First Photogrammetry Article Published

New Photogrammetry Article

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I’m very glad to present you with my first (but not last) published article on the topic of Photogrammetry in Archaeology! The December edition of The Post Hole, that has recently been released, features a paper on “The use of Photogrammetric models for the recording of archaeological features”, which I wrote during the summer, and which I’m sure you will find of some interest.

It deals specifically with archaeoloogical features on site, and it looks at accuracy, methodology and uses, especially when it comes to recording. The aim of it is to show that far from being technology for technology’s sake, Photogrammetry can contribute greatly to our understanding of an archaeological site, as well as reinforce and improve traditional methods of recording such as section drawing and plans.

The article is based on a few sites I worked on, and that have featured on this website before, such as Ham Hill and Caerau.

This is however just scratching the surface of a technology that is now appearing more and more frequently in publications, and that will eventually become a fundamental part of archaeological recording.

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Roman Villa Reconstructed In 3D

Based on the plan of an actual Roman Villa, this is a fly through of the model. It’s a way to explore this living area and get a more authentic feel of what it would have been like to actually live in the Roman times.
The model was made using Google Sketchup, and the final project sees furniture and details added in to make it even more realistic. This however is the building at present, showing how archaeology can be brought to life using 3D modelling software.
A more detailed account on how this model was made can be found previously on this website.

Ham Hill Iron Age Skeletons Turn Digital

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Three of the skeletons found at the site of Ham Hill, Somerset during the 2013 excavation are now available to view online at the following links:

https://sketchfab.com/show/70d864c4736435710bc65b6f21d81c03

https://sketchfab.com/show/821565c7ce0b98e1b7764c73a9f07492

https://sketchfab.com/show/fa694aff0fb5949e2f396a5fb2da37b0

The skeletons were discovered during this year’s excavation carried out by the Cambridge Archaeological Unit and Cardiff University, at the site of an important Iron Age hill fort. They are only some of the many human remains found, some of which were carefully placed within a number of pits, while others were located symbolically within an enclosure ditch, often with body parts missing.

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The models themselves were made using Photogrammetry and specifically 123D Catch, which required very little time for quite good quality. The aim of this was to preserve a record of the skeletons in situ for further interpretation once they had been removed from the location they were discovered in.

Given the complexity of the subject, the results seem to be very promising. Time was a big factor when making the models, as they had to be removed before damage occurred. Some of them were also in tight spots, which made it hard to access some of the standard angles, but overall this was counterbalanced by taking a larger number of photographs than normally (around 30 per skeleton). The lighting conditions also proved to be ideal, as there was an overcast sky, but also sufficient sunlight coming through to really emphasise the surfaces.

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For further information on the skeletons I suggest reading the article at http://www.bbc.co.uk/news/uk-england-somerset-23928612

Roman Villa Reconstruction Preview

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I have talked endlessly before on this blog about the use of Google Sketchup in the archaeological world, so pardon yet another example on the topic. I recently started recreating a typical Roman Villa using plans from a number of sites and any source of information I could find. The final plan is to not only create the structure itself, but also include many more details, such as furniture, statues, etc.

Having completed the main structure I thought I would share the results as they stand, as a sort of preview to the completed work, and explain some of the aspects of making the model. In the next couple of days I’ll also post a fly-through video which is currently rendering, to give an even better impression.

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This model was an interesting one to make, as it was more complex in some aspects than the ones I did before, and it combined opened and closed spaces, with equal importance given to both. The plans I found were very good for the ground floor, which is pretty accurate, but for the top floor there is a definite lack of information, mainly due to the lack of archaeological evidence. Therefore I had to resort to sketch reconstructions which are based on personal interpretation, which I am not usually fond of. Similarly the roof and the inside of the rooms is mostly conjecture on my part, based however on ideas found in texts. Overall then the model is much more interpretive than for example the Parthenon model I made, but at the same time it is more useful as the Parthenon is actually standing, while the villa is not.

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Something I noticed from making this model is the efficiency with which Sketchup deals with lighting. In the past I wasn’t a big fan of the lighting conditions as I found that inside spaces were too dark, and outside spaces were too bright, however in this case I find that this is in no way an issue, possibly because we have both inside and outside. The rooms are still a bit dark, but with the addition of external windows that I’m adding in the next phase, they should be quite faithful to reality, while the internal courtyards are bright, but not unnaturally so. As a whole the results are quite satisfying, and when objects are placed within the model they will also look realistic due to this.

ImageAlso , rounded edges tool is still a favourite of mine, but I now use it less frequently. In large models some walls look more realistic with rounded edges, but not everything does. Door frames for example look equally good without, and given that it effectively adds many more lines to the model, there is really no need to round them off. For walls, I found that adding a slight slope at the bottom really makes it less blocky and much nicer to the eye. On a more practical note, creating components is still the greatest tip I can give with Sketchup. I found that making each floor and roof a separate entity made it much easier to edit, as you could hide upper floor when having to edit the lower one, and vice versa.

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As mentioned before, as soon as the animation finishes rendering I shall post a new update. I realise that recently I have been posting less and less, but I assure you it is only for practical reasons. I am currently involved in the writing of an archaeological based radio show, which is taking up a lot of my spare time, as well as working on a number of sites. Also these models do take their time to be made, so I’d rather wait a bit and publish something good rather than many very random posts. Finally a few of the projects I have been working on have the disadvantage that I can’t actually publish any of the results, which means there are a few things that I am doing that I can’t write about specifically. Therefore I apologise if sometimes it takes a bit longer to post something new.

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Using Iphone Camera for Photogrammetry

I mentioned before I recently received an Iphone 4s, and having been a strong supporter of Windows against Apple, I am slowly being converted over. Apart from the great thing of being able to carry my models around and show fellow archaeologists without risking the life of my laptop, I have started exploring the advantages of having a pretty good camera on me at all times.

By using the 123D Catch app, it is possible to instantly create amazing models wherever you are, but how accurate are 3D models made using the Iphone camera? I don’t have the app itself due to a lack of 3G, but I have been going around site the last week or so and have taken a number of photographs and then processed them once got home.

Once again I experimented with larger and smaller objects and features, comparing the results I got with those done with regular SLR cameras. I can’t actually upload the images due to site restrictions, but I created a model of a toy car as an example. I followed the usual methods of recording, so to not alter the results in any way.

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These are some of the points I have found:

Image stitching: Comparing the number of images that stitched in normal models and those done with the Iphone’s camera there is a bit of a difference between the two. Especially with similarly coloured images only some of the images are stitched together. This however happened only on a few occasions and as such doesn’t constitute a major flaw.

Point cloud: The number of points within the models done with the Iphone seem to be equal, if not more than those in the normal photographs. I believe this is because the Iphone seems to adjust the colours and lighting automatically and digitally, which makes the photographs seem more consistent. On the other hand this also seems to have the negative effect of artificially changing the images, thus playing with the contrast and colour balance, which affects the accuracy of the model.

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Textures: The textures in the Iphone models seem to be extremely good, probably due to the digital adjustment mentioned above. In this case I wouldn’t say this is a problem, and the results are quite bright and distinct, which is a good thing when analysing the models.

General look: This is the point I have the greatest issues with. The number of keypoints the program finds made me expect extremely crisp models, but they look to me much more murky than they should. The digital altering of the images, and the fact that the size of the images is below the 2 MBs makes the model much less accurate, and the results suffer greatly.

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Overall though I am happy with this method. If the models were of extreme importance, I wouldn’t even consider using the Iphone camera, but for simple and less important models it is perfect. The practical nature of being able to capture images in a matter of minutes and have them upload directly to my Dropbox is great, and on more than one occasion I’ve been caught without my camera, so it is a great alternative.

Some Issues with Photogrammetry

This is based on some of the work I did for my dissertation. I realised that as it stands it isn’t likely to be published, so I thought I should at least share some of the concepts and ideas that I used for it.

Creating Photogrammetric models for archaeology can be a simple process, but there are some cases in which problems may rise, due to the shape of the objects or the type of surface. We’ve already seen how large features can require certain considerations when photographing, to simplify the work of 123D Catch.

But there are other issues as well:

  • Curved surfaces: If for example we are looking at a pot fragment and we are photographing it from the inside and the outside, the fact the surfaces are concave and convex rather than flat means we may have some difficulties. In general, convex surfaces are easier to manage than concave surfaces, as, provided that the angle of the two spirals of photos is big enough, the pattern of points is such that it provides sufficient information to the program to deal with the surface. If, however, the surface is concave then the same does not apply, and the outcome of the rendering depends on the size of the object. A large surface will generally provide sufficient detail for the program to recognise it and deal accordingly, but a smaller sample often does not have the same results, and the only course of action is to adjust the illumination to create as much contrast on the surface as possible, although this also does not always work. Similarly, if the object has elements which overlap in the photos, these can present some problems, as the program often assumes that they are on the same level. In this case, it may be necessary to increase the number of photos input to help clarify, as well as manually unstitching and stitching all photos that have not been properly placed.

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  • Translucent surfaces: These can cause problems with the camera, as they alter the contrast depending on the angle and lighting. In this case, it is important to make sure that the lighting is uniform and the object fixed, hence making it necessary to circle the object rather than rotate it.
  • Uniform texture: If the colour of the object is too similar throughout, thus not providing enough difference and contrast to allow the selection of keypoints, adjusting the light to bring out as much contrast as possible may assist in the creation of the model. One particular case of this is objects that have similar sides, like the image below that looked very similar from different angles. On the other hand, 123D Catch seems to cope quite well with this case, allowing the smallest of details to be picked out from the texture.

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There are of course many other cases in which we have problems using 123D Catch, but these described are some of the most common. The fact that these issue exist though doesn’t mean that the software is extremely faulty or useless, as we are dealing with some rare exceptions, while generally models should be produced easily and with none of these issues.

Initial Uses of 3D Printing in Archaeology

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3D printing is the new thing, no doubts about it. There is so much potential to be unleashed with this technology, and finally we are breaking through the last barrier that stops us from 3D printing every day, which is cost. I wrote an article a month ago about the subject, and already the price for a basic 3D printer has halved, from 1500 £ to 700, and it is bound to decrease even more with the end of the patent which should be next year. Soon every household will be able to print out designs downloaded from the internet of any object they may desire, and with scientist at work on printing food and many other things, the possibility are endless.

Given this boom in interest and popularity, and the detail of which 3D printers are capable of, it would be foolish to think that the archaeological world can avoid being swept in. From exact replicas of artefacts, to miniature sites for display, we are soon going to be treated to new ideas in archaeology.

3D-printing

Some of these ideas have already started producing some results, and one of the most interesting articles I have found is this one: http://www.webpronews.com/3d-printers-are-helping-researchers-recreate-mummies-2013-08

I won’t go into detail on the background, as you can read the article yourself, but the main story is that a group of archaeologists have managed to 3D print mummies using x-ray images, therefore leaving the bones within the bandages.

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The real thing to notice here is the beautiful detail achieved by the archaeologists involved. The skeletons are perfectly replicated, leaving little to interpretation and preserving something that may easily get damaged if unravelled. I’m assuming that the best approach in this case would be using a CT scan to get the 3D model, rather than from a series of simple X-rays, as these would be too inconsistent to work with. This does create the problem of having to get this type of equipment for archaeological use.

Falcon

This experiment however is important for one main reason: it is something we could not do before. Often with new technology the problem is that people see it as technology for technology’s sake, as in something without an actual practical use that we do simply because we can. Recreating skeletons of mummies without damaging the actual bones relies entirely on 3D printers, and it is not possible to find any traditional approach to it. It therefore shows that the potential is there and it can bring innovation.

Sketchup for Archaeology – Olynthus House

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Having talked for the last few days about Sketchup and its uses in Archaeology, I thought I’d complete this line of enquiry by showing you another model I made during my second year and briefly presented before, a house from the Classical Greece site of Olynthus.

Much like the houses of Zagora I covered before, the house at Olynthus is a great example of domestic space in the classical world, with an inside courtyard and different rooms of which for the larger part we know the function. The reason or Olynthus in particular is that in this case the houses have all the elements of houses in the Classical period, and the base plan is repeated throughout the entire town.

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The main reason I chose this model was that it was a challenge. Previously I had only reconstructed the Parthenon, so I was not entirely used to closed spaces. In addition, I had the actual site reports handy, which meant I could reconstruct the house reliably, with little left to imagination. Finally, it gave me a chance to investigate issues of lighting within closed spaces, and settle a debate that I’d read about, regarding a possible need of a flue to provide lighting to some of the rooms.

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Apart from the use of components, that I’ve discussed already, I found two interesting things with this model: the use of visualisation to understand the use of space, and the aforementioned lighting tool.

One of the main issues I was having with the house was the presence of a ladder, which would have allowed transit to the upper stories. The location I originally intended for it didn’t actually fit, something that I only realised when looking at an initial draft of the model. It was too steep, and if it extended any further to reduce this it would have blocked one of the doors. Therefore I decided that the location had to be wrong, and tried many different positions that could be possible. The one I finally settled with was the only one that “looked” right, and after reading the report again it turned out there was a base for the ladder in some of the houses in that exact spot.

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This is probably insignificant on the long term, but it made me think that the only way I realised the position was wrong was with the added dimension, as the 2D plan didn’t give me sufficient information to realise.

The issue with lighting was part of a debate I was reading, about an area of the house interpreted as a flue. Some suggested this area was open at the top, in order to allow lighting, while others thought that the lighting in the room was sufficient to carry out basic activities. I therefore created an entire street by repeating the house, and placed windows as suggested by the report. I then rendered the images with and without a hole in the ceiling.

dark oikoslight room 2

The results are not of the most conclusive, although there is a difference between the two rooms. This does however suggest that a hole in the roof would have not been sufficient, so it is possible the flue was used to conduct smoke from a fire within the room.  Again, in this particular instance the results are not ideal, but in other models the idea may have more success, especially in enclosed spaces.

Sketchup and Archaeology – Iron Age Roundhouse

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One of the projects I’ve been working on has been reconstructing a roundhouse we found at Caerau, Cardiff, using Sketchup to create the main frame, and V-Ray to render it as an image. This will then be used to fade over some footage of the archaeological site, to show a transition between what we can see and what would have been present on site.

For this purpose I created a very basic roundhouse model, coupled with a fortification mound and a sheer drop behind it. All of this was based on the GIS data I had of the site, so it does represent what we actually found on site.

The model itself is pretty simple, but it gave me a chance to play around with a few different elements of Google Sketchup, which will then be useful for more complex models. In particular I was looking at the application customised textures, the creation of backgrounds, and the use of rounded corners to create realistic mounds.

Customised textures is one of the main points of 3D modelling, and is extremely useful to give the model a more realistic feel. The problem is that it is really hard for someone as artistically challenged as myself to create good textures, so I resorted to using a combination of pre-made ones instead. I used Photoshop to layer three different grass materials, and I rendered patches of each more opaque, to create many different coloured patches. This made the ground surface on the model much more realistic, as it’s  not a repeating pattern any more, but a more complex and varied one, with different shades in different areas.

I then realised that one of the elements that really made the model lack realism was the background. The Sketchup standard rendering mode is to create a background that looks like the sky, which with particular angles is fine, but that becomes a problem if we want to get specific images, like in this case.

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Therefore at first I decided to create a large cylinder shape around the entire model, and then paint it using a stock image of a panorama found online. This failed as the cylinder is actually made of many different faces, each of which started the texture from the origin point, thus making it repeat. Therefore I decided to use a flat surface instead, creating a sort of shield I could move around where needed, and that could be placed in the background of the rendered image much like a green screen in video editing.

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Finally, The mound itself looked extremely blocky, as Sketchup is not ideal when it comes to rounded surfaces. I tried using the Rounded Angle Plugin that I’ve mentioned before, and made the area of impact quite large. The result was exactly what I wanted, as it created a much more realistic mound, although it’s not ideal for the base, which can be a problem from some angles.

Overall I think these three tips are really useful, and I shall be using them from now onwards to create better large scale models, and especially to simplify and improve the rendering process.

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