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.
Impact GIS was recently appointed by Kilbeacanty Graveyard Committee to undertake aerial/drone surveys of two graveyards near Gort in County Galway, with a view to mapping and recording the graveyards.
Drone surveys were undertaken using ground control points (GCP) surveyed in with a survey grade GNSS (GPS) and the imagery captured was then processed using Pix4D to produce detailed orthophotography. Extra GCPs were surveyed in to check the accuracy of the final orthophotography. A review of GCPs in the final orthophotography found their accuracy to be within 1 to 2 cm. The orthophotography was imported into QGIS and used to producing mapping, the marking up features, including bounding walls, paths, grave plots, the locations of headstones etc. Draft mapping has now been issued to the client, who will use it to align grave numbering with previous surveys. Impact GIS and Galway County Council will then host a photographic workshop, training local volunteers to undertake a photographic survey of the graves and headstones within the graveyards. Details for all graves and memorials will be added to the GIS database and uploaded, with photographs, to Galway County Council’s Galway Graveyards website.