Rodrigo F. Leandro

Searching for the Optimal Relationships Between SIRGAS2000, South American Datum of 1969 and Córrego Alegre in Brazil

Brazil has moved towards the adoption of a geocentric system, SIRGAS2000. With the adoption of this system, starting in 2005, a great demand has been created towards transforming the current data sets from the South American Datum of 1969 (SAD69), in its two distinct realizations, and the Corrego Alegre frames into SIRGAS2000. The fact that these four frames will co-exist until 2014 creates positive and negative situations. Due to the distortion between those frames, the relationships among them cannot be well established with Helmert transformation parameters alone. To solve this problem, five Study Groups were created to look for the optimal relationships for coordinate transformation between those frames. The approaches being investigated to augment the parameter transformation are based on: Collocation, Delaunay, Regular grids (NTv2 and Sheppard method) and Neural Networks. The research is currently going on. This paper describes the current efforts towards defining the optimal relationships among these four frames, from the mathematical point-of-view. The work described in the paper has been carried out under the scope of the National Geospatial Framework Project (www.pign.org), sponsored by the Canadian International Development Agency. Leonardo C. Oliveria Secao de Ensino de Engenharia Cartografica, Instituto Militar de Engenharia, Praca General Tiburcio, 80-6◦ andar, Rio de Janeiro, RJ, 22290-270 Brazil Marcelo C. Santos Department of Geodesy and Geomatics Engineering, University of New Brunswick, P.O.Box 4400, Fredericton NB., Canada E3B 5A3

Global Assessment of UNB’s Online Precise Point Positioning Software

The GPS Analysis and Positioning Software (GAPS) is a GPS precise point positioning (PPP) application developed at the University of New Brunswick (UNB). GAPS exists in two forms: a web-based positioning service, to which users can upload GPS observations to be processed, and a command-line executable version, which can be used to process large amounts of GPS data in a fast and convenient manner. The objective of this paper is to summarize the main approach used in the online version of GAPS; to present the modeling options available to the user through the online interface, and to assess the accuracy of GAPS by processing a global network of IGS stations for a period 1 year; and to assess the achievable accuracy of GAPS by comparing the results with external sources and similar evaluations encountered in the literature. Results obtained indicate that GAPS can achieve at least 1 cm level accuracy for any component at any location in the world.

Feeding Neural Network Models with GPS Observations: A Challenging Task

Much has been done in terms of functional and stochastic modelling of observations in space geodesy, aiming at the development of adequate adjustment models. One of the techniques, which has been the focus of more attention in the last years, is the Neural Network model. Although not trivial to be used, this kind of model provides an extreme adaptation capability, which can be an issue of fundamental importance for certain applications. In this paper we discuss the use of GPS observations in Neural Networks models, providing a brief description how a neural model works and what are its restrictions, as well as how to treat the GPS observations in order to satisfy them.

An Empirical Stochastic Model for GPS

In addition to functional models, stochastic modeling of observations plays an important role in GPS data processing. The stochastic model has influence over several issues of coordinates determination with GPS, such as the covariance matrix of the observations (which leads to weighting scheme) and the estimated covariance matrix of the parameters. In this paper we present an empirical stochastic approach to create observation covariance matrices for GPS. Our approach aims to a more realistic and complete information about the stochastic behavior of GPS observations and an improvement in quality and quality control of estimated coordinates.