Adjustment Methodology in a Regional Densification of a Terrestrial Reference Frame

Abstract

Additional information is available at the end of the chapter http://dx.doi.org/10.5772/50548 IntroductionThe measurement of geodetic networks by satellite positioning is becoming more and more common, given the advantages of this technology to solve the main problems of geodesy: Planimetric geo-reference to a geocentric system  Independence of intervisibility between points  Increase of relative precision.The purpose of working under the Network scheme is to have superabundant observations that allow adjustment by estimating parameter (coordinates) values and precisions.Given the versatility of the method of indirect or parametric observations, it has become the most widely used as a method of geodetic adjustment.The Adjustment Method by Non-Conditioned Indirect Observations, also known as Method of Coordinate Variation, or Parametric Method has been widely accepted in Geodesy. by means of the use of observation equations, in which the parameters are the coordinates.This adjustment made under the application of the method of minimum squares, estimates parameters as well as their precisions.It allows to incorporate equations of coordinates, which are essential when introducing the reference frame and generating an external control.In the adjustment, an appropriate management of the coordinates requires: The introduction of fiducial coordinates with a precision better than the precision of the network to be adjusted. The adoption of appropriate weights to these coordinates, in order not to create unnecessary deformations. New Approach of Indoor and Outdoor Localization Systems 28These objectives, as will be shown in this chapter, are strongly correlated.The strict frame introduction by fixing the fiducial points could often result in an unfavorable option because it induces loss of precision to the network, caused by internal deformation. On the contrary it is possible to generate a free or quasi free adjustment omitting the introduction of the datum in order not to cause deformation to the network. Finally, it is possible to achieve a condition of balance by adopting the appropriate strategy, the optimum quantity and distribution of fiducial points. This solution must achieve the required precisions and the densification of the selected reference frame [2]. Adjustment strategy Internal precisionBefore the datum input it is necessary to estimate the internal precision of the network to be adjusted. Knowledge of network internal precision will allow the definition of tolerances when datum is introduced.This analysis is possible because of the existence of superabundant observations that is to say in the presence of degrees of freedom. In the satellite positioning techniques the adjustment over observations made in different periods or days is very important since these observations are affected by factors that change through time such as the tropospheric and ionospheric delay, oceanic and terrestrial tides, etc. This is the reason why it is necessary to measure the points of the networks in different sessions...