| LiDAR (Light Detection and Ranging) technology is a freshly new mean to access GIS data, with great advantages which can not be matched by common photogrammetry. Since the accuracy of LiDAR system data can not meet the requirements of mapping, and the nominal value of a large number of LiDAR systems imported can not be known, domestic indicators are being developed for LiDAR in our country, and therefore, the calibration of LiDAR systems is needed to be researched greatly. In this paper, based on LiDAR instruments developed in our country, laser ranging error determination and calibration methods are designed, instrument cone scan angle and scan angle error correction methods are analyzed in-depth, and based on the analysis, error correction methods are given. In this paper, the work and innovations are as follows:1. According to the composition and working principles of LiDAR system, positioning formulas for LiDAR system are derived in detail. Comparing with the formula parameters, LiDAR system errors are discussed. And then, the major causes of each error and its impacts on point cloud data are given,2. LiDAR ranging error is analyzed in detail, a simple and feasible method for the determination of the laser ranging error is designed, and the error results are summarized and discussed. Then, a two-step ranging error calibration method is proposed. The first step is calibration of errors cased by different echo intensity. Based on error value and the relationships between echo intensity, curve fitting formulas are derived to fit the error. The second step is the calibration of fixed system errors. Based on theoretical experience and data analysis of errors, curve fitting formulas are given. Comparing the effect before and after error calibration, it can be seen that the method is quite feasible and effective.3. In order to analyze the causes of LiDAR instrument cone scan angle and its impact on point clouds, differences between the impact of cone scan angle error and pitch angle error to point clouds are discussed. Moreover, a testing method to estimate the size of the cone scan error scan is proposed. Though it is not perfect, the method has a certain effect to estimate the general scope of cone scan angle from experimental results. And of course, the method has to be improved further.4. The causes of scan angle error are analyzed, and methods to measure scan angle error are given. According to the law of scan angle error, curves are fitted and parameters are obtained, Experimental results show that the method is feasible and has obvious effects on error calibration. |
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