Whether you’re an artist, an archaeologist, a surveyor, a photographer, or an engineer, you might need to capture three-dimensional data of objects or environments in the wild. In this article, we’ll explore the most popular scanning technologies for outdoor applications, their strengths and weaknesses, and how to choose the right tool for your project.
First, let’s define what we mean by scanning. Scanning is capturing the shape, texture, colour, and other features of an object or space and turning them into a digital 3D model that can be viewed, manipulated, analyzed, or reproduced. Scanning can be done using various sensors, such as cameras, lasers, sonars, radars, or lidars, that emit or receive signals and measure their reflections or echoes. Scanning can also involve processing and combining multiple data sets into a single coherent model, which requires specialized software and hardware.
Now, let’s dive into the leading technologies for outdoor scanning.
Photogrammetry is the art and science of extracting 3D information from real objects (including humans). By taking overlapping photos of an object or a landscape from different angles and distances and using computational algorithms to match and triangulate the features in the images, photogrammetry can create accurate and detailed 3D models.
Photogrammetry can be done with consumer-grade cameras, drones, or specialized rigs. It can produce high-resolution models that bring realism into the 3D model. Photogrammetry has the advantage of being affordable, flexible, and non-invasive, as it doesn’t require direct contact with the object or terrain. Photogrammetry is also great when it comes to capturing the texture of an object. The quality of the texture is defined by the quality of the camera, allowing you to scale up just by getting a better camera.
However, photogrammetry has some limitations, such as sensitivity to lighting conditions, shadows, reflections, and occlusions, which can affect the quality and completeness of the models. Photogrammetry also requires some expertise in photography and software and can be time-consuming and computationally intensive.
LiDAR stands for Light Detection and Ranging and is a remote sensing technology that uses laser pulses to measure distances and create 3D point clouds of surfaces and objects. LiDAR can penetrate vegetation, water, and other obstacles and capture high-resolution and range data. LiDAR can be mounted on aeroplanes, helicopters, or ground vehicles and can cover large areas quickly.
LiDAR has many applications in forestry, geology, hydrology, urban planning, and archaeology and can reveal invisible or hard-to-detect features with other methods. However, LiDAR has some disadvantages, such as cost, complexity, and safety issues (laser radiation can harm eyes and skin). LiDAR also requires post-processing and filtering to remove noise and artefacts from the data and to convert the point clouds into useful models.
Structured light scanning is a technique that uses a projector and a camera to project patterns of light onto an object and capture their deformations. By analyzing the distortions of the patterns, structured light scanners can calculate the 3D shape of the object and generate models with high accuracy and resolution. Structured light scanners can work indoors and outdoors and capture data in real-time or in batches. Structured light scanners have some advantages over other methods, such as speed, precision, and portability, and can be used for quality control, reverse engineering, and inspection. However, ambient light, vibrations, and reflective or transparent surfaces can affect structured light scanners and may require calibration and synchronization.
Photonic Mixer Device (PMD)
Outdoor scanning with Photonic Mixer Device (PMD) technology captures high-resolution 3D images of objects and environments in real-time. PMD technology utilizes light signals to measure distance, allowing for accurate depth perception and precise object recognition. This technology is particularly well-suited for outdoor scanning applications as it can operate in various lighting conditions, including bright sunlight. In addition, PMD technology is compact and lightweight, making it easy to deploy in various settings. As a result, outdoor scanning with PMD can be used in various industries, including agriculture, construction, and transportation, for applications such as object detection, mapping, and monitoring.
To sum up, Photonic Mixer Device (PMD) technology, photogrammetry, lidar, and structured light are all methods for capturing 3D images. PMD technology uses light signals to measure distance, while photogrammetry calculates the distance by analyzing multiple 2D images. Lidar uses lasers to measure distance, and structured light projects patterns onto an object to calculate depth. Compared to photogrammetry, PMD technology is more accurate and faster, particularly in low-light conditions. Lidar is capable of capturing more detailed and precise 3D images than PMD but is more expensive and requires more power. Structured light is best suited for smaller objects and indoor environments, while PMD technology is better suited for outdoor scanning applications. Regarding texture quality, photogrammetry shines supreme and allows the most realistic results. Overall, each technology has its own strengths and weaknesses and should be chosen based on the application’s specific needs.