Photogrammetry vs Lidar
Drones can dramatically expedite surveys, autonomously covering vast areas of ground in a fraction of time. By flying over areas with sensors, drones can create digital representations of complex land environments, allowing surveyors to analyze the ground below. As remote sensing technology makes advancements, there are growing opportunities to create value in new industries, from telecommunications to environmental science to construction.
But what type of remote sensing is right for your use case? In this article, we’ll explore two popular methods, LiDAR and photogrammetry, and discuss how to choose a remote sensing technology for your application.
What is Photogrammetry?
Photogrammetry is a technique for taking thousands of pictures of an object from different angles and stitching them together to create a detailed 3D model. By finding common points and patterns between high-resolution images, photogrammetry software can reconstruct an object’s 3D shape with impressive accuracy. This technology is incredibly versatile, making it handy for applications like video game development in addition to mapping, construction, and even archaeology.
LiDAR Explained
LiDAR, or Light Detection and Ranging, is a remote sensing method using light in the form of a pulsed laser. A LiDAR sensor emits rapid laser pulses and times how long it takes for them to bounce off objects and return. Using this information, the sensor calculates the distance to the object. By repeating this process thousands of times per second, a LiDAR sensor can map the shapes of objects and the contours of land. When laser ranges are combined with position and orientation data from integrated GPS and Inertial Measurement Unit systems, scan angles, and calibration data, LiDAR can generate a "point cloud" of spatial data. Each point in the point cloud has a latitude, longitude, and height that corresponds to a particular point on the Earth's surface from which the laser pulse was reflected. The point clouds generate other geospatial products, such as digital elevation models, canopy models, building models, and contours.
LiDAR can be topographic, using a near-infrared laser to map land, or bathymetric, using a water-penetrating green light to also map ocean floors and shorelines.
When to Use LiDAR
Simply put, LiDAR is more accurate and detailed, but considerably more involved and expensive. LiDAR systems themselves are considerably pricier than RGB cameras, and heavier as well, meaning they require heavier and more expensive drones for support. Because LiDAR requires more complex software and more external calibration, they typically require hiring a more experienced specialist, who is more expensive as well. So which operations are worth using LiDAR for?
High Precision: LiDAR is ideal over photogrammetry for use cases that require a high degree of precision and detail, especially surveying applications such as mining, geology, archaeology, and land mapping. LiDAR can detect precise measurements of small objects. The technology is particularly great for precisely measuring items like cables, which are typically too thin to be detected using traditional methods. If the surveying work at hand necessitates precision above all else, LiDAR should be your tool of choice.
Thick Vegetation: If the subject terrain has a high proportion of vegetation coverage, LiDAR is a good option as well — certain LiDAR lasers can penetrate through overgrown vegetation and forest canopies that would obscure a photogrammetry RGB camera’s view.
Low Visibility: If the levels of light at a given jobsite are low or inconsistent, LiDAR is a better option. Without the use of cumbersome external illumination, LiDAR can be utilized to conduct nighttime surveys or low-visibility activities.
When to Use Photogrammetry
Stitching photographs together is less expensive and operationally simpler. Photogrammetry post-processing software is more affordable and intuitive than LiDAR software, and requires less external data to calibrate — just camera calibration, ground control points, and basic flight planning. However, photogrammetry is less accurate, especially without a very high-quality camera, a high number of ground control points, and an RTK or PPK-enabled drone such as the Flyby Robotics F-11.
Photogrammetry is a preferred choice over LiDAR in use cases where detailed visual information of the environment is crucial, such as construction progress monitoring, creating 3D interactive maps, and surveillance, due to its ability to capture high-resolution images and provide comprehensive visual data.
Detailed Visual Information: With a high-quality camera, photogrammetry captures high-resolution visual imagery that LiDAR point clouds alone do not. This is ideal for construction progress tracking, in which construction companies create 3D reconstructions of buildings to update clients on project status, as well as environmental change detection, in which ecologists track melting glaciers or shifting coastlines. Photogrammetry can capture beautiful images of historical preservation as well, including artifacts or architecture.
