Home Guides LiDAR visualisations explained
LiDAR visualisations explained
Hillshade, SLRM, sky-view factor, openness and VAT are different ways of turning a grid of ground heights into a picture. Each shows some features well and hides others.
Hillshade
Hillshading computes how brightly each cell would be lit by a light at a chosen direction (azimuth) and height. It looks natural and is easy to read, but features aligned with the light do not show, and the eye can read a hollow as a bump. The usual convention is a light from the north-west, about 45 degrees above the horizon.
Multidirectional hillshade
Several hillshades from different directions are combined into one image, so features are visible whatever their orientation. The result is flatter to look at than a single hillshade.
Simple local relief model (SLRM)
A smoothed copy of the terrain is subtracted from the terrain itself. What is left is the local relief: the heights of features relative to their surroundings, with the large-scale shape of the hill removed. The size of the smoothing window decides which features remain. A small radius keeps narrow banks and ditches; a large one keeps whole enclosures. The method was published for archaeology by Ralf Hesse in 2010.
Sky-view factor
Sky-view factor measures how much of the sky is visible from each point, within a search radius. Ridges and flat ground see most of the sky and are bright; ditches, hollows and the foot of a bank see less and are dark. It does not depend on a light direction. It was introduced as a relief visualisation by Zakšek, Oštir and Kokalj in 2011.
Openness
Positive openness is similar to sky-view factor but measured as angles above the surface; it emphasises convex features such as banks and edges. Negative openness, measured below the surface, emphasises concave features such as ditches.
Slope
Slope shows the steepness of the ground. It outlines the edges of banks and scarps clearly and is one of the layers in the VAT composite.
VAT (Visualisation for Archaeological Topography)
VAT blends hillshading, slope, positive openness and sky-view factor into one greyscale image, using fixed settings published by Kokalj and Somrak in 2019 and implemented in the Relief Visualization Toolbox. It is designed so that a small feature looks the same wherever it is and whichever way it faces, which makes it useful for systematic searching.
Which one to use
- To look at a known site: hillshade, turning the light, and LiDAR over satellite.
- To search an area for low earthworks: SLRM at a small radius, VAT or multidirectional hillshade.
- On steep ground: SLRM or sky-view factor, which remove most of the effect of the hillside.
Related
Sources
- Environment Agency, National LIDAR Programme and LIDAR Composite DTM (1 m), Open Government Licence. © Environment Agency copyright and/or database right.
- Natural Resources Wales and Welsh Government LiDAR (1 m), Open Government Licence. Contains Natural Resources Wales information © Natural Resources Wales and Database Right.
- Historic England (2018). Using Airborne Lidar in Archaeological Survey: The Light Fantastic. Swindon: Historic England.
- Hesse, R. (2010). LiDAR-derived Local Relief Models: a new tool for archaeological prospection. Archaeological Prospection 17(2), 67–72.
- Zakšek, K., Oštir, K. and Kokalj, Ž. (2011). Sky-View Factor as a relief visualization technique. Remote Sensing 3(2), 398–415.
- Kokalj, Ž. and Somrak, M. (2019). Why not a single image? Combining visualizations to facilitate fieldwork and on-screen mapping. Remote Sensing 11(7), 747.
Last updated 2026-10-16.