The developments in applications of GPS over last 10 years have done at a higher rate than advancements in the realization of GPS constellation.Owing to the advantages of high accuracy, all weather conditions, no requirements of intervisibility between measuring points, GPS is playing more and more important role in high precision positioning missions in structure/construction health, land formation, and movement monitoring etc. In order to meet a particular purpose objective, a properly configured GPS measurement can meet most of the possible static and dynamic measurement needs in such applications for absolute positioning and relative displacement. GPS has enormous benefits to myriad military, civil, commercial and scientific users around the world. The use of GPS in various areas such as Navigation, Surveying, navigation/Landing Systems, Farming, Weather Forecasting, Fleet Management provides the stimulus for its future improvement. Thus the book is useful for error estimation in observed GPS data using signal processing techniques. The estimated data may be used for measurement of overhead conductor sag in power transmission lines and for vehicles tracking in real time.