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Recent advances in mobile GPS/GIS mapping technology
Laser Range Finders While GPS technology has made rapid advances, there are still inherent problems with data collection when utilizing GPS. First, there is the need for occupation of the point where GPS readings are required and sometimes its just not possible to reach the point of interest. Second, the point may be reachable, however, due to other factors, such as disturbance of wild life, areas of high traffic volume, or even evidence in crime mapping, you may not want to get there. Third, in some areas, GPS receivers cannot receive the signals, such as, in heavy tree canopy areas and near high rise buildings. Fourth, GPS mapping is slow if you have to map several features such as trees in a forest or electric poles on a road because you have to occupy each individual feature. To overcome some of the limitations of the GPS technology, laser range finders have now become available at a reasonable price and performance. These units can be used with or without GPS. The key to laser mapping is: you do not have to get there from here and occupy the feature! Instead, just shoot it with the laser. (See Fig. 4)  Figure 4 What makes a laser mapping system work The eye-safe diode pulse laser measures distance without reflectors and has a tilt sensor built in to provide vertical angles. In addition, it has an option for a digital flux gate compass or angle encoder (not affected by magnetic fields) to provide an azimuth reading. The mapping grade range finders provide an accuracy of about 5 cm to 1.5 meters. Maximum range varies from about 500 ft to 2000 ft. The Laser Range Finder can be used in different ways depending on the application, for example, direct GPS integration, indirect GPS integration, or Independent Laser Mapping Direct GPS integration In cases where you have a clear view of the sky and are getting GPS signals, you can place the laser range finder at the same spot where the GPS antenna is placed - in fact on the same range pole if possible. The laser unit sends the distance and azimuth readings to the GPS data collector and the software converts the laser readings to LAT/LONG based on the GPS antenna position as the reference. (See Fig. 5)  Figure 5 Indirect Laser/GPS integration In cases where GPS signals are not being received, the GPS antenna is placed in a clear area where signals are available and the Laser is placed in any suitable area where maximum number of features are visible. The laser sends the distance and azimuth readings to the data collector and the software calculates the LAT/LONG of the features based on the antenna position. (See Fig.5)  Figure 6 |