3D Scanning: Laser Scanner Versatility Factors
Professional Surveyor Magazine - January 2010
Because a scanner’s cost is much higher than that of a conventional surveying instrument, organizations considering purchasing a scanner often place a high value on a scanner’s ability to effectively address a wide variety of applications and site and project logistics. Part 1
(the October issue) described the first nine of the versatility factors listed below, through “dual-axis, tilt compensation.” Part 2 describes the remaining instrument-related versatility factors, picking up with “environmental capabilities.”
• Personnel versatility
• Accuracy at range for the scene
• Accuracy at range for targets
• Ability to resolve fine details at range
• Absolute range
• Deployment cost
• Field of View
• Dual-axis, tilt compensation
• Environmental capabilities
• Camera imaging
• Fit with time windows
• Compatibility with standard survey accessories
• Power supply options
• Control interface and data storage options
• Field QA capabilities
• Miscellaneous factors (several)
Environmental capabilities apply not only to a scanner but also to its associated digital cameras and external control interfaces such as laptops. Factors include ambient lighting conditions, temperature, ruggedness conditions, and dust/humidity. The useful range of phase-based scanners is reduced in bright sunlight, sometimes significantly, while pulsed scanners are basically unaffected by ambient lighting.
I continue to be amazed at the ingenuity of surveyors to contrive solutions to make scanners (and other instruments) work well under temperature conditions beyond manufacturers’ specs. Nevertheless, everything else being equal, scanners with better environmental specs can make life easier in extreme conditions.
Scanners are often used in conjunction with digital cameras. Any scanner can be used with an external camera so that the camera imagery can be used in the office to aid in creating deliverables, including texture-mapped deliverables.
Scanners with internal cameras, especially those with high zoom capabilities and high resolution cameras and displays, offer added valuable versatility in that users can also take advantage of digital imagery in the field for quickly and accurately selecting the scene to be scanned and for quickly finding and scanning targets. Internal camera imagery can also be used with point clouds for more efficient office processing and for creating texture-mapped deliverables, an increasingly common client request.
Fit with Time Windows
Some projects have limited time windows in which to access a site/scene and conduct a survey. Nuclear plants, tunnels, airport runways, railways, hazardous areas, and crime scenes are examples. Scanners that can be quickly carried into the site, set up, operated, taken down and removed, and that involve minimal number of targets are best for these scenarios.
Based on my experience, projects with these constraints are relatively few compared to the total number of scanning projects, but they’re often a good fit for laser scanning.
Compatibility with Standard Survey Accessories
Some scanners fit this bill more than others as far as compatibility with standard tribrach mounts, standard tripods, GPS antennas, standard batteries, survey prisms, built-in laser plummets, etc. In addition, the more types of scan targets that can be used by a scanning system, the better.
Power Supply Options
Scanners consume much more power than conventional instruments, so power supply solutions are important. The more options you have, the better. Can you use total station batteries? Do you have to use generators or car batteries? How long does a charge last and how long is the battery charging time, etc.?
Control Interface and Data Storage Options
The more control options and the richer each control option is, the better from a versatility standpoint. Likewise, the more options for data storage the better.
All scanners can be used with laptop control. Laptops provide the most horsepower for control and in-field QA, but they can be logistically inconvenient. Wireless control, either via laptop or handheld, also provides added versatility to address various site logistics. Extensive onboard controls provide the greatest logistical convenience, and the industry is heading toward more scanners with onboard controls with increasing capabilities.
Field QA Capabilities
Scanner vendors provide various tools for field QA. Many are in the form of software or onboard firmware or are associated with embedded camera imagery. Questions to ask from a versatility standpoint are “Can I view the scans while scanning and/or immediately after a scan? Can I view them onboard or only via laptop? Can I view and immediately check target scans? Onboard, via handheld, or only via laptop? Can I easily check scan data in the field against known points from other instruments?”
Various other factors can occasionally come into play or are ones that certain vendors may cite. These include:
Flexible mounting orientation:
Occasionally it can be helpful to mount a scanner upside down or at an angle (these cases are uncommon). One caveat: use rigorous QA if you do this.
Some scanners can be operated in “profile mode” in which the scanner’s mirror spins, but the scan head does not rotate. Profile mode enables use of a scanner on a moving platform (e.g., vehicle, train, boat). As the mirror spins and the platform moves, a spiral-type scan pattern is created. Today, there are more than 100 times as many static/tripod based scanners in the market as there are kinematic/mobile scanners, so use of this profile mode is uncommon.
Some scanners can be used to stakeout points, which can be useful if the scanner is the only tool you have at the site and you only need a few points.
These are basically software and firmware utilities that let a user develop their own interface solution for controlling a scanner. An example: permanently mounting a scanner to periodically monitor a structure or scene without operator intervention.
Today, scanners output data in vendor-unique formats. Many vendors cooperate with each other to share data formats so that one vendor’s data can be easily used in another vendor’s software. From a versatility standpoint, the more software that can directly support a scanner’s output format, the better.
Some vendors try to shine a spotlight on this feature to push whatever class/visibility of laser scanner they make, but my observation from a practical standpoint is that the only meaningful constraint in the market has been the avoidance of class 3B scanners, as they require many additional safety precautions for eye protection.
Otherwise, class 1, 2, and 3R scanners, with visible or invisible lasers, are widely used every hour of every day by extremely safety-conscious police agencies, transportation and aviation authorities, factories, industrial plants, construction sites, etc. without incident. So, as long as the scanner is not 3B, you’re okay from a general versatility standpoint with respect to laser classification/visibility.
Many versatility factors determine the overall versatility of any scanning system. Since surveying companies or departments typically want to be able to tackle a wide variety of opportunities, scanners with the best overall versatility have been the most popular types of scanners in the market. Part 3
of this series will explore versatility factors for laser scanning software.
About the Author
Geoff JacobsGeoff is senior vice president, strategic marketing for Leica Geosystems, Inc.
» Back to our January 2010 Issue