April 30th, 2019 by Katrina Engelsted
In the next few sections, we will go over what LiDAR and photogrammetry are and how they are used to collect data. We will also address their practical use in the field, as well as the cases in which one might be better than the other.
What is LiDAR?
The acronym LiDAR stands for “light detection and ranging.” Simply put, LiDAR is a laser beam-based technology that uses laser light to help create maps. A laser beam and a sensor are used in conjunction to determine where objects are in relation to the sensor as well as each other.
This technology can be mounted on ground-based devices, airplanes, helicopters, satellites, and UAVs. LiDAR use on UAVs is increasingly popular as it is less expensive than using aircraft and satellites, and faster and more efficient than using ground-based tools.
LiDAR system components
Lidar consists of four main components.
The vehicle on which the LiDAR system is mounted, such as a plane, UAV, satellite, or ground based system. This will have the LiDAR unit mounted to it. This is the device that contains the sensor and the laser.
A GPS receiver is also located on the device. This receiver is used to determine not only the latitude and longitude of the objects that are scanned but the altitude as well.
An inertial measurement unit helps to improve GPS receiver accuracy. The unit determines the angle of the vehicle. For example, the inertial measurement unit will keep track of the angle of the plane as it flies over the targeted area.
A computer is used to record all of this data. It records the burst of light that is sent out from the LiDAR system as well as the reflected light energy that is recorded from the LiDAR system. The time that it takes for the light energy to get from the object back to the LiDAR system is used to determine distances and altitudes.
What is LiDAR Used For?
LiDAR technology is used by many different industries and government agencies. It can be used to help predict the weather, create topographic maps, survey water bodies, and even create autonomous vehicle navigation systems.
An example of LiDAR data in use is the NOAA using it to monitor coastlines. This LiDAR data has been made public and is available here.
Another example might be the use of LiDAR data to create a pipeline corridor map. LiDAR data use, in this instance, would help the pipeline company access the terrain to plan construction and maintenance work.
What is Photogrammetry?
Photogrammetry uses cameras to create photographs that can be used to create measurements. In essence, it takes 2D photographs and converts them into 3D models.
Like LiDAR, a photogrammetry system can be mounted on ground-based devices, planes, helicopters, satellites, and UAVs. Also, as with LiDAR, UAVs are becoming popular vehicles for photogrammetry systems.
Photogrammetry systems components
A photogrammetry system consists of a few essential parts, they are:
The vehicle to which the photogrammetry system is mounted. A satellite, UAV, helicopter, plane, or ground-based vehicle can be used to carry a photogrammetry system. The vehicle used to carry the system can be as simple as a person with a tripod or as advanced as a satellite in Earth’s orbit. But, nowadays, the most common vehicle for a photogrammetry system is a UAV.
The camera will take photographs from different angles.
The GPS system and inertial measurement unit both work to determine where the camera is and what angle the vehicle and camera are at when these pictures are taken. The computer will store this data or transmit it back to a larger and more powerful server.
A computer. This data will then need to be processed by advanced software to create useful information. Photogrammetry usually requires much more data analysis and detailed maps. Photogrammetry can often take five times as long to create when compared to LiDAR data post production times.
What is Photogrammetry Used For?
Photogrammetry is used to create maps, drawings, and 3D models. Engineers, land surveyors, real estate firms, and many other businesses have found ways to use photogrammetry.
An engineer might, for example, use photogrammetry to help them plan a highway, a railroad, or even a dam. Before starting a new development project, a real estate firm could use photogrammetry to survey a particular piece of land.
Another example would be the use of photogrammetry to create accurate aerial views of pipelines for natural gas. They could then use this data to help keep the gas lines free from growing vegetation or inspect potential landslide hazards.
Advantages of LiDAR vs. photogrammetry
Advantages of LiDAR
Advantages of photogrammetry
|Extremely accurate when it comes to surveying an area, especially when collecting data from the ground.||Can create full-color 2D and 3D models, whereas LiDAR can only capture data in monochrome.|
|Captures more data, faster than photogrammetry.||When taken from UAVs or other aerial vehicles, photogrammetry systems can often create models more accurately.|
|Data can be captured in low-light settings, including completely dark environments.||This accuracy can also be achieved at a much lower price point. The laser source and detector, timing electronics, mirror, and motor are all more expensive for LiDAR than photogrammetry technology, according to csengineermag.com.|
|Data can be processed faster into usable information and maps than photogrammetry. According to Geoawesomeness.com, the raw data from LiDAR can be processed in just a few minutes. Comparatively, photogrammetry can take five to ten times longer.||Equipment for photogrammetry is lighter than LiDAR. This means a lighter UAV can be used. A larger UAV might need a more experienced operator to fly.|
When to Use LiDAR Over Photogrammetry
LiDAR excels in low-light environments and in creating astonishingly precise models. It’s also great to quickly collect and interpret data. This makes it ideal for projects where specific timelines need to be met.
A situation in which one might want to select LiDAR over photogrammetry is in high vegetation survey areas. This is because the vegetation will create shadows and obscure the ground, making it more challenging to collect accurate data using photogrammetry.
An example of this could be the U.S. Forestry Service using LiDAR to monitor a state forest section’s health. In industry, it could be a company using LiDAR to help autonomous vehicles navigate a highway at night.
When to Use Photogrammetry Over LiDAR
Photogrammetry can create full – color maps with images that are much more detailed than those created by using LiDAR. Often at lower prices.
In industry, a mining company may want to use photogrammetry to show the elevation and terrain around a mine or transport route, such as a pipeline or railroad. This information might help prevent natural disasters like floods and landslides.
A government agency may want to create topographic maps that can be used to help with rescue operations. For example, a drone might be sent to an area that is experiencing wildfires. Photogrammetry could be used to map areas that are currently fire-affected to help rescue crews evacuate surrounding areas.
This is not the only area where the government could use photogrammetry. One surprising way in which it is currently being used is in crime scene investigation. They use photogrammetry to quickly create a record of the crime scene so that it can quickly be cleaned up before the investigation is complete. This has become especially helpful in traffic collisions as roads can be reopened without any delays from crime scene investigators.
LiDAR and photogrammetry both use some of the same vehicles to collect their data. With the data they collect, they can also create some of the same resources.
These technologies, however, are both very different, and they both have strengths and weaknesses that complement each other. Sometimes using LiDAR data will be more beneficial than using photogrammetry, while other times the reverse will be true. In other cases, you might want to collect data using both of these technologies.
SolSpec uses LiDAR and photogrammetric units mounted to UAVs to inspect gas and oil pipeline pathways. Our fast data gathering and turnaround, as well as the latest in LiDAR and Photogrammetric technologies, facilitate regulatory compliance and environmental safety.