Explorations in Photogrammetry – Part 1

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Our first assignment in AFF 621: Remaking the Physical involves photogrammetry.   Photogrammetry is a technique used to create three dimensional images of an object.  This is accomplished by taking a series of photographs of an object, where each photograph overlaps by at least 60%.  Special software is then used to create point clouds that “stitch” the pictures together into a three dimensional representation of the object.[1] 

Over a series of several blogs, I intend to document the process of photogrammetry used for my photogrammetry assignment.  The assignment itself calls for the creation of two different 3D models using photogrammetry. One of the models is to be a bowl housed at the National Museum of Ireland where the pictures can be taken in a controlled environment. The second model is to be one of my own choosing; however it must be taken in an outdoor setting where little environmental controls exist, thus giving us the opportunity to experiment with lighting, aperture, shutter speed, etc. The blogs will cover the following:

  • my trip to the National Museum of Ireland in Dublin
  • my choice of topic for the second model and the process involved in the actual photography
  • my experiences with the editing and creation of the actual models (2 separate posts)
  • an analysis of 3D printing and the service I would use to print my object

My Day at the Museum

For the first part of our assignment, we visited the National Museum of Ireland.  This was a fantastic opportunity to not only visit the museum, but to see some of the artefacts up close.  We spent the entire day in the museum photographing a number of bowls which dated from some time around 2,000 BCE. The Bronze Age era bowls themselves were largely used as drinking vessels and likely held some kind of beer.  Many of the bowls have a sun pattern on the bottom that some archaeologists speculate was tied to the worship of the sun by the indigenous people[2].

The process of photographing these objects was quite different than it was for photographing the second part of my assignment (the latter of which will be detailed in a future blog post).  As we were in a controlled environment, we were able to avail ourselves of a number of lighting techniques that wouldn’t be feasible outside such a setting.  One of these (which is also a personal favourite) was the lightbox.  lightbox The lightbox is white canvas-type cube that, as one of my classmates pointed out, looks much like a collapsible laundry basket. The object is then placed inside the lightbox and lights are placed around the outside.  The material of the lightbox acts as a sort of diffuser, softening the light and eliminating shadows. The image to the right shows the final setup of our lightbox.  The lights are positioned from all angles in order to provide the most light. This includes not only from the sides and front but also from above.  Once the object is placed on the turntable (which is positioned in the centre of the lightbox), the object can be slightly rotated in between each picture, allowing for the creation of the overlap between images necessary to produce an accurate model using photogrammetry.

Once everything is set up, the actual photography can begin.  As I mentioned above, the object is placed on the turntable within the lightbox, which allows the object to be easily rotated. Shane Using the EOS Utility (software provided by the Canon website, the manufacturer of the digital camera we used), we were able to preview each image on the laptop and adjust various settings as necessary.  Primarily I worked with the aperture (to define not only the light available but also clarity of the background and depth of field) as well as the ISO (which can allow for more brightness but must be used carefully so as not to introduce any visual “noise” into the image).  I decided to leave the shutter speed set to automatic, as adjusting this is more of an advanced technique and given the controlled environment, I didn’t feel it was necessary to adjust.  Once all of the adjustments were made, the process of photographing the images was quite simple.  Very few adjustments needed to be made in between images, and I was largely able to move from one image to the next with little intervention with the camera.

I decided to take images from four different angles, beginning at straight on, and then adjusting the angle of the camera up in order to capture further detail. The bowl was then flipped, and the process repeated in order to capture the bottom part of the bowl.  I was able to capture approximately 150 images in about 50 minutes (excluding the initial setup of the lightbox).

Acknowledgements

Special thanks to the National Museum of Ireland and their Archaeology department for allowing us to photograph some of their objects. The pictures taken of the bowl featured in this post and my previous post were courtesy of National Museum of Ireland – Archaeology. All rights reserved.

Coming Up Next…

In my next blog, I will discuss the outcome of these images, the steps taken to clean up the images for contrast, brightness, clarity, etc., and the process of utilising Photoscan Pro to create the 3D model.  I will also assess the quality of the images taken and what steps, if any, I would take in the future to ensure a higher quality of image as well as what lessons I can take away from this aspect of the assignment.

References

[1]US Bureau of Land management Publication: Tech Note 248 on Photogrammetry.

[2]Flanagan, Lauren. Ancient Ireland: Life Before the Celts. Gill & Macmillan, Ltd. 1998.

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