An Overview of Key 2D Scanning Methods
3D scanning is the process of analyzing a real-world object or environment to collect data on its shape, color, and potentially its appearance or other surface characteristics. The collected data can then be used to construct digital 3D models for use in a wide variety of applications like manufacturing, quality control, and cultural heritage preservation.
There are many technologies available today that leverage different principles for scanning physical objects accurately in two dimensions. This article provides an overview comparing five prevalent methods — explaining how each one works at a basic level and highlighting their relative advantages and limitations.
Table of contents
· Laser Triangulation
· Photogrammetry
· Structured Light
· Laser Pulse Ranging
· Contact Digitizing
· Summarizing the scanning method tradeoffs:
· In Conclusion
Laser Triangulation
Laser triangulation scanners are an extremely common type of 2D scanning hardware today. As the name suggests, these scanners utilize laser beams to analyze surfaces by means of triangulation.
A single laser dot or line is projected onto the object being scanned. This laser light reflects off the surface, with the reflection imaged by a sensor. The angle of the reflected beam relative to the originalorientation encodes distance information that can be used to map the surface. The process repeats across the object to build up a 2D scan.
Benefits:
- Extremely high resolution and scanning accuracy for capturing intricate object detail
- Fast scan speeds
Limitations:
- Sensitive to varied surface properties — transparent or glossy finishes can be problematic
- Only one laser line, requiring longer scans
Overall laser triangulation delivers precision while being easy to implement. This makes it ideally suited for quality assurance workflows like comparing manufactured parts to CAD models.
Photogrammetry
Photogrammetry is the science of making measurements from 2D photography, especially for reconstructing the exact positions of surface points. This principle is leveraged by photogrammetry scanning systems that can create full 2D models from a series of photographs capturing the subject from different angles.
Specialized algorithms analyze common points across the multiple photographs. Using information on camera parameters like focal length, hundreds of thousands of surface points can be plotted to high accuracy without ever contacting the object physically.
Benefits:
- Completely non-contact process allows scanning delicately or remotely
- Outperforms other techniques for objects with complex geometry
Limitations:
- Difficult to achieve precision better than 0.1mm
- Computationally intensive analysis places high demands on scanning software/hardware
While photogrammetry does not match the accuracy of triangulation scanning, continuing improvements in computer vision and computational power are making this limitations less restrictive.
Structured Light
The structured light scanning approach is similar to laser triangulation, but substitutes the single laser with a structured pattern of light projected onto objects. This pattern might be bars, grids, or other shapes that establish a frame of reference.
The way that these shapes deform when striking surfaces encodes detailed information about the surface itself. This allows for reconstructing the surface geometry in fine detail. Common light patterning techniques include digital light processing (DLP) projectors or laser speckle projectors if coherent laser light is preferred.
Benefits:
- Rapid non-contact scanning method
- Surface color/texture also captured unlike lone laser spots
Limitations:
- Sensitive to ambient lighting conditions
- Shadowing effects can interfere with data capture
The speed and versatility of structured light systems lend them well to inline industrial scanning applications. They also have begun diffusing into the mainstream through consumer devices like the Microsoft Kinect.
Laser Pulse Ranging
Laser pulse ranging operates by timing Laser pulses. The core principle is to measure the time delay between laser light being emitted and reflected light detected. Since the speed of light is a known constant, calculating this time interval lets you extrapolate the distance traveled.
Scanners sweep rotations of focused laser pulses across targets, building up millions of precise time-of-flight distance measurements. This data gets transformed into detailed 3D maps of subject surfaces.
Benefits:
- Extremely high accuracy down to ~0.3mm precision
- Large range up to hundreds of meter scanning distances
Limitations:
- Struggles with dark objects that absorb too much laser energy
- Fast processing required which increases costs
The superb accuracy and range of laser pulse ranging suits it for large scale scanning needs — ranging from surveying building sites to creating digital terrain maps from aerial scanning.
Contact Digitizing
Contact digitizing as the name denotes relies on physical contact between a measuring device and the object surface in order to collect dimensional data. This might employ touch probes, measuring arms, or other apparatus capable of plotting XYZ coordinates on surfaces.
As contact digitizers manually trace contours, they can achieve extremely high accuracy down to tiny fractions of a millimeter. Their sequential scanning process also captures hard-to-image surfaces like polished or transparent materials.
Benefits:
- Gold standard for precision to ~0.05mm accuracy
- Effective on transparent/reflective/convex surfaces
Limitations:
- Time consuming manual operation
- Limited in object size/geometry due to required surface access
This personalized approach suits contact digitizing for specialty applications like dental implants or duplicating sculptures where sub-millimeter perfection is paramount.
Summarizing the scanning method tradeoffs:
The above comparison helps illustrate why particular scanning techniques stand out in certain applications over others — playing to the strengths and weaknesses inherent in each approach.
In Conclusion
This has been a whirlwind tour of five diverse yet widespread methods that expand our ability to digitize physical objects and scenes through 2D scanning. From leveraging laser ranging, camera imagery, projected light patterns and more — scientists have created versatile non-contact scanning implementations alongside fine-detailed contact digitization for specialized use.
Automated scanning can be hundreds of times faster than manual measurement, while also delivering superior accuracy. The efficiencies this enables for quality assurance, archiving, and product design continue to drive efforts enhancing current modalities like laser triangulation and photogrammetry. Indeed, pushing the boundaries of precision, working volume size, and acquisition speed form the cutting edge to bring our physical world into the digital realm.
Have experiences with a 2D scanning application for industrial, heritage, or creative purposes? Please share your first-hand perspective in the comments section!
This post is originally published at 3dprintjunction.com
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