BRONZE AGE CAIRN & STONE SETTING IN ÄNGGÅRDSBERGEN. 3D modelling using Structure-from-Motion Photogrammetry.

Abstract

Some research has been made on Cairns and Stone settings but no in-depth analysis. The aim was to analyse and do 3D models over a study area of a Cairn and a Stone setting. This was done by using Structure-from-Motion Photogrammetry, and the data (photographs) was collected with a drone and a system camera. Field mapping was done in the area with the human eye. To build the 3D models, DEM, process several maps and statistics, the computer programs Agisoft Metashape, Topography Visualisation Toolbox and ArcGIS Pro was used. Agisoft Metashape was first used to build a dense cloud, dense cloud with point confidence turned on, and a mesh. Next was to build the texture of the model, which is the final 3D model. Later on was also DEM and Orthomosaics produced and exported. When finished with Agisoft Metashape, the mesh layer was used in Topography Visualisation Toolbox to produce different sort of maps. In this report was the blended map in colour used for a good result which shows where in the big Cairn there once was a stone coffin. Thereafter the DEM produced in Agisoft Metashape was used in ArcGIS Pro to do a pre-study in statistical purposes. The tools focal statistics and minus was used to get a better contrast of the Cairn and Stone setting. This data could be used later on for further analysis of the rocks, which could be done manually or by using AI. In the area were a quartz vein and three different kind of rocks found. The rocks found were a medium to coarse-grained granite with a lot of potassium feldspar, a very well foliated granite which have a medium to fine grain size and consists of a lot of potassium feldspar and a coarse-grained pegmatite which also consists of a lot of potassium feldspar. The pegmatite and the quartz vein are not so common in the area, so they have probably come from further away. In the study area have also interpretations been made on the directions and shape of the stone coffin, and which rocks could have been part of the roof/upper part of the stone coffin. Half of the big Cairn has a specific long axis direction and a direction of which the rocks are pointing at. There have also been found some possible quarries nearby.