GPS drift, put simply, is the difference between your real-world location and the location reported by a GPS receiver. This discrepancy arises primarily due to the inherent limitations in the accuracy of consumer-grade GPS devices.
Here's a breakdown of the factors contributing to GPS drift:
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Atmospheric Interference: The signals from GPS satellites travel through the Earth's atmosphere, where they can be affected by the ionosphere and troposphere. These atmospheric layers can cause the signals to slow down or change direction, leading to errors in position calculation.
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Satellite Geometry: The accuracy of GPS depends on the arrangement of satellites in the sky. If the satellites are clustered together in one part of the sky, the accuracy will be lower than if they are spread out. This is known as Dilution of Precision (DOP).
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Signal Obstructions: Buildings, trees, and other obstacles can block or weaken GPS signals, causing errors in position calculation. This is particularly problematic in urban areas and forests.
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Receiver Quality: The quality of the GPS receiver itself also plays a role. More expensive receivers typically have better antennas and signal processing capabilities, which can improve accuracy. Consumer-grade GPS receivers, designed for affordability and ease of use, often sacrifice some accuracy.
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Multipath Errors: GPS signals can bounce off surfaces before reaching the receiver, creating multiple signals arriving at different times. The receiver may have difficulty distinguishing between the direct signal and the reflected signals, leading to errors.
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Intentional Degradation (Selective Availability - SA): While no longer active, it's worth noting that in the past, the U.S. government intentionally degraded the accuracy of GPS signals for civilian users. This was known as Selective Availability (SA), but it was discontinued in 2000.
While precise GPS is available via Differential GPS (DGPS) which uses ground based reference stations to improve accuracy or via very high end GPS devices, consumer grade devices will always have some amount of drift present. The amount of drift depends on all the factors listed above.
