Errors sources elimination for accurate evaluation of displacement using global positioning system

To avoid errors and increase the quality of displacement assessment, we should know that positioning system depend on several different errors modeling the computation procedures. The principal physical parameters (orbit, solar wind, etc) of the satellite constellation, the measures at receiver´s level, as well as the software used in network adjustment are the main sources of errors, susceptible to blemish the three dimensions (X, Y, Z) components of baselines especially the vertical component because the lack of information on Geoid undulation in the area of study[2]. We can list some of these sources, in order to have an accurate idea which allows us to avoid them and thus elaborate GPS observation strategy where expected accuracies could be reached. Among them, the most important are, the signal propagation due to ionosphere and troposphere crossed, orbit error, multipath, receiver antenna phase center variation and satellites GDOP (Geometry Dilution of Position). Certain corrections (ionosphere, mono frequencies receiver case) are transmitted as the parameters by the ephemeris in the navigation message. By citing these errors, we do not omit the strategy of treatment itself which consist to use the best combination of carrier wave received by the satellite such as refining coarse acquisition, or using best combinations which are, L1&L2, L1, L1+L2, and many others[8]. Although taking in consideration these precautions, several errors remain no detectable and request more attention in the time of pretreatment by the different software intended to the network adjustment. In this paper, we have intended to avoid as possible all thee sources of errors and thus we could reach sub centimeter accuracies over the points coordinates observed by receivers which mean the best estimation of planimetric and three dimension distances computed by the estimated coordinates.