A Comprehensive Beginner's Guide to Drone Photogrammetry

Recent Developments in Drone Photogrammetry

Recent advancements in digital photography, drone technology, and photogrammetry software have made it possible to conduct high-precision surveys at relatively low costs across a wide range of scales. These innovations have opened up new opportunities in fields such as archaeology, heritage preservation, structural inspections, emergency mapping, and more. Whether you're new to drone photogrammetry and looking to get started, or you're already familiar with the technology and looking to deepen your expertise, you’ve landed in the right place.

Factors to Consider When Choosing a Photogrammetry Drone

Selecting the right photogrammetry drone involves careful consideration of several key factors to ensure optimal performance and suitability for your specific needs. Below, we’ll delve into these factors in detail:

Flight Time

Flight time is critical as it determines how long the drone can stay airborne to capture data. Opt for a drone with a flight time of at least 20 minutes to cover larger areas efficiently without needing constant battery swaps. Consider factors like battery capacity, power management efficiency, and payload weight.

Transmission Range

The transmission range refers to the maximum distance at which the drone can communicate with the remote controller or ground station. Long-range drones, with ranges exceeding 2 kilometers, are preferable, especially in remote or challenging environments, to maintain a stable and reliable connection.

Camera Quality

The quality of the drone’s camera plays a vital role in capturing high-resolution images for photogrammetry. Key parameters to assess include:

• Dynamic Range: A wide dynamic range ensures that details in both bright and dark areas are properly captured, resulting in accurate and visually appealing photogrammetric outputs.
• Lens Quality: High-quality lenses minimize distortions, aberrations, and vignetting, ensuring sharp and clear images that enhance the accuracy of the photogrammetric process.
• Global vs. Rolling Shutter: Global shutter cameras capture images simultaneously across the entire sensor, minimizing motion artifacts and improving accuracy. Rolling shutter cameras, on the other hand, capture images line by line, which can introduce distortions in fast-moving scenarios. For precise results, prefer drones with global shutter cameras.
• Aperture: The aperture determines the amount of light entering the camera and affects image sharpness and depth of field. Opt for drones with adjustable apertures or wide fixed apertures (e.g., f/2.8 or lower) to accommodate various lighting conditions and achieve optimal image quality.

Photogrammetry Accuracy

Accuracy is paramount in photogrammetry. Evaluate the drone’s positioning system, such as GPS or GNSS, and its accuracy specifications. Look for drones that offer high positional accuracy, typically expressed in centimeters, to ensure precise georeferencing and measurement accuracy in the final output.

Software Compatibility

Ensure that the drone’s captured data is compatible with popular photogrammetry software solutions. Check if the drone manufacturer provides integration or compatibility with commonly used software packages for data processing and 3D reconstruction. This compatibility ensures a seamless workflow and the ability to leverage advanced software functionalities for analysis and visualization.

RTK vs. PPK

Decide whether real-time positioning accuracy or post-processed accuracy is more important for your project. Real-Time Kinematic (RTK) systems provide instantaneous positioning corrections during flight, while Post-Processed Kinematic (PPK) systems apply corrections after data collection. Choose the system that best suits your specific project requirements and accuracy needs.

Drone Types

Evaluate the advantages and limitations of different drone types:

1. Fixed-wing UAVs offer longer flight times and larger coverage areas, making them suitable for large-scale mapping projects requiring extended flight endurance and efficient coverage.
2. Multirotor drones provide more flexibility in terms of flight maneuvers, hovering capabilities, and precise data collection. They are ideal for smaller areas or projects that require detailed inspection or close-up imaging.
3. Hybrid VTOL (Vertical Take-Off and Landing) drones combine the benefits of fixed-wing and multirotor drones. They offer both efficient mapping capabilities and versatile maneuverability, making them suitable for various applications, including surveying, inspection, and mapping of complex terrains.

What is Drone Photogrammetry?

In essence, drone photogrammetry uses a drone to capture numerous two-dimensional images over a geographic area and compiles them into accurate three-dimensional terrain models and orthomosaic maps with specialized photogrammetry software. More than just a collection of photographs, drone photogrammetry allows you to see the same ground point from different angles and altitudes. From there, you can easily create a 3D map that includes a range of useful visual cues, such as color and texture.

Photogrammetry has a rich history, originating in surveillance and reconnaissance over 170 years ago. During World War I, pilots combined photography with manned flights to gather intelligence from behind enemy lines. Without context, photographs alone were of little value, so these pioneers used local landmarks and landscape features to determine the direction of objects in images. In the decades that followed, these practices evolved with the advent of new tools, from stratospheric U2 aircraft to advanced weather satellites, to modern drone photogrammetry.

Today’s photogrammetric maps are constructed using advanced GIS software to produce surveyor-level measurements of landscapes and infrastructure. These maps are detailed enough to provide valuable insight into environmental conditions in the field.

How Does Drone Photogrammetry Work?

Drone photogrammetry is a two-stage process, including image capture and image processing.

Image Capture: The first step is to capture the images needed for the project. This can be done with a still camera or video camera mounted on a drone. The 3D modeling drone will capture a large number of high-resolution photos of an area that overlap each other to make the same point on the ground visible from different angles and elevations.

Image Processing: The aerial photos are then processed manually or using photogrammetry software, which combines or “stitches” the images into a single high-resolution orthomosaic aerial map and 3D models. Photogrammetry software corrects for distortions in the camera sensor and lens as well as errors caused by variations in the terrain, resulting in high-quality maps and 3D models.

Benefits of Drones for Photogrammetry

Drones can be a valuable tool for photogrammetry, offering the following benefits:

Improved Efficiency and Accuracy: Drone photogrammetry makes it possible to obtain a large amount of detailed information about the target area quickly and remotely. Since drones can fly lower than manned aircraft and are equipped with advanced technology, they deliver 3D models with accuracy up to the centimeter level.

Enhanced Safety: Photogrammetry drones allow you to capture images from remote locations and transmit them securely to computer systems, allowing surveyors to easily access data in hard-to-reach or unsafe areas, such as places with severe volcanic activity, crime or war zones, complex terrain, and harsh weather conditions.

Cost-Effective Solution: Drone photogrammetry is an accessible method. Historically, aerial photogrammetry was restricted to large engineering companies and public agencies due to financial barriers. With the advent of drones, costs have dropped significantly, making this type of service affordable even for small and medium-sized organizations.

How Accurate is Drone Photogrammetry?

Each step in the process of collecting data and creating output from the drone has the potential to add a small element of error to the final result. Several variables affect the overall accuracy of drone photogrammetry, including camera size, number of photos collected, photo overlap ratio, flight altitude, GPS signal strength, and ground sampling distance (GSD).

With the CA-103 61MP full-frame camera and a PPK GNSS receiver, the JOUAV CW series VTOL drone is capable of achieving a Ground Sampling Distance of 5-8mm per pixel, depending on terrain and flight altitude. This means the best possible relative accuracy in the model would be down to 1cm horizontal (x-y) and 1.5cm vertical, enabling precise spatial and volumetric analysis.

Real-World Applications for Drone Photogrammetry

Drone photogrammetry has found applications across a wide range of industries:

Oil & Gas

Oil and gas companies use drone inspection for pipeline construction and infrastructure maintenance, as well as for remotely inspecting and observing equipment, infrastructure components, and other company assets. Drones can provide a 360-degree view of objects to monitor site operations and keep a close eye on new facilities. The AI tracking function of the drones can also automatically identify and locate damage or leaks, helping to speed up repairs and minimize local impact. Remote monitoring with drones is now making fully automated offshore oil and gas inspection a reality.

Mining & Quarries

Drones are widely used in mining, from surveying and inventory management to hazardous gas and leakage detection. Drone photogrammetry can be used to generate detailed digital surface models, digital terrain models, and 3D models of a mining site, enabling accurate volume calculations. Using accurate site models generated from aerial drone imagery, mine managers can more effectively design and manage the state of road construction at mines and monitor site progress on a weekly or monthly basis. Drones can also inspect hard-to-access places for identification of crevices, erosion, wall damage, and any other potential damages, preventing accidents and ensuring worker safety.

Agriculture

For companies managing large areas of land, drone photogrammetry can be used to capture images of crops. With these bird’s-eye views, they can detect crop growth, estimate crop yields, and identify issues like soil erosion and crop diseases. Drones can carry different payloads at the same time, providing farmers with real-time and accurate diversified data that they can act on immediately.

Utilities

Photogrammetry is often used by utility companies to measure infrastructure in remote areas such as power line inspection, solar farm inspection, and wind farm inspection. Photogrammetry with drones can be used to prepare for maintenance work and repairs before engineers arrive on site, greatly reducing the manpower and resources required for infrastructure safety and improving worker safety.

Environmental Monitoring

There is also a strong demand for UAV photogrammetry in environmental monitoring. They use photogrammetry to study issues such as land change, pest infestation, invasive plant growth, wildfire risk, and more. Drones are increasingly popular with first responders, who can use drone footage of the aftermath of a flood or fire to develop rescue strategies and reduce risk later on.

Best Drone for Photogrammetry

Now that you already know that not just any drone is good for photogrammetry and, more to the point, that there are many requirements that a mapping drone needs to meet, we're going to show you the best photogrammetry drone options on the market.

An overview of the top 5 photogrammetry drones:

PH-20	CW-007	CW-15	CW-25E	CW-30E
Drone type	Six-rotor	VTOL	VTOL	VTOL	VTOL
Flight range	30km	30/50km	30/50km	50/100km	100/200km
Payload capacity	10kg	1kg	3kg	6kg	8kg
Max. flight time	70min	120-180min	120-180min	120-240min	350-600min
Max. flight speed	64.8km/h	61.2km	61.2km	72km/h	90km/h
Wind Resistance	17.8 m/s	10.8-13.8m/s	10.8-13.8m/s	13.9-17.1m/s	13.9-17.1m/s
Available payload	Ortho camera, spectrum sensor, LiDAR	Ortho camera, spectrum sensor, LiDAR, aeromagnetic system	Ortho camera, oblique camera, LiDAR, aeromagnetic system	Ortho camera, oblique camera, LiDAR, SAR, aeromagnetic system	Ortho camera, spectrum sensor, oblique camera, LiDAR, SAR, aeromagnetic system