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The GPS makes corrections for receiver clock errors and other effects but there are still residual errors which are not corrected. GPS receiver position is computed based on data received from the satellites. Errors depend on geometric dilution of precision and the sources listed in the table below.
Precise positioning is increasingly used in the fields including robotics, autonomous navigation, agriculture, construction, and mining. [2]The major weaknesses of PPP, compared with conventional consumer GNSS methods, are that it takes more processing power, it requires an outside ephemeris correction stream, and it takes some time (up to tens of minutes) to converge to full accuracy.
HDOP AND GPS HORIZONTAL POSITION ERRORS; Article on DOP and Trimble's program: Determining Local GPS Satellite Geometry Effects On Position Accuracy. Notes & GIF image on manually calculating GDOP: Geographer's Craft; GPS Errors & Estimating Your Receiver's Accuracy: Sam Wormley's GPS Accuracy Web Page
A typical CORS setup consists of a single reference station from which the raw data (or corrections) are sent to the rover receiver (i.e., the user). The user then forms the carrier phase differences (or corrects their raw data) and performs the data processing using the differential corrections. In contrast, GNSS network architectures often ...
GPS time was set to match UTC in 1980, but has since diverged. The lack of corrections means that GPS time remains at a constant offset with International Atomic Time (TAI) (TAI – GPS = 19 seconds). Periodic corrections are performed to the on-board clocks to keep them synchronized with ground clocks. [79]: Section 1.2.2
The post-processed measurements allow more precise positioning, because most GPS errors affect each receiver nearly equally, and therefore can be cancelled out in the calculations. Differential GPS measurements can also be computed in real time by some GPS receivers if they receive a correction signal using a separate radio receiver, for ...
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A course line is drawn on the aeronautical chart along with estimated positions at fixed intervals (say every half hour). Visual observations of ground features are used to obtain fixes. By comparing the fix and the estimated position corrections are made to the aircraft's heading and groundspeed.