Restoration of digitized graphic data with multiquadric method incorporating trend surface function
In order to facilitate the reprocessing of older paper contour maps,it is necessary to digitize the maps first,followed by a two-dimensional grid generation,and the quality of this gridded data significantly influ-ences subsequent data processing outcomes.Given the uneven nature of digitized data from contour maps,issues of data distortion often arise during grid generation.This paper introduces a method for grid generation that integrates global multiquadric(MQ)method with trend surface functions.The approach begins by constructing low-order trend surface functions based on known discrete points.Subsequently,it utilizes the difference between known discrete points and low-order trend surface functions to formulate a MQ function.This involves superimpos-ing the low-order trend surface with the MQ function to create a novel surface.This method effectively mitigates the distortion effects of MQ function in data-sparse regions.Interpolation tests conducted on model data,elevation data and digitized data from magnetic contour maps validate the fidelity of this grid generation method,showcasing its effectiveness in preserving data accuracy.