Photogrammetry: Aerial Survey / Drone Survey
Photogrammetry, or the combination of maps and photographs, is a process that uses these images to extract measurements and other data. The outputs of photogrammetry can range from various kinds of 2D orthomosaic maps to 3D models. Once the drone data is collected, it is transformed into real-world measurements and distances. For a successful aerial survey, the data collected during a drone survey must be translated into these measurements and distances. Therefore, understanding the process before creating a flight plan will help a drone operator provide accurate data. In addition to this, the parameters of a drone flight are determined by the desired outcomes of the client. You can see several use cases in our article: Overview: Drone Mapping / Photogrammetry/ Aerial Mapping / Aerial Survey Drone Survey
Ground Control Points (GCPs)
The ground control points (GCPs) in a drone photogrammetry aerial survey are the fixed targets placed at various points to guide the flying camera. Generally, there are five GCPs positioned at the highest and lowest points of the survey area. These targets should be securely placed, not covered with vegetation, and visible from the air. The position of the GCPs must be accurately measured with the help of a receiver that is capable of RTK positioning. UAO uses built in RTK modules on our surveying drones.
Typically, ground control points (GCPs) are too small to be visible from high-altitude drones. Additionally, the contrasts between them are too high, making the accuracy of the aerial photo unreliable. However, with Aerotas ground control points, they are large, 16″ x 16″, easily visible from a distance, and are painted in bright, contrasted colors. Moreover, their optimized colors help them stand out during photogrammetry.
Ground control points are a key part of the photogrammetry process. They help improve the global accuracy of aerial maps and provide a precise reference for virtual design and construction. They are used for precision mapping by surveying companies. Furthermore, precision mapping is essential for virtual design and construction. If you are considering drone photogrammetry aerial survey for your next project, make sure to consider ground control points.
A GCP should be level and of a known height. Another important factor for accuracy is the ground sample distance. This distance is calculated based on the center points of successive pixels in a digital image. This means that one pixel on the digital map is equivalent to five cm in the real world. This is the fundamental requirement for accurate aerial photogrammetry. In a drone photogrammetry aerial survey, ground control points are important to obtain accurate data.
Ground Sample Distance (GSD)
The GSD, or Ground Sample Distance, of a drone photogrammetry aerial survey is critical to its accuracy. While the standard GSD for aerial photogrammetry is 1.5 to 2.5 cm per pixel, some surveyors recommend ground sample distances as low as one centimeter per pixel, which is very low and would decrease the amount of acreage per flight and increase the risk of collision.
A digital aerial photo is made up of a matrix of pixels. Each pixel is actually a small square. The GSD refers to the distance between the center of consecutive pixels. This distance is essential in photogrammetry, which is used to create 3D topographic maps. The GSD is based on the flight altitude and focal length of the drone, so the higher the altitude, the greater the GSD.
A lower GSD means higher-resolution imagery. A high GSD, meanwhile, means lower resolution. A typical GSD is five centimeters per pixel, while a high-resolution map has a GSD of two to three centimeters per pixel. Altitude and distance to the structure also impact GSD. A higher altitude increases GSD, but a lower distance means less ground is covered by the lens.
A high-resolution digital map is a common goal of aerial photogrammetry beginners. Despite this, they often choose a small GSD when planning their missions. But this approach typically results in long flight times, hundreds of photos per acre, tens of hours of processing, and large output files. A proper GSD should be selected to meet your digital map requirements.
Accuracy
The accuracy of a drone photogrammetry aerial survey depends on several factors. The terrain profile, flight speed, image overlap, and GPS conditions all contribute to the quality of the imagery. You can learn more about these factors by reading this article. In addition, the use of drones for photogrammetry is not limited to mapping. It is also possible to use drones to collect imagery of buildings, bridges, and even cities.
A drone’s accuracy is related to its positional accuracy. While the data it generates is generally close to real-world locations, its relative accuracy varies. Ideally, the accuracy of a survey should be greater than its pixel size. A good benchmark for measuring accuracy is sub-centimeter precision. However, sub-centimeter accuracy is preferable. Additionally, a drone’s image geotagging and GPS errors are likely to be larger than the accuracy of the data captured by the drone.
Adding ground control points, or GCPs, to a drone photogrammetry aerial survey increases its accuracy. These points are distinctly marked areas on the ground that can be seen by the drone camera. These targets are assigned coordinates, which the drone can use to align itself with. The ground control points are determined using highly accurate RTK GPS surveying equipment. GCP coordinate data is then used as reference in photogrammetry software. Ground control points significantly increase the accuracy of a drone photogrammetry aerial survey.
The accuracy of a drone photogrammetry aerial survey can be compared to ground-based surveys by a licensed surveyor. This is because a drone’s GPS receiver records the center point of each photo. In addition to this, photogrammetry software helps turn the data into a product. With these advantages, drone photogrammetry aerial surveys are gaining popularity and are becoming more accurate.
Cost
The cost of a drone-based photogrammetry aerial survey is significantly lower than the cost of traditional manned aircraft for similar tasks. Drones are capable of drawing in a variety of features on a parcel, which reduces the amount of man hours needed to manually measure the improvements. A drone can capture a wide variety of data, including terrain, vegetation, and topographic relief. A cost-effective drone photogrammetry aerial survey service is one that can be used to help businesses and developers make better decisions.
A drone survey can be more accurate than traditional methods, because it can see objects from a much wider angle than an ordinary aerial survey. While consumer drones typically rely on public satellite data to achieve precision, the results are often only 3-5 metres horizontally and almost meaningless vertically. In order to get the most accurate data, drone photogrammetry aerial surveys need to have an absolute accuracy of at least 1cm.
Drones can reach areas where vehicles cannot go, and are able to take more detailed images in less time. In addition to reducing planning lag times, drone-based mapping services provide higher-resolution imagery than satellite-based solutions. The technology also eliminates the risk of harm to human lives and equipment during ground-based mapping. The cost of a drone photogrammetry aerial survey is comparable to the cost of a traditional survey, which could be $5,000+
Drone-based photogrammetry aerial surveying improves productivity, and eliminates downtime in survey pits. Drone-based data collection reduces man-hours and costs while generating large sets of accurate data. With the cost of a drone aerial survey service, a business can benefit from higher productivity. And, drones’ capabilities also help companies increase profits, as they can cut down on man-hours and costs associated with surveying pits.
If you or your company is looking for drone survey / photogrammetry solutions, contact UAO via the form below. Or visit our contact page to find our email address and phone number. Contact