Glossary

Plain-language explanations of the drone and humanitarian terms used in this guide.

Drone terms

AGL (above ground level)

Height measured from the ground directly below the drone, rather than from where it took off or from sea level. Keeping a constant AGL over hilly ground keeps the level of detail even.

AOI (area of interest)

The area you want to map, usually drawn as a boundary on a map.

Elevation model

A map of heights. A surface model (DSM) includes buildings and trees; a terrain model (DTM) shows the bare ground.

Geofencing

Restrictions built into a drone's software by the manufacturer, which warn you or stop it flying in certain zones (such as near airports). Separate from government flight authorization.

GCPs (ground control points)

Marked points on the ground whose exact location is measured with a precise GPS device. They're used to line up the final map accurately. Only needed when precise measurement matters, for example for 3D or elevation outputs.

GeoTIFF

An image file that also stores where on Earth it is, so mapping software can place it correctly. The usual format for sharing finished drone maps. A COG (Cloud Optimized GeoTIFF) is a version that works well on the web.

GSD (ground sampling distance)

How much ground one pixel in the image covers. A GSD of 4 cm means each pixel shows a 4 x 4 cm patch. Smaller numbers mean more detail.

Gimbal

The motorized mount that holds the camera steady and controls which way it points.

LiPo battery

Lithium polymer battery, the type used in most drones. Light and powerful, but a fire risk if damaged.

NOTAM (Notice to Air Missions)

An official notice of a temporary airspace restriction or hazard, such as an emergency helicopter operation.

Orthomosaic

A large, flat, top-down map image stitched together from many drone photos, and corrected so that distances can be measured on it.

Overlap

How much each photo shares with its neighbours, along the flight line (front overlap) and between flight lines (side overlap). Processing needs plenty of overlap to stitch photos together.

Photogrammetry

The process of turning many overlapping photos into maps and 3D models.

Point cloud

A 3D model of an area made of millions of individual points, each with a position and colour. Usually shared as a COPC (Cloud Optimized Point Cloud) file, which, like a COG, can be viewed on the web without downloading the whole thing.

RTH (Return to Home)

A safety feature that flies the drone back to its take-off point automatically, for example when the battery is low or the signal is lost.

RTK / PPK

Ways of correcting a drone's GPS position to within a few centimetres, either during the flight (RTK) or afterwards (PPK). An alternative to ground control points.

VLOS (visual line of sight)

Being able to see the drone directly with your own eyes, not only through the screen. Required in most countries. In practice, a small drone can be hard to pick out at mapping altitude, so keeping a clear view of the whole flight area matters as much as tracking the drone itself.

Humanitarian terms

Assessment working group

The group that coordinates needs assessments in a response, so organizations don't duplicate each other. Aerial assessment coordination usually sits within it.

Information management working group

The group that coordinates how data and maps are collected, managed, and shared in a response.

NDMA (national disaster management authority)

The government body responsible for disaster preparedness and response in a country. Names vary between countries.

OCHA

The UN Office for the Coordination of Humanitarian Affairs, which coordinates international humanitarian responses.

UNDAC

The United Nations Disaster Assessment and Coordination team: experts deployed at short notice to help a government assess and coordinate the response to a sudden emergency.