The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
https://doi.org/10.5194/isprs-archives-XLII-3-2511-2018
https://doi.org/10.5194/isprs-archives-XLII-3-2511-2018

# SOLVING THE RATIONAL POLYNOMIAL COEFFICIENTS BASED ON L CURVE

G. Zhou, X. Li, T. Yue, W. Huang, C. He, and Y. Huang

Keywords: RPC model, Tikhonov Regularization method, L Curve, orthorectification, rigorous sensor model, ill conditioned equation

Abstract. The rational polynomial coefficients (RPC) model is a generalized sensor model, which can achieve high approximation accuracy. And it is widely used in the field of photogrammetry and remote sensing. Least square method is usually used to determine the optimal parameter solution of the rational function model. However the distribution of control points is not uniform or the model is over-parameterized, which leads to the singularity of the coefficient matrix of the normal equation. So the normal equation becomes ill conditioned equation. The obtained solutions are extremely unstable and even wrong. The Tikhonov regularization can effectively improve and solve the ill conditioned equation. In this paper, we calculate pathological equations by regularization method, and determine the regularization parameters by L curve. The results of the experiments on aerial format photos show that the accuracy of the first-order RPC with the equal denominators has the highest accuracy. The high order RPC model is not necessary in the processing of dealing with frame images, as the RPC model and the projective model are almost the same. The result shows that the first-order RPC model is basically consistent with the strict sensor model of photogrammetry. Orthorectification results both the firstorder RPC model and Camera Model (ERDAS9.2 platform) are similar to each other, and the maximum residuals of X and Y are 0.8174 feet and 0.9272 feet respectively. This result shows that RPC model can be used in the aerial photographic compensation replacement sensor model.

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