What Is Photogrammetry & How Can Drones Be Used?

We all know that a picture is worth a thousand words. Drone photography is valued for its beauty and ability to capture the bigger picture. However, those images don’t just have benefits for photographers and hobbyists: enter the world of photogrammetry.

What is photogrammetry?

So, what is photogrammetry? Simply put, it is the process of measuring from images. Pix4D is a market leader in this industry, releasing a variety of products that use aerial imagery to extract information and measurements. These images can be taken with a handheld camera, a plane, or a drone.

The value in this is fairly clear: you get highly detailed images. Stitching them together to create a 3D structure or orthomosaic can capture details that users can zoom in to or analyze in detail. With a drone, these orthomosaics can be very useful in mapping and surveying an area, especially when services like Google Maps don’t have enough detail or are not up-to-date enough.

Using drones for photogrammetry

The exciting thing about working with drones is that outputs based on their images aren’t just limited to 2D. Drones have a relatively precise geo-location system due to their need to return to a ‘home’ base and navigate safely in the air. This geo-referencing means that the images they capture have embedded data about the location of the drone and what it was photographing. These details can then be uploaded together and used to generate a georeferenced 3D model of the area being photographed. Photogrammetry software can convert the information from the images and location into x, y, and z coordinates that represent a point in space. The collection of these points and images is called a “point cloud”.

Naturally, precision matters if you want to use that 3D model for anything “big” – like construction, mapping, or research. If you have precise enough results, you can outdo conventional maps or imagery – one study found that Google Earth’s accuracy in a city varied from 0.1  to 2.7 meters, with ground sampling distance (GSD) at 15 centimeters  (the distance between two pixel centers measured on the ground). You can get much better GSD and overall accuracy  with drones, but this is where it can get more technical.

One method of ensuring pin-point accuracy is to use Real-Time Kinematic (RTK). An RTK drone connects to a virtual reference station (VRS) or base station via the device controlling the flight using a GSM or Wi-Fi data-link connection. This means camera positions are calculated in real-time, referring to ground references, and the locations of the drone are accurately captured. Another method for improving accuracy is using Ground Control Points or GCPs. These are points on the ground – usually marked with a square with 4 alternating black/white blocks on it, like a section of a checkerboard – that have known coordinates. These known coordinates help act as a point of reference for the whole model. Using these methods to improve accuracy results down to the centimeter.

What is Photogrammetry used for?

There are several key industries Pix4D’s users apply it for. I’ve broken them down into our key industries:

Agriculture

For agriculture, we have a specific software called Pix4Dfields. It turns drone images into actionable field insights showing crop changes throughout the year. Using multispectral cameras on the drones means the software can identify how the plants reflect infra-red light, and thus, the state of chlorophyll within leaves and give an insight into the overall health of the plants. This can then be compiled into a map of the field to show areas of stress or disease. Agronomists use that information to target treatment and resources, as part of precision agriculture – which saves time, money and most importantly helps the environment. 

Mapping & surveying

Mapping is one of the most obvious options for working with photogrammetry. Whether you work in 2D or 3D, there’s software to help. Pix4Dmapper was our first product and still focuses on this, but we also now have Pix4Dmatic designed for large projects, able to process over 10,000 images in one go – that could be around 6 square kilometers. These maps can be used for any land use planning projects.

Public safety

Drones are fast and can access areas that people either can’t reach or are too slow to get to. Pix4Dreact is our intuitive and user-friendly public safety software, working on producing 2D maps rapidly on site. These maps can help get situational awareness about a disaster – whether it’s a fire, landslide, or hurricane. Our software has been used to map the Australian and Californian wildfires in 2020 amongst other situations as part of tracking the fire, damage assessment, and recovery.

Inspection

Again, drones can get to places people can’t. So with Pix4Dinspect, we use specific flight plans to gather information for inspections. Our main example is telecom towers, where the towers need to be managed and inspected for maintenance or new installations – such as 5G. The inspection software has integrated AI, helping it identify faults as well as the angle, size, and length of antennas. A full inspection can take just 2 hours – and no one has to climb dozens of meters up.

So what’s the future?

Working with drones has never been more exciting. The hardware is evolving, and so is the software. Photogrammetry is now being complemented by 3D laser scanning, or LiDAR, which can bring added precision and details not available from aerial imagery. Drones themselves are also changing – they can carry heavier loads, and are being used for spot-spraying as well as emergency services to carry supplies to trapped people.

Drones are going to keep evolving. Various countries are now using them in trials – others, such as Rwanda, are using them to deliver medical supplies. As drones change, so will the opportunities they provide. The software using drone imagery is also changing, becoming faster and more powerful. If you’re interested in reading more about photogrammetry, check out our blog.

About the author – Eloise Mitchell

Drone Photography Bible would like to thank Eloise Mitchell for submitting this guest article. Eloise Mitchell works for Pix4D, a market leader in photogrammetry software technology. Their products enable clients to digitize reality and measure from images taken from planes, drones, phones, or any other camera.

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Notes

The images used are found on the following links:

• https://unsplash.com/photos/N_FDXbXwQmc
• https://unsplash.com/photos/SOoakFA6brI
• https://unsplash.com/photos/Cfu0mT9bRJw