We describe a universal approach to network-based real time kinematic (RTK) positioning that provides precise, instantaneous (Epoch-by-EpochTM) positions from multiple base stations. We demonstrate this approach for the 10-station Orange County Real Time Network (OCRTN) in southern California, where distance to closest base station can range up to 35 km within the county. The flow of data is fully controlled by the Geodetics RTD (Real Time Dynamics) software. RTD also monitors the network’s integrity and geometry Epoch-by-EpochTM and allows the site coordinates to adjust to accommodate ground motion due to tectonic/seismic deformation and ground subsidence. RTD establishes a server/client relationship with the Geodetics Smart Client, which resides on a Windows CEbased PDA. Unlike conventional network RTK, the positioning calculations are performed by the client and not in the receiver. Thus, it is a universal approach and compatible with any geodetic-quality GPS receiver. The client collects raw or RTCM data through a direct serial connection to the local receiver, and base station data from the server through TCP/IP. RTCM data from at least 3 (user-selectable) base stations can be acquired with current CDMA, GPRS or GSM wireless technologies at a receiver sampling rate of 1 Hz, and with a latency of 1 second. A streamlined data format can more than double the throughput. At each observation epoch, the Smart Client performs an instantaneous rigorous network solution. Epoch-byEpochTM technology provides single-epoch initialization and re-initialization, compared to several seconds to several minutes for an ambiguity-fixed solution with conventional in-the-receiver RTK and other networkbased solutions. We demonstrate that the precision (onesigma) of a single-epoch position is less than 1 cm in the horizontal and 4-5 cm in the vertical. Precision and reliability can be improved by observing multiple epochs at a site, thereby averaging out multipath and related effects. We also demonstrate that the RTD/Smart Client combination is well suited to the navigation of dynamic platforms with respect to multiple base stations.
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