LiDAR, Photogrammetry, & Mapping 101 for Public Safety

It's easy to think that drones are only good for taking photos and videos. Powerful payloads and software, however, significantly extend the utility of UAVs in other applications. One prominent use of these platforms is for aerial mapping, and some public safety agencies are finding that it makes their response more effective. In this article, we briefly cover two mapping methods and ways that your agency could implement aerial mapping into its workflow.

LiDAR

LiDAR is the abbreviation for Light Detection and Ranging. At its very basic, LiDAR systems use laser pulses to measure distances by recording the time it takes for the light picked up by the integrated sensor. For 3D scans, LiDAR units emit laser pulses at a rapid rate in all directions. Software marks each measurement with a point, creating a highly detailed point cloud that makes up the final 3D render.

Pros:

• Highly accurate
• Works in all lighting conditions
• Detailed scans

Cons

• Expensive
• Requires specialized hardware
• Limited to creating point cloud maps

Photogrammetry

Whereas LiDAR uses lasers to create renders, photogrammetry uses overlapping pictures. The accompanying software uses camera metadata and GPS information to triangulate light rays intersecting at a specific point in the designated space. The result of these triangulations is a highly detailed 3D map of the metro terrorist scenario at UTAC 2021 in the facility's mockup underground subway tunnel:

Pros:

• Uses available imaging systems
• Multiple output formats (orthomosaics, point clouds, textured meshes)
• The most accessible measurement system

Cons:

• Not the most accurate
• Limited to environmental lighting conditions

Public Safety Applications

LiDAR and photogrammetry have clear public safety applications due to their accuracy and rapid turn-around times. Most recently, both systems are deploying on drones, an effective solution for mapping large areas quickly. Mapping applications also allow public safety agencies to increase the impact of their UAS programs and get more out of their platforms.

Crime Scene Investigation

3D mapping is rapidly becoming an integral tool in collecting evidence, particularly crash reconstruction. Evidence technicians can promptly scan the scene of the accident using a drone. Software compiles the image data into a computer render, which investigators then use for analysis off-scene. They can take measurements and identify trajectories all within the 3D model. Having digital recreation also means accident sites are cleaned up quickly to reopen roadways.

Disaster Response

Photogrammetry and LiDAR also serve as critical tools in disaster response. Because the disasters impact large areas, it can be difficult for responding agencies to understand the scale of the situation. Fortunately, 3D mapping provides decision-makers with an accurate, interactive scene overview. Furthermore, they can identify the areas with the most critical damage and steer responders clear of potential hazards. Finally, mapping offers a convenient way to monitor recovery progress.

Mapping Solutions

DJI Mavic 2 Pro

With a 1-inch Hasselblad sensor and compact airframe, the Mavic 2 Pro is the perfect photogrammetry platform. The Mavic 2 Pro is compatible with the powerful PIX4D software for rapid outputs.

DJI Phantom 4 RTK

An older model, the Phantom 4 RTK is no less of a capable mapping drone. Also compatible with PIX4D, the Phantom 4 RTK brings the advantage of an RTK unit for precise positioning.

DJI Matrice 300 and Zenmuse P1 payload

Currently, the M300 with Zenmuse P1 payload is one of the best drones for photogrammetry workflows. The M300 airframe is an industry workhorse, with exceptional obstacle avoidance, range, and endurance. The P1 payload is a 45MP, full-frame camera that features Smart Oblique Capture, ensuring images are captured at the appropriate angle for the mission. The result of this combination is an ultra-detailed 3D map accurate to centimeter levels.

DJI Matrice 300 and Zenmuse L1 payload

For missions that require LiDAR mapping, the M300 paired with the Zenmuse L1 payload is among one of the best solutions. Comprised of a Livox LiDAR module, an RGB camera, and a highly accurate IMU, the L1 can scan up to 2 km^2 area in a single flight. One standout feature of the L1 payload is its Point Cloud LiveView. Operators can see the LiDAR scan in real-time on the controller as the aircraft makes its passes. This feature is essential for SAR teams that would need an updated topographic map before beginning their mission.

Conclusion

Photogrammetry and LiDAR have their distinct advantages and drawbacks. Both, however, are highly effective methods for rapid mapping and are significant improvements over traditional assessment procedures. Are you interested in a photogrammetry or LiDAR solution for your agency? Contact a FLYMOTION representative or visit our website.