Robust Co-registration of External Laser Altimetry Points and Stereo Images

Gaofen-7 (GF-7) is China's first submeter stereo mapping satellite, and the laser altimetry system equipped on it is used to improve its elevation positioning accuracy. The elevation positioning accuracy of GF-7 may be limited by the absence of a laser altimetry system. Therefore, it is necessary to study the combined adjustment of external laser altimetry points (LAPs) and GF-7 stereo images. In this study, we proposed a method consisting of registering LAPs to GF-7 stereo images followed by combined adjustment. The registration method adopts a coarse-to-fine scheme: the LAPs are reprojected to stereo images to obtain coarse coordinates, then fine coordinates are acquired by least-squares matching and using the epipolar geometry constraint. The proposed method can effectively improve the registration accuracy: the root mean square error (RMSE) of the registration is subpixel, compared with about three pixels when only random sample consensus (RANSAC) is applied. At the same time, the number of LAPs is also increased tenfold when using the proposed method. In the subsequent combined adjustment, the RMSE of the elevation positioning is decreased from about 5.5 to 1.3 m.