Technology has made it simpler to transform physical structures, objects, buildings and other features of the environment into digital data. Two of such digital data representations are point cloud and photogrammetry. These digital data representations are widely used in surveying, architecture, construction, mapping, engineering, heritage and 3D modeling.
In simple terms, these innovations and other digital data processing techniques are ways of acquiring and representing shape and appearance of real world environments. These shape and appearance data are digitally captured and representative of the real world features and environments. The digital data thus captured are electronically processed by appropriate software to create digital designs, measured data, digital maps, visualizations etc.
How Point Cloud Data Is Created
Different technologies can generate a point cloud. For example, laser scanners can measure distances to surfaces and thereby create point clouds. Another example is LiDAR systems, which are broadly used in different industries such as surveying, mapping, forestry and transportation.
Also, photogrammetry is able to provide 3D data in the form of a point cloud. In contrast to laser light, however, photogrammetry uses pictures, whereby the position of the pictures relative to each other has to be known. Therefore, a camera needs to be moved to different positions.
Point Clouds in Construction
Point clouds allow construction workers to compare existing conditions to designs and plans. Construction site scans capture wall and floor planes as well as other elements.
This is beneficial when working on existing buildings because plans may not show all of the building elements and could be out-of-date. Point clouds can capture and document elements that a user may not be aware of, and can help educate the design and construction teams on potential elements that may impact a building.
Photogrammetry and Point Clouds Together
The software used for photogrammetry uses elements of various imaging techniques to determine the position of known features in a picture. These features, along with other measurements, can then be used to compute a 3D representation of a target, thereby generating a point cloud.
From the point cloud, images can be processed to produce other 3D representations such as digitally surface models, which can then be used for various end uses, ranging from construction to archaeology.
Choosing Between Different Capture Methods
What is photogrammetry? The best capture method is dependent on the situation. If distance measurements are of utmost importance, then laser scanning or LiDAR might be better methods. However, if appearance and texture, as well as 2D photography, are needed, then photogrammetry might be more suitable. Some projects integrate both methods.
Processing 3D Data after Capture
Collecting the data is just the first step. There is still a significant amount of work to be done. The data collected is in the form of a point cloud, which still contains background information, unwanted points, and noise. This data needs to be filtered and information redundancy removed. The computer software used is flexible enough to be used for data classification, point alignment and dataset preparation.
Photogrammetry projects are also dependent on processing. Images first need to be aligned and matched. 3D information needs to be extracted and defined. The final result can be exported in a variety of formats, including textured models, maps and meshes, based on the project needs.
Creating 3D Models from Captured Data
3D models can be generated from point clouds or photogrammetry data. A point cloud can be converted to a textured mesh in photogrammetry, if desired.
Source data is critical to the final quality of the result. More photos, more scan points do not guarantee better outcomes.
Uses in Cultural Heritage
Documentation of historic sites and monuments with laser scan technology or photogrammetry is a non-invasive way to capture the site shape and details. Photogrammetry can provide a visual record of site features and can be combined with a point cloud to provide detail and dimensional information.
Documentation has a variety of uses including education, research, planning of restoration activities, and providing a reference for future needs. Photogrammetry and 3D laser scan can also provide details of components of a site for product development.
Uses in Product Development
Images or a 3D laser scan can provide details of a component of a product or site that may be useful for product development.
A scanned reference component can be used to eliminate the need to collect dimensional data of the product or site component for reverse engineering or product prototyping.
Conclusion
The basics of photogrammetry and point clouds provide a good foundation to learn more about 3D capture. A point cloud represents surfaces by a set of 3D points. Photogrammetry, on the other hand, uses photographs to describe 3D information.
The best method to use for a given task is dependent on a number of factors. These factors may include the properties of the surface to be captured, the size of the task, and the equipment available. In general, both methods have the potential to digitally capture information about physical objects for various applications.
FAQs
Is photogrammetry hard to learn?
It is not too hard to learn the basics of the technique, but reaching a level of precision and professionalism requires practice, and knowledge of photography, image processing, scaling, and alignment, as well as 3D software.
Can a phone be used for photogrammetry?
It is possible to use some photogrammetry applications to create 3D models using images captured with a phone, but the results depend on the phone’s camera, lightning conditions, subject, and coverage.
Why are lots of photos required for photogrammetry?
Multiple photos are required to show different viewpoints of the same feature. Software identifies the same feature in different photos and calculates its position in 3D space.
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