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Image based 3D modelling of an archaeological excavation

At the excavation of Bispevika B8A, we make use of the most advanced techniques to document our finds. Particularly challenging is the documentation of shipwrecks. In order to document every single detail of a wreck at the exact location where it sank about 450 years ago, we make use of a technique called image based 3D modelling, or photogrammetry.

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    Hand drawing, made in 1986, of the Medieval ship Isegran 1. Dag Nævestad/Norwegian Maritime Museum

Archaeologists love technology, especially when it makes our job easier. Traditionally, boat finds were hand-drawn using measuring tapes, pencils and paper. Later they were measured in with survey instruments such as a total station. Although these techniques can be very accurate, they require a lot of time and the results are limited to geometric shapes such as points and lines, without texture or color.

Anno 2019, we have techniques at hand that produce faster and more detailed results. At the excavation in Bispevika we use a technique called photogrammetry which uses images to obtain geometric information. By taking a large number of images from different points of view, it establishes a geometric relationship between the images and the scene. In the case of the Bispevika boats, we use about 900 images for each boat in order to build a 3D model.

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    The principle of photogrammetry Theia-sfm.org (2016)

From the images, the software creates a point cloud containing millions of 3D points, which are connected to each other and form a mesh. The texture from the images is projected on this mesh and results in a 3D model.

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    A wireframe and textured 3D model of Bispevika 18. Norwegian Maritime Museum

The 3D models are used to create an orthophoto, which combines all the images that were used to create the model into one large image. This image is on scale, which means that we can use it to measure all the planks, finds, and other parts that belong to the boat digitally. The archaeologists in the field use this orthophoto to sketch all the individual boat parts and their position. Behind a computer, all the boat parts will be drawn digitally on top of the 3D model so that we can virtually reconstruct all the details of the boat. By using ground control points which are measured with a total station, the entire 3D model is georeferenced; placed in its correct position in space.

Today, this method of using photogrammetry is well established in archaeology, both on land and underwater. Using this method, we can document boats in the field more accurately than ever before. In the link below, you have the chance of seeing a 3D model of Bispevika 18 as documented in the field by yourself.

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Nævestad, D & Kloster, J. 1986. Isegranskipet. Foreløpig rapport om skipsfunn ved Fredrikstad. Norsk Sjøfartsmuseum. Oslo 1986.