LIDAR Mapping Information

LIDAR mapping is a new method used for mapping and surveying. This three-dimensional mapping system is very popular for engineers, planners, mapping technicians, GIS professionals, and surveyors. Compared to similar methods for three-dimensional information gathering, it is very accurate, relatively fast, and cost-effective. LiDAR mapping is used for topographic surveys and related applications.

LIDAR stands for Light Detection and Ranging. For a LIDAR-created map, topographic data is collected using aircraft-mounted lasers. The lasers send several thousand pulses per second, and can usually measure elevation changes within six inches. By measuring the time delay from sending the laser pulse and detection of the reflected signal, LIDAR can measure how far the airplane is from the ground with considerable accuracy. These laser devices are pointed straight downward, detecting the aircraft’s elevation from the ground directly underneath it as well as slightly to the left and right, covering a fairly wide section of land on each pass. Typically, the laser can collect information over a strip measuring about 1000 feet wide from an altitude of 2000 feet.

It is possible to cover nearly 400 square miles in one 12 hour surveying session, with millions of individual elevation reference points. Compared to traditional surveying methods, this LIDAR-based 3D map can be made much faster. In fact, LIDAR contour mapping has already nearly replaced traditional methods. It is many times faster than using a surveying station or electronic version of the old surveyor’s transit tool, or other low-tech surveying methods.

Because LIDAR instruments only collect data about elevation, these tools must be used in conjunction with GPS devices so that elevation and location may be correlated. For this reason, GPA instruments are mounted on the aircraft along with the LIDAR.

The data itself is stored in a file with three coordinates, “x,y,z.” X refers to longitude, Y to latitude, and Z to elevation. Once the data has been collected by the aircraft, it is processed into a computerized layout of the land known as a digital elevation model, or DEM. The digital elevation model can automatically draw contours, or lines connecting points with the same elevation. These contours show at a glance whether the terrain is relatively steep or relatively flat, an essential piece of knowledge if you’re considering building on the land. This map includes evidence of manmade features like roads and natural features like lakes and hills. However, because these are shown on the map by elevation only, determining the nature of these features may require aerial photography or an actual site visit.

LIDAR mapping is unobtrusive, and does not require setting foot on the terrain being measured. This is advantageous in situations where there is limited access to the land from the ground, or where the terrain is dangerous. Examples include very steep slopes or large mud flats, or areas where too many trees make surveying from the ground difficult.

LIDAR is often used to map archaeological features to create maps of features that may not be readily apparent from the ground. LIDAR can also penetrate groundcover and forest canopy, making it ideal for heavily forested sites. LIDAR is often used to track topographic changes along shorelines. Its uses in construction and building trades are wide-ranging, including the planning of construction project, highways, and mines, and the creating of flood plain models.

Charles Lee Iner, RLS
August 2009