Photogrammetry

Photogrammetry is based on stereo photography and involves taking a series of slightly overlapping images of the same object, and the processing of these photos by specialist software to create 3D computer models. It is an inexpensive and practical way of recording rock art, as the required field equipment is relatively cheap and light to carry. This recording technique has been used in other rock art projects, such as the Northumberland and Durham Rock Art Project, which was of particular inspiration for W.R.A.P.

W.R.A.P. WORKFLOW

In the field, wooden blocks (scale bars) are placed around the rock in order to produce scaled models. A series of oblique photos are first taken to get an overall sense of the stone. Vertical photos, overlapping by 50-60% at least, are then taken of the decorated surface. The rock surface should be fairly dry, as too much moisture causes noise in the finished model.

Once all the necessary photos are taken, they are inputted into a 3D reconstruction software (Agisoft Photoscan). The software seeks out points of overlap between the photographs to create a point cloud. The next step of the processing is the “build geometry” phase, which produces a solid model. Texture can be added to the model, drawing from the colours and textures of the photographs. Other 3D mesh processing software (Meshlab) is then used for further editing and for exploration of different ways of presenting the model.

This project uses SMR (Sites and Monuments Record) numbers to identify the individual panels. In some cases, SMR numbers have yet to be assigned, and townland names were used to identify these sites.