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LASer (LAS) for light detection and ranging (LIDAR) is a binary data file format for use with LIDAR devices. Users enter data into these files as raw or edited and processed points. Unlike the American standard code for information interchange (ASCII) text file format, LAS LIDAR files allow users to deliver and exchange, analyze, and manipulate data. The advantages of using LAS files include smaller file sizes, ease of accessibility, and greater data maneuverability. LAS proponents also claim that ASCII files require more operator input for viewing specific file aspects.
Geographical or topographical LIDAR files consist of measurements of impulses reflected back to a LIDAR receiver from distant objects. Computers traditionally maintain the returning impulses, or cloud points, in ASCII text file format. While any text editing software could open and read the data, the files were large because they contained millions of measurements.
A number contained within the ASCII files, for example, might require ten bytes to store each measurement. Using LAS software, the same number only requires four bytes. Compressing LIDAR information with LAS programs saves a great deal of space on a computer because geographical files typically contain hundreds of gigabytes of data. Some suggest that using LAS LIDAR reduces file sizes anywhere from 35% to 80%. The smaller size of LAS LIDAR data files also decreases the time required to select, open, and view the file.
LAS binary formats increase options for viewing LIDAR data. Geologists, for example, might choose to view single file strips or multiple layers at once. A file may be examined as individual points or combined with profile tool software, providing three-dimensional attributes. By inserting a grid over particular areas of an open file, users can zoom in or out of specific regions of the illustration. Users can also subdivide files into different classifications.
Organization options with the LAS LIDAR software allow users to classify point clouds by class, distance or return density. Grouping point clouds by building, ground, or vegetation are common classifications. Elevation is another means of categorizing data. Dividing data by density may involve low intensity point clouds that generally depict dark or rough surfaces. High intensity return data usually indicates reflective or smooth surfaces.
LAS LIDAR files might also indicate the minimum and maximum scan angles at which the receiver detects returning impulses. LIDAR devices with transmitters and receivers in the same unit may emit impulses in a straight line downward. When the signal reflects off a surface and returns in a straight line back up to the receiver, this usually denotes a zero degree angle. This concept can be visualized by drawing a line from one point to another and back again. Impulses emitted in a straight line downward, reflect off multiple surfaces and return horizontally, usually indicating plus or minus 90 degree angles.
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