One of the frequently asked questions about the differences between Photogrammetry and Lidar for companies who are considering this technology is which one is best to use for survey and mapping. This post will try to answer this question from a very high level.
Now, before we explore the difference between these two augmenting but competing technologies, we have to start with this simple question: “What is your reason for buying?”
By answering this question, it will become easier to decide whether you use lidar or photogrammetry for your survey application.
PHOTOGRAMMETRY VS. LIDAR IN FLIGHT AUTOMATION
One of the common mistakes most companies make is in data collection and mission planning: Photogrammetry and Lidar are vastly different in the flight profile.
When you’re collecting photogrammetry data, the flight orientation of the drone is irrelevant. During the data post-processing phase, each image will be layered on top of one another and triangulated.
Now, there are a lot of people who are excited about very affordable Lidar systems for creating 3-Dimensional point clouds. However, from a quality control standpoint, the data may or may not be positionally accurate. The point cloud may be very pleasing to look at but may fall short of the expected accuracy requirements of the statement of work.
PHOTOGRAMMETRY VS. LIDAR IN APPLICATION
Now, in the sense of practical application, photogrammetry is much better for bare earth scanning unless you’re dealing with very low contrast and need much faster data. It is also more accurate for horizontal structures.
However, Lidar is best used for collecting vertical structures, for example, cell phone towers. It is important to state here that the right resolution is required. This will be discussed further in another post, and where photogrammetry is lacking. Lidar is also the go-to system when conducting vegetation penetration missions (also known as foliage penetration.) Penetration of a forest or jungle canopy is a very specialized skill set, requiring a more robust Lidar sensor than is normally used for a standard survey mission.
(Important note: The Lidar sensor is only half of the equation; the Inertial Measurement Systems (IMU) is critical for a successful collection.)
In context, you can use them both concurrently for more accuracy and detail, but this requires proper mission planning.
For example, MODUS uses the photogrammetry portion to deliver a product for urban analysis, because Planimetric data on roadworks is better with a camera than with Lidar. However, Lidar data is combined with the photogrammetry data product, which provides for vegetation penetration and is part of the final deliverable, provided to the customer. Again, depending on the Statement of Work, you may need to use both systems.
PHOTOGRAMMETRY VS. LIDAR IN MINING INDUSTRY
Using the mining industry as an example, it depends on what the usage will be to determine photogrammetry vs. Lidar. The biggest factors to consider are the changing environment, the expected volume, the required turnaround time, and what is the yielded analysis.
Therefore, when you are trying to decide between a Photogrammetry or lidar collection, the question to ask is:
- Can you keep up with the changing environment?
- Are you doing excavation?
- Do you have aggregates that are being piled up?
- Are there enough aggregates for a good comparison?
Photogrammetry is better in collecting data aggregates because it’s cheaper, but Lidar is much faster, with a quicker turnaround time. With a Lidar mission, aggregate data is normally processed and delivered within ten minutes of the drone landing.
Are you for scaling (image volume?)
When a very large number of images collected (3,000 to 5,000) and timely reporting is required, Lidar may be a better solution based on the quick turnaround.
These are a few of the things that differentiate Lidar from Photogrammetry. Additionally, not previously mentioned but it is important to discuss, is that photogrammetry has a problem in dealing with shadows. If there is no control over light sources (depending on the time of day, and the mission profile) it is possible that some cliff facets reporting might not be accurate. In short, photogrammetry is good unless you’re doing volume and scale.
In conclusion, the question of which system is the best one for your survey mapping is dependent on your specific requirements and industry. Both photogrammetry and Lidar are important systems, when used within their respective capabilities, and functionalities.
If you want to learn more about mapping and want to have an actual experience with the software, visit our program at https://learn.modus-ai.com/