Topographic surveys are what LiDAR is primarily used for. At the scanning rates used by Lasermap, ground positions and elevations can be collected as close as 2 feet (0.5m) apart. This provides a very detailed survey of the ground, which can then be used to produce a digital terrain model (DTM), This model is generally far more detailed than any other technology can produce economically.

From this data, detailed contours can be produced, or the DTM data can be used in almost any CAD, GIS or terrain modeling software. An accurate DTM can also be used in the production of very accurate orthorectified aerial photography. These applied maps and orthophotos then provide the necessary information for important decision making processes in both government and commercial environments.

DIGITAL TERRAIN MODELS

A digital elevation model (DEM) is a digital representation of ground surface topography or terrain. It is also widely known as a digital terrain model (DTM).

LasermapUSA uses LiDAR data to produce a detailed DTM in a much shorter time frame than using any other technology. The LiDAR system emits energy pulses at frequencies of up to 50,000 Hertz - that is 50,000 times per second. These pulses are reflected off the ground, vegetation and man-made structures at different time intervals, allowing the distances between emission and reception to be calculated. Using these distances, along with the attitude of the laser (from the inertial measurement system) and its position (from the GPS), the position and elevation of each spot can be calculated. With the high pulse emission rates, the laser can obtain as many as 3,000,000 3-D points per minute. Depending on the flying height, the aircraft speed, and the frequency and width of the laser scan, the ground point density can be as close as 0.5 meter (2 feet).

An accurate DTM can be used for various types of mapping applications, to produce contours, and for orthorectification of aerial photography.

CONTOUR MAPPING

At the scanning rates used by Lasermap, ground positions and elevations can be collected as close as 2 feet (0.5m) apart. This provides a very detailed digital terrain model of the ground. From this data, detailed contours can be produced. Resultant maps show contour lines that trace out areas of equal elevation.

The above sample contour map depicts a simple hill and provides the following information.

• The elevation of land is typically its height above sea level. The numbers written on contour lines indicate the elevation of the lines. Topographic maps would be very cluttered if all contour lines were labeled, so only the heavier lines show labels.
• The elevation of unlabeled contour lines can be determined using the contour interval at the bottom of the map. The contour interval tells the vertical distance between neighboring lines. By counting the number of contours from a labeled line, and multiplying by the contour interval, you can calculate the elevation of any contour line.
• For points located between contour lines, you can estimate the elevation by examining the distance to the two closest contours.

With Lasermap's state-of-the-art equipment and software and with careful attention to quality control and proper calibration, topographic survey data can be used to produce highly accurate topographic maps and/or 3-D models with 0.30 meter (1 ft) contours.

For more information on how LasermapUSA utilizes LiDAR to produce Digital Terrain Models and Contours, see LiDAR – DATA COLLECTION AND SERVICES.