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 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.
Impact GIS undertook a drone survey of Killirsa Graveyard in County Galway to generate high resolution orthophotography for mapping of grave plots. Grave plots were mapped using Geographic Information System (GIS) software, allowing for data associated with each grave plot to be stored in an accompanying database. See the slide show below.
Bing aerial imagery of Killursa
Online sources of aerial photography are not of a sifficiently high resolution to be able to map grave plots
Drone survey of Killursa
High resolution orthophotography generated from a drone survey
Extract of drone survey
An extract from the drone survey showing the resolution of the orthophotography
Grave plots and other features mapped
Grave plots and other features mapped using Geographic information system software
Map of plots with reference grid
A 10m x 10m grid with alphanumeric labels overlaid to aid in locating individual grave plots
Killursa map with index of names
Index of names referenced to 10m x10m alphanumeric grid
Why use GIS?
Firstly it is probably best to explain what a Geographic Information System is. It’s all in the name, it is as system that allows you store information which is associated with location (geographic data). Most relevant to this project, GIS allows you to draw polygons, such as the squares and rectangles of the grave plots, and each one of these, as well as being spatially correct (in the right location), can have information about it stored in a database. So each grave plot can have the names, dates, inscriptions etc. stored and this information can be sorted, searched, filtered etc. This can form the basis of labelled paper maps, a searchable database, interactive online maps etc.
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.