What is drone photogrammetry?
Drone photogrammetry is the process of taking and stitching together many photographs to create accurate measurements, 3D models, and maps of real-world objects or environments. Many images are taken at routine intervals along a flight path with a survey drone, then drone photogrammetry software is used to organise and overlap the photos into an orthomosaic.
Traditionally the photographs used in photogrammetry can be captured using a variety of devices, such as cameras or laser scanners, depending on the application and the level of precision required. Photogrammetry is widely used in fields such as architecture, engineering, surveying, geography, and archaeology, as well as in the entertainment industry for creating 3D models and visual effects in films and video games.
What are the benefits of using drones for photogrammetry?
Drone photogrammetry offers a range of advantages over traditional surveying methods, including cost-effectiveness, speed, accuracy, and safety.
Here are some of the benefits for photogrammetry compared to other methods:
- Aerial perspective: Drones are capable of capturing images from a unique aerial perspective that is not possible with ground-based cameras. This perspective can be especially useful for mapping and surveying large areas or inaccessible terrain.
- Cost-effective: Drone photogrammetry can be more cost-effective than traditional surveying methods, as it can reduce the need for ground-based surveying equipment and personnel.
- Time-efficient: Drone photogrammetry can also be much faster than traditional surveying methods, as drones can cover large areas in a shorter amount of time.
- Safety: Drones can be used to survey or map hazardous or inaccessible areas, reducing the risk to human surveyors.
- Flexibility: Drones can be used in a variety of settings and can be quickly deployed to collect data in different locations.
As drone technology continues to improve, they’re becoming an increasingly important tool for a wide range of mapping and surveying applications.
Areal vs Land Based Photogrammetry
Both aerial and land-based photogrammetry have their strengths and weaknesses, and the choice of which method to use will depend on the specific project requirements. Aerial photogrammetry is typically used for larger areas or features that require a broad overview, while land-based photogrammetry is more suitable for smaller, detailed features.
Aerial photogrammetry can also include photos taken from an aircraft rather than a drone. Aerial photogrammetry can be more cost-effective and time-efficient than traditional ground-based surveying methods, as it eliminates the need for surveyors to physically access the area being surveyed.
Land-based photogrammetry can be more accurate than aerial photogrammetry, as it is easier to control the camera and the ground control points needed for accurate image processing.
Drone Photogrammetry vs LiDAR
LiDAR is a remote mapping technique that is often confused with drone photogrammetry but some drones such as the Matrice 300RTK with the Zenmuze L1 camera can do both.
Drone photogrammetry and LiDAR are both technologies used in remote sensing and geospatial mapping. While they share some similarities, there are also some significant differences between the two.
What is LiDAR
Lidar (Light Detection and Ranging) is a type of remote sensing that uses laser light to measure distances and create high-resolution 3D maps of objects and environments. It works by emitting laser pulses that bounce off the target object or surface and return to the lidar sensor, which measures the time-of-flight of the light to calculate the distance.
By analyzing the timing and intensity of these reflections, this method makes a detailed point cloud of the terrain that can be used for digital elevation models (DEMs) and other types of geospatial data.
Drone photogrammetry, on the other hand, works by taking a series of overlapping aerial photographs with the drone camera which are combined to make an orthomosaic.
How Drone Photogrammetry Works
Drone photogrammetry works by using a drone to capture a series of overlapping aerial photographs of the terrain or object that needs to be mapped.
The steps for drone photogrammetry are:
- Flight planning: The first step is to plan the drone’s flight path using specialized software. The software will calculate the optimal altitude, speed, and camera settings for capturing the necessary photographs.
- Drone deployment: Once the flight plan is set, the drone is deployed and flown along the predetermined path while taking photographs at regular intervals. The drone is usually equipped with a high-resolution camera and a GPS receiver to capture accurate location data.
- Image processing: After the drone has captured the necessary photographs, they are downloaded to a computer and processed using specialized photogrammetry software. The software identifies common features in the overlapping images and uses them to create a 3D model of the terrain or object.
- Model creation: The photogrammetry software generates a point cloud of the terrain or object by analyzing the 3D coordinates of the common features identified in the overlapping images. The point cloud is then used to create a digital surface model (DSM) and orthophoto.
- Data analysis: The DSM and orthophoto can be used to generate a range of geospatial data, including topographic maps, elevation models, and volume calculations. This data can be used for a range of applications, including land surveying, construction planning, and environmental monitoring.
What equipment is needed for drone photogrammetry?
To perform drone photogrammetry, you will need several pieces of equipment, including:
- Drone: A drone is the primary piece of equipment needed for drone photogrammetry. The drone should have a high-resolution camera that is capable of capturing detailed aerial photographs. Ideally, the drone should also be equipped with GPS and a 3 axis gimbal to ensure accurate positioning and stable flight.
- Ground control points (GCPs): Ground control points are physical markers that are placed on the ground to provide a reference point for the photogrammetry software. The GCPs should be surveyed accurately with high-precision GPS equipment.
- Software: You will need specialized software to plan your flight, process your images, and generate your 3D model. There are many options available, including open-source software and commercial solutions. I go through some of the software options in the drone mapping article.
- Computer: Drone photogrammetry requires a powerful computer with a dedicated graphics card to process large volumes of image data.
What camera setting are needed for drone photogrammetry?
The camera settings needed for drone photogrammetry can vary depending on the specific project and the type of camera being used. However, there are some general guidelines and best practices that can help ensure high-quality results. Some of the key camera settings to consider for drone photogrammetry include:
- Aperture: In general, it’s best to use a small aperture (higher f-stop number) to maximize the depth of field and ensure that the entire scene is in focus.
- Shutter speed: It’s important to use a fast enough shutter speed to avoid motion blur in the images, especially when the drone is moving or encountering windy conditions.
- ISO: In order to avoid image noise and maintain high image quality, it’s best to use the lowest possible ISO setting.
- Image format: RAW or TIFF format is preferable over JPEG because they retain more information and are less compressed, allowing for better post-processing.
- Overlap and sidelap: To ensure sufficient overlap between images for accurate photogrammetric processing, it’s recommended to set the camera to capture images with 80-90% overlap and 60-70% sidelap.
- Resolution: Higher camera resolution can result in more detailed images, allowing for greater accuracy in the final 3D model.
- White balance: It’s best to set the camera’s white balance manually to ensure consistency in color representation across all images.
For an intro into these settings take a look at Drone Photography for Beginners.
Overall, it’s important to choose camera settings that will allow for accurate and consistent capture of the terrain or object being mapped, while also maximizing image quality and minimizing distortion. It’s also important to test and calibrate the camera settings before beginning any photogrammetry project, to ensure that the final results are accurate and reliable.
Can any drone be used for photogrammetry?
Not all drones can be used for photogrammetry for a few reasons:
- Accuracy: One of the most important aspects or areal surveying or drone photogrammetry is accuracy. The drone must have GPS with RTK or PPK accuracy and the ability to follow waypoints for automating the flight path.
- Camera quality: The primary requirement for drone photogrammetry is a high-quality camera capable of capturing detailed and accurate images. Not all drones come equipped with high-quality cameras, and even those that do may not have the resolution or image quality necessary for accurate photogrammetric processing.
- Stability and control: Drone photogrammetry requires stable flight and precise control over the drone’s movements. Not all drones are designed for this type of work and may lack the necessary features such as GPS, altitude hold, and obstacle avoidance, which are critical for accurate mapping.
- Battery life and range: Drone photogrammetry projects can take a long time and require the drone to cover large areas. Drones with short battery life or limited range may not be able to cover the necessary area, or may require frequent battery changes, which can interrupt the flight and cause inconsistencies in the image data.
- Processing power: Drone photogrammetry requires a significant amount of computing power to process the large volumes of image data captured during the flight. Not all drones are capable of transmitting or storing the necessary data, and may require additional hardware or software to process the images.
What is the best drone for photogrammetry?
The overall best drone for photogrammetry is the DeltaQuad Pro #Map. This drone has a generous flight time of 110 minutes with 1200 hectares of coverage, up to 100km range from the controller, a very high 61MP resolution camera and, unlike most fixed-wing drones doesn’t require a runway for take off.
To see how the specification of this photogrammetry drone compares to multirotor drones, check out the article What to Look for in a Survey Drone where I compare the DeltaQuad Pro with the Matrice 300 RTK, Wingra One and Mavic 3 Enterprise.
