Aerial survey methods have come a long way in the last few years in terms of availability and cost of equipment. Two of the most prominent aerial imaging methods used to create 3D point clouds are photogrammetry and LiDAR. 3D point clouds are useful because they allow surveyors to easily and quickly create a basis for inserting 3D objects into a mapping environment. Those objects, in turn, create context and provide detail for your topographical surveys. Given a choice between photogrammetry and LiDAR, does one technology have an advantage over the other though?
What is Photogrammetry?
Photogrammetry uses high-resolution cameras installed on a UAV drone to take a series of two or three-dimensional images. As the aerial drone takes multiple passes over its target, it is able to capture the landscape from multiple angles. Photogrammetry then uses software to patch the collection of raw images together to form a composite view of the object or landscape. This 3D point cloud can be used to create a realistic model of objects, terrain, or other real-world elements that can then be inserted into your topographical map.
What is LiDAR?
LiDAR, which stands for Light Detection and Ranging, is the primary alternative to photogrammetry. When installed on a UAV, LiDAR utilizes focused bursts of light in the form of rapid laser bursts to map the ground below. The system then measures how long those bursts take to hit an object and return to the sensor. LiDAR builds a composite image of the terrain by measuring the distance between the object and the drone.
Because LiDAR does not take an actual photographic image the way photogrammetry does, the point clouds that it builds are monochromatic, as opposed to vibrant, full-relief images. The main advantage LiDAR has is that in areas of dense vegetation, it can sometimes pierce the canopy better than photogrammetry, or at least exploit the space between the vegetation more effectively. That said, photogrammetry has a number of advantages that outweigh LiDAR’s ability to see through to the forest floor.
Advantages of Using Photogrammetry Over LiDAR
While each method of creating 3D point clouds has its own set of applications, photogrammetry has a distinct advantage for survey professionals looking to accurately model 3D objects into a topographical environment.
The cloud point models generated with LiDAR are monochromatic. LiDAR is unable to capture photorealistic images due to the nature of the technology. Therefore, the resolution of photogrammetry cloud point models is much higher. Photogrammetry is easier to interpret without resorting to post-production, color overlays that take additional time and resources to render, resulting in actionable topographic information right off the bat.
The cost of both LiDAR and photogrammetry equipment has steadily decreased over the past few years as the technology has become more accessible for commercial purposes. However, in a head-to-head comparison, camera equipment capable of photogrammetry boasts a distinct cost advantage over LiDAR equipment. To outfit your UAV with LiDAR equipment can cost upwards of $50,000, whereas photogrammetry equipment is a fraction of that cost with high-end equipment totaling no more than $20,000.
Accuracy is a tricky topic, but it’s worth mentioning. In general, LiDAR is more universally accurate, but aerial LiDAR requires a ground control point, or GCP, in order to obtain a high level of both relative and absolute accuracy. Photogrammetry excels at relative accuracy due to the level of detail in its 3D Point clouds, and it is fully capable of high absolute accuracy with an experienced survey professional piloting the UAV.
For professional surveyors, an eye in the sky can make all the difference in terms of quality, detail, and accuracy. Mile High Drones help your survey professionals with a wide range of 3D modeling services such as topographical maps, digital elevation models (DEM), and cloud point photogrammetry. Contact us today to learn more about our aerial imaging solutions.