Precise GPS Positioning: Prospects and Challenges

Carrier phase-based GPS positioning is now an indispensable tool for a wide range of precise applications in navigation, surveying and geodesy. To address such a variety of applications, many implementations of precise GPS techniques have been developed. Almost all techniques involve 'relative' positioning, in which one GPS receiver/antenna's coordinates are determined with the aid of measurements also made at a stationary base or reference receiver. In essence all of these techniques may be categorised according to a small number of attributes. Is the technique implemented in the post-processed or real-time mode? Does the scenario involve static or kinematic positioning? Is the inter-receiver distance comparatively short (say <10km) or very long (e.g. >1000km)? Is a single base station involved or a reference network of receivers? and so on. Each of these attributes also determines the data processing strategies that should be employed to ensure accurate and reliable positioning results. Over the last two decades 'precise GPS positioning' has played a role similar to F1 motor racing. That is, challenges to carrier phase-based GPS positioning spur research on new hardware, new data processing algorithms and new operational procedures, which are then incorporated into mainstream surveying and navigation 'products'. In this paper, the challenges, progress and outlook for high precision GPS positioning will be discussed, with particular emphasis on identifying the constraints and commenting on the prospects for addressing them in the near and medium term.