Abstract
A field of approximately 20m2 of petroglyphs at Evenhus in Frosta, Nord-Trøndelag, Norway has been digitized with a mobile, low-cost 3D camera developed by SINTEF. The rock art was illuminated by parallell light stripes producted by a standard, off-the-shelf video projector. When images are captured with a camera placed at an angle with the projector, the deflection of the light stripes allows us to calculate the exact 3D shape of the object. A 3D model of the entire field of petroglyps at Evenhus was obtained by stitching together 50 individual 3D images, each of around 0.6m2 with approximately 20% overlap. The entire data acquisition was performed in one single day. The result was a 3D model that consists of approximately 60 million data points. Because of the large amount of data and limitations in system memory, intelligent techniques for data reduction had to be applied. The preferred solution was to use texture maps to represent local height deviations in the rock carvings, while a decimated 3D model was used to represent the shape of the mountain itself. Image analysis techniques was applied on the texture maps to amplify local height deviations and enhance the the actual rock carvings while suppressing the effect of the curvature of the mountain. The resulting 3D model with texture is suitable for further analysis, such as to study erosion and to reveal distinctive marks made by different types of tools.