Detailed knowledge of the topographical features of land is crucial to mankind. This data is critical for safety during construction and provides insights into agriculture. Mapping is a critical part of monitoring ecosystems and monitoring environmental health in an age of rapid, widespread environmental change. Drone mapping is one of the ways that this information can be collected.

A brief history

Aerial photography has been used to gather geographical data for over a century. The first aerial photograph is credited to the photographer Gaspar Félix Tournachon, who took photos from a hot air balloon in 1858. Aside from taking photos of landscapes, photography from the sky was used in World War I to provide insight into enemy positions and create photomaps for tactical operations.

After World War I, this budding technology was applied to areas of civilian interest. Progression in drone technology coincided with the emerging revolution of the digital camera and in the early 2000s, inexpensive and reliable drones came to consumer markets.

The advent of drone photography

With recent advancements in telecommunications, batteries and solid-state devices, low-cost fixed-wing drones have become a feasible solution in the military, research and civil sectors. As a result of booming technical advancements, the civil operation of fixed-wing drones has increased in prevalence. Different uses in commercial sectors or for leisure and entertainment are constantly evolving.

Quantum-Systems Trinity F90+ has a 90-minute flight time. Source: Skyscrab/CC BY-SA 4.0Quantum-Systems Trinity F90+ has a 90-minute flight time. Source: Skyscrab/CC BY-SA 4.0

On-board cameras provide high-resolution information for low-altitude applications. Images collected from drones can aid in scientific data gathering, precision agriculture, geological surveys and monitoring forest fires. As well, drones can be used for surveillance for military and law enforcement purposes.

Drones can be equipped with a variety of sensors too. In Central America, drones equipped with lidar sensors uncovered ancient ruins.

Advantages of fixed-wing drones

Fixed-wing drones have many advantages over manned aircraft in mapping applications. They can fly through tighter spaces while being closer to the ground and can be adapted for risky flights to accident-prone areas. Fixed-wing drones have advantages over quadcopters in applications that do not need ultra-high-resolution data or require covering exceptionally large areas. Their use is often limited to projects that can support the higher cost when compared to multirotor drones.

 A U.S. Air Force Global Hawk drone. A U.S. Air Force Global Hawk drone.

Fixed-wing drones aptly used by the military include models such as the Predator and Global Hawk, though they are large and expensive. Small UAVs that have less than a 6 foot wingspan are primarily developed by universities and research laboratories. Smaller drones face different design challenges, such as an increased need for a lightweight frame and compact hardware.

Table 1. Comparing common drone features. Table 1. Comparing common drone features.

An introduction to drone photogrammetry

Today, digital mapping and Geographic Information Systems (GIS) technologies provide high-quality data and maps for planning applications. Digital terrain models can show differences in elevations and points of interest. Photogrammetry can be used to generate both point clouds and 3D meshes.

Drone photogrammetry typically follows two flight patterns:

1) Nadir horizontal grids

Nadir means that the camera is pointing directly down during a drone flight. Should structures be the object of interest or vertical terrains, this flight pattern will not work well as nadir photos are taken from only one angle.

The drone will typically fly at a consistent above ground level (AGL) elevation. The elevation will be determined by the resolution of the images taken and the ground sampling distance (GSD) of the photogrammetric data.Nadir horizontal grid flight plan diagram. Nadir horizontal grid flight plan diagram. A lower GSD translates to a higher resolution. Likewise, higher altitudes of flight correspond to a greater GSD and a lower resolution.

Flight control apps allow a pre-programmed grid with photos scheduled to be taken automatically. The amount of frontal overlap should be around 75% and the side overlap should be around 60%, with a greater amount of overlap for more complicated and rugged terrains. For example, overlap should be at least 85% for forests and dense vegetation and best results are often obtained with a GSD higher than 10 cm/pixel.

Screenshot of Pix4Dmapper nadir horizontal grid flight plan.Screenshot of Pix4Dmapper nadir horizontal grid flight plan.

2) Oblique normalized grids

This flight pattern may be necessary for tight areas or for complex vertical subjects, such as a rockface. Oblique photos comprise this type of flight pattern. These photos are typically captured through manually planned flights.

Both nadir horizontal grids and oblique normalized grids can be used in conjunction, while more complex flight patterns are needed for 3D reconstruction of urban areas or rugged terrain. In these cases, the camera angle should be set between 10° and 35° to capture facades (0° is when the camera is facing directly down).

Mapping applications in conservation and agriculture

Fixed-wing drones can be used to obtain Digital Surface Models, which are geographically accurate renditions of vegetation and other structures. Biomass in forests can be estimated through mapping to provide key indicators of the carbon stock contained within the forest. This has implications for climate change mitigation strategies.

Additionally, the health of a forest can be monitored such as the dieback of a specific tree species. The loss of the tree species could indicate a more serious and widespread outcome for that landscape. Mapping can also be used to track species populations. The data is useful for protecting habitats as well as for managing resources. The use of drones in vegetation monitoring is an extension of mapping applications for drones.

Mapping technology can also be applied to help manage soil fertility and productivity. Soil management is key to precision farming where monitoring the nutrients in soil is vital. Soil maladies and variability can be identified from mapping.

Future applications

For engineering industries, the versatility offered by drones will continue to adapt and blend with other technologies. Image recognition and AI occupy the current limelight and can automatically analyze drone data with greater ease. AI can be used to automate drafting when making site plans by creating survey ready planimetric drawings. Previously, this feat was only possible by a human, but now it can be efficiently performed by a drone.

Fixed-wing drones in mapping allow for quicker and cheaper data collection when compared to traditional methods. New types of data that were previously unattainable, due to cost or terrain, can benefit from drone technology.

References

Desmond, K. (2018). Electric Airplanes and Drones: A History. McFarland & Company.

Díaz-Delgado, R., & Mücher, S. (2019). Drones for Biodiversity Conservation and Ecological Monitoring. Mdpi AG.

Tal, D., & Altschuld, J. (2021). Drone Technology in Architecture, Engineering and Construction: A Strategic Guide to Unmanned Aerial Vehicle Operation and Implementation (1st ed.). Wiley.

About the author

Jody Dascalu is a freelance writer in the technology and engineering niche. She studied in Canada and earned a bachelor's of engineering. Jody has over five years of progressive supply chain work experience and is a business analyst. As an avid reader, she loves to research upcoming technologies and is an expert on a variety of topics.

To contact the author of this article, email engineering360editors@globalspec.com