t use CT data because this vertebra has never been CTed; it’s too big to fit through a medical CT scanner, and probably too fragile to be packed up and shipped to an industrial CT machine like they used on Sue (not to mention that would require a significant chunk of money, which is probably not worth spending on a problem that can be solved in other ways).

So, photogrammetry to the rescue, or am I just deluding myself? Let me know what you think in the comments.

Finally, I should mention that the idea of superseding photographs with 3D photogrammetric models is not original. I got religion last week while I was having beers with Martin Sander and he was showing me some of the models he’s made. He said that going forward, he was going to forbid his students to illustrate their specimens only with photographs; as far as he was concerned, now that 3D models could be cheaply and easily produced by just about everyone, they should be the new standard. Inspiring stuff–now I must go do likewise.

Some previous posts on Sauroposeidon: