LiDAR and Photogrammetry: Part 1 – Technological Differences
This is the first article in a 2-part series discussing the technological and pricing differences that exist between LiDAR and photogrammetry data collection.
Drones have revolutionized the way many industries collect data, and in the realm of geospatial data collection, two prominent technologies stand out: LiDAR (Light Detection and Ranging) and photogrammetry. By using LiDAR or photogrammetry technologies, drones can quickly and accurately capture data that was previously difficult or impossible to obtain. These technologies are pivotal in applications ranging from environmental monitoring and urban planning to autonomous vehicle navigation and archaeological site documentation. Each of them has unique characteristics, advantages, and applications. This article aims to elucidate the differences between LiDAR and photogrammetry, shedding light on their working principles, data types, accuracy, applications, and more.
LiDAR
The Essence of LiDAR
LiDAR, short for Light Detection and Ranging, is a remote sensing technology that employs laser pulses to measure the distance between the sensor and the target surface. ?This revolutionary technique is similar to radar but uses laser light instead of radio waves. ?LiDAR sensors emit laser beams and measure the time it takes for these laser pulses to bounce back after striking an object or surface. ?By analyzing these return times, LiDAR creates detailed 3D point cloud models.
Key Characteristics of LiDAR
Laser Emission.? One of the fundamental aspects of LiDAR is its active nature.? It emits its laser pulses, which means it operates independently of external lighting conditions.? This is particularly beneficial for applications that demand data collection during the night or in densely vegetated areas.? However, if LiDAR point cloud colorization is required, then LiDAR data capture requires the presence of either daylight or artificial lighting.?
Data Type.? LiDAR data is unique because it consists of individual point measurements, leading to a dense point cloud. ?Each point in the cloud carries information about elevation, intensity, and more. ?As a result, LiDAR is celebrated for its ability to generate highly detailed 3D representations of surfaces.
Accuracy and Precision.? LiDAR system absolute accuracy is highly dependent upon and largely determined by the inherent accuracy of the system’s IMU (Inertial Measurement Unit) and is less affected by the accuracy of associated Ground Control measurements.? As a general rule, higher-end LiDAR systems are equipped with more accurate IMUs.? State-of-the-art LiDAR systems and data collection workflows are able to achieve near centimetre-accurate absolute accuracy.
Cost and Equipment.? While LiDAR is a powerful technology, it comes at a cost. ?The equipment, including laser scanners and specialized hardware, can be expensive. ?High-end LiDAR systems are typically used for professional applications and research.
Applications.? LiDAR finds extensive use in various fields, including but not limited to:
Data Density and Coverage
LiDAR offers exceptional data density, meaning it can capture an immense number of data points within a small area.? However, its coverage may be limited by factors like the sensor's field of view and range.? This limitation necessitates careful planning and multiple passes for comprehensive coverage in larger areas.
Photogrammetry
The Essence of Photogrammetry
Photogrammetry is a technique that uses photographs or images taken from different angles to calculate the position and geometry of objects or terrain.? It relies on the principles of triangulation and feature matching in multiple images to construct 3D models.? In essence, photogrammetry is the art and science of extracting 3D information from 2D images.
Key Characteristics of Photogrammetry
Natural or Artificial Light.? Photogrammetry primarily relies on natural or artificial light sources present during image capture. ?As a consequence, it is most effective during daylight and in clear weather conditions.
Data Type.? Photogrammetric data is generated by processing photographs, leading to the creation of 3D models. ?These models can be represented as a mesh or a point cloud derived from image features. ?Unlike LiDAR's individual point measurements, photogrammetry operates on data which has been extracted feature-rich images.
Accuracy and Precision.? The accuracy of photogrammetry can be influenced by various factors, including the quality of the photographs, camera calibration, and the accuracy of ground control points. However, with the implementation of an expertly executed system of ground control, it is possible to achieve sub-centimetre absolute accuracy with photogrammetry.?
Cost and Equipment.? Photogrammetry can be more cost-effective than LiDAR, as it often utilizes digital SLR (single lens reflex) cameras for data capture. ?This affordability has made it accessible to a broader range of users.
Applications.? Photogrammetry's versatility is evident in the diverse applications it serves:
领英推荐
Data Density and Coverage
High-density photogrammetry is possible with properly calibrated, high-resolution RGB data capture sensors and high-data overlap.?? ?Photogrammetry can also cover larger areas in a single flight or imaging session.? The coverage area of photogrammetry can be extensive, making it a suitable choice for broad-scale mapping and monitoring.
Comparing LiDAR and Photogrammetry
Choosing the Right Technology
The decision to use LiDAR or photogrammetry depends on various factors, including project requirements, budget constraints, and the environment in which the data will be collected.? Let's delve into a comparative analysis:
1.??? Accuracy vs. Cost
Both LiDAR and photogrammetry are capable of achieving high levels of accuracy if properly implemented.? If the highest level of LiDAR system accuracy and precision (near-centimetre absolute accuracy) is required, a high-end LiDAR system will be required in addition to a RTK GNSS enabled drone and an expertly implemented system of independent Ground Control.? These technological requirements of course come with an associated cost, which we will examine in detail in the second part of this series. ?
Photogrammetry is capable of achieving sub-centimetre absolute accuracy with a RTK GNSS enabled drone, properly calibrated high-resolution RGB digital camera, and an expertly implemented system of independent Ground Control.? These technological requirements come at a reduced associated cost when compared to LiDAR.
For applications where accuracy can be balanced with cost-effectiveness, photogrammetry offers a compelling alternative. ?It is often used in construction monitoring, where 3D models of building sites are required for project management and progress tracking.
2.??? Data Density vs. Coverage
Both LiDAR and photogrammetry excel in providing dense point clouds with detailed 3D information. ?Photogrammetry offers broader coverage in a single session but may produce less dense point clouds or meshes if vegetation is present. ?When dealing with vast, open areas, such as agricultural land monitoring, photogrammetry can provide efficient and cost-effective data.
3.??? Equipment and Data Collection
The choice between LiDAR and photogrammetry also depends on the available equipment and the specific needs of the project. ?LiDAR requires specialized hardware, such as laser scanners and associated systems. ?Photogrammetry, on the other hand, can be accomplished with digital SLR cameras, which is widely available commercial technology.
4.??? Application Suitability
Consider the application's requirements when choosing between LiDAR and photogrammetry:
LiDAR: ?Ideal for applications which require LiDAR's ability to penetrate tree canopy cover and high-vegetation. ?It shines in topographic mapping, forestry management, and autonomous vehicle navigation.
Photogrammetry: ?Well-suited for applications that demand 3D modeling, such as construction monitoring, building and structural reconstruction, vertical surface reconstruction, cultural heritage documentation, and aerial surveying.? ?
Synergy Between LiDAR and Photogrammetry
In practice, these technologies are not mutually exclusive.? In fact, they often complement each other. ?Integrating LiDAR and photogrammetry data can provide the best of both worlds. ?For example, using LiDAR for terrain modeling of vegetated areas and photogrammetry for building modeling can result in comprehensive 3D maps for urban planning.
Conclusion
LiDAR and photogrammetry are two indispensable technologies in the world of geospatial data collection. ?They have unique characteristics and strengths that cater to diverse applications. When choosing between the two, it's essential to consider factors like accuracy, cost, data density, and coverage. ?In many cases, the synergy between these technologies offers a comprehensive solution for complex projects. ?Whether it's charting the topography of a city, preserving historical landmarks, or navigating autonomous vehicles, LiDAR and photogrammetry are pivotal tools that continue to shape our understanding of the world.
_______________________________
Grayson Lee is a subject matter expert in the industrial application of drone technology.? He is director and chief pilot of Digital Content Solutions Inc. Grayson is a Transport Canada Advanced sRPAS pilot, a Transport Canada compliant training provider and flight reviewer, as well as a Pix4Dmapper certified user, a FLIR Level I sUAS thermographer, and an AIIM certified confined space drone pilot. He specializes in point cloud generation and aerial 3D modelling using both LiDAR and photogrammetry (mapping) as well as inspection of critical infrastructure and high-value assets.
#drone #dronepilot #dronemodelling #dronemapping #photogrammetry #LiDAR #pointcloud #3Dmodel #DCSdigital