Aerospace technology has made giant leaps in the past few decades. One of the most useful applications of advanced aerospace technology is in survey.
There was a time when ground survey was the only option in every application, from agriculture to urban planning.
From the point of view afforded by current technology, ground survey was the epitome of inefficiency. It required more personnel and significantly more time. As a result, it was expensive. And for certain applications, it was limited.
But ever since we could fit payloads on airplanes, helicopters, and more recently, drones, survey has been revolutionized. Large tracts of land can now be surveyed within hours and with just a few personnel.
In addition, sensor technology has been growing rapidly. It is now possible to capture high-definition images from high up in the air, which has unlocked numerous applications, including the development of three-dimensional models.
Now, urban planners can fly over a city and estimate its population from the 3D models of its buildings. A developer can get the information to plan for land use in a project within minutes.
This article will give an overview of how modern aerial survey is carried out.
What is Aerial Photogrammetry?
To understand how modern survey is done using drones and other aerial vehicles, a basic understanding of photogrammetry comes in handy.
What is Photogrammetry?
Photogrammetry is a technique used to derive three-dimensional imagery from a series of two-dimensional photographs. Overlapping 2D images are stitched together with the help of special software to come up with a 3D representation of the object or area under study.
Photogrammetry is one of the techniques used in the creation of 3D content.
At a basic level, photogrammetry can be implemented through multiple cameras. Each of the cameras takes the photo of an object from a different angle. Multiple images of the object taken from multiple angles are then stitched together.
Photogrammetry has its origin in the stereoscopic vision of human eyes. To view the world in 3D, we capture images using both our right and left eyes. The two fields of view overlap and are processed simultaneously in the brain to give us depth perception.
How Does Aerial Photogrammetry Work?
When performing photogrammetry using drones, helicopters, and planes, they are equipped with payloads that contain cameras.
For photogrammetry to work, multiple overlapping photos of an object or area have to be taken. When using aerial vehicles, this is achieved by using the same sensor to capture overlapping photos in quick succession as the vehicle flies over an area.
Afterwards, the photos are fed into a software for point matching. Point matching is the process of finding common points in images and using them to determine the three-dimensional spatial properties of a scene.
Such software enables three-dimensional models of areas to be derived from aerial photographs.
Advantages of Aerial Photogrammetry
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- Quick collection of data. Planes, helicopters, and even drones can capture images for use in photogrammetry at a fast rate.
- Cost-effectiveness. The shorter time taken and the less manpower required mean that the use of aerial vehicles in surveys is more cost-effective.
- Versatility. Depending on what you want to survey, you can use either a drone, a helicopter, or a manned plane. Each is suitable for a set of applications. For example, if continuous survey of a plot of land needs to be done during development, a drone is the best option.
- Repurposing. The imagery collected for one purpose can be easily used for another purpose, provided it’s about the same object or area.
- Safety and improved access. Aerial vehicles can be used to survey areas that would otherwise be hard to reach and plagued with safety hazards.
Oblique vs Nadir Imagery
When payloads are attached to aerial systems for survey, they can be configured to take either oblique or nadir imagery.
An oblique aerial system takes images at an angle from the vertical axis. On the other hand, nadir imagery is taken vertically. In a nadir system, the sensor perfectly aligns with the vertical axis.
An oblique aerial system results in images that feel more natural to the human eye. We are used to viewing the things around us at an angle rather than from directly above them.
In addition, oblique imagery helps get more accurate three-dimensional information about objects from the photographs.
Application of Aerial Survey
The use of aerial vehicles in survey has resulted in unprecedented utility across a range of applications.
For a long time, airplanes and helicopters dominated this space. However, over recent years, the capability of drones has improved to the point where they are better suited for survey in certain applications.
The cost of drones has continued to fall and they are gradually replacing manned planes and helicopters in survey.
However, planes and helicopters are still suitable for some applications. For example, if you want to survey a large area, or to carry heavy sensors, you are better off using a plane.
In another example, if you need to hover over an area during a survey, your best option will be a helicopter though drones can offer the same capability in certain situations.
How Do You Know Which Aerial Vehicle to Use?
To know the best aerial vehicle to use for your survey needs,here are some of the factors you should consider:
- Location. There are many location-based factors to consider. If you are surveying an area with many buildings or with narrow streets, your only option is a drone. If you are surveying an area that is indoors, you will have to use a special type of drone, one that has features such as built-in collision avoidance.
- Size of the project. If you have to survey large tracts of land, for example along the corridors of infrastructure projects, you will have to use a manned plane. Large projects typically require manned planes while small projects require drones.
- The deliverables required. The deliverables you need will determine the sensors you use. Some deliverables require the use of multiple sensors. Drones are limited in the weight of payloads they can accommodate.
- Safety. When surveying high-risk areas, it would be best to use unmanned aircraft.
