Photogrammetry by drone - what does it consist of and which drone will be best for it?
Precise control of the flight path and high quality cameras make modern drones capable of providing highly accurate spatial data. What's more, it is often much cheaper than traditional measurement methods. Such activities are referred to as drone photogrammetry. What exactly is photogrammetry, why is it so important and what kind of drone for photogrammetry will work best?
What is photogrammetry?
Photogrammetry is a field of science and technology that focuses on acquiring information about physical objects and their location from photographs. Typically, aerial or satellite imagery is used for photogrammetry. The first solutions of this type appeared as early as the mid-19th century, when balloons were used for photogrammetry. With the further development of technology, aircraft and satellites and later drones began to be used.
The role of drones in this area has grown especially in recent years. Photogrammetry by drone offers many benefits - such devices allow to quickly and cost-effectively acquire precise data from the air. Instead of hiring aircraft or using satellite data, just program a drone mission and start collecting material. In practice, photogrammetry provides access to a wealth of valuable data. Using properly taken photographs, for example, it is possible to create accurate 3D terrain and object models, orthophotos or point clouds representing 3D objects. Such capabilities mean that drone-based photogrammetry is being used in a growing number of fields - from surveying to archaeology.
Fotogrametria a lidar
In the context of spatial data collection, it is also worth noting another technology that can be used in parallel with photogrammetry. We are talking about lidar (sometimes the notation "LIDAR" or "LiDAR" is also used, as an abbreviation for Light Detection and Ranging). Both methods have their strengths and both serve similar purposes. However, they are based on completely different principles of operation.
Drone photogrammetry is based on images. Sets of images must be made with great accuracy and coincide in the correct proportions. Specialized software then analyzes the stored images, using common points in adjacent images to reconstruct the 3D terrain or object. The higher quality and precision of the images, the more accurate the final models or maps will also be.
Lidar, on the other hand, works on the principle of emission of laser pulses. The measuring device then measures their return time after bouncing off the surface. This means that highly detailed models can be obtained even where photos do not give full information - such as in densely forested areas.
However, this does not mean that lidar is always a better solution. Drone photogrammetry covers many lidar applications while being much cheaper and more accessible. In many cases - especially in open areas - the data collected by the drone is also accurate enough to successfully replace costly laser scans.
Where photogrammetry is used?
The application of photogrammetry covers many sectors. On top of that, it is worth noting that new applications for this field are constantly being found. Currently, photogrammetry is used primarily in the following areas:
- geodesy - for creating 3D terrain models, orthophotos and other types of maps, as well as for preparing field documentation;
- construction - photogrammetry is useful m.in. in the field of spatial modeling, as well as in analyzing the progress of work, especially in large-scale investments;
- agriculture - Drones can be used, for example, to analyze the condition of crops, as well as to plan agricultural operations;
- environmental protection - Monitoring of landscape changes, flood analysis, collection of data on the state of the environment in the area;
- archaeology - Drones support site reconstruction and documentation of sites or work progress.
In each of these areas, drone photogrammetry makes it possible to speed up data collection in the field and reduce costs. Although a drone for photogrammetry costs more than standard models, in the long run it is a much more cost-effective solution than traditional photogrammetry. The usefulness of drones in various scenarios cannot be overlooked either. The small size of the devices and the ability to adjust the flight path practically at will make photogrammetry drones particularly valuable where response time is important - such as in the analysis of landslides, construction disasters or natural disasters.
What drone photogrammetry is all about?
Drone photogrammetry is based on taking pictures of the area from the air using a specialized drone. A key piece of photogrammetry drone equipment is a camera with a mechanical shutter, which, unlike the electronic shutter, effectively eliminates blur. It is what makes it possible to obtain sharp and stable images, which are the foundation of any accurate photogrammetry. Importantly, these images must partially overlap - usually the longitudinal coverage is approx. 70%, and transverse 60%-70%. This allows the software to later combine them into a single structure, recognizing common points in subsequent photographs.
Specialist Alan advises: "Drones DJI have a factory-set ground coverage of 70/80%, but I usually increase it to 80/90%, and sometimes even 85/95%. The process then takes a little longer, but I have confidence that the resulting model will meet the accuracy of the design. It is also crucial that the images are stable and sharp - this is the basis of good photogrammetry."
Once the material is collected, the images from the drone are loaded into the photogrammetric software. The most popular solutions in this field are m.in. DJI Terra, Pix4D and Agisoft Metashape. Their functionality focuses on analyzing aerial photos to then create from them an orthophotomap, terrain model, point cloud or 3D mesh - depending on your requirements. In addition, solutions such as the following are often used for such tasks rTK (Real-Time Kinematics) system, which provides precise determination of the drone's position.
What are the benefits of drone photogrammetry?
Drone photogrammetry offers many benefits. First and foremost, we are talking about speed - With a drone, it only takes a few minutes to make a flight over an area of up to several hectares. Thus, for large projects, dozens of hours can be saved. Another important issue is precision, especially for drones with RTK systems. The latest developments in this field provide accuracy up to 1 cm. Not without significance is also security - using a drone, there is no need for operators to enter dangerous or hard-to-reach areas. Cost is also worth mentioning: although a drone for photogrammetry is noticeably more expensive than standard models, in the long run it is a much more cost-effective option than traditional photogrammetry.
Which drone will be best for photogrammetry?
A drone for photogrammetry should be selected primarily in terms of the scale of projects and budget. Most solutions of this type can be found in the Enterprise series from DJI. Here are some suggestions that are perfect for professional applications:
- DJI Matrice 350 RTK - flagship model DJI in the professional segment. It features an RTK system, powerful batteries, and a reinforced design that provides a high payload capacity. The device is also compatible with mapping camera and lidar DJI Zenmuse L2. For photogrammetry, we especially recommend the connection to the camera DJI Zenmuse P1, which provides tremendous capabilities in even the largest surveying or industrial projects.
- DJI Matrice 4E - The latest model in the DJI Enterprise line with the current best price/quality ratio. The drone features an even more compact design than the Matrice 30, but definitely matches it in terms of accuracy and quality of measurements. The device is equipped with an RTK system and a set of advanced cameras suitable for photogrammetry and inspection.
- DJI Mavic 3 Enterprise - the most budget option - a specialized version of the popular drone DJI Mavic 3. It features a camera with a mechanical shutter and RTK support, and the whole thing weighs just 1 kg. The DJI Mavic 3 Enterprise drone will be perfect wherever mobility and speed are important.
It is also worth noting that all of the above models have in common compatibility with popular photogrammetric software, in particular with the platform DJI Terra. Also noteworthy is the high accuracy of measurements. These are drones of the highest quality , which can easily replace standard surveying methods. When choosing a drone for photogrammetry, it is also a good idea to avoid drones with a thermal imaging camera. This is because lenses of this type are often noticeably inferior for RGB photography. The most important functions are RTK system and mechanical shutter - with this combination you can count on accurate measurements and the ability to prepare precise terrain models.
What to look for in drone photogrammetry?
Drone photogrammetry requires proper preparation. The basis is to understand the most relevant aspects of both technical and operational. First and foremost, care should be taken to proper planning of the flight - significance has m.in. choosing the right altitude, which has a direct impact on the resolution of images and ground coverage. Too little height will increase the number of images and processing time, for too much height can reduce data quality. Another important issue is the proper coverage of the photos. Failure to maintain correct proportions can result in gaps in the 3D model or errors in the orthophotos.
The drone, on the other hand, must be equipped with rTK system and a camera with a mechanical shutter. It is advisable to choose devices that are resistant to various weather conditions - during measurements you often have to face wind, rainfall and low visibility. In turn, when it comes to the flight itself, you also need to keep in mind the legality of the operation: if the space requires it, you must report the flight, as well as have the appropriate operator credentials. For longer operations, spare batteries will be useful.
Drone photogrammetry is an invaluable support in many areas. Drones can serve as advanced surveying tools, which will ensure high accuracy, efficiency and safety of measurement work. To achieve the best results, choose the right device and keep in mind the key principles of flight. This will enable you to get effective, professional measurements that provide a lot of valuable information in surveying, construction and more. Among the recommended solutions, it is worth noting in particular drones DJI Enterprise - can be found at the MegaDron store.en.
