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Airborne Lidar measurement technology, as an efficient way of acquiring three-dimensional geographic information,
plays an important role in building DSM and DEM rapidly. Because the airborne Lidar measurement system usually
integrates multiple devices including GPS receiver, INS, laser rangefinder and CCD camera, the relative geometric
position and attitude relationships among these devices must be accurately measured in order to get the points with high
precision and thereby satisfy the accuracy requirements of produced DSM and DEM. It is proved that the misalignment
of airborne Lidar system, which is represented by angle deviations of yaw, pitch and roll, is the most significant source
of systematic error in airborne Lidar measurement. In this paper, the effect of pitch angle error on the 3D coordinates of
measured point is firstly analyzed. On this basis, a calibration method of the pitch angle deviation for airborne Lidar
system by using the geometric characteristics of spire houses is put forward. The proposed pitch angle deviation
calibration method consists of four key steps: (1) Initial pitch angle calculation. In the light of the offset distance
between the ridge lines of the same house acquired by airborne Lidar system flying in opposite directions, an initial pitch
angle deviation can be calculated. After separating the effect of pitch angle deviation, the rectified laser point cloud data
are obtained. (2) Roof plane equation determination. The plane equations of both roof slopes are determined by fitting
algorithms with the 3D coordinates of points located in the same spire roof. (3) Distance standard error calculation. The
distance of each point to the roof plane is computed and applied to the calculation of distance standard error. (4) Final
pitch angle deviation calculation. Taking the distance standard error as the overlapping criterion, the pitch angle
deviation correction is iteratively calculated according to the aforesaid procedure until the distance standard error is less
than a given value. The final pitch angle deviation is the sum of all the pitch angle deviation corrections. Experiments
show that the proposed calibration method is correct and effective.
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