Explorations in Photogrammetry – Part 3

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In part 3 of my photogrammetry series, I will discuss the second aspect of the photogrammetry assignment: using an outdoor object.  While the mechanics of this aspect of the assignment were similar to that of the first part (see Explorations in Photogrammetry – Part 1 and Part 2 for more information), this part of the assignment presented unique challenges.  As I mentioned in earlier posts, while working at the National Museum of Ireland, I was working in a controlled environment.  The object was small and placed on a rotating table.  The camera itself was on a stationary tripod. And most importantly, we utilised artificial light and a lightbox to ensure proper and consistent lighting.  I had none of these luxuries for the second aspect of this assignment.

For the second part of the assignment, I was tasked with creating a 3D model, with the subject of the model being something outdoors—the challenge being the lack of a controlled environment, especially in regards to lighting conditions.  I chose a sepulchre as my subject, one of the many objects in the cemetery behind St. Patrick’s College on South Campus here at Maynooth University.  The cemetery itself is rather small and houses mainly priests and nuns who have served St. Patrick’s College (although supposedly there are 2 unmarked graves of students who took their own lives and whose deaths have entered into folklore regarding the “Ghost Room” on campus[1]). The cemetery has a number of interesting markers, sepulchres and a crypt. The sepulchre I chose was that of Rev. Jacobi Hughes who, according to the inscription, served as Dean of St. Patrick’s College for 15 years. I found the sepulchre architecturally interesting with a number of interesting angles and faces, which is why I chose it as my subject piece.

Taking the Photos

The process of taking the photos of the object was rather different than it was for the photos taken at the National Museum.  First, I had to be very aware of any shadows being cast—not just of shadows cast by the object and any surrounding objects, but also of shadows cast by myself.  Too many shadows would make it difficult for the software to accurately compile a point cloud.

Ideally, it is considered best to take photos on a cloudy day.  Given I am in Ireland, one would think this wouldn’t be a difficult task; however it would seem the weather was not my friend, and the sun decided to shine high and bright the entire time I was attempting to take pictures.  This meant I had to be very careful with how I positioned myself while taking the pictures.  Due to the size of the object, I had to move around the object in order to capture it from all of the requisite angles (as opposed to the bowl at the National Museum which sat on a turntable that I could then rotate).  As such, I often found myself having to reposition the view finder on the camera and hold the camera at odd angles in order to ensure my shadow wouldn’t fall on the object as I attempted to capture it.

Another downside was the lack of a true preview.  While working with the camera at the National Museum, I was able to keep it connected to my laptop, where I could preview every picture and, if necessary, make constant adjustments to the settings.  This was not feasible with the sepulchre object, as I was moving around the object and could not keep the camera connected to my laptop.  I had to rely on the view finder on the camera itself for a preview—an option which isn’t ideal for truly examining an image upon capturing it.

I was able to apply some lessons learned from the National Museum, however.  In this instance, I used a much higher aperture setting (I kept the f-stop set at 22) and allowed the camera to adjust the ISO, so as to optimise this setting.  Overall, I feel these pictures were much sharper and of a higher quality than the pictures taken while at the National Museum.

Coming Up Next…

In part 4, I will explore the process of creating the 3D model of the sepulchre. Specifically, I will be discussing the differences between the construction of this model and that of the bowl model from part 2. I will also assess the quality of the model and what areas of improvement could have been made to create a better object.

References

[1] Sam. “The Ghost Room in Maynooth“. Come here to Me. 20 July 2012. Web. 3 April 2015.

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