3D mapping, also known as photogrammetry mapping is the science of making measurements from photographs. The output from photogrammetry software is typically a 3D map, a 3D drawing or a 3D model of some real world object or land mass. There are two primary types of photogrammetry: aerial and close range. Aerial Photogrammetry is the process of using a drone (or aircraft) to produce aerial images, which can be turned into a 3D model or stitched map layer. Close range photogrammetry is when images are captured using a handheld camera or with a camera mounted to a tripod. The output of this method is not to create topographic maps, but rather to make 3D models of a smaller object.
Why you need it?
Land management / cartography / urban planning
Survey drones generate high-resolution orthomosaics and detailed 3D models of areas where low-quality, outdated or even no data, are available. They thus enable high-accuracy cadastral maps to be produced quickly and easily, even in complex or difficult to access environments.
After post-processing with a photogrammetry software, these same images can produce very detailed elevation models, contour lines and breaklines, as well as 3D reconstructions of land sites or buildings.
Precise area measurements
High resolution orthophotos let you make highly-accurate distance and area measurements.
Stockpile volumetric measurements
With 3D mapping software, it is also possible to obtain volumetric measurements from the very same images. This fast and inexpensive method of volume measurement is particularly useful to calculate stocks in mines and quarries for inventory or monitoring purposes.
It is much easier to fly a drone than to manually capture the data by going up and down a stockpile. Since drones are capturing the data from above, operations on site won’t be interrupted.
How aerial 3D maps and models are created
The way the photogrammetry tends to work is fairly simple: a drone flies over the target area, capturing photographs and recording data to enable you to put together a comprehensive survey of your land, or building, from up above.
The drone camera will capture hundreds, even thousands of overlapping photos of the ground, structure or model. The photos will overlap each other, with an overlap of 70 to 90%. The 3D map or 3D model is then created using aerial image stitching algorithms. That is why it is impossible to fly accurately by pilot navigation. The drone will fly using autonomous programmed flight paths called waypoints and take photos at a specified distance interval.
Each photo captured will also have its GPS coordinates (Geotagging) saved, which also assists to build the 3D map. A geotagged photograph is associated with a geographical location. Usually this is done by assigning at least a latitude and longitude to the image. Other fields may be optionally included such as altitude and compass bearing.
Drone surveying deliverables
Photogrammetry software is able to produce several types of data files described below.
Drone images are corrected for image distortion and stitched together during post-processing to create a highly-accurate orthomosaic map.
File formats: GeoTIFF (.tiff), .jpg, .png, Google tiles (.kml, .html)
3D point cloud
A densified point cloud can be generated from drone images. It provides a very accurate model for distance (slant and horizontal), area and volume measurements.
File formats: .las, .laz, .ply, .xyz
Digital surface and terrain models (DSM, DTM)
Drone images can also be used to create DSM and DTM models of the area.
File formats: GeoTiff (.tif), .xyz, .las, .laz
3D textured mesh
The 3D textured mesh is a reproduction of the edges, faces, vertices and texture of the area shot by the drone. This model is most useful for visual inspection or for when external stakeholders or public involvement is essential for a project.
File formats: .ply, .fbx, .dxf, .obj, .pdf
How accurate is a drone survey?
The performance and type of drone, the quality of its components, the camera resolution, the height at which the drone flies, the vegetation, and the method and technology used to geolocate the aerial images can heavily influence the accuracy of drone survey mapping. At this point, it is possible to reach an absolute accuracy down to 1 cm (0.4 in) GSD under optimal conditions with a high-end surveying drone.
The best drone for your land surveying project depends on many factors, such as the size of the survey site, desired output quality, and your budget and preferences.