Recent developments in digital photography, software, and drones have made high-precision photogrammetric surveys more accessible at a lower cost across various scales. These advancements have enabled the use of photogrammetry drones in multiple fields such as archaeology, heritage architecture, structural inspection, emergency surveys, and more.
If you're interested in drone photogrammetry and unsure where to start, or if you're already using this technique and want to enhance your skills, you've come to the right place!
Key Considerations When Choosing a Photogrammetry Drone
When selecting a photogrammetry drone, several key factors should be carefully considered to ensure optimal performance and suitability for your specific needs. Let's explore these factors in detail:
Flight Time
The flight time of a drone is crucial as it determines how long it can remain airborne to capture data. Look for a drone with the longest flight time, typically exceeding 20 minutes, to ensure sufficient coverage of larger areas without frequent battery swaps. Consider factors like battery capacity, power management efficiency, and the weight of the additional payload.
Transmission Range
The transmission range refers to the maximum distance at which the drone can communicate with the remote controller or ground station. Opt for long-range drones, preferably over 2 kilometers, to maintain a stable and reliable connection, especially when operating in remote or challenging environments.
Camera Quality
The camera's quality plays a vital role in capturing high-resolution images for photogrammetry. Assess the following parameters:
Dynamic Range: Look for a camera with a wide dynamic range that can handle scenes with varying lighting conditions. This ensures that details in both bright and dark areas are properly captured, resulting in accurate and visually pleasing photogrammetric outputs.
Lens Quality: Opt for a drone with a high-quality lens that minimizes distortions, aberrations, and vignetting. A well-designed lens reduces image distortion and captures sharp and clear images, enhancing the accuracy of the photogrammetric process.
Global Shutter vs. Rolling Shutter: Global shutter cameras capture images simultaneously across the entire sensor, minimizing motion artifacts and improving accuracy. In contrast, rolling shutter cameras capture images line by line, potentially introducing distortions in fast-moving scenarios. Prefer drones with global shutter cameras for precise and artifact-free results.
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 crucial 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
Consider 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:
- Fixed-wing UAVs offer longer flight times and larger coverage areas, making them suitable for large-scale mapping projects that require extended flight endurance and efficient coverage.
- 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.
- 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?
Drone photogrammetry uses a drone to capture a large number of two-dimensional images over a geographic area and compiles them into accurate three-dimensional terrain models and orthomosaic maps using 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 first originated in surveillance and reconnaissance and has been used for 170 years. 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 appearance 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 overlaps each other to make the same point on the ground visible from different angles and elevations.
Source from emjcorp.com
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 useful tool for photogrammetry, resulting in 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 also equipped with the most advanced technology, which delivers a 3D model with accuracy up to 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, and crime or war, complex terrain, and harsh weather conditions.
Cost-effective Solution: Drone photogrammetry is an accessible method. Due to the financial factor, aerial photogrammetry was restricted to large engineering companies and public agencies. With the arrival of drones, values have dropped considerably, which makes it possible to hire this type of service even by 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 the 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
The following is the full overview of drone applications of photogrammetry:
Oil & Gas
Oil and gas companies use drone inspection typically for pipeline construction and infrastructure maintenance, and also rely on them to remotely inspect and observe 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.
In addition, remote monitoring with drones is now making fully automated offshore oil and gas inspection a reality.
Mining & Quarries
There is a wide range of real applications of drones in mining, from surveying, inventory management, and stockpile estimation, 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, so you can easily perform very accurate volume calculations.
Using accurate site models generated from aerial drone imagery, mine managers can now more effectively design and manage the state of road construction at mines and monitor site progress on a weekly or monthly basis.
With the high-resolution images from drones, mining companies can inspect hard-to-access places for identification of crevices, erosion, wall damage, and any other potential damages. This has gone a long way towards preventing accidents and ensuring the safety of workers.
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.
The 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 drone 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.
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