Shopping for a laser scanner? There's a lot of great technology to choose from. Below is a Top Ten list of buying criteria to help you make the best choice for your business. How you weigh these criteria will depend significantly on the markets you serve, the skill and experience of your people, and in some instances, what is available in your market.
Top Ten Considerations for Buying a Laser Scanner1. Software: The best place to begin may be at the end. What software is available to process the data once it has been acquired, and is this a good fit with your customers' work processes? The flow of data from the instrument to the expected deliverable is worth very 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. Trade-offs in optimality of data acquisition may be justified if the downstream work process benefits. In some cases the client may have much to say about what scanner or software is used on a job.
2. Accuracy: What accuracy can be expected from the scanner system? Accuracy is 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 also give the standard deviation. You want to be sure that your instrument and the software used to process the scan data will deliver the results you and your customers need.
3. 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: What is the speed of the device? How long will it take to get 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 captured and averaged, and the expected standard deviation in the measurement.
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 required to capture the complete scene and its control points. Fewer setups typically mean more efficient scanning and fewer chances for error.
The issues of accuracy and range, and speed and field of view are often coupled. If needed, ask for clarification so that the measurement throughput and the accuracy and dynamic range are stated on a self-consistent basis. While it's clear that all of 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.
5. Strength: How well does the instrument withstand the environment? Make sure the instrument can operate in the environmental conditions it will be exposed to. How will performance be affected by temperature, humidity, dust and vibration? Beyond this, scanning in environments with toxic chemicals, nuclear radiation or other agents can degrade scanner performance. Ruggedness is a factor, too: a scanner well-suited to capture 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.
6. Ease of Use: What about its ease of use? 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 as a stand-alone device? How straightforward is it to calibrate the instrument? How often do calibration procedures need to be performed? What facilities are required for this?
7. Eye Safety: What is the instrument's eye safety classification? This factor includes 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 since regulations for the safe use of lasers vary throughout the world. In the United States, 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's 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 nation 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.
8. Suppliers: Buyers also need to research the instrument supplier. How stable is the company? This can be difficult to determine since terrestrial laser scanning is far from being a mature market. However, 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?
9. More supplier-related questions: Are training and service support readily available? It's enough of a challenge to be scanning 200 km 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. If a nuclear power plant needs to be scanned, some areas of these plants are not available except during scheduled outages, which take place only every 18 to 24 months.
Finally, what are the vendor's development plans for the future? For example, can the instrument be upgraded? Some vendors have a program for field upgrades to enhance system performance. With others, it's a new purchase decision every time.
10. Cost: Finally, how much does the scanner cost? Of course no one makes a purchase decision without considering cost. Scanner list prices start at about $30,000 and can be as much as $200,000 fully loaded with software, maintenance, training and support.
This Top Ten List for "How to Buy a Laser Scanner" was compiled by Tom Greaves, senior analyst at Spar Point Research LLC, Danvers, Mass.