Recent years have seen an increase in the use of drones for surveying.
Unmanned aircraft (UAVs) enable teams to collect valuable aerial insights quickly, efficiently, safely, and at an affordable price point - and help to improve decision-making, communication, and revenue generation.
Professionals in surveying and mapping have long used LiDAR and photogrammetry as essential tools. However, drone technology has changed the way data is captured to a greater extent.
Whether or not to use LiDAR or Photogrammetry will be familiar to established surveyors not not to those who are new to the field. In this article, we'll take a closer look at both methods to compare their benefits and drawbacks. There is no absolute right or wrong when it comes to which is better.
There is no absolute right or wrong when it comes to which is better.
What is Lidar?
LiDAR stands for light detection and ranging. In LiDAR sensors, light pulses are emitted and then measured for the time it takes for them to reflect off the ground and the intensity with which they do so.
LiDAR technology has been around for decades, but only recently has it become small enough to integrate into a drone's payload. The instrument's sensor records the light reflected and calculates the distance travelled, giving you the measurement.
LiDAR sensors are part of the process. To create a point cloud that accurately represents terrain and its topography, LiDAR combines other high-accuracy systems such as satellite positioning (GNSS data) and inertial measurement units (IMUs).
Also, it is important to know that the LiDAR sensor only measures positions without RGB data, which can make the monochrome dataset difficult to interpret. False colors based on reflectivity or elevation are often used to visualize the data to make it more meaningful.
When to use Lidar?
Drone Surveyors can use LiDAR as a key tool to improve their work.
It can be used for a variety of purposes, but certain mission types may be more suited to it.
These can include:
Farming & Landscaping
The use of 3D mapping is essential to implementing effective irrigation systems on large farms. Farmers need accurate knowledge of the terrain to construct levees on large plantations, for example. Drones equipped with LiDAR can collect data in a single pass, allowing farmers and consultants to roam a large field quickly. In the past, the field had to be dried up enough so that trucks could manoeuvre it.
Terrain mapping
Compared to ground survey methods, LiDAR offers significant savings. By analyzing pulsed laser light reflected from an object's surface, LiDAR can determine its position, velocity, and other characteristics by detecting distant objects, including leaves, shrubs, trees, and grass. Ground operators can use this to create a 3D model of topographic terrain contours.
Mine Inspections
Drones with LiDAR technology aren't just for outside operations; they've also been helpful in inspecting mines. In this case, the LiDAR doubles as a collision detection tool, allowing simultaneous localization and mapping (SLAM), which provides companies with inspection data and enables the drone to operate semi- or fully autonomously.
Drone operators and miners can use this type of equipment to inspect a mine after a planned explosion to ensure the structure is stable before sending in humans.
What is Photogrammetry?
A photogrammetric measurement is simply a way to measure distances through photographs. To create accurate and realistic world models, these photographs are processed with special software.
The photogrammetry process relies on reflections of ambient light from the imaged surface or object. Due to this, cloud cover, camera angle, and time of day can greatly influence its results.
For accurate photogrammetry, you need hundreds or thousands of images. A lot depends on the size of the site in question and the degree of accuracy you are looking for.
To obtain the ground sample distance needed, drone pilots will have to determine the best flight altitude. Additionally, you will need to set up an overlap for each picture so that your software can stitch the images seamlessly together.
Working with photogrammetry has the main benefit of being accessible. In the past few years, drone technology and mapping software have streamlined workflows and made accurate maps and 3D models accessible to organizations with decent drone cameras.
A mapping mission is relatively straightforward, so long as you know how to calibrate your camera, plan a flight, and plot your ground controls.
However, photogrammetry has some downsides.
In order to produce accurate maps and models, you need to have a quality camera on your drone and a quality drone.
Ground sample distance (GSD) depends on sensor size, aperture, resolution, focal length, and altitude.
When to use Photogrammetry
In a wide range of vertical industries, drone photogrammetry is being adopted by more and more businesses, organizations, and departments.
Photogrammetry is a better option for many applications. In particular, this is true when working on plans with orthomosaic maps, collaborating with 3D models, or providing project status updates for relatively low costs.
Photogrammetry is suitable for:
An accessible, context-rich scan that requires minimal post-processing and expertise
Untrained eyes can easily understand maps and models
Visually assessing datasets
How accurate is LiDAR versus photogrammetry?
Comparatively to photogrammetry, LiDAR produces scans with greater detail and accuracy. The fact that it can operate well in adverse conditions - such as low light or lots of vegetation - makes it the ideal system for situations in which you place the highest value on accuracy.
There can be up to 500 points per square meter in LiDAR point clouds, and the vertical elevation can be determined to be within three centimeters. As a result of a high density of data points, your dataset is more robust, allowing you to process the findings more efficiently.
Photogrammetry is not inherently inaccurate, however, the terrain can still be detailed even if it's relatively simple and there is no dense vegetation - especially if you're also using an RTK positioning module.
Differences between LiDAR and photogrammetry data
Data collection methods such as LiDAR and Photogrammetry are distinctly different.
LiDAR creates a 3D point cloud by combining thousands of data points. To turn it into something visually accessible, you'll need to incorporate color from different datasets.
Photogrammetry involves processing and stitching together hundreds or thousands of images to create something useful: be it a 3D point cloud, a map, or a navigable model.
In comparison to cloud-based photogrammetry software, LiDAR processing is much less prevalent. So you'll need an on-site specialist who can turn those raw data into something useful and the right software.
Capturing High Quality Data
Whether you use Lidar or Photogrammetry, it's important to ensure that the data collected is of as high quality as possible for improved post processing. Using adaptive mission planning software will help you automate and capture high quality data as your drone flights will follow a pre-programmed sequence of steps - whether it's following a smooth flight path for Lidar flights or maintaining the correct overlaps for photogrammetry flights.
Summary
We hope this post has provided you with an insight into the difference between LIDAR and Photogrammetry. As we explored above, one isn't necessarily better than the other. In the end, the best solution depends on the task at hand.
If you’d like to learn more about LIDAR and photogrammetry missions supported in Hammer, please visit our mission tutorials.
To learn more about our enterprise solutions, including mission collaboration, flight analytics and more please contact us at team@hammermissions.com