Isis rises from the clouds: converting 3D meshes into point clouds

Sneak peek of my model of the Iseum in 3DSMax.
Untextured

As the Generic Viewer only accepts point clouds as inputs, we had to find a way to convert my 3D model of the Iseum into a point cloud.

I know. The idea would make many modellers (including me) cringe. And I can already hear the puzzled voice of my colleagues asking “just WHY?”. All the painstaking work I did on labelling the different elements would be lost in the process. All the layers would probably be smashed together. And what would happen to the details?

I am not going to ignore this issue, just to leave it aside for the moment. We took some time just to make experiments. It may not lead anywhere. It may not be useful to my research. The process of converting a 3D mesh into a point cloud may involve such a loss of information that it is unreasonable to pursue it. But we just wanted to find out.

How do you do that?

Here you can see the difference between people coming from a humanities or technology background. I started being fascinated by the idea of making a digital imaging of a virtual space. Is that possible? Can you do a photogrammetry of a space that is already digital? While I was pondering these slightly surreal thoughts, and getting lost in their philosophical implications, Alexandra had already found an option in Meshlab that transforms meshes into point clouds. As simple as that.

The Iseum as point cloud in the GV. The software generated
the map and calculated the areas.
The pink dots are the viewpoints

So we exported the Iseum in collada (.dae) from 3DSMax (the only Max exporting format that can be opened in Meshlab), we imported it into Meshlab and generated a point cloud.

We tried out different point densities, and then we settled for 5 millions. And there it was, my temple as a cloud!

I was happy to see that the conversion had worked less problematically than I was expecting. But, at the same time, it can’t be ignored that, even in a quite simple and regular untextured model like mine, everything looked pretty much simplified. The question if the benefits of the semantic annotations and the spatial calculations are worth the information loss is still open.

So, we managed to overcome the first major issue: we had a point cloud version of the virtual space. But, still, it was not suitable for the GV because in a CAD model there are not fixed viewpoints. 

We thought that the key was to keep treating the virtual space as a real one. And do, virtually, all the things we would do in a material space to make the GV work. So, we placed some hypothetical view points in the model and recorded the coordinates in the 3D space. 

screenshots of the virtual panorama
in the texturised ekklesiasterion

Again, I was glad for the success of the experiment. It gives a certain pleasure to push the boundaries of digital tools and software, and to see how much you can stretch them and make them do things they were never supposed to. On the other hand, I was losing information again. I had just turned a virtual space that is entirely explorable, 360 degrees, into a space whose view is constrained by the position of viewpoints.

We missed one last element to simulate the imaging of a material space in the GV: photographic panoramas, taken from the positions of our artificial viewpoints to texture the point cloud.

Again, we tried to think of the digital space as it was a real one. So I placed a (virtual) camera at the same coordinates of one of our viewpoints, and took sequential pictures of the space, with at least a 40% overlap (so, in the end, my idea of a photogrammetry of a virtual space wasn’t that crazy…).

To be fair, our viewpoints weren’t very strategically placed. But, luckily, I thought of putting at least one in a sensible place: the ekklesiasterion. The chronological layer of my model I’m working on (the hypothetical reconstruction of the Iseum as it might have looked like before 79) is meant to be untextured.

I could have left it untextured in our experiments with the GV as well, and just render the camera view of the elements in the not-too-bad 3DSMax solid colour palette (which is a feast of purple, lime green and turquoise, not too dissimilar from my summer wardrobe).

However, I thought that the best use I could make of the GV and its feature was to use it to express the complex relationships between the walls of the ekklesiasterion, the frescoes that have been found there and are now exhibited in the Museum of Naples, and the documentation of those frescoes that have been produced at the time of the excavations.

So, I textured (quite quickly, I’m afraid) the north, west and south wall of the ekklesiasterion with a digital copy of the graphic documentation of the walls commissioned at the time by the Borbons. On the black and white engravings (a not-good-enough picture from a copy of Elia's book) I have superimposed colour pictures of the fragments now exhibited in Naples (if you think that was a straightforward task, you have never had anything to do with Pompeian documentations…).

I didn’t have an equivalent texture for the east wall (the entrance one, with the arches). I could have left it untextured but, just to simulate a minimum of homogeneity, I applied a quick black and white masonry texture to it. 

The ekklesiasterion in the GV, (almost) ready to be annotated

I froze the camera at the exact coordinates we had given the GV for that viewpoint, and moved the target of the camera along the walls, capturing the panorama, as I was doing a photogrammetry. Move the target. Render the camera view. Print the screen. Repeat.

I thought of removing the roof from the model of the ekklesiasterion, to handle better the movements along the walls, and I twitched the light a little bit to get a better illumination.

Actually, I was a bit worried about the light. My model is not finished yet, so I haven’t spent much time working on a well balanced and realistic lighting. I just put some standard 3DSMax omnilights where I need them when I’m modelling. I wondered if the artificiality and inconsistency of lights in the renderings we used to build the panorama might bother the system. But I was over worrying and the system was definitely smarter than I thought.

So, while Alexandra is still working on the last details, it seems that my Iseum is ready to be annotated in the Generic Viewer

Embrace your inner dr. Frankenstein: documenting heterogeneous sources

There are a few things I have noticed writing the documentation of my 3D model in RDF, that I had not realised before starting thinking about it.

When I started my research on the ontology, I assumed that assigning one source to each element of the 3D model would have been more than enough to document sufficiently a 3D visualisation of cultural heritage.

But then I found out that a single source not always could provide all the information I was looking for. I (and possibly many others in this field) have to put together pieces of information that not only come from various archives but that have often different format, author and history. I know, it sounds like a terrible mess…

The ekklesiasterion of the Iseum in Pompeii, the north
wall visible between the arches of the east one.
Picture from pompeiiinpictures

For example, let’s look at the hypothetical restoration of the Iseum pre catastrophe. If we take the north wall of the ekklesiasterion, we can say that the width of the wall has actually been measured. So, the source for that specific information is the measurement taken on site and recorded by the researcher (in this case me) and available online at a certain url. The depth of the wall, however, cannot really be measured, definitely not with the equipment I had with me. So, the value I have assigned to the depth of the north wall of the ekklesiasterion in my model is simply based on the depth of the east wall of the same room, that can be measured because it has arches in it. The guess is supported by the fact that the depth of the walls appears to be quite consistent across the entire architectonic complex. So, the source for this other bit of information, is another element (the east wall) that has actually been measured. Last, it is not possible to know how tall the wall was before the eruptions.

For the more hypothetical elements, I have relied on Piranesi’s drawings as they have proven to be a thorough and, all in all, acceptably reliable visualisation. Thus, the height of the north wall has yet another source.

As you can see, the problem here is that not just each element, but even each dimension of the element can have a different source (it’s not always the case, but it has happened). 

For this reason, I have decided to enter, for each feature, transition or constrain, the attributes hasHight, hasWidth, hasDepth, and use them not only to express the numeric value, but also (or mainly) to connect them to the related source.

Is this level of documentation, although expressed synthetically through RDF triples, sustainable? I’m not sure yet…

Boris Karloff(*) as the Creature of Dr. Frankenstein
Image from giphy

To achieve a higher consistency, I could have tried to derive all information from the richest source, which is probably Piranesi. This would have been a perfectly acceptable choice, and the outcome would have been “an hypothetical restoration of the Iseum in Pompeii according to Francesco Piranesi”.

Nonetheless, I followed a different approach. Although I don’t want to state any degree of preferability among the different sources, I have chosen to use hard measurements each time they were available. Also, information derived geometrically from the actual remains has been considered preferable to the one derived from drawings or other secondary sources. Piranesi’s data, in the end, have been mostly used for the things that cannot be measured, that I didn’t measured (for various reasons) and that do not exist anymore.

I know that this choice makes my model a little frankenstein of information, but, in the first place, even the most detailed elevation or cross section cannot show all the information needed to produce a 3D model that is actually visible 360° in space. 

Second, my aim is not to produce a new groundbreaking hypothesis on the restoration of the Iseum but to provide a way to connect the 3D model to its sources. From this perspective, it is actually interesting to me to see how much I can stretch the potentiality of my system, and to give an idea of the richness and diversity of data virtual archaeologists deal with.

(*) trivia: glorious actor Boris Karloff is one of the King's College London illustrious alumni.

Robespierre's tears and other stories about the truth of images

W.J. Stillman, Picture of the Parthenon
 Athens, 1870. From Antiquity and Photography
Getty Digital Collection

I have spent the last weeks reading about representation of cultural heritage. I went a little bit into reception studies, touched art and photography history and took some dust off my semiotic background. As you can expect, the issues are many, complex and diverse. Especially when we talk about ancient cultural heritage. But there are a couple of points I want to highlight. 

The first one is that every representation (in any medium) is an interpretation. There is always something of the person that is producing it, the culture they belong to, and the tools that are using. This probably sounds redundant and definitely not new. Unless you are attending a 3D imaging conference. Then, you will probably hear concepts like «perfect copy» and «objective recording» more times that you are comfortable with. 

I thought academics had already agreed many years ago on the fact that photographies do lie, or, better, represent the author’s personal view of reality. Inexplicably, the concept doesn’t seem to apply to new imaging techniques such as photogrammetry or laser scanning. 

The second point is that cultural objects (well, probably all objects but let’s talk about cultural heritage) are not fixed in time. They change and evolve, like living things. It becomes even more apparent when we talk about buildings. They are planned, built, damaged, restored, altered, repurposed, abandoned.

So, actually, when we produce a visualisation of something we should always clarify which moment of the «life» of the object we are actually representing.

To deal with the chronological dimension, some 3D visualisation projects have introduced a timeline. For example, UCLA's Digital Roman Forum and Digital Karnak show how buildings have changed, as singles and in relationship with each other. In Digital Karnak, more specifically, it’s possible to pick a period and see which buildings have been built, modified or destroyed at the time.

I found this approach very informative. However, it kind of assumes that the only segment of the life of an object (or place) we’re interested in is from when it is produced to when it is abandoned or destroyed.

Fragonard, J., 1775 Travellers viewing a skeleton at
Pompeii. (Such "discoveries" were often staged
to please prestigious guests)

I think that what happens to cultural heritage when it is discovered, recorded, exhibited and disseminated is still an interesting matter. Objects keep changing, even after their uncovering. Even when they are closed in a glass cabinet. And I am not only talking about material changes, but also about how changes the way we look at them.

Let’s consider Pompeii. The circumstances of its destruction often make people think that it came out from the earth exactly as we see it now. That it emerged perfectly intact, as, to use Lazer's words, a sort of Sleeping Beauty castle. Which is rather far from the truth. A quick look at pictures of the excavations shows how much the place has been changing in the last 250 years: how much of it has been restored, adjusted, twitched, when not completely staged for the tourist’s gaze.

So, my point is, mainly, that all representations are partial and biased. And using cutting edge techniques doesn’t change it. They can be more or less accurate, but are always subjective. Which is not a bad thing per se, as long as there is a general awareness of the limits of the representation process, and, even more important, when we can compare different interpretations that enrich and complement each other. 

And I’m afraid we, somehow, ended up with multivocality and multi-authorship. Again.

To make up for this, I’m going to tell some (possibly funny) stories connected to representations and interpretations. Many, but not all of them, involving Pompeii. Starting with one of my favorite anecdote about the “truth of images” by father of cinema Sergej Eisenstein:

I cannot resist the pleasure of citing here one montage tour de force of this sort, executed by Boitler. One film bought from Germany was Danton, with Emil Jannings. As released on our screens, this scene was shown: Camille Desmoulins is condemned to the guillotine. Greatly agitated, Danton rushes to Robespierre, who turns aside and slowly wipes away a tear. The sub-title said, approximately, 'In the name of freedom, I had to sacrifice a friend...' Fine. 

But who could have guessed that in the German original, Danton, represented as an idler, a petticoat chaser, a splendid chap and the only positive figure in the midst of evil characters, that this Danton ran to the evil Robespierre and... spat in his face? And that it was his spit that Robespierre wiped from his face with a handkerchief? And that the title indicated Robespierre's hatred of Danton, a hate that in the end of the film motivates the condemnation of Jannings-Danton to the guillotine! 

Two tiny cuts had reversed the entire significance of the scene!

(Eisenstein, S. 1949. Film form: Essays in Film Theory)

What is essential is visible to the eye (if you're in my model)

I hope the ghost of Antoine de Saint-exupery won't haunt me for having played with the wise words of his Fox characters, inverting their meaning. I wasn't suggesting a triumph of shallowness and prejudice, but just introducing a brief premise about my 3D modelling process. 

F. Piranesi's hypothetical restoration of the Iseum (detail)
showing the roof's supporting structure.
From builtindex

I have said that the first phase of my modelling will focus on the present archaeological evidence in situ. I might have called it “what is still there”. The expression is not entirely correct because what I am going to model is actually what we can see of what is there (assuming that we were free to  explore the whole Iseum as much as we like). 

In practice, this means that, for example, I am going to model the Purgatorium's underground space, even though it is not immediately visible and it is not accessible to modern tourists without a permit, but is potentially both visible and accessible.

On the other hand, I won't model what is not visible. To explain ti better, I can use an hypothetical example: let’s imagine that the roof of the Temple had survived. In that case, I would model only the ceiling (which is what an observer could see from inside the Temple) and the external elements such as the tiles or the architrave (which is what an observer could see from the outside of the Temple). But I wouldn’t model the (invisible) supporting structure. 

I am sure that modelling what actually allows a roof to stand (for many centuries!) is of massive interest in the study of architecture and ancient building techniques. 

As I am more interested in how a building was seen and experienced by people (either at as a Roman Temple or as a modern Touristic Attraction), I have decided  to include in my 3D model only what is accessible to the eyes of a human being that is allowed everywhere in the modelled space. 

The matter would be different if the hypothetical roof would be damaged. Then, the internal structure would be visible to visitors and part of their experience (and, therefore, object of my representation).

Everything has (at least) two faces: about walls and normals

At the walls, by S. Bakalovich
from wikipedia

 To explain how I am going to deal with constraints, I will use the simplest, and most common, type of them: walls. Although they often look just as think lines on a plan, walls cannot be represented as flat two dimensional areas. That would contradict our experience and wouldn’t make any sense geometrically, as walls are three dimensional objects with different depth. 

It is possible that at the very beginning of your 3D modelling career you are tempted, quite naively, to simply trace the shape of your walls and extrude them as a solid. In case, the puzzled expression of your supervisor and the question “what is that supposed to be? Minecraft?” will quickly tell you that you’re on the wrong track.

What you are supposed to do (or, at least, what I am going to do) is to build two separate surfaces, one for the interior and one for the exterior, without modelling what is in between (i.e. the actual thickness of the wall).

There are a few reasons why I agree it is a sensible approach.

First, walls (as well as every other constraint) may display different material or decorations on the inside or the outside. So, in the model, they will probably have different textures assigned. 

Also, as we were discussing in the other posts, there is a logical (or ontological, in the linked data meaning of the word!) benefit in it. A wall often delimits two different spaces. But, more specifically, one side of it delimits one space and the other side delimits another space (or spaces). For example, the wall that separates the ekklesisaterium from the sacrarium, is the internal southern wall of the ekklesiasterion on one side, but, on the other side, it is the northern internal wall of the  sacrarium.

It may sound confusing at the beginning, but, after you get used to that, it is a simple yet effective convention that has proven his usefulness in my previous models already. I think it will also suit well the RDF modelling and help dividing meaningfully my digital archive.

If there weren’t enough reason to justify a separate management of the two surfaces of a wall (or other constraint), game and VR engines give us another good one: normals. Surfaces are visible only from one view, either from the interior on the exterior. Even if we had a wall with the same identical texture (let’s say a generic masonry), to allow a 360° virtual view of it, we still would need two surfaces: one looking towards the interior and one looking towards the exterior. This is the only way a character (or a camera) can have a realistic view of a virtual building when it is walking into a space as well as when it is walking around it.

Lured by the sistrum: the choice of the Iseum

Francesco Piranesi, The Temple of Isis at Pompeii

If you have ever met me in person, it is very likely that I have mentioned the Temple of Isis in Pompeii, at a certain point. Even if you didn’t ask about it. Even if, to be honest, there was little (or no) connection with the conversation topic.
To be precise, the area I’m working on, experimenting with the potentiality of RDF applied to 3D environments, is the Pompeian Iseum. The sacred complex includes, besides the proper temple, other public spaces for the cult, and the private spaces where (probably) the isiac priest(s) used to live.

There are many reasons behind my choice.
First, the digital unification of one of the Iseum’s rooms (the Ekklesiaterium) was the case study for my MA dissertation in Digital Humanities at King’s College London. The Iseum, in fact, has one of the richest and best preserved collections of artefacts and decorations that are exhibited in the Archaeological Museum of Naples. The corpus is so relevant that it has a dedicated space within the Museum itself.

Besides the conclusions of my dissertation, the Iseum is certainly the groups of buildings in Pompeii I am most familiar with. Moreover, I have already collected a personal archive of digital resources, partly produced by myself (such as digital pictures and measurements) partly found in online repository, partly digitised from printed sources. While researching for my MA dissertation, I obtained access to areas of the Iseum that are usually interdict to the public (such as the interior of the temple, the interior of the ekklesiasterium and the purgatorium) as well as to documents that are relatively rare (such as the original drawings by John Soane, at the Soane Museum and the 1941’s illustrated publication by Elia and the Warbourg Institute). I thought it was a good idea to capitalise the information that I gathered and to produce a 3D visualisation able (among other things) to show and make virtually explorable, parts of the Iseum that are usually unaccessible to the average visitor.

Another reason is that the Iseum was one of the first excavated complex, so it is featured in many accounts, records, watercolours and guide books.

Imaginary interior of the Temple of Isis in the Italian movie
Gli ultimi giorni di Pompeii.
From http://ithankyouarthur.blogspot.co.uk/

In addition, when the place was dug up, the site was still personal property of the Bourbon King and he hired very skilled professional from the Neapolitan Academy of Fine Arts to produce a visual documentation of various features of the building(s) as they were when they had been unearthed. Some of these engravings (now exhibited at the Museum of Naples) are the best information we have about some elements that do not exist anymore.
The fact that the Temple of Isis and the Iseum appear so often in official and unofficial literature about Pompeii, is not merely a matter of “age”.
The temple captured the attention and the imagination of many visitors. Its Egyptianising flavor made it look mysterious, if not slightly sinister. It became quickly an iconic building in Pompeii, and it is featured in many novels (such as the hugely popular Bulwer Lytton’s one) and even peplum movies.

As interpretations and narratives connected to ancient heritage, are part of what I want to represent, the Iseum seemed to  confirm its relevance under this respect too.

The Pompeian Iseum has been very often reproduced. Francesco Piranesi, for example, has studied the place and its architecture in depth. However, it is very seldom shown in its completeness, most of the visual interpretations focusing on the Temple and the Purgatorium alone. My model aims to represent all the different components of the Iseum, (potentially) allowing the investigation of their visual and functional interactions.

On top of these very sensible reasons, there is a more irrational one: the Iseum, in its charming funkiness and lack of symmetry, simply rocks (but I can’t write that in my PhD).

An Introduction

Woman with wax tablets (so called "Saffo")
Archaeological Museum of Naples
Wikimedia Commons

I am a PhD student in Digital Humanities and Classics at King’s College London and this is a blog about my research. It is meant to be a digital notebook to fix ideas and share them with colleagues and other people interested in the same topics. 

I study 3D visualisation of archeological heritage, more specifically Pompeian buildings and artefacts. I am focusing on some methodological issues of 3D modelling such as the documentation of the research process and the representation of multiple hypotheses. 

I think that introducing 3D visualisations in the study of the Ancient World would change and enrich our knowledge of the Past, and  I’m trying to find a way to make it possible and easy.

Here I will discuss museum exhibitions, archaeological sites, my own interviews to the public, old and not-so-old accounts of visits to Pompeii and Herculaneum, the image of these places that has been disseminated by cultural products (literature, post cards, movies), touristic guides and official excavation records. 

I will do my best to put together again, logically and visually, things that have been separated many years ago but should be seen and understood together because they complete each other and give sense to each other.

I am interested in the cognitive and emotional relationship that people build with these ancient artefacts and how digital technologies can represent and enhance such a bond. This is a complicated way to say that I want to understand why and how people fall so deeply in love with Pompeii. 

I like to talk, and write, about the idea of «place» and its existence in geography, perception, memory and imagination. And I will probably try to convince you that the best way to engage the audience with the Past is through storytelling. My cunning plan is to actually tell you a lot of stories about Pompeii. You probably won’t believe them at the beginning, but I promise they will be true. Almost all of them.