This inaugural survey of laser rangefinders is a reflection of the importance of this tool for geomatics professionals. While laser rangefinders have been available for well over a decade, their capabilities as well as their portability have steadily improved their desirability for a variety of applications. Instead of a single product, some manufacturers are now developing a product line with more advanced features.
The most ubiquitous use of laser rangefinders likely continues to be in conjunction with GPS-based mapping systems. Since most of these devices are reflectorless, they are perfect for determining the location of inaccessible points from a GPS-established position. The inaccessibility may be due to lack of GPS signal at the point of interest, or it just may be physically impossible or difficult to get there, as in the cases of transmission towers behind locked gates, features of buildings well above street level, or points of interest across or in roads or bodies of water. When a laser rangefinder is used as an additional sensor that extends the positioning capabilities of the GPS system, an additional feature to accomplish this task is electronic data transfer of the distance and related information from the rangefinder to the GPS controller. This data transfer may occur through a command sent from the "master" GPS system to first make a measurement and then send the data, or to automatically or manually follow a measurement that is initiated on the rangefinder by the user. Use of rangefinders in this capacity has increased the desirability for built-in slope reduction capability (tilt sensor). Another development to supplement the use of the laser rangefinder with GPS mapping activities was to include an electronic compass, so that the complete vector could be measured. While not all laser rangefinders have the slope reduction and azimuth determining capabilities, they have all improved in characteristics such as range, weight, power requirements and accuracy.
In addition to their use with GPS systems, laser rangefinders have been well established in several industries including forestry, mining, construction and a variety of other natural resource management and monitoring fields. With the inclusion of the slope reduction and azimuth capabilities, depending on whether the device is handheld or mounted on a tripod, the user can make an appropriate selection to achieve the level of accuracy desired. While the accuracy of total stations is not achieved, the convenience, speed and portability of the technology makes it a sound choice, especially where it is impractical, impossible or imprudent to use a total station.
The gains in performance, coupled with the laser rangefinder's rich set of features, make it an ideal instrument for many surveyors, mappers and other geomatics professionals. Pointing systems, which began with sighting telescopes mounted on top of the units, now also include heads-up displays (HUDs), markers in the field of view of binocular systems and visible laser dots. Development of this technology is also occurring in the way of software. Software functions run the gamut from calculation of coordinates to intersections to determining azimuth and distance between two observed points. Other software routines found in this batch include various options to determine height, coordinates, vertical distances between the observer's position and the point being observed, or between two observed points, settings to prevent false measurements by eliminating the distance ranges at which clutter along the line of sight may return a spurious signal, and inversing between points. Some have internal data collection capabilities.
The alleged distances these devices reach vary from 200 feet in reflectorless mode for one and 6,000 m (~20,000 ft) to a reflector with another. Measurement accuracies vary from 0.5 ft at the short end of the ranges to 6 ft at the long end. Measurement times, which vary from 0.1 s to 1 s, are sometimes selectable, which affects range and accuracy. Operating times vary, and many offer a variety of battery options. At least one manufacturer has begun integrating Bluetooth technology into their rangefinders so that if the controller is equipped similarly, cable-free operation is feasible.
The IP Rating System
The IP rating system is becoming more common to define resistance to dust and moisture intrusion. IP stands for ingress protection. The first digit of the number refers to dust protection and the second relates to protection from water.
In the laser rangefinder survey IP numbers vary from a low of 54 to a high of 67. The IP numbers by themselves do not complete the definition. Details about conditions of time, pressure and depth must still be stated by the manufacturer for the rating to be meaningful. The (paraphrased) definitions for the included numbers are as follows:
Dust (first digit)
- 5 Dust protected-not totally impervious to dust, but does not enter in sufficient quantity to interfere with satisfactory operation of the equipment
- 6 Dust-tight-no dust enters
Water (second digit)
- 4 Splashing water protection-water splashed from any direction will have no harmful effect
5 Water jet protection-water emitted from a nozzle in any direction towards the enclosure will have no harmful effect
6 Heavy seas protection-water from heavy seas or powerful jets in any direction towards the enclosure shall not enter the enclosure in harmful quantities
7 Immersion protection-water ingress in a harmful quantity shall not be possible while the enclosure is immersed under the defined pressure and time conditions