LiDAR Data

Producer Field Guide

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LiDAR (Light Detection And Ranging) is an optical means of measuring reflected light from distant objects to determine range, and from this information, to determine position. LiDAR uses 1.064 nanometer wavelength laser light pulses, and Bathymetric LiDAR uses 532 nanometer wavelength light because the green penetrates the water better, to measure distances by recording the time delay from the transmitted pulse and light reflected back from objects. Coupled with accurate position and orientation systems, LiDAR systems can take accurate 3D measurements of objects and surfaces using high sampling densities. Applications include engineering, remote sensing, forestry, geomatics and more.

LiDAR systems can be divided into two major types: terrestrial and airborne. Terrestrial systems are operated at ground level scanning in a horizontal direction while rotating about a vertical axis.

Airborne LiDAR

Airborne LiDAR systems are mounted in an aircraft. LiDAR sends out a series of pulses oscillating back and forth in a pattern. The collection patterns can be triangular, sinusoidal, linear, or elliptical, depending on the sensor and the settings. The data is a semi-regularly spaced network of points. The application of this data is more oriented toward direct measurement of the earth's surface used in conjunction with GIS, remote sensing or photogrammetric applications, such as land cover mapping, hydrology analysis, site selection, and so forth. This section focuses on the processing and management of airborne LiDAR data in such geospatial applications.

Processing Tools

A number of different tools exist for processing airborne LiDAR data. The majority of these applications process LiDAR data stored in the LAS File Format (LAS) format.

One of the first tools that anyone working with point data needs is some type of viewer. Because LiDAR data consists of collections of 3D points, these viewers are most often 3D tools that usually work by with the assumption that all of the data can be read into memory at once. Since LiDAR data collections can be in the billions of points, it is easy to have LAS files which cannot be viewed because of memory constraints. This is also a common problem for many processing tools, which also make the assumption that all of the data can be first read into memory. This has led to a convention of cutting LiDAR data sets into tiles of a maximum size and then processing large datasets a tile at a time.

However, its practical adoption is limited since many of the traditional tools are not yet point cloud ready. However, ERDAS IMAGINE has the ability to read point cloud data directly in planimetric, 3D, and profile views, measure in 2D and profile view, and perform other operations.