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The Precise Point Positioning of the Global Differential GPS System
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Welcome to GREAT Alert!
The positioning data stream
for Natural Hazard Monitoring.

  High Rate, Real-Time GNSS Site Positions
  This website is the gateway for obtaining high-rate (1 Hz) real-time coordinates of GNSS tracking sites around the world.
  To obtain real-time UDP data stream of the site positions, you need to do the following:
  1. Register here
  2. Download the Client application here
  3. Run the client application on your Linux computer.
  You will need to supply an IP address and port number to which the UDP data stream will be sent. Please verify that firewalls do not block the UDP data stream (as is common for some organizations).
  The Client, written in python, allows you to get the position time series including the covariances. You may pipe the data stream to your custom filter in order to detect any site motion. Sample output corresponds to siteName, GPS time tag (J2000), X (m), Y (m), Z (m), cov(XX), cov(YY), cov(ZZ), cov(XY), cov(XZ), cov(YZ):

sey1 475136782 3602870.471 5238174.620 -516275.337 0.000971 0.000961 -0.000236 0.001850 -0.000324 0.000214
quin 475136782 -2517231.265 -4198595.012 4076531.128 0.000316 0.000214 -0.000219 0.000686 -0.000325 0.000601
  The real-time coordinates of the site are derived via a precise point positioning (filter only) approach using the RTGx software. The key attributes of the estimated approach are:
  • Based on real time, 1 Hz, dual frequency measurements of phase and range from the GNSS receiver at the site
  • Using real time GNSS orbit and clock states from the GDGPS System
  • Site position coordinates and clocks are estimated as unconstrained white noise at 1 Hz update rate
  • Zenith tropospheric delay and gradients are modeled a random walk processes
  This service is jointly sponsored by The GREAT (GPS Real Time Earthquake and Tsunami) Alert Project and the Global Differential GPS (GDGPS) System.
  For more information about this service or about the GREAT Alert Project, please contact
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