Drones capture a birds eye view of the ground in amazing detail but are capable of so much more when their imagery is processed using photogrammetry.
Impact GIS recently undertook a drone survey of a graveyard to inform discussions between Galway County Council and the National Monuments Service. Galway County Council are seeking to expand the graveyard and the National Monuments Service were concerned about potential impacts on an early christian enclosure associated with the graveyard.
The easiest way to have a meaningful discussion about the potential impacts, is if everyone is able to visualise clearly what’s there, however a review of available aerial photography wasn’t much help.
Other techniques, such as surveying profiles, require a degree of mental gymnastics to ‘see’ what is there.
Impact GIS recommended a drone survey. Photogrammetry generates a 3D model of the ground surface (also referred to as Digital Surface Models (DSM) or Digital Elevation Models (DEM)), which can be processed using GIS software to produce a hillshade representation, where the software generates shading/shadows based on the relative position of a simulated light source.
The video below demonstrates the importance of light for identifying potential archaeological features. Flat light or overcast conditions, which limit shadows, make it extremely difficult to differentiate the small topographical changes that may be indicative of archaeological features.
In the video below a drone / UAV survey was undertaken to create a detailed 3D model or Digital Surface Model (DSM). The DSM, as a software construct of the 3D surface of the ground, can have its texture changed and can be lit from any angle providing the shadows that may otherwise be lacking.
Impact GIS recently undertook a photogrammetric survey, on behalf of Moore Group, of an historic well exposed during road realignment and upgrade works in Dublin. Located to the north of Phoenix Park, along Blackhorse Avenue, the Well is noted as ‘Poor Man’s Well’ on both the 6 Inch (circa 1830) and 25 Inch (circa 1900) historic Ordnance Survey maps. The following 3D model was created from a measured, photographic survey and used to produce a series of figures for inclusion in the excavation report for the project.