Direct PDF download link for Mallison and Wings 2014

I keep getting emails requesting a PDF of the paper I wrote with Oliver Wings (link to blog post) on how to do photography for photogrammetry. That’s because the download link on the journal’s web page of the article is so well hidden that most people miss it.

Well, here it is!

Can you find it on the web page? It’s where it says “JPT No12”😉

Posted in Open Access publishing, photogrammetry | 3 Comments

Photogrammetry tutorial 12: How to preserve strike and dip or cardinal directions in your 3D model

Photogrammetry is a really nice and easy way of surface digitizing specimens in collections, but also useful in the field. Recently, Marie Attard, a colleague working in England, asked me to help with a project that deals with rock surface shapes. I don’t want to say too much, but this I can tell: she wants to capture rock surfaces on cliff on which birds lay eggs. Obviously, in this case, it is not only of interest what the surface shape is, but also what the surfaces tilt is in the field: is it level, or does it tilt toward the cliff edge or toward the cliff wall? And while you can simply use a geological compass to measure this, write the info down and be done with it, wouldn’t it be nice if the same info is also included in your 3D file?

If you follow the tutorials I previously posted here, you’ll be using long scale bars placed around and maybe even on your specimen for scaling. These scale bars will usually rest on the ground or table under your specimen more or less horizontally, but they are not useful for “leveling” your model. Well, they kinda are, and there is a neat trick for how you can make a model come out right-side-up (roughly), but that’s not good enough for the bird nesting site thingy.

So, Marie and I thought about this a bit, and soon came up with an elegant solution, one that actually does a bit more than we aimed for! Here’s how you

Preserve strike and dip of a surface in a Photoscan model

First of all, you best use a special kind of scale bar. It should be L-shaped, and for convenient in-program marker placement in Agisoft Photoscan it should have three of the automatically recognizable markers printed on the ends of the two arms of the L and at their meeting, with the distances between them known exactly. Here’s how they can look (screenshot of print file created by Marie Attard)

Lshaped scale bars

(As you can see, Marie ingeniously also added a label at one edge saying “cliff edge”. In the field, you simply align that side of the scale bar with the cliff edge and already you have preserved the information of the cliff edge’s strike in your model. This means that you can’t preserve the geographic direction using the same scale, though. You then need two scales)

So how do you use such scale bars to preserve strike and dip of a surface? First, you place one scale bar flat on the surface. Then, you put a compass on it, aligned with the edge of the scale bar, and rotate the entire thing until the edge points due North. Now, you level the scale bar. If you use a geological compass, or any other that has a round precision bubble level, you can use that. However, I personally find it easier to use a tool that you can buy cheaply for e.g. caravans: two combined bubble levels.

Tlevel

Putting this on the scale bar you now need to level it by shoving tiny pieces of cardboard or so under it. That can be a bit of a bother, and Marie came up with some ingenious solution: she bought a mini tripod on which she mounts the scale bar. Either way – once the scale bar is level, you start taking your photos of the surface as you normally would. If you wish to preserve some other information, e.g. the cliff edge direction mentioned above, you can use a second scale bar aligned with it.

Then, once you have taken the photos you need for scaling the mode, you remove the scale bars and proceed to take your photos for model creation – otherwise your 3D model will have the scale bars in it.

And all the rest is done in Photoscan!

Align your photos normally, including the scaling images. Remember to make them inactive afterwards, so that they do not contribute to the dense point cloud and thus the 3D model. Now, let Photoscan detect markers, or manually place the markers on the scale bars on your images. Make sure, if you do this manually, to name the in-program markers so that you recognize them properly.

Now, create your scale bars in Photoscan, scale the model – all as you would always do it.

Finally, go the the “markers” section of the reference pane. Here, you will find all your markers, and here you can set world coordinates for them. The marker at the meeting point of the two scale bars that form the L gets the coordinates 0,0,0, the two others get the same plus the respective length of the scale bars added to the X for one and the Y for the other. Click UPDATE and voila, your model is level!

Obviously, you can preserve any direction in the field by placing a scale bar edge along it. It need not be due North, it can also be a cliff edge, or whatever.

 

 

Posted in Digitizing, How to, photogrammetry | 2 Comments

Making Mike Taylor gloriously green-eyed

It has become a bit of a tradition that I use this blog to make Mike Taylor of SV-POW! (and much other) fame a tiny bit jealous. By posting photos of the Museum für Naturkunde Berlin dinosaurs, for example a selfie with the skull of the Giraffatitan mount, or from other unusual perspectives – photos a normal visitor can’t ever take, and photos Mike (despite getting better access as a researcher) didn’t take during his short Berlin visits. His real-life job has given him far too little time to come visit. Still, the MfN Berlin dinosaurs have featured prominently on SV-POW! again and again. In fact a very special bone, the 8th cervical of Giraffatitan individual SII featured in the very first post there.

Mike, aside from being a very esteemed colleague in the same league as Eric Snively, Larry Witmer, Matt Wedel, Andy Farke, “Dino” Frey, Aki Watanabe, Michael Pittman, John Hutchinson, Viv Allen, …..    oh, jeez, I better stop before this becomes a ten page list of cool people in paleo!
Anyways, Mike is not “only” a really cool colleague and (American-style) friend, but also someone I personally trust in the way Germans trust their friends (which is on a totally different level than a US-style friend).

Given the affinity of Mike for the Giraffatitan‘s 8th cervical it is, I guess, especially suitable for making Mike all green-eyed. After all, while it was on display in 2005, today it has a new number (MB.R.2181.47 or MB_R_2181_47 in the computer-palatable version), rests in a wooden box in the bone cellar, inaccessible and hidden from view, and gathers dust – except for Wednesday two months ago. On that Wednesday, it was moved out by the MfN preparators to the hallway, and the sides of the wooden box were taken off, and the sand bags that stabilize the vert were taken away. For this:

Obiwan

3D SCANNING!

Artist Alicja Kwade wanted high resolution scans of various bones, and for this very special occasion the museum OKed access. Alicja payed for the scanning of several vertebrae and ammonites by a professional surveying firm, matthiasgrote PLANUNGSBURO. Now, a lot of people have told me that they know some firm or other, and that said firm will quickly create perfect scans. A lot of people simply buy an expensive scanner, know roughly how to handle the software that comes with it, and them call themselves “experts”. Well, typically I have these conceited scanning “expert” for breakfast…… but not these guys! I was very impressed by their knowledge and experience. They know exactly what they are doing, know how to work to order (e.g., not creating a model at far too high a resolution, which means unnecessary cost), can do top-notch models if needed, brought a wide range of tools, all of which they knew exactly how to employ – it was great fun and quite informative to see them at work! And both the boss, Mr. Grote, and his two employees are very nice people, with whom I had some fun conversations.

Still, any such opportunity to scan difficult objects is a challenge for me, and this is especially true when someone else is scanning the same object at the same time! Can I scan as fast, as accurate, as detailed as them? Can I predict my data capture time and scan resolution and accuracy accurately? Does my data capture approach work at all? In short, can I hack it? I have recently become pretty cocky, given the success of the digiS bone cellar project‘s success, but that concerned rather simple bone shapes. This time, as I quickly saw, I was pitted against the elite of 3D scanning, and the specimens were of an entirely different level of complexity. Not that I expected the experts to beat the resolution of the model I was going to try and make with the scan they needed to do for Alicja – theirs would be for rapid prototyping on a CNC milling machine, and therefore of limited resolution, whereas mine would be aimed at way-more-then-enough for all science and exhibition uses I can currently imagine. But , knowing how scanning people tick, I was expecting them to additionally go for a top-notch scan anyways, going way beyond the ordered level of detail and resolution. And given the tools they brought and their expertise, I must admit that I was a bit afraid of working too quickly, taking too few photos and ending up with a model that has errors or big gaps, and compared badly to theirs.

In the end, as the photo above shows, along with an Artec Spider scanner they did bring the Big Gun – the Faro ScanArm with laser scanner. And they did go for a very high resolution and high accuracy scan. Which means that my best scan would have to measure up to a really excellent scans by them……. *gulp* I was quite a bit tempted to forego my usual happy-go-lucky high-speed scanning routine for a calmer, more thorough approach, maybe even using a tripod, simply to make sure that I drive quality up as high as I can. But then, the comparison is only fair if I stick to the same effort expended and use the same tools that I normally do!

So, they scanned with the Faro Scanarm and an Artec Spider scanner, and I used my trusty old Canon EOS 70D with a cheap LED ringlight. No tripod, no extended scan planning. Just my usual happy-go-lucky approach.  Several vertebrae were set out on the work table in the Bone Cellar – not much room to work in, but sufficient for the artec scanner and my camera. The huge cervical 8 of Giraffatitan was moved to the hallway outside the bone cellar to allow better access with the Faro scanner, as can be seen in the photo above. And there it was that I went at it with my camera.

Overall, I took 754 images, the first 20 with scale bars placed all around the bone, the rest overview and close up photos without scale bars. Here’s one of the former:

overview image with scale bars

The scale bars use the pre-made markers that come with Photoscan, so that the software can automatically detect them. This time it worked like a charm, saving me quite a bit of time. Matteo Belvedere is to be thanked for fighting with Photoshop to create the file from which we had the scales printed – thank you very much, Matteo! I used a bunch of 0.5 m scales, because scales half as long to slightly longer than the specimen you scan are best: they provide the least proportional error without causing extra work capturing them. And I must say that the resulting accuracy is pretty pleasing! Below you can see a screenshot showing the scale bars and their respective errors:

accuracy

note that the average deviation between the scales, each 500 mm long, is less than 0.33 mm, i.e. less than 1/15th of a percent😀 Photogrammery FTW!

After taking the scale bar photos I removed the scale bars from the bone. The same process – removing the photos with scale bars – I later repeated in the Photoscan project file, after alignment: I made the images unavailable for model creation. This way, they are there for scaling, but are ignored for construction of the dense point cloud, and do not litter the model. Because of this approach I can place scale bars ON the bone itself, instead of just around it, which gives me more flexibility. In some cases, like digitizing trackways, placing the scales on the specimen you wish to digitize is the only way to place them, so remembering the trick of using them for alignment and scaling but blocking them later is helpful.

The additional 734 photos fall into three distinct categories:

  • images I took while “rastering” the bone
  • images where I deliberately pointed the camera into recesses and at other difficult points
  • overview images

The first category obviously is necessary to deliver a model that shows the entire bone at high resolution. I makes up about 1/3 of the total, because the photos need to overlap quite a bit. The second category makes up more than 1/3, not because I really needed that many (despite the plethora of deep, air-sac-caused depressions in the bone), but because I took way too many images, to make sure that I had enough to cover all the many nooks and crannies. Better having too many photos resulting in extraordinary calculation times than ending up with a model with unnecessary holes! Last but not least, the overview images are necessary to guarantee a good alignment of the other images. Yes, you can omit them, but if you take a series of images down one side of the bone and another up the other side, there is a high risk that your model will “warp” a bit. Overview photos keep this in check.

Rastering is best done by doing one set of photos with the camera pointed at the center of the specimen, then (for complex shapes like verts), another with the camera tilted left by ca. 30°, and another with the camera tilted right at 30°. Or up and down, depending on the shape of your specimen and how you place it. Or all of them – up, down, left, right….. and so on. Here, I made sure I used “straight”, “left” and “right”, as well as “up”. “down” images weren’t needed as a separate set, because of the geometry of the vertebra.

Then came the “recesses” part, which basically means pointing the camera at the midpoint if a hole, then moving it on the surface of an imaginary sphere but keeping it pointed at the same location. I did this for every single freakin’ depression….. *sigh*. I much prefer proper titanosaurs; they relocated their air sacs into the bone and have rather smooth outer bone surfaces. Much easier to digitize!

All in all, I spent 45 minutes and 21 seconds on photography, which does include a short 20 meter walk to a door and back to let some people in, as well as the time required to pick up and toss aside the scale bars. Divided by 754 images this means I took a photo every ~3.6 seconds. That may sound impressive, but it is actually slow work for me. Usually, I just aim the camera by eyeballing the brightness of the ring LED light on the bone. In this case, however, I felt the need for a more thorough approach, and used the 70D’s twistable touch live view screen to aim the camera and select the focus point. Usually, I achieve photo rates of 0.8/s, not .02777/s, but the live view screen makes shutter release slower, and the process of taping the screen each time to select the focus point and trigger the camera also is slower than simple blind point&shoot. Still, if I can’t easily go back and re-shoot a specimen, I’d rather spend more time and make sure I can guarantee a good model.

So, did all this effort give me a model I can be proud of? Can I hold my own against one of the best scanning crews out there? I can’t really judge, because I haven’t seen their models yet, but on the other hand I believe the results speak for themselves:

details

Yes, you read that correctly: the model has, in the highest resolution possible, some 484 million points in the dense cloud! Meshing a tiny part of itdelivers a 80+ million polygon mesh!

dense cloud

This is the full dense point cloud in all its glory! Note the hole at the bottom, where the vertebra rests on a plaster support made to fit. No way was anyone going to lift the vert up so I could take photos of its ventral side. It is way too heavy and fragile! We have very accommodating collections curators and managers at MfN, but lifting this bone is way outside anything they would ever consider – and rightly so! And a close-up – click for full size:

dense cloud close-up

This area is less than 15 cm wide… oh yes, the resolution is amazing🙂 Now let me show you the mesh…… below is a total of the dense cloud with a small part I meshed right away superimposed. Note that I did NOT yet clean the dense cloud at this stage, which is why there are ugly black rims on top and so on. The meshed area resulted in >80 million polygons, here decimated to 1 million.

dense cloud with mesh

and a zoom-in on the mesh (with slight smoothing):

mesh

yes, that hole you see is real! The bone really is that thin🙂 I put two markers on the two sides of the neural arch that the mesh happened to cut. You can use Photoscan as a measuring tool by simply scaling a model creating markers and a scale bar from them, setting it to length 0, and checking the error – that’s the length of the scale bar (assuming you scaled your model correctly before). The thickness of the bone is really just

mesh

~4.569 mm! And despite the enormous size of the specimen, my happy-go-lucky model managed to keep the two sides consistently separate, except for the spot where there is a real-life hole in them, too:

hole in bone

So, overall, I am *very* pleased with my results! I haven’t seen the scans by Grote yet, so I can’ really say how I measure up against them, but I have once again been able to capture a very high detail model of a difficult object with simple, affordable and mobile equipment.

So, Mike, here it is now in all it’s glory – or should I say, in a small percentage of all its glory? As this is only a 74 million polygon model after clean-up, and if I ran this at ultra high resolution I’d expect it to have around 600 million. It is detailed enough, though, as it is….

mesh
click to embiggen

mesh
click to embiggen

Posted in digiS, Digitizing, Dinopics, Dinosauria, FUN!!!, Giraffatitan, MfN Berlin, photogrammetry, Sauropoda, Sauropodomorpha, Tendaguru | 1 Comment

“Liberation from the Bone Cellar” – a progress report

Here’s a short update on how my digiS 2015 project is coming along. Yes, 2015 is still running, due to a bunch of unforeseen circumstances a huge theropod sticking its ugly skull into my affairs and demanding to be photogrammetrized in a big hurry. digiS 2016 is also running, which means that I have about 50% of the computing power at hand that I need – ugh! Our IT is doing all they can to keep me happy, which is way more that their jobs dictate they should do, but they can’t work miracles. I am enormously grateful, and really hope that my work makes the higher-ups in the museum realize how excellent the support is IT gives researchers at the museum.

Now, where are we with regards to “Liberation from the Bone Cellar” – a project title not quite as tongue in cheek as it may sound, as the work conditions in the basement are really suboptimal enough to make many research approaches barely feasible that really should be easy in an ideal world.

Well, I am glad to report that things are finally chugging along nicely! Both my computer screen and that of my colleague Bernhard Schurian are usually populated with views like this:

batch process result

(click to embiggen for readability)

What you see here is a batch process file in Agisoft’s awesome Photoscan Pro. Each batch contains the photos taken of one bone (both top and bottom side), and we run an overnight batch process for photo alignment for all chunks. Then, we optimize the resulting sparse point cloud, scale the models, and run another batch process for dense point cloud calculation. Then, the results must be manually cleaned – after all, we do not want to have all kinds of background data in the files. The screenshot was taken just after cleaning of the dense clouds. As you can see, in this case there are 6 chunks, i.e. 6 bones. The second and third are marked inactive, which means that we had some sort of problem with them. Usually, what gives us trouble are photo sets that do not align perfectly, usually because we run the models with fairly low sample point ratios (max 10.000 per image). Instead of stopping work on the other chunks while we fix these problems, we typically just ignore them, finish the rest of the chunk, and then come back and deal with the problems. Usually, this simply means re-running the alignment with more sample points (40.000 or unlimited).

Each of the six chunks has been aligned, and you can see the number of photos per chunk, the number of resulting points in the sparse cloud, as well as the number of markers we already assigned. In the two chunks that have been expanded you can also see the number of aligned images each: in the first 169 of 175, but in reality 173 as the first two show the label, which equates to an alignment quota of over 95%, and in the second 163 of 165-2=163, a quote of 100%. Considering the free-hand photography at close quarters that we did this is a pleasing result🙂

You can also see the setting (Medium quality) and resulting number of points of the dense point clouds: over 7 and 9 million points, respectively. That’s way more than 99% of all science uses of the models will ever need, and in fact way more than 99% of all science uses can handle! I expect to get meshes with around 9 to 13 million polygons, and such big files are a bother to load. Mounting a full skeleton, or even just a girdle + limbs, at this resolution will crash most computers!

The key thing we are proud of you can see at the bottom left of the image: the average error between our scale bars. For the “small” bone fragment in the open chunk we used four scale bars, one of which is 20 cm long, and the other three are 25 cm long. The average distance between them in the model, which in an ideal model would be zero, here is 1.3 mm, i.e. slightly over half of a percent of the average scale bar length – and this is one of the worst models we produced (which is why I show you this one). Most have three zeros after the comma, not two! That is an amazing accuracy when you consider the far-from-optimal conditions in the Bone Cellar and the speed with which we acquire the data: I usually take less than 7 minutes per bone including transport!

So, overall, I’d call digiS 2015 an overwhelming success – for us, for paleontology as a whole, and for all our colleagues out there who want to quickly capture a lot of data during collection visits. While our photography method is physically exhausting, the results show that digitizing 10 to 20 big bones per day in collections is entirely feasible.

 

Posted in digiS, Digitizing, MfN Berlin, photogrammetry, Tendaguru | 2 Comments

a selfie (digiS2016)

I rarely take selfies. Mostly because I hate being photographed, but also because I do not see the need to show everyone in the world everything I do. Here’s one, though, that I just had to take, mostly in order to get Mike Taylor to swear at me😉

Giraffatitan selfie

I took this while working on my 2016 digiS project, when I was busy getting close-up shots of the neck vertebrae of the Giraffatitan mount. They are fiberglass, because the original bones could not be mounted. I still need a fairly god scan of them, so that once we scan the original bones in detail we can put the high-res scans into the place they should have on the 3D model of the mount.

Posted in digiS, Digitizing, Dinopics, Dinosauria, FUN!!!, Giraffatitan, Mammal pic, Mammalia, MfN Berlin, photogrammetry, Sauropoda, Sauropodomorpha, Tendaguru | 5 Comments

Digitizing entire dinosaurs 1 (digiS 2016)

Last year I received funding to digitize a lot of big bones of the Tendaguru collection from the Museum für Naturkunde’s Bone Cellar. This year, I was lucky to again secure funding from the digiS programme. This time, it’s for digitizing the mounted skeletons in the Dinosaur Hall, the mounts my esteemed colleagues M&M (Matt and Mike) called “a shedload of awesome“.  The reasons are fairly straightforward and simple: due to digiS 2015 we now have better digital access to the individual single bones from Tendaguru than to the partial skeletons of better preservation that form the largest parts of the mounts!

Now, that’s only true of a selection of dinosaurs in the hall. We already have excellent high-resolution models of the original material of Kentrosaurus and Elaphrosaurus, and of their (plaster) skulls. The models were created by David Mackie, then of RCI, who laser-scanned them one by one. You’ve seen the Kentrosaurus scans already, for example in my paper on range of motion of the skeleton, about which I should actually blog on of these days. The Elaphrosaurus models haven’t been used much yet, so here’s a link to a post with a bunch of photos of the mount.

So, for the digiS project, we’re mainly talking Giraffatitan, Dicraeosaurus, and Diplodocus.

hall_hdr

However, the project also aims to get models of the entire skeletons of all animals, not just bone-by-bone. Although such models must necessarily be of lower resolution – after all, each individual bone we scanned in the bone cellar leads to a model with usually more than 6 and up to 30 million polygons! – they offer the great advantage of showing the bones in articulation, as mounted. And that is something we do not yet have of both Elaphrosaurus and Kentrosaurus.

Obviously, I did previously try to align the individual Kentrosaurus bone scans into an articulated skeleton, the results of which did not only make it into the above-mentioned paper, but also served as the basis for a 3D volumetric model of the animal. That model was used for both my paper on Jurassic baseball batters from hell (direct link to paper here) and my paper on the effect that osteoderm distribution has on the position of the center of mass (not really much of an influence, it turned out). However, that skeletal pose was not an attempt to re-create the MfN’s mount’s pose, but just an attempt to get the bones correctly articulated.

So, how do I plan to get a low-resolution model that is good enough for one-by-one replacement of the low-res bones by the high-res laser scans? Well, in fact, that task has already been done🙂

Kentrosaurus 3D model rough

This is the dense point cloud of a photogrammetric model, made from 120 photos taken by my very capable colleague Bernhard Schurian. All images aligned with ease. The model has some 8 million points, but that number will shrink as I clean it. Here’s an overview of the camera positions:

Kentrosaurus 3D model w cameras

The limiting factor in model resolution here is not the number of photos but the resolution of the photos versus the size of the object on them. Simply put, at best you can expect to distinguish, as separate points, two neighboring pixels. Therefore, the bigger the object you model in your images, the higher the resolution. If you show an entire dinosaur the resolution is much lower than if you photograph only part of it. The higher resolution of the latter approach comes at the cost of having to take many more photos, though.

Vice versa, for a given view, the model will be of higher resolution the more resolution your camera offers. A 50 megapixel camera is much better than a 12 megapixel one. In this case, Bernhard used a Canon EOS 5DS R, which has a 50 megapixels sensor. This means that far fewer images are needed than in my previous attempts,  but it does not directly translate to shorter calculation times. After all, 2x 25 MPX is the same amount of point data as 1x 50 MPX.

For scaling we used a number of scale bars scattered all around the skeleton. You can see their digital representation in the images above as yellow lines. Each is 50 cm long, and the final error in the model between them is pretty stunningly low: 0.000998 m! Yes indeed: that is an average error smaller than 1 mm! Less than 1/25th of an inch for my US friends. Let’s interpret this to mean that each scale bar is around 2 mm off – for the length of the entire dinosaur this gives us a divergence of less than 1 cm. Color me impressed!

Kentrosaurus 3D model closeup

Now, one thing such a model is not, and that is perfect! The chance that the insides of bones are captured is virtually zero, as is true for the vertebral centra and, because of the many osteoderms in the way, the dorsal spines, and there always is a lot of floating nonsense data between the bones. The image above shows part of that cleaned up, much more work awaits😦 However, the external surfaces come out quite nicely in this model, due to the diligence of Bernhard, who made sure that all images are excellently exposed and perfectly in focus. Well, no surprised, he is a master photographer😉

Kentrosaurus sample photo

As a direct consequence, the software found features all over with ease: each point is a feature, each blue one is a feature the software was able to re-recognize on another image. The limit was set to a total of 40,000 points per image, and to 4000 matches between images.
Kentrosaurus sample photo w points

What’s next? Well, cleaning the model. Then I’ll calculate a polygon mesh, import that into the CAD program of my choice (Rhinoceros NURBS modelling for Windows 5.0) and start aligning the old high-resolution scans. I’ll show you how that’s done once I have the first few bones aligned.

Posted in 3D modeling, Berlin, Dicraeosaurus, digiS, Digitizing, Dinosaur models, Dinosauria, Diplodocus, Elaphrosaurus, FUN!!!, Giraffatitan, Kentrosaurus, MfN Berlin, Ornithischa, photogrammetry, Sauropoda, Sauropodomorpha, Stegosauria, Tendaguru, Theropoda | 2 Comments

some more pictures of Tristan the T. rex

T. rex maxilla

When Niels Nielsen, his brother and I sat down to plan the posture for Tristan we faced a few limitation. Obviously, the posture had to be biomechanically possible. We also wanted it plausible, i.e.: we wanted to show the animal in a pose that it probably used regularly, and not just some freak thing. Also, the room it is shown in poses some limits. It’s height means we can’t show Tristan sky-falling (as if we wanted to), and there is a row of cast-iron columns down the middle of the room, too. Additionally, there is only one entrance, so the skeleton had to placed in the hall in a way that allowed a circular path around it, with people coming in through one half of the big door and going out the other, separated by a mobile barrier.

It was quickly clear that neither Niels nor the museum wanted Tristan to be posed sitting down, mating, or jumping (not that I think the latter a biomechanically very feasible option anyways). As a standing pose is not very dynamic we were left with some sort of rapid locomotion pose. Because Tyrannosaurus was a poor runner, as has been amply shown, this left a slow run or very rapid walk pose. Which I guess 80% of all mounts worldwide show. In the end, after much playing around with different options, we decided on a running pose in which Tristan is taking a sharp left turn around a “tree” – one of the cast iron columns. However, Tristan has just noticed the tiny figure coming into the room (the visitor) and has swivels his head around. Decision time – continue going left or snap up the human for a snack?

T. rex
This is the view from the door, and as you can see the posture as mounted doesn’t match exactly the pose I described above. What happened?

In order to be able to plan properly I created a roughly scaled 3D model of Tristan. It is nothing but a quick&dirty photogrammetric model of famous AMNH 5027, with a 3D skull based on Stan (BHI 3033), scaled to match the expected size of Tristan. Additionally, I used floor plans and some quick manual measurements to recreate Saal 14 as a very rough model. I’ve shown this in the last post in one view:

Tristan_planning

here’s another one:
Tristan_planning
A top view of the hall, with colored arcs showing the field of view between columns from various points. Note how the tan one on the bottom left is planned to show the entire animal without obstruction in a right lateral view. I also made sure that the light green one gives you a chance to take a left lateral view photo in which the column in the middle does not hide the legs.

Also, note the quite strong lateral bending of the torso and the strong rotation between the long axis of the ilia against the torso and against the legs. In fact, the left foot, supposed to be at the very end of the support phase, is massively in-turned. If you draw a straight line over the metatarsus and toe three it roughly points just to the left (in the animal’s view) of the bottom column. The hips point slightly further left, whereas the right foot, just before midstance, points even further left. That’s a pretty typical pose for having made a strong left turn over the supporting (left in this case) foot and continuing over the other foot. Once the posterior foot lifts off it should immediately abandon the in-turn.

As mounted, Tristan shows the intended lateral bending of the torso. For reasons unknown to me, however, the right hindlimb and hip were mounted without the strong left-twist, and the left foot was kept in-turned despite having been altered to be posed just after toe-off. Therefore, it should actually have been moved to point more forward rather then inward. As a consequence of the rotation of the hip out of the planned position, Tristan’s tail tip now is a lot closer to the wall than intended, and the pose looks less energetic. Additionally, for a bunch of reasons, the skull is not turned to the right quite as much, so that Tristan’s nose isn’t pointed exactly at the door. The pose is still quite dynamic, but my pre-planned side-view photo location is ruined, because now the skull is rotated so that it is seen in posterolateral instead of lateral view.

Another view does work out pretty well. If you come into the room, turn left and walk around, then pass the row of columns again at the back end of the hall, you can look right and see this:

Tristan_planning
Peekaboo!
In fact, this is intended as a quote of the Allosaurus cast mount in the dinosaur hall, which has its head stuck out into the entrance hall (where the head is fleshed out, whereas the rest of the animal is shown as a skeleton). The Tristan mount is quite a photogenic thing from this position, as you see the neck and skull against a bare wall as background, quite uncluttered.

Tristan’s real skull is exhibited “like a jewel” (as a radio station put it today) in a glass cage at the end of the hull. There are no non-glass supports at the corners, and the entire hall is dark (therefore hardly anything reflects on the glass), so that the visitor’s view of the huge jaws is practically unhindered. Discreet spotlights give enough light to see the bones well without putting big highlights on them.

Tristan_planning

In various places around the hall the exhibition team placed see-through screens on top of steles that carry text placards posing the research questions we will try to investigate. Onto the screens beamers project videos with text and film. Much of that is…. well, I’d say it is more funny than scientifically pleasing. The extremely short preparation time meant that we had to use a lot of stock imagery, with the predictable result that the motions of animals look rather horrible. Bouncy, floppy, physically impossible – you name it. Still, the short presentations summarize our knowledge and proposed research quite well. Deplorably, however, they also include videos of the researchers, filmed (obviously) with the help of greenscreens. Those bits are kinda cheap-looking, and in fact pretty hilarious! I, for one, was asked to walk quickly on a treadmill, and the video now shows a T. rex coming after me. However, the treadmill (obviously) had no rail to hole on to and was uncomfortable short for someone my size. Also, they kept telling me to look over my should at a Rex that wasn’t there – and the combined video places it in slightly the wrong position relative to me to make things work. I had a good laugh when I saw the final sequence. It is kinda nice, though, that you can see Tristan through the screens, as long as the presentation isn’t too bright.

Tristan_planning

Your truly not-running from a fat, transparent, flollopin abomination of a stock-video T. rex.

Overall, however, I am very happy with the exhibit! Once again, the MfN exhibition people and graphics designers and all have done a masterful job! Add to that the extremely short timeline and all the mishaps along the way (like the skeleton arriving way too late, the replica skull getting done at the last minute, and so on) and it is a miracle that we could open on time.

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ROARRRRRR!!!!!!

 

 

 

Posted in 3D modeling, AMNH, Berlin, classic CAD, Digitizing, Dinosauria, MfN Berlin, photogrammetry, Theropoda, Tristan, Tyrannosauridae, Tyrannosaurus | 2 Comments

Tristan the T. rex is here!

And here he finally is: Tristan the Tyrannosaurus rex!

As of a few seconds ago the press embargo has ended, and I can finally show you all what a wonderful specimen I was press-ganged into living for allowed to work on during most of 2016.

Tristan

click to embiggen; image by Carola Radke, MfN Berlin. © Carola Radke.
Tristan in left lateral view.

Tristan is a loan to the Museum für Naturkunde by Danish businessmen Niels Nielsen and Jens Peter Jensen. Actually, its full name is Tristan-Otto, after the sons of Niels and Jens Peter. The story of how the two businessmen came to loan the specimen to the museum has been dragged through the press repeatedly, and will be repeated a few more times. Therefore, I’ll rather focus on how things unfolded for me, and show you all the wonderful photos I took of the specimen and the dig site visit and so on – all the photos I had to keep secret for so long.

It all started for me on January 3, 2015, with an email from MfN-director Johannes Vogel – he of the luxuriant mustache and Darwin relations. As the email was sent in the evening and as I had (atypically) turned off the ringer on my cell phone, I read the email on January 4, and for a split second got confused with 1/4/2015 and 4/1/2015. After all, this just had to be a hoax:

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Posted in digiS, Digitizing, Dinopics, Dinosauria, MfN Berlin, photogrammetry, Theropoda, Tristan, Tyrannosauridae, Tyrannosaurus | 15 Comments