How to Buy a 3D Laser Scanner: Top 10 Checklist

Please post any tips or advice you have in general relating to laser scanning either whilst onsite or office based.
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Phil Marsh
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How to Buy a 3D Laser Scanner: Top 10 Checklist

Post by Phil Marsh » Mon Oct 01, 2007 9:48 pm

In the market for a laser scanner? There's a lot of great technology to choose from. Innovations in hardware and software are reported every month. To help you make the best choice for your business, here's our top 10 list of buying criteria. Of course, how you ought to weight these criteria will depend significantly on the markets you serve, the skill and experience of your people, and what is available and supported in your market.

1. Work process. The best place to begin is the end. What software is available to process the data once it's been acquired, and is it a good fit with your work processes or your customers' work processes? The flow of data from the instrument to the expected deliverable is worth serious consideration. Workflows for civil engineers designing a bridge are very different than workflows for piping engineers revamping a refinery unit. Software capability varies a lot. Some point-cloud software products work best with MicroStation, some with AutoCAD. Some applications are more friendly with Intergraph software, others with AVEVA. How open is the data format? This is a concern if you need to separate the hardware decision from the post-processing software decision. Of course this is less of an issue for customers who place high value on one-stop shopping. Tradeoffs in optimality of data acquisition may be justified if the downstream work process benefits. In some cases the client may have a lot to say about what scanner or software is used on what job and that is what matters most.

2. Accuracy. What accuracy can be expected from the scanner system? By accuracy, we mean the degree to which the results obtained from the scanning system correspond to the physical dimensions of the object being measured. Typically laser scanning providers specify accuracy of their devices as plus or minus a given unit distance (fractions of an inch, millimeters, or centimeters in the case of some very long-range scanners) at a given range (target distance), and will typically also provide the standard deviation. Here you want to be sure that your instrument and software used to process the scan data will deliver the results you and your customers need.

3. Dynamic range. What is the instrument's dynamic range -- that is, the useful working range of the instrument in the conditions under which it will be operated? The working range of terrestrial 3D laser scanners starts around 1 meter, and can be as great as 1 kilometer. Useful range is a function of not only the device but also the reflectivity of what's being measured, as well as ambient lighting and humidity conditions. Typically dynamic range gets traded off against acquisition speed.

4. Speed of the device. How long will it take to get those measurements? Are the measurements averaged? How many points are captured per second? The savvy buyer understands there is a tradeoff between the number of points that are captured and averaged, and the expected standard deviation in the measurement.

5. Field of view. What field of view (FOV) does the instrument have? FOV in different instruments can range from a window of 40 x 40 degrees, to 270 degrees vertical x 360 degrees horizontal, to 360 x 360. (Of course no scanner can see through the tripod it's mounted on). FOV is important - the greater the FOV, the fewer setups are required to capture the complete scene and its control points. Fewer setups typically mean more efficient scanning and fewer chances for error.

Issues (2), (3), (4) and (5) are coupled. The measurement throughput and the accuracy and dynamic range need to be understood on a self-consistent basis. While it's clear all the above issues need to be considered, it's not immediately obvious how to use them to rank and compare scanner performance. Indeed, making meaningful comparisons of speed, accuracy and dynamic range is not trivial. We expect this task to get easier as the industry develops standard protocols and reporting procedures for evaluating system performance.

6. Operating environment. Make sure the instrument will operate in the environmental conditions to which it will be exposed. How will performance be affected by temperature, humidity, dust, vibration? Scanning in environments where toxic chemicals, nuclear radiation or other agents can degrade scanner performance is another level of consideration. Ruggedness is a factor too: a scanner well suited to capturing the interior architectural detail of a church may not be the same tool that you want to mount on a boom bolted to a truck to capture bridge clearance data.

7. Ease of use is yet another category of concern. Here the considerations are: How heavy is the device? How big is it? Can it be transported as carry-on luggage on an airplane? What are the power requirements? Can batteries be purchased at the local big-box store, or in remote locations? Does it need a dedicated laptop, or can it operate standalone? How straightforward is it to calibrate the instrument? How often do calibration procedures need to be performed? What facilities are required for this? How often does it need to be factory-serviced?

8. Eye safety. This is a hornet's nest of vendor claims and government regulations. Manufacturers promote the safety of their devices as a marketing tool, and the debates are sometimes confusing. Meanwhile regulations for the safe use of lasers vary throughout the world. In theU.S., manufacturers must comply with regulations for lasers and laser products issued by the Center for Devices and Radiological Health (CDRH) of the Food and Drug Administration (FDA). In Europe and elsewhere, regulations issued by the International Electrotechnical Commission apply. The U.S. Department of Labor, Occupational Safety & Health Administration (OSHA) also weighs in with standards and directives related to exposure to laser hazards. And the American National Standards Institute ( ANSI ) sets standards that are referenced by the U.S. Department of Labor. Further, some states in the U.S. have adopted their own standards and enforcement plans. Buyers need to consider the potential for workers or the public to be exposed to the laser beam. In particular, will workers on the site be using survey instruments or other optical devices through which the laser beam might accidentally be viewed? The setting in which the laser scanner will be used is a guide to what level of eye safety is appropriate.

9. Supplier stability. The next domain of concern has to do with the supplier of the instrument. First, how stable is the company? Terrestrial laser scanning is far from being a mature market, and we think it unlikely you'll want to cut yourself off from innovation. On the other hand it would be foolhardy to purchase an instrument from a company that you think might not be around in six months -- where will replacement parts and service come from if needed?

More supplier-related questions -- Are training and service support readily available? It's enough of a challenge to be scanning 200km offshore in the North Sea. In the event of equipment damage or failure, how available is a backup unit? Some asset owners we know insist that a backup scanner be available within reasonable distance. The reason is simple -- the window of opportunity to scan some facilities is sharply limited. For example, if a nuclear power plant needs to be scanned, some areas of these plants are not available except during schedule outages, which take place only every 18 to 24 months.

What are the vendor's development plans going forward? Can the instrument be upgraded, for example? Some vendors have a program for field upgrades to enhance system performance. With others, it's a new purchase decision every time.

10. Cost. Of course no one makes a purchase decision without considering this. Scanner list prices start at a decent price but can rise dramatically once fully loaded with software, maintenance, training and support.
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