An introduction to recording built heritage with 3D photogrammetry

Have you ever wondered what photogrammetry is? Or wondered how it is done? Well 11 volunteers attended a training workshop about 3D photogrammetry last week. This was part of the training delivery of the Dairy Days project.

So what is it? Photogrammetry is a method of using a series of overlapping 2D digital images to produce a 3D model. It has many potential applications in archaeology and heritage (both built and objects), as well as wider uses – measuring planets, industrial parts and in police crime scene investigations. The computer programme finds common landmarks on the photographs (parts where the photographs overlap). The software builds these up to made a 3D model. These models produce a great non-destructive record which can give much more information than photographs alone. The models can then be interpreted.

The day involved a number of presentations.

Before lunch the whole group walked to a nearby field barn armed with their cameras. Although the conditions were not ideal – with the sun appearing and disappearing behind clouds and a lot of wind – it was a good opportunity to take photographs that could be inputted into the software. We first started with a walk around the barn, going over how to take the photographs as well as giving an introduction to the features of the building. They then put their new knowledge into practice.

The field barn was likely constructed in the late 18th century and would have been used to house (about 4) cattle over the winter. The barn has a door into the mew (where the hay is kept) and a door into the byre (where the stalls for the cattle are). The layout with 2 doors makes this a Type C barn. It also has neatly coursed through stones, many putlog holes, and coping on the west gable for the prevailing weather (which we can attest to with the wind). There is also a small brick outshot.

There is great variety in the field barns of Wensleydale (and the Yorkshire Dales) due to factors like location and date.

To make a photogrammetric model of a field barn you require a great number of photos taken at different heights, angles and distances from the building. As a minimum the photos need to overlap by at least a third (so the software has enough common points). It is harder to capture recessed or projecting features and require more photos specifically at different angles. It is particular tricky to capture the roof – it is good to use surrounding topography of the land, it was too windy to use equipment to help on the training session.

Once we had the photos (and had eaten lunch) we then had a look at how to generate a 3D model. The software we use to create the models is Agisoft PhotoScan Professional (however there are a number of free open-source packages online.) Unfortunately due to time constraints we could only make a model of one attendee’s photos

This was the model that was created on the day. It shows how tricky it can be to capture the roof. This model was made at quite a low quality to make it quicker to process.

Before the day was finished attendees heard about the built heritage of dairying in Wensleydale. We’re going to have a specific blog post about this subject so keep your eyes peeled.

We got some amazing feedback about the event:

This was an excellent session combining both theoretical and practical skills. The additional context that the historical element provided glued the whole session together.

Photogrammetry is easier than you might think and can produce amazing results

Hopefully volunteers will now create a number of models of the dairying heritage in Wensleydale.

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