What is a drone survey?
A drone survey is the process where with the use of a drone camera, someone capture aerial photos with the purpose of creating 2D or 3D maps. During a drone survey the ground is photographed several times from different angles, and each image be tagged with coordinates.
To understand why we need to collect the drone data in a certain way, we need to understand what is the process of transforming the aerial photos in to a map.
What is Photogrammetry?
Photogrammetry is the technology of extracting 3D information from photographs.
A photogrammetry software is automatically searching on common points between images. When it finds two matching points on two different images, the software will create one 3D point. When there is a high overlap between two images, the common area captured is larger and more common points can be matched together. The more common points there are, the more accurate 3D points can be computed. Therefore, the main rule is to maintain a high overlap between the images.
What types of drone image acquisition paths can we use for drone surveying?
Single grid
The recommended overlap for most cases is at least 75% frontal overlap and at least 60% side overlap . It is recommended to take the images with a regular grid pattern . The camera should be maintained as much possible at a constant height over the area of interest to ensure the desired Ground Sample Distance (the size of one pixel from the photo in real world)
Side and Frontal Image Overlap (source support.pix4d.com)
Real life example of single grid image acquisition
Double Grid
Is basically made from two single grids perpendicular to each other. This method is used mainly for the 3D reconstruction of the building facades, with data acquisition from multiple angles.
Real life example of double grid image acquisition
Orbit
The Orbit data acquisition means flying in a circle around your selected point of interest at a set altitude, height and radius, and taking interval photos. This data collection method is used usually for 3D reconstruction of different objects. For better results is to fly orbits at different heights and with different camera angles.
Real life example of orbit image acquisition
Things you should consider before process to drone data collection
Weather Conditions: One of the biggest challenges associated with using drones for data collection is weather conditions. Most of the drones are not waterproof so rain and snow can damage your drone. High winds can shift your drone from off course, can create the motion blur effect on you photos and or even crash.
Technical Limitations: Drones are limited by their technology, and this can impact the quality and accuracy of the data collected. Factors such as battery life, sensor resolution, and processing power can all affect the performance of a drone and its ability to collect data.
Regulatory Requirements: In many countries, there are strict regulations governing the use of drones for data collection. These regulations can limit the areas where drones can be flown, sou better check for any rules and regulation, and also for any flight restriction that applies in your area.
In conclusion, because of its versatility and effectiveness, drone data collection is becoming more common for mapping projects.
There are ways to overcome challenges such weather conditions and technical constraints that come with using drones for data collection. Drones can be an excellent alternative to conventional land surveying methods if data collection is timed with the weather, the correct equipment is used, and local laws are respected.
I would like to conclude with this recommendation: explore the advantages of automatic data collecting in drone mapping and consider about how to implement it in your future projects.
If you're interested in learning more about drone mapping or need professional services for your mapping needs, contact Stefan Niculescu at stefan@stefanengineering.co.uk or 03330906842
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