Recent developments in digital photography, software, and drones now make it possible to carry out high-precision photogrammetric surveys at relatively low cost over a wide range of scales. Photogrammetry with drone is now practiced in many fields: archaeology, heritage architecture, an inspection of structures, emergency surveys, etc.
Interested in drone photogrammetry and not sure where to start? Or maybe you are already a user of this measurement technique and you wish to deepen your knowledge and skills? Then you've come to the right place!
What is drone photogrammetry?
In short, drone photogrammetry uses a drone to capture a large number of two-dimensional images over a geographic area and compiles them into accurate three-dimensional terrain models and orthomosaic maps with specialized photogrammetry software.
More than just a collection of photographs, drone photogrammetry makes it possible to see the same ground point from different angles and altitudes. From there, you can easily create a 3D map that includes a range of useful visual cues, such as color and texture.
Photogrammetry first originated in surveillance and reconnaissance and has been used for 170 years. During World War I, pilots combined photography with manned flights to gather intelligence from behind enemy lines.
Without context, photographs alone were of little value, so these pioneers used local landmarks and landscape features to determine the direction of objects in images.
In the decades that followed, these practices would be evolved with the appearance of new tools, from stratospheric U2 aircraft to advanced weather satellites to modern drone photogrammetry.
Today's photogrammetric maps are constructed using advanced GIS software to produce surveyor-level measurements of landscapes and infrastructure. These maps are detailed enough to provide valuable insight into environmental conditions in the field.
How does drone photogrammetry work?
Drone photogrammetry is a two-stage process, including image capture and image processing.
Image capture: The first step is to capture the images needed for the project. This can be done with a still camera or video camera mounted on a drone. The drone will capture a large number of high-resolution photos of an area that overlaps each other to make the same point on the ground visible from different angles and elevations.
Source from emjcorp.com
Image processing: The aerial photos are then processed manually or using photogrammetry software, which combines or “stitches” the images into a single high-resolution orthomosaic aerial map and 3D models. Photogrammetry software corrects for distortions in the camera sensor and lens as well as errors caused by variations in the terrain, resulting in high-quality maps and 3D models.
Why use drone photogrammetry?
Drones can be a useful tool for photogrammetry, resulting in the following benefits:
Firstly, drone photogrammetry makes it possible to obtain a large amount of detailed information about the target area quickly and remotely. Since drones can fly lower than manned aircraft and are also equipped with the most advanced technology, which delivers a 3D model with accuracy up to centimeter level.
Secondly, photogrammetry drones allow you to capture images from remote locations and transmit them securely to computer systems, allowing surveyors to easily access data in hard-to-reach or unsafe areas, such as places with severe volcanic activity, and crime or war, complex terrain, and harsh weather conditions.
Thirdly, drone photogrammetry is an accessible method. Due to the financial factor, aerial photogrammetry was restricted to large engineering companies and public agencies. With the arrival of drones, values have dropped considerably, which makes it possible to hire this type of service even by small and medium-sized organizations.
How accurate is drone photogrammetry?
Each step in the process of collecting data and creating output from the drone has the potential to add a small element of the error to the final result. Several variables affect the overall accuracy of drone photogrammetry, including camera size, number of photos collected, photo overlap ratio, flight altitude, GPS signal strength, and ground sampling distance (GSD).
With the CA-103 61MP full-frame camera and a PPK GNSS receiver, the JOUAV CW series VTOL drone is capable of achieving a Ground Sampling Distance of 5-8mm per pixel, depending on terrain and flight altitude. This means the best possible relative accuracy in the model would be down to 1cm horizontal (x-y) and 1.5cm vertical, enabling precise spatial and volumetric analysis.
Real-world applications for drone photogrammetry
The following is the full overview of drone applications of photogrammetry:
Oil & gas
Oil and gas companies use drones typically for surveying large areas for pipeline construction and inspection, and also rely on them to remotely inspect and observe equipment, infrastructure components, and other company assets.
Drones can provide a 360-degree view of objects to monitor site operations and keep a close eye on new facilities. The AI tracking function of the drones can also automatically identify and locate damage or leaks, helping to speed up repairs and minimize local impact.
In addition, remote monitoring with drones is now making fully automated offshore oil and gas inspection a reality.
Mining & quarries
There is a wide range of real applications of drone in mining, from surveying, inventory management, and stockpile estimation, to hazardous gas and leakage detection.
Drone photogrammetry can be used to generate detailed digital surface models, digital terrain models, and 3D models of a mining site, so you can easily perform very accurate volume calculations.
Using accurate site models generated from aerial drone imagery, mine managers can now more effectively design and manage the state of road construction at mines and monitor site progress on a weekly or monthly basis.
With the high-resolution images from drones, mining companies can inspect hard-to-access places for identification of crevices, erosion, wall damage, and any other potential damages. This has gone a long way towards preventing accidents and ensuring the safety of workers.
For companies managing large areas of land, drone photogrammetry can be used to capture images of crops. With these bird's eye views, they can detect crop growth, estimate crop yields, and identify issues like soil erosion and crop diseases.
The drones can carry different payloads at the same time, providing farmers with real-time and accurate diversified data that they can act on immediately.
Photogrammetry is often used by utility companies to measure infrastructure in remote areas such as power line inspection, solar farm inspection, and wind farm inspection.
Photogrammetry with drone can be used to prepare for maintenance work and repairs before engineers arrive on site, greatly reducing the manpower and resources required for infrastructure safety and improving worker safety.
There is also a strong demand for UAV photogrammetry in environmental monitoring. They use photogrammetry to study issues such as land change, pest infestation, invasive plant growth, wildfire risk, and more.
Drones are increasingly popular with first responders, who can use drone footage of the aftermath of a flood or fire to develop rescue strategies and reduce risk later on.
Photogrammetry vs. LiDAR: which is better?
Although digital photogrammetry is the most used measurement method by drone users around the world, drones with LiDAR technology have been gaining popularity for generating 3D models for a number of commercial applications.
If you want to understand more clearly the difference between photogrammetry and LiDAR, just keep reading!
What is a LiDAR and how does it work?
LiDAR, which stands for Light Detection and Ranging, is a remote sensing technology that has been gradually incorporated into aerial drone mapping for a range of specific applications.
If aerial photogrammetry is based on the overlay of a large number of 2D aerial images used to generate a 3D model, the LiDAR approach is based on direct measurements. LiDAR uses a high-power laser to emit precise laser pulses at a target object. By measuring the timing and intensity of the returned pulse, it provides a dense cloud of points on the terrain and ground that can be used to generate a 3D model in specific software.
With the development of LiDAR technology, the weight and size of these devices have been reduced significantly, making the LiDAR drone increasingly common.
What are the main differences between drone photogrammetry and LiDAR?
drone photogrammetry and LiDAR are both technologies capable of producing excellent data results for aerial mapping, however, they differ significantly in their price and applications will depend on many factors that must be evaluated beforehand to make a technical decision.
To give you an idea of how, when, and why to use each method, below you can find the main difference between drone photogrammetry and LiDAR.
Drone photogrammetry is cheaper than LiDAR
Digital photogrammetry and LiDAR are both technologies capable of producing excellent data results for aerial mapping from drones, however, they differ significantly in terms of applications and price, etc. To give you an idea of how, when, and why to use each method, below we will show the main differences between digital photogrammetry and LiDAR.
Photogrammetry is cheaper than LiDAR
By far the main difference between these two aerial survey methods relates to the cost of acquiring the equipment.
A drone-based LiDAR system can cost you $60,000 or more for the hardware alone, as this equipment is far more expensive than conventional sensors and drones that carry out photogrammetry.
In fact, drone photogrammetry has been developed over the last few years and for a large proportion of the technical applications of drone surveying, you won't find much difference in detail or accuracy between it or the products produced by LiDAR.
This means that although LiDAR is a good option in very specific circumstances, the best option in terms of cost will always be traditional photogrammetry.
LiDAR can see through vegetation
LiDAR can provide high vertical accuracy when conducting aerial surveys in densely vegetated areas. This is because LiDAR emits a large number of laser pulses in the near-infrared spectrum which is able to penetrate dense foliage, directly acquiring high-precision 3D terrain data of the ground surface.
This makes LiDAR an ideal method for aerial surveys of forestry management. The device has replaced traditional forest inventory methods and has been used to estimate the amount of planted and native forest.
However, drone photogrammetry, as it is a very affordable method and its results are very close to LiDAR, is best suited for sparsely vegetated areas or for projects where 3D modeling of the forest structure is not strictly required.
For this reason, photogrammetry is used to manage volumes and structures in mining and civil construction. In these fields, conventional aerial photogrammetry methods are economically more accessible solutions, producing outputs with the same level of detail and accuracy.
LiDAR can be used in low-light or no-light environments
As they are self-illuminating devices, LiDAR systems can operate in low or no-light environments, and even perform aerial surveys at night.
Photogrammetry, on the contrary, is highly dependent on sunlight and aerial photogrammetry can only be carried out when there is sufficient light and is very sensitive to occlusion.
This can be frustrating when you will not be able to carry out aerial photogrammetry on cloudy overcast days as the clouds will block the sunlight from entering.
Under these circumstances, LiDAR would be the best option, even if they are more expensive equipment. Depending on the extent of the area to be mapped and the financial return these projects will provide, LiDAR systems can be a good long-term investment option.
LiDAR is the most accurate surveying solution
Regarding detail and accuracy, both LiDAR and photogrammetry can provide excellent results for 3D modeling.
While LiDAR systems typically have a higher level of detail. Nowadays, drone photogrammetry methods are producing very similar or even better outputs, which depend largely on the sensor quality, the proper execution of the flight, and the data processing.
LiDAR cannot capture RGB colors
The biggest disadvantage of LiDAR systems in terms of detail is that these systems cannot capture RGB colors and you will not identify the texture characteristics of the mapped area in the 3D model generated by LiDAR.
To overcome this obstacle, 3D models by LiDAR often use fake RGB colors, however, the visual quality is always not as good as the data results generated by drone photogrammetry. If you need a model that is consistent with the visual features, LiDAR will not work.
However, there are already LiDAR drones on the market that combine LiDAR technology and RGB sensors, and while they are a little more expensive than traditional models, it is possible to generate 3D models with true colors.
How to choose drones for photogrammetry?
With the many drone options on the market, choosing a photogrammetry drone is not an easy task and you will need a solid knowledge of some factors before deciding to buy.
Here we will present everything you need to keep in mind before investing in a drone model for aerial mapping.
The first step for you to choose a photogrammetry drone is to define what will be the main applications of your equipment.
Drones have many commercial applications and to meet each of them, you will need specific technological resources that will be responsible for ensuring operational excellence and adequate quality of aerial mapping products and by-products.
Even drones with photogrammetry may not be the best equipment for technical inspections or aerial surveys for areas with dense vegetation.
If you are a beginner and don't know where to start, a good tip is to conduct good market research, assess what the main mapping needs are in your area and identify some applications of interest to guide your investment.
To choose a mapping drone, in addition to knowing what your main application is, you also need to know how much you are willing to invest and what financial return this equipment will give you.
If you are a beginner, investing in a powerful drone may not be the best idea, and in most cases, it is better to start with an affordable one that can meet your main purpose.
While drones are the main device needed for aerial mapping, you will also need good hardware and software to support the processing of the data, which will significantly increase your initial investment.
Therefore, when estimating the drone you want to invest in, it is also important to do your market research and understand the hardware and software required for data processing. You will also need to incorporate these values into the total cost of your investment.
One of the most important factors to consider when choosing a drone is flight time. In mapping large areas, the longer a drone stays in the air means less frequent battery changes per mission and the faster you can complete a mission.
Typically, professional multi-rotor drones are limited to around 20-30 minutes of flight time, while fixed-wing drones extend to 2-10 hours, depending on the wind direction and whether they carry any payload.
The camera on board the drone is the most important technical resource for survey photography. You need to make sure your drone has a high-resolution camera, and more importantly, a mechanical shutter.
Most commercial drones, such as the DJI Mavic 2, use an electronic shutter. These shutters are not efficient for aerial mapping and can render distorted images, especially if a large number of photos are taken in a short period.
When using electronic shutters in surveys aimed at digital photogrammetry, you will need to correct these distortions after the flight, increasing the data processing time and significantly reducing the quality of the data results.
By using a mechanical shutter, you will not need to correct aerial images and the quality of the generated 3D models is considerably higher.
For this reason, if you are planning to invest in a drone for survey photography, be sure to look for a model with a mechanical shutter.
Sometimes you may need a big drone that can carry multiple payloads. In this situation, a drone that can be deployed within minutes is essential. Besides, it is often quite difficult to carry larger drones to remote areas for operations.
Best drone for photogrammetry
Now that you already know that not just any drone is good for photogrammetry and, more to the point, that there are many requirements that a mapping drone needs to meet, we're going to show you the best photogrammetry drone options on the market.
JOUAV CW series VTOL drones are valuable options due to their multiple feature set, including:
- The drones combine RTK with PPK options. RTK is used for accurate autonomous vertical landings, while PPK is used to output highly accurate POS data, providing absolute horizontal accuracy down to 1cm and vertical accuracy down to 2-3cm (This result is flying over hard surfaces and using well-marked, highly visible, manually measured checkpoints and a well-established base station).
- Using a full-frame 61-megapixel CMOS sensor, JOUAV CW series drones can fly at a high altitude and get low GSD images. In optimal conditions, these drones can achieve a Ground Sampling Distance of 5-8mm per pixel.
- The camera is specially designed for CW series drones, which have 4 corners of protection to ensure the camera maintains a stable image while in flight.
- Unlike other fixed-wing drone, JOUAV CW Series VTOL drones take off and land smoothly in confined areas, on gravel roads, between trees, or in mountainous areas.
- CW series drones have a large cabin space and extensive electrical interfaces that allow them to carry a wide range of mission payloads. Moreover, its modular design supports deployment within minutes.
- These drones have a system self-test function that automatically returns the aircraft in the event of a malfunction, ensuring a safe flight.
- IP54 certification, proving that CW Series drones can work in fog, smoke and snow, and other adverse weather conditions.
Listed below are the specifications of seven CW series VTOL drones for photogrammetry:
|Max Take-off Weight (MTOW)||3kg||3kg||29.5kg||31.58kg||31KG||45kg||112kg|
|Payload||Ortho camera, oblique camera, LiDAR, gimbal camera, aeromagnetic system||Ortho camera, oblique camera, LiDAR, gimbal camera, aeromagnetic system||Ortho camera, oblique camera, LiDAR, gimbal camera||Ortho camera, oblique camera, LiDAR, gimbal camera||Ortho camera, oblique camera, LiDAR, gimbal camera||Ortho camera, oblique camera, LiDAR, gimbal camera||Ortho camera, oblique camera, LiDAR, gimbal camera|
How much does a photogrammetry drone cost?
The entire high-end photogrammetry system costs between US$ 4,000 and US$ 13,000. The accompanying UAV costs around US$10,000 to US$16,000. Additional costs include accessories for the drone, batteries, base station, and GPS, which can add up to US$10,000 in overall costs.
Best photogrammetry software
JOUAV FlightSurv is the best drone mapping software, specifically designed for professional drone photogrammetry and multiple operations applications. It is an all-in-one software solution that supports mission planning and control, cloud services, and data processing.
This photogrammetry app has very powerful mission planning and execution capabilities, allowing you to automate drone flights and image data transfer, and deliver centimeter-level mapping results. Also, FlightSurv supports multiple survey areas, multiple sorties, and multiple modes of operation.
With RGB, thermal, and multispectral imaging capabilities, FlightSurv can meet the mapping needs of industries such as civil engineering, agriculture, engineering, mining, public safety, education, and construction.
Offering unparalleled efficiency and user experience, FlightSurv allows you to import images in bulk and quickly create detailed 2D and 3D visualizations with a single click. If you are just starting with drone mapping, FlightSurv is the most suitable software for you.