Visualising archaeology – Hillshades from Drone Surveys

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.

East-west profile across Quansboro graveyard and its environs
East-west profile across Quansboro graveyard and its environs
North-south profile of Quansboro Graveyard and its environs
North-south profile of Quansboro Graveyard and its environs

 

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.

Hill shade of height model generated from a drone survey of Quansboro Graveyard and environs.

The importance of light

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.

Mapping Killursa Graveyard

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.

 

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.

01-bing  Killursa drone orthophotography  Orthophotography generated from drone data  04-graves-other-features  Map of plots with reference grid