Structure from motion (SFM) is a photogrammetric technique which uses two-dimensional images to reconstruct three-dimensional structures or objects. It is one of many methodologies which can be employed to create 3D models. For instance, another popular technique is 3D Laser Scanning. However, SFM has effectively become a way to make the creation of 3D models more accessible to a wider group of people including reducing or eliminating the requirement for expensive equipment. The technique is frequently utilised within both Buildings Archaeology and archaeological fieldwork.
This could be to create models of any important artefacts recovered during an excavation- such as Thania Vipenei’s Etruscan Urn which is now housed in the Archaeological Museum of Perugia, Italy. It is also used to create models of buildings. This is especially useful for the mapping of elevations or the documentation of specific architectural details - such as stone capitals. However, 3D laser scanning is much more frequently used for the creation of models of the interiors of extensive buildings due to being a much more rapid technique - albeit, a much more expensive one!
How Does it Work?
The SFM software must be supplied with a series of images documenting an object or building. It then uses areas of overlap within these shots to stitch these images together. This allows them to be reconstructed in the 3D workspace. Because the data used to create these models is the photographs themselves, it is extremely important that a sufficient number of images is taken. These must cover all of the areas of the subject in order to produce a complete model with no missing features. One of the key difficulties in making these models is capturing enough images of higher levels of buildings - especially roof structures which are much less visible from ground level. It is therefore useful to have access to a higher vantage point or to specialist equipment like drones when applying this technique to taller buildings. It is also important to take high-quality images of the subject to ensure the clarity of the model. This is best achieved using a DSLR camera; however, results are still possible even using a mobile-phone camera! Free or low-cost apps are even available to download which enable models to be created entirely from a smartphone device. This provides valuable opportunities for public engagement strategies and allows the technique itself to become widely accessible at entry-level.
What Have We Done?
Our team has been experimenting with SFM techniques by applying them to various historic buildings. Take this ruined agricultural building as an example. This model was processed rapidly as part of one of our training exercises. Much more time can still be spent ‘cleaning’ and processing these models to produce a high-quality finished product. A measurement taken between the two ends of the elevation using a tape measure would also allow this model to be scaled using CAD. Because this structure was a single storey roofless ruin, photographs taken from ground level were able to capture the entire front elevation of the building. This model provided a much clearer image of various construction breaks in the stonework alongside details of the doorways to investigate the various agricultural functions of the building. These models also allow our entire team to gain clear understandings of the key features of the buildings which we are working on, even if they have not been to site themselves.
What Can I Do?
If you would like to learn more about 3D models, it is worth exploring open-source model building and sharing platforms. One of the most popular resources for this is sketchfab. This website allows users to buy professional models or to showcase their work on the platform. It also allows users to view free 3D models which can be shared and embedded elsewhere. Such platforms form key ways for the cultural heritage sector to fulfil its key priorities of increasing public education and participation in the historic environment, as they provide vital opportunities for public engagement with historic buildings and artefacts in a way which is often more accessible than visiting a museum or building itself. Be sure to share any of your future creations with us!