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On Base of analyzing the shortcomings of the methods used commonly to fit the GPS precise ephemeris, the paper proposes the new method using Fourier series to fit the GPS precise ephemeris. It expounds the basic principle of the method and presents the steps of implementation. Experimental results prove the high accuracy of the method and can replace the other methods completely. It gives the appropriated order of series and the initial value of iteration. It sums up briefly the use of the method.

Lidar has provided one new method for the digital elevation model (DEM). It has the advantage of gaining the three dimensional information, the wide measuring range, the high spatial and elevation resolution. What the lidar system gains is the cloud data, which can produce the digital surface model of the scanning area directly. However, if we want to withdraw the digit terrain model, still need to classify and process the cloud data. This article introduce how to use Lidar post-processing software such as POS software, the ALS40 post-processing software as well as the Terrasan module and the LPS module deal with the cloud data together, finally produce DEM in the ERDAS software.