LiDAR is an airborne laser detection and ranging system installed on an aircraft. It generates LiDAR data images by measuring the three-dimensional coordinates of ground objects.
Airborne Light Detection And Ranging (LiDAR) is a space measurement technology that integrates three technologies: laser scanning, a global positioning system (GPS), an inertial navigation system (ms). It can quickly and accurately Obtain surface information is another major technological revolution in surveying and mapping circles following GPS technology.
Compared with traditional aerial surveys, airborne LiDAR has the advantages of fast speed, high accuracy, and rich three-dimensional information. The airborne lidar system is combined with the digital aerial camera, the airborne GPS and the inertial navigation system (INS), and the large-capacity high-speed computer is used, and after special software processing, the digital elevation model (DEM) and digital orthophoto map can be quickly completed (DOM) mass production: The plane accuracy of LiDAR data can reach 0·2m, and the elevation accuracy can reach 0·1m.
In foreign countries, airborne LiDAR has about 10 years of commercial application history; in China, airborne LiDAR also has about 3 to 4 years of commercial application history. Combined with the current technological progress and application status of LiDAR, the relevant links of LiDAR technology application have basically taken shape. In foreign countries, LiDAR hardware equipment has become mature and stable, and its performance has been optimized; professional and efficient processing software for LiDAR data has been successfully developed and gradually put into use, and basic data processing software is basically mature; and domestic and foreign LiDAR applications The field is also expanding and deepening, and has been widely recognized by a large number of industrial fields. It has been successfully applied to large-scale DEM, DOM mapping, power and highway routing, urban planning, forest investigation, coastline monitoring, and 3D digital city Construction and other industries.
2LiDAR data acquisition and processing
2.1 Acquisition of LiDAR data
To obtain LiDAR data, you first need to select the LiDAR equipment according to the design requirements, and then select the appropriate aerial height, flight time and air belt design according to the parameters of the LiDAR equipment and the performance of the aircraft. The LiDAR system is an advanced active sensing system. Rely on sunlight, so night flight can be considered when acquiring ground three-dimensional information. During flight operations, it is necessary to avoid the weak GPS signal period according to the actual ephemeris data in the survey area, in order to avoid rabbits, vegetation, especially crops. For ground interference, it is recommended that you choose to fly in autumn and winter.
2.2 Classification and processing of LiDAR data
LiDAR data include many types, such as buildings, vegetation, water bodies, ground surface, pipelines, etc. If you want to extract DTM (DigitaI Terrain Model), you must separate the non-surface type points from the surface points, that is to say. Data classification. At present, most of the force methods based on LiDAR data point filtering are based on information such as the elevation changes of the 3D laser data feet. In general, there are mainly moving window methods, iterative linear least squares interpolation methods, based on Topographic slope filtering and moving surface fitting methods.
2.3 coordinate conversion
The laser point coordinates calculated by the POS dynamic positioning belong to the WGS84 coordinate system, and the general survey area adopts the local coordinate system, so the final result needs to be obtained through coordinate conversion. The coordinate conversion includes two aspects: the conversion of the plane coordinate system and the conversion of the normal height. The conversion of the plane coordinate system is generally obtained through the joint measurement of local coordinates using the seven-parameter method. The normal height conversion is calculated by the quasi-geoid fitted by the elevation control points of the survey area.www.isurestar.net