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

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.

Tristan_planning

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:

Continue reading

Posted in digiS, Digitizing, Dinopics, Dinosauria, MfN Berlin, photogrammetry, Theropoda, Tristan, Tyrannosauridae, Tyrannosaurus | 14 Comments

more Juramuseum & the Kulturgutschutzgesetz

The previous post about the Juramuseum was full of fish, although it did end with a few higher vertebrates. All flattened, though. This time, there’ll be more higher verts, and the spineless stuff will be in 3D! Let’s start with more dinosaurs, theropod dinosaurs to be precise. However,

Obiwan

so please be patient and watch this space next Wednesday :) Also, there is this German tapewormword Kulturgutschutzgesetz lurking at the end of the title. Thus beware!

Juravenator skull

This is a close-up of the skull of Juravenator starki (click to embiggen this and other images). It is an amazing little beast, and I love the teeth. But let me progress to what you likely are really waiting for: the Eichstätt specimen of Archaeopteryx lithographica!

Juravenator skull

Juravenator skull

This specimen is very small, and has an extremely good head, of which I have an extremely bad close-up photo:

Juravenator skull

For the sake of completeness, here’s the counterslab, too.

Juravenator skull

Knowing the Berlin specimen so well I was struck by three things right away: how dark the Eichstätt specimen’s limestone slabs are, how small the animal is, and how little the Juramuseum has done to make it stand out in the exhibit. It is just one of many specimens in a part of the exhibit that deals with birds and flights. There are a bunch of simple push-button experiments that try to explain how wings and feathers work in flight, there’s this display of different feather types:

Juravenator skull

and there are a bunch of models of the in vivo look of extinct dinobirds, too. Including a really huge one:

 

model

model

I didn’t take a pic of the label, thus I have no idea if this is supposed to be a Phorusrhacid or (more likely) Gastornis, and it is impossible for me to tell from the model. I’ve seen skeleton (casts) of terror birds and the Messel monster before, many times, and the always look amazingly big. Still, this model, which for once is not completely drab or exceedingly colorful, makes their size so much more real, especially the huge head and the sturdy feet – way cool!

Other models include Sinosauropteryx prima, Caudipteryx zoui and a Confuziusornis, all of which are also shown as casts. One can quibble about the feathers and colors and all of each of these, but overall I have seen much worse many times. These all do not look freaky.

models

Same goes for the inevitable model of Archaeopteryx.

Archie

Overall, it is a very nice exhibit about flight and volant and non-volant dinosaurs, but after being exposed to the Naturkundemuseum Berlin’s “Federflug” special exhibit it all looked a bit dull and grey. I guess there are two main reasons for this difference. One is that the MfN exhibitions team is just absolutely awesome. They can take anything and give it that noble, serious, quiet look that makes you feel it is special while making you focus on it. A far cry from the oh-so-common lights&sounds attack you experience especially in US museums. Eichstätt has that feel, too, just not at the top-of-the-league quality I am used to from Berlin. The other factor is probably as important, and quite mundane: money! While Berlin is horribly underfunded for a big Western natural history museum, there is always enough funding available to optimize the looks of exhibits. In any case, the Juramuseum Eichstätt is cool as is!

Now, I promised you fans of spineless stuff that there would be 3D spineless stuff. Here you go!

Perisphinctid

This is, a guess, the standard fossil associated with Southern Germany: an ammonite. In fact, it is a steinkern (literally: stone core), or natural cast of the inside of the shell, and even I with my long-forgotten haphazard training in ammonite taxonomy (I did study at Tübingen!) can tell it belongs into the Persisphinctoidea, by the splitting ribs and the constrictions (one is well visible on the lower right). In fact this is a Lithacoceras aff. ulmensis.  If you have ever collected fossils in the White Jurassic (limestone deposits of the latest Jurassic) of the Swabian Alb mountains you know these small to mid-sized shells only too well. Preservation as natural casts is the norm, and sometimes the suture pattern is pressed into the steinkern (top part of above specimen), too. The sutures is nothing but the negative of the contact area between the outer shell and the partitions between shell chambers. It plays a huge role for taxonomy.

In the Solnhofen Limestone deposition was very slow, and most fossils are therefore flattened, but the trough in which the layered limestone was deposited lay between small reefs. And in these we find 3D preservation, sometimes of incredibly good quality. The specimen above and those below come from a dolomitized reef in the Steinberg mountain near Großmehring, and the dolomitization has ruined the corals so they cannot be determined. The steinkerns, though, as exquisite.

snail

snail

Archie

A bunch of steinkerns of marine snails (Purpuroidea gigas, Pleurotomaria and I believe another Purpurodiea). And, below, a couple of Cossmanneas.

Cossmannea

nautilid
An almost-Nautilus! Pseudaganides belongs in a sister group to modern-day nautilids.

clam

Let’s have some clam chowder: Isoarca explicata

Archie

Pholadomya sp.

Archie

Pinna. They often get quite big. I have one from near Dotternhausen that is some 20 cm long.

Archie

Pterocardia corallina. The left one is a steinkern, whereas the right one is preserved with its shell.

Archie

Paradiceras aequivalve. A clam that lived in places with stronger currents than the reef-dwellers shown above. Its thick shell anchored it well.

Now, before we get to the brachiopods and corals, there is something I must comment on. Currently, the German government is trying to develop a law to protect (national) cultural heritage. It is called Kulturgutschutzgesetz. That is, at first glance, an excellent idea! The law is supposed to make it much harder to sell art and archaeological artifacts of dubious provenance. Considering how much stuff is being smuggled out of Iraq and Syria and sold on the black market I believe it is high time that we force dealers to provide paperwork to show specimens are legal – period!

However, as is all too often the case, the German government and its entire executive support in the form of federal ministries and federal departments of all kinds makes the same uneducated stupid mistake so many laypeople make: they apparently believe that palaeontology and archaeology are the same discipline! And so the smart people working there actually made the law apply to palaeontological collections and specimens, too. Without, may I add, do the usual and ask palaeontologists to comment on the proposals! OOPS!

The first draft of the law, the second version of which by now has passed the cabinet(!), was so monstrously stupidly written that it actually forbade preparing fossils by defining them as unalterable Nationales Kulturgut (national cultural heritage) while still in the ground – provided they are either scientifically important or worth or more 50.000 €.

A twist I especially like – a particularly idiotic twist, too – is that depending on how you read the law some fossils would become cultural heritage because of scientific importance, which might be determined how? It is left open for debate in many cases. So one could interpret the law to mean that a fossil that was not cultural heritage becomes cultural heritage a posteriori because someone publishes a paper on it. A paper that may be based on data obtained by destruction of the fossils, which now a posteriori would become illegal and punishable by law.

Granted, that requires a pretty weird interpretation of the law, but until the courts decide on such matters you can’t be sure what’s gonna happen. Same for a fossil that, hypothetically, you sell while still in the ground, and that you sell for less than 50.000 €, and that nobody ever publishes on – is it now NOT national cultural heritage? Even if it is another Archaeopteryx? Idiots abound in certain Berlin circles…

A key problem with the law is that it does not do what, for example, Bavarian state law does: distinguish between opera and res. Opera is an opus – an object created by man. Res is a thing. If you define unprepared fossils as natural heritage (treat them as res), and prepared fossils as works of man, and differentiate the protection of the two, you avoid a hell of a lot of problems that you get when you merge the two into one category. An ammonite that has been prepared so it can be used for science, a meteorite that has been cored and thin-sectioned, and so on – these are clearly specimens that must be protected differently from the gazillions of microorganisms making up limestone that you could but nearly never do analyze.

Another issue is the incredible amount of paperwork that natural history collections will face with regards to loans, de-inventorying and other totally normal collection activities.

Oh yeah, and did I mention that you’re supposed to provide documentation of the provenance of cultural heritage specimens? That’s another good idea, but you have to do it retroactively back to 1992!

Yes, you read that correctly: retroactively back to 1992! Bought an ammonite at a fair in 1998? Well, please do contact the dealer-whose-address-you-never-had and ask him for documentation! What the goddamned freakin’ fuck????????? Until our beloved government starts handing out time machines this is utterly impossible! It is also a very unusual shift of the burden of proof: suddenly and retroactively, you need to prove that you own a fossil legally, instead of someone else having to prove that something about it is fishy.

Jeez, I get too worked up about this. I even can’t be sarcastic anymore. Let me get to one more key point and finish this. Why do I mention all this in the context of the Juramuseum? Because one area that the law – even before it has been finalized! – is having a massive impact on is the private collectors’ scene. Particularly, due to the wonderful German federal system creating wide variation between states, particularly to Bavarian private collectors. Bavaria, I do not need to remind you, is the state the Solnhofen Limestone deposits happen to occur in. What’s going on there is rather depressing and scary: private collectors, uncertain about how their fossils will be treated, have started pulling loaned specimens from museums!

This and other links below go to German language articles. These are must-reads for Germans, and all others should spare themselves the misery. So please be glad I am not linking English versions ;)

Now, the Juramuseum is lucky. As opposed to some other museums, notable the famous Bürgermeister Müller Museum in Solnhofen, most of its specimens are not loans, but are owned by the Bavarian state. For example, all he wonderful invertebrates from the Steinberg shown above and below were collected and prepared by one Heinz Haberl. Mr. Haberl started collecting in the quarry in 1972, and has given the many wonderful fossils to the Juramuseum as a gift. They are now owned by Bavaria, and thus not in any danger. They are – and this is a prime example of the importance of private collectors to science in Germany – the means by which scientists were able to time the quarry’s sediments to ca. 151-152 million years before present, i.e. upper Kimmerridgian to lowest Tithonian age, and thus slightly older than the Solnhofen limestone. Without Haberl’s diligent collection and preparation of ammonites, this dating would not have been possible at this accuracy.

This is just one of very many examples of laypeople helping science. There’s millions more. And all that is threatened in the future and also partly in the past (remember 1992?) by a sorry excuse for a draft of a law. Read, if you can bear it, a lawyer’s comments prepared at the request of the Mineralientage München. Admittedly, this is a brief written at the behest of a party with a special interest – but even if one takes that into account, it is still scary.

The German Palaeontological Society has some harsh words for the new proposed law (PDF download). I couldn’t find an English version, and believe me – unless you are German, you really do not with to delve into this any more. If you are German, though, consider contacting your political representatives and giving them an earful. The Swiss and Austrian Palaeontological Societies have joined the German one in the above-linked statement, by the way – they are equally appalled. By the way: Austria managed to write a 7-page law to coply with the EU directive. The German draft is 156 pages long.

So, per angusta ad augusta: let’s see some more beautiful fossils while we still can! Here’s some brachiopods from the Steinberg.

brachiopod
Juralina insignis

brachiopod
Torquirhynchia speciosa

and a sea urchin – a rather blurry picture, just to prove they were there.
brachiopod

The corals of the reef at the Steinberg were all rather ruined by dolomitization. Some of them still look pretty, but for science they are not that useful For one thing, you can’t determine the species.
brachiopod

brachiopod

brachiopod

It speaks volumes about Mr. Haberl and many other collectors that their specimens found their way into public exhibits, either as long-term loans or gifts. And not only the top, most beautiful or most scientifically publishable specimens, but also the more mundane fossils that should be collected and preserved for completeness sake. Science is about being doggonely thorough, not about glitz. And there are very many private collectors out there who understand this, and live by it. The proposed Kulturgutschutzgesetz is a kick into their faces as much as it is one into the face of thousands of scientists. I really hope that the law dies a quick and timely death, so that in about a year I can blog here about the many other museums in the Solnhofen area without having to show you a lot of photos of suddenly bare walls. :(

 

Posted in Dinosauria, idiots abound!, rants, sad news, Solnhofen Limestone, spineless stuff (invertebrates), spineless stuff (politicians), Theropoda | 6 Comments

Juramuseum Eichstätt

Everybody knows fossils from the Solnhofen limestones. At least one fossil. This one: the Berlin specimen of Archaeopteryx lithographica.

Obiwan

(from Wikipedia under Creative Commons Attribution-Share Alike 3.0 Unported license)

But the Solnhofen Limestone is about much more than dinobirds, and in fact the entire area is about much more than just the Solnhofen Limestone! And a great place to see a lot of fossils and more is the Juramuseum Eichstätt, which is located in the Willibaldsburg above Eichstätt.

The whole area is incredibly picturesque, with the town of Eichstätt on the Altmühl river itself being a Bavarian Baroque church town, which means plenty of pretty imposing buildings in a wonderful landscape. The Willibaldsburg is a huge castle, the medieval part in its various stages of construction well preserved and with equally well preserved bastions from the 1600’s surrounding it. It offers a stunning view of Eichstätt and the sharp bend in the Altmühl’s course, and houses a very nice Biergarten (no need to translate that term, I guess), a museum that shows archaeological finds (Roman, Celtic, and so on) and palaeoanthropological as well as palaeontological exhibits from ice age times, and the Jura Museum.

fish

The Willibaldsburg as shown on the museum’s tickets.

I recently spent a very short visit there, less than an hour in fact, and with three small children in tow (however, they loved it and didn’t whine!). During that time I managed to take a few photos of some of the more amazing exhibits, so let’s dive into the Jurassic World of Bavaria.

One thing most people don’t realize about the Solnhofen Limestone is that it is a marine deposit, and as such so beautiful, so mysterious… so full of fish. Lemme show you some.

fish

fish

fish

Top to bottom, these are Asthenocormus giganteus with a bit of prey in its stomach,  Sauropsis sp., and Aspidorynchus acutirostris, a gar-like fish. The museum features a number of aquaria, too, trying to show what the Jurassic coral-reef and lagoon dominated landscape looked like, and in one of the them show gars (Lepisosteus oculatus) – not a fish you will see often.

spotted gar

Similarly, the museum has a tank with Limulus polyphemus, which matches very nicely indeed with the fossils:

fish

fish

What’s preserved here is a track of a horseshoe crab that for some reason got into the oxygen-deprived waters at the lagoon bottom, ran around for a bit trying to get out, and succumbed. One of the really rare cases where a trackmaker actually can be found dead at the end of the track. If only most dinosaurs had died that way, too ;)

Some more cool fossils from the Solnhofen Limestone:

fish

fish scales close up

fish

Aspidorynchus acutirostris again, this time in dorsoventral instead of lateral compression.

Enough fish?
Well, you ain’t seen nothing yet! Some of the fish are just incredible :)

fish

These look more like fish flattened in a printer’s press yesterday, or prints of color photographs on limestone, than real fossils. But they are oh so very real! Click to zoom in on the images. I hope to go back soon, with time on my hands to get really good photos of the fossils and the labels :)

fish

fish
close-up of the above

fish

This Turbomesodon relegans is so amazingly beautiful that I could look at it for hours on end!

fish
not all fish are that exquisitely preserved, but even tiny Leptoleptides sprattiformis are often extremely detailed.

fish

fish

fish

the absolute whopper, though, as the fishes in the special exhibit “the best fishes” (or so) that they added somewhen after my previous visit. Check this out (and excuse the poor photo, I was in a hurry).

fish
The color! THE COLOR!!!!!!

Makes me long for smoked trout with lemon ;)

 

OK, enough fish already, on to other creatures.

fish

A somewhat pornographic-looking view of a turtle. The museum thoughtfully placed the specimen on top of a mirror, so that we can also see the upper side of the shell.

fish

and a lizard, which under UV light shows soft tissues very nicely. The posterior tail has been regenerated.

fish

and finally, a dinosaur: Juravenator starki!

fish

so, although….

Obiwan

and although this post hasn’t arrived at Plateosaurus, I still think this is a good opportunity for a break. More soon – I am not even half done with my very hasty tour of the wonderful Juramuseum!

Posted in "fish", Aquariums, Dinopics, Dinosauria, ichnofossil, Lacertilia, lower vertebrates, Solnhofen Limestone, Theropoda | 7 Comments

Tristan 3D printing

So, you’ve all been faithfully following this place in the hope of catching an early glimpse of the greatest T. rex to ever grace a European museum? A preview that shows a tiny bit of the majestic bones? Or maybe a few terse comments on the bones, their preservation or the number of them preserved? Maybe you’ve seen photos on Facebook of some 3D prints of individual skull bones of Tristan?

Well, today I can do a bit better than that. This is exactly the theropod you are looking for!

print_01

Well OK, this is a 1:10 scale selective laser sintering copy of the photogrammetric files I made of all the skull bones, with a handful of CT-based files thrown in: the missing bones that were added as hand-crafted models and the bones that do far didn’t work out as photogrammetry. There’s very little CT in this, because the skull is quite complete, and because I’ve gotten quite good at photogrammetry of even the most insidious objects. I’ve had some important help with the latter, too – from Uwe Moldrzyk, the head of the MfN’s exhibition team found out about cylcododecane spray for me (it makes a non-glossy cover and evaporated off, slowly enough for photogrammetry), and especially from Matteo Belevedere, who spent many a day shooting the hell outta Tristan with me. Many thanks to you two! :)

print_02

In fact, the real skull is even better than this 3D print, because there are two teeth missing in the model that are present as fossils, but weren’t attached to the maxilla when I took the photos that led to this model. So it is now time to get all excited!

I have posted and will post more about the difficulties of photogrammetrizing such difficult objects – black, shiny, and with complex shapes, but obviously there is much more to say about Tristan than just the technical aspects of scanning. How did the skull bones fit together (and how did I mount them)? How complete is the skull, and the postcranium, and in what state are the individual bones? Can’t say much today, but I can promise that my colleague Daniela Schwarz will be very busy producing an anatomical description, and my colleague Oliver Hampe is taking a very close look at a bunch of pathologies.

For now, I’ll end this teaser with a photo that is part of my digitizing effort, in which you can see nicely how the cyclododecan spray helps creating photogrammetrizable surface properties.

print_01

Posted in Digitizing, Dinopics, Dinosaur models, Dinosauria, MfN Berlin, photogrammetry, Theropoda, Tristan, Tyrannosauridae, Tyrannosaurus | 5 Comments

Photogrammetry tutorial add-on: The consequences of optimizing a sparse point cloud

If you build a photogrammetric model following the workflow I suggest in this post, one of the steps is optimizing the sparse point cloud (tie point cloud) via gradual selection and deletion of points. Here’s why that matters.

Below you see a screenshot of a model of a sauropod bone. The sparse point cloud is shown as produced in-program by aligning the 190 images (one image doesn’t count, as it shows the label, and accordingly wasn’t aligned).

01

(click to enlarge)

Note that there are close to 200,000 tie points connecting the images.
Now, I used Gradual Selection to select lower-confidence tie points, and deleted them. After optimizing the alignment the point cloud looks like this:
01

(click to enlarge)

In this case, I deleted nearly 50% of the tie points, which are down to just over 100,000. Now compare the errors shown in the screenshots! The very same two scale bars of 25 cm length that differed by 0.000557 m (you need to add the two errors to get the total discrepancy), slightly over half a millimeter, now differ by only 0.00032 m, i.e. 57% of the previous error!

Ok, admittedly this almost-doubling of accuracy doesn’t make much difference in this case, but imagine you’re modelling a specimen with fine details. Sauropod vertebrae with their fine laminae come to mind. Decreasing the error by half means that your chances of getting the fine details modelled without too much error and messy edges doubles!

Let me end this with a view of the derived mesh. Ain’t sauropod bones beautiful? (oh, and this is medium density only! The mesh could be much better resolved).

01

(click to enlarge)

Posted in Dinosauria, How to, photogrammetry, Sauropoda, Sauropodomorpha, Tendaguru | 7 Comments

Photogrammetry tutorial 11: How to handle a project in Agisoft Photoscan

Over the course of the last year I have helped a bunch of people with their photogrammetry projects. Usually, they needed help with the photography – understanding how the program works, so that they take the right amounts of photographs in the right places. Or with camera settings. Or with the set-up for easy and quick models that show the underside of a specimen, too.

Recently, however, I realized that a lot of people also have problems making the most out of their photographs in their photogrammetry software, most of them using Agisoft‘s really easy to use Photoscan. They’d run through the “Workflow” menu of Photoscan and end up with model that were OK or so-so, based on photographs that should deliver really excellent models.

Below, therefore, I’ll describe how I use Photoscan to create high-quality models. Models like the one in this screenshot:

Screenshot from Photoscan

(click for larger size. note that I decreased model size from ca. 45 million polygons to 10 million)

PLEASE NOTE: this post assumes that you are using Photoscan Pro, not the standard version! Some steps described below are not available in the Standard Version!

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Posted in Conferences, digiS, DigitalSpecimen 2014, Digitizing, How to, MfN Berlin, photogrammetry | 2 Comments