LIDAR vs. photogrammetry: what sensor to choose for a given application
In drone survey missions, the choice between a photogrammetry or LIDAR depends heavily on the exact application. You also need to consider operational factors, such as cost and complexity. Knowing what outputs you really need will help you make the right decision.
In this article, we’ll explore the ways photogrammetry and LIDAR are actually quite different from each other, even if some of their outputs look similar. We’ll then dive into the specific benefits and applications of each method.
What’s better—LIDAR or photogrammetry?
Simply put, taking pictures and using software and base station data to line them up and geotag them is relatively simple compared to active sensing. For photogrammetry data capture, you have a camera and PPK unit working in harmony. For LIDAR data capture, you have three pieces of sophisticated hardware casting out millions of data points and recording their activity based on precise location information, on board and on the ground. Yet in both cases, to capture and process the data is getting easier and more accessible.
The key difference between photogrammetry and LIDAR revolves around their strengths and weaknesses—and when you know what these are, you can see they actually complement each other for complex projects. While LIDAR offers precise outputs that outline canopy and reach through thicker vegetation to provide terrestrial information, photogrammetry results in life-like and accurate perspectives.
LIDAR vs. photogrammetry accuracy
Vertical vs. horizontal accuracy
Photogrammetry offers excellent horizontal accuracy down to 1 cm, but due to the predominantly nadar nature of capture, the vertical accuracy will be half to a third as good (you can often double or triple the value). Oblique payloads can capture higher accuracy and detail, but still not as tight as LIDAR.
LIDAR captures horizontal accuracy down to 2 cm and can grab vertical data at this level as well. Why? It’s not as impacted by terrain and lighting. In fact you can capture LIDAR data at night.
Best environments to get accurate data
In the case of photogrammetry surveys, clear and open areas with terrain that is somewhat variegated will be ideal. Super rugged areas can introduce shadows and noise, so evaluate what kind of details you need on a case-by-case basis. So long as you are flying under clouds, you can get the details you are looking for by following these guidelines.
LIDAR is more robust in complex and rugged areas with vegetation and tree cover so long as it is not closed canopy. Note: LIDAR light pulses do not move through anything, they diffuse around them, and they do it tightly just like light would enter a crack in the ceiling to provide details of the floor … but without the crack, the light won’t penetrate.
LIDAR vs. photogrammetry accuracy: key differences
| Photogrammetry | LIDAR | |
|---|---|---|
| Data type | Geotagged photographs | Laser pulse point clouds |
| Horizontal accuracy | Down to 1 cm | Down to 1 cm |
| Vertical accuracy | Good 2-4 cm | Slightly better 1-3 cm |
| Performance in vegetation | Limited due to shadows/obstructions | Better: Pulses diffuse to reflect the ground and complex surfaces |
| Performance in complex terrain | Less effective in low contrast | Excels in complex/difficult terrain |
| Environmental limitations | Results depend on lighting, shadows and texture | Can even work in the dark |
Accuracy in complex environments
Photogrammetry vs. LIDAR in specific applications
Both photogrammetry and LIDAR are useful across the full range of sectors, including construction, mining and land management as well as forestry. To understand how they differ inside specific use cases, you need to look at how they work combined with the area you want to map.
Topographical maps featuring light vegetation (sparse treestands or open canopy) are best captured with high-resolution RGB data capture available through payloads like the RX1R II with PPK. The resolution and photorealistic results are useful in cases like wildfire management in residential areas, and have been used by some of the world’s largest urban fire and rescue services, since the information serves many stakeholders who need a real view of what’s happened.
Photogrammetry is also capable of centimeter-level absolute accuracy, offering dependable, survey-grade results to government agencies, as in this Indiana Port Authority survey case. Finally, and not the least important is price and ease of workflow. For businesses like this vineyard, which would benefit greatly from detailed and accurate information without extensive training and overhead.
Topographical maps with medium vegetation can be obtained via a combination of photogrammetry and a method to capture the ground below the vegetation. To capture the additional information below the vegetation, drone LIDAR is optimal. Combining drone photogrammetry and LIDAR keeps the price down while guaranteeing high accuracy plus the resolution and photorealistic results. Detailed tutorials offering a reasonable learning curve on this approach are available.
Large-scale topographical maps featuring heavy vegetation are best acquired via drone LIDAR. A digital terrain model (DTM) of the forest ground provides useful information for project planning in construction (e.g., the planning of new roads), forest biomass or detailed information on vegetation and habitats via topography and underlying terrain. These kinds of applications will always require LIDAR to normalize topographical data, as is shown in research that examines the strengths and limits of photogrammetry in such cases.
Typically state agencies try to maintain reasonably accurate digital terrain models (DTMs) of the forest grounds. For these kinds of large-scale projects, drone LIDAR with an efficient fixed-wing system is the most cost-effective option available.
If the forest is really dense but there is still light penetration, you may need to go with a higher-end drone LIDAR system like Riegl—this can cost a lot more but then you have a system to repeat the surveys anytime you want vs. paying for airborne surveys less frequently.
Bare-Earth mining, volumetric and natural resource surveys are best handled by high-end RGB payloads like the RGB61 by Wingtra. Even massive surveys, like those performed by an energy firm in Finland and the US, are ideal with the right drone and RGB camera.
Established mining firms like Jellinbah and Westmoreland have offered examples of how they’ve incorporated photogrammetry into their workflows because of the accuracy, resolution and photorealistic results that enable efficient mine management.
On top of this, photogrammetry is cost effective and saves time not only to capture and process data related to cut and fill volumes, stockpile assessments and status reports, but also to share this information and reconcile with contractors and stakeholders.
In this example above, WingtraOne was used to efficiently create surveys over tens of thousands of hectares (2D RGB map on left, 3D Digital Surface Model on right).
Power line surveys for vegetation control can be done with drone LIDAR or, in some cases, high-resolution photogrammetry and powerline extraction features on software like Pix4Dsurvey. A good example is this one from Poland, where FlyTech UAV used photogrammetry to revolutionize its powerline vegetation management. Research is ongoing around photogrammetry as a go-to, cost-effective solution that is even incorporated into a management update to the largest European power grid operator.
Power line pole tower inspection benefits from live video inspection with a multicopter carrying an RGB or thermal payload. These are usually relatively small areas that multicopters can maneuver around and take oblique shots of easily and safely, as this overview demonstrates. With this method, you get all information within a very short amount of time. Zoom cameras allow detailed inspection that can not be offered by photogrammetry or LIDAR.
Image credit: Pix4D—green lines indicate LIDAR data that supplements the photogrammetric map.
Rail track inspection is still most often carried out from the ground—by a train equipped with ultrasonic, LIDAR, and visual sensors. Inspection from the air with either photogrammetry or aerial LIDAR is gaining more and more interest but both methods are in early stages.
High-resolution photogrammetry offers data that avails outputs with all of the essential details accurately and autonomously while saving time. Plus the photorealism adds an element of easy identification and versatility that can answer to a range of questions. In the end, more and more firms are making the case for this methodology.
City mapping with vertical structures requiring 3D vantage points has been widely demonstrated with photogrammetry based on imagery captured with a payload featuring oblique capabilities. For cityscapes with many high-rises and intense levels of vertical detail, multicopters work well, although their ability to cover wide-spread areas per flight is compromised.
VTOL drones carrying oblique payloads can still capture wide areas and achieve impressive vertical accuracy. In fact, more and more cases of city mapping are being reported with VTOL drones.
Final thoughts
In the end, we see that since the dawn of reliable, mid-range drone LIDAR, both photogrammetry and LIDAR offer efficient, cost-effective and productivity boosting data for a range of use cases across the spectrum of sectors.
The big deal now is that, if you have an efficient system, you can get this data whenever you want. Before, you used to have to hire survey crews or schedule and pay for an airborne survey that did not produce the kinds of accuracy and resolution drones make possible. Everything is getting easier, cheaper and faster without sacrificing quality.
The key now is to choose the system that saves you the most time and headaches along the way while fetching consistent results.
FAQ
Is LIDAR more useful in forestry applications than photogrammetry?
It really depends on what you need to assess and if you need ground-level information. When you are approaching a forest and need terrain info, this should be an automatic signal that you will need LIDAR.
Yet if you need forest health information, drone photogrammetry with a multispectral payload will give you the insights you need. Photogrammetry will give lifelike views of canopy and even bark if you have a good oblique payload like MAP61.
So you really need to be certain about the kinds of analytics you need and trace those back to the system and payload. Also a VTOL will be ideal since you have the option for take-off and landing inside tree stands.
Can you do photogrammetry and LIDAR together?
Yes, and it’s actually a common practice. These two methods—now that they are more affordable—truly complement each other. LIDAR rains light points down to capture areas that shadows or vegetation might render difficult to capture with photogrammetry.
Then, photogrammetry offers maps that give a life-like context to the LIDAR point cloud so that analysis can be conducted on any front possible.
Both methods get you centimeter level accuracies. With an efficient system you can even capture the same area twice just as fast as a less efficient could capture it only once.
What is photogrammetry?
In photogrammetry, a drone captures a large number of high-resolution photos over an area. These images overlap such that the same point on the ground is visible in multiple photos and from different vantage points. In a similar way that the human brain uses information from both eyes to provide depth perception, photogrammetry uses these multiple vantage points in images to generate a 3D map.
The result: a high-resolution 3D reconstruction that contains not only elevation/height information, but also texture, shape, and color for every point on the map, enabling easier interpretation of the resulting 3D point cloud.
Drone systems that use photogrammetry are cost effective and provide outstanding flexibility in terms of where, when, and how you capture 2D and 3D data.
What is LIDAR?
LIDAR, which stands for “light detection and ranging,” sends out pulses of laser light and measures the exact time it takes for these pulses to return as they bounce from the ground. It also measures the intensity of that reflection.
LIDAR is a technology that has been around for many decades but has only recently been available in a size and power feasible for carrying on drones. And advances in this lightweight drone LIDAR category are happening quickly.
