Everything You Need to Know About UAV LiDAR Mapping
If you’re currently planning a land survey, you may be wondering about the advantages and disadvantages of LiDAR mapping technology. Through UAV LiDAR mapping, environments can be mapped down to extraordinary detail, even through brush and foliage. UAV LiDAR mapping is the most technologically-advanced and convenient solution today and understanding the technology behind it is critical to understanding its core benefits.
What is LiDAR mapping technology?
In a nutshell, LiDAR:
- Uses laser light to determine the distance between a sensor and an object, whether on the ground or from the air.
- Penetrates through minor obstructions, which may include tree canopies, man-made objects, and brush on the ground.
- Creates a point cloud, which can then be used to create a detailed terrain and object models.
LiDAR (“light radar”) mapping technology uses multiple pulses of laser light to determine the distance between a sensor and an object. These light pulses are sent out extraordinarily quickly – up to millions of points a second. Sensors use the amount of time that it takes for these pulses to be bounced back to determine how far away an object is.
In LiDAR surveying, laser lights are bounced from above along the terrain to create a 3D model of the terrain, which is extremely detailed. As laser light can go through objects such as tree foliage and brush, LiDAR can be used to create an accurate model of terrain even if the terrain is over-grown or developed.
LiDAR has been in use since the 1960s, and it is currently the most accurate form of creating models of digital elevation. Some forms of LiDAR can even be used to map terrain under water, such as riverbeds and shallow lakes. LiDAR is often used in conjunction with advanced software solutions, which determine the type of objects that are being scanned by the LiDAR in addition to just elevation.
Through the use of advanced software platforms, LiDAR can be used to not only record elevations but also accurately identify things such as street lamps, power lines, or even birds. Software systems compare different elevation studies with potential items on the ground and are consequently able to identify the difference between things such as man-made items and things such as bushes.
LiDAR is used throughout industries such as agriculture, archeology, geology, and even law enforcement. The most popular alternative to LiDAR is another technology called photogrammetry.
What is the Relationship Between UAVs and LiDAR?
- Unmanned aerial vehicles (UAVs), often referred to as drones, can be deployed over virtually any terrain for the purposes of fast scanning.
- Unlike manned aerial vehicles, UAVs do not present safety hazards to operators and can be used low to the ground.
- UAVs are cheaper and faster than manned aerial vehicles, saving companies both time and money on their surveying.
LiDAR can be used by land as well as via the air. When used by land, for instance, LiDAR can be used in the “speed guns” that police use to determine whether someone is speeding. For the mapping of terrain, however, LiDAR is almost always used via an aircraft. These aircraft can be manned or unmanned.
When used in conjunction with a manned aircraft, LiDAR scans are more costly, less precise, and more dangerous. Multiple individuals need to be on a manned aircraft, as both the craft and the scanner must be operated. Aircraft can crash, which could cause injury or even death to those onboard. Further, manned aircraft cannot fly low to the ground, which means their scans are of lower resolution.
Comparatively, Unmanned Aerial Vehicles (UAVs) are able to fly with a single operator, can fly low to the ground, and will not injure anyone if they crash. UAVs can be deployed to cover large areas of an environment at once and can quickly create high-resolution scans, which can then be directly imported into the relevant software.
Used together, UAV and LiDAR technology forms the most powerful surveying tool presently available.
What is the difference between LiDAR and Photogrammetry?
Photogrammetry is a method by which a large number of overlapping photographs of a region are taken and then processed to determine the measurements between multiple points. It is a fast and affordable method of mapping large areas of land quickly.
As photogrammetry uses 2D objects to interpret 3D space, it can only produce many of the same deliverables, depending on the terrain. With big data and new analysis tools, photogrammetry can be accurate enough for smaller projects or projects that need to cover a very large expanse at a lower than average cost. This is why photogrammetry is often used for projects that need to map entire cities.
Photogrammetry has one technological advantage over LiDAR: it also provides seamless imagery of the mapped area. As it relies upon photographs, it is capturing the color and the texture of the terrain, which means that photogrammetry maps can be more understandable to the human eye even if they are less accurate overall. LiDAR scans can still be textured, but these textures may not be as accurate.
However, this advantage is often side-stepped by using photogrammetry and LiDAR together, to create accurate 3D data that has also utilized photogrammetric imaging. This process is both more involved and more expensive but can produce both human-readable and machine-readable models.
As photogrammetry requires that the 3D space be derived from 2D images, it produces fairly low-resolution results and often cannot identify smaller or thinner objects. Power lines, for instance, are often not viewable through photogrammetric data. Finally, photogrammetry does work on photographic technology, which means photogrammetry has to be completed during the day and it has to be done during the appropriate weather conditions. UAV LiDAR mapping has fewer environmental concerns.
In terms of cost, photogrammetry is substantially less expensive than LiDAR, and it can also be used with UAV technology. In fact, UAV technology remains the most effective way to complete surveying regardless of wither LiDAR or photogrammetry is being used. However, this cost savings may not be substantial if it comes at the ultimate cost of a delayed project or mistakes being made.
LiDAR captures the data that is necessary for modeling terrain; this is highly specific, highly technical data that needs to be worked on by professionals. Photogrammetry produces large volumes of photographic data, which then needs to be parsed using the appropriate software.
Does Your Survey Need LiDAR or Photogrammetry?
Both of these technologies are still in use today for an important reason: they’re both useful tools given the right circumstances.
If you’re wondering whether your survey needs LiDAR or photogrammetry, you can ask yourself the following questions:
- Is there anything obscuring the terrain from above? If there are trees, bushes, or manmade objects above the terrain, photogrammetry isn’t going to be able to penetrate down to get an accurate elevation.
- Is there a reason why you would need full-color maps? If your project needs accurate terrain color, you may need to use photogrammetry or to combine photogrammetry with LiDAR.
- Is there a need to model small objects? Photogrammetry cannot pick up small objects, such as power lines, which makes it unsuitable for projects that need higher resolution.
Other than specific use cases, LiDAR is generally the better tool — if the budget is there for it. Many people believe that the future of surveying may actually be in combined LiDAR and photogrammetric mapping, but few argue that LiDAR isn’t the superior technology when the two are compared.
LiDAR mapping technology is still more expensive than some alternatives, but the use of UAV can make it a faster and more cost-effective solution overall. In many projects, LiDAR may be able to pay for itself in terms of time and cost saved — and, as it becomes an industry standard, the costs related to it have been steadily decreasing. For those who need accurate, fast, and safe results, the best choice is almost universally UAV LiDAR mapping, though you may still want to consult a professional land surveyor to find out which option is best for your specific project.
