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GPS to GIS

GPS Critical Settings

Critical Settings are considered "critical" due to their impact on the quality of GPS data.

The components of the critical settings are:

  • Position Dilution of Precision (PDOP) no greater than 6
  • Elevation Mask - A minimum satellite elevation angle of 15 degrees
  • Signal to Noise Ratio (SNR) a minimum signal level of 6
  • Data collection Mode, in the 3-D manual mode.

The PDOP (or GDOP) value is determined by the geometry of the satellites. As the the satellites being used to determine position get closer together the PDOP will rise and position accuracy will decrease.

The Elevation Mask determines how high on the horizon the satellite must be before the receiver will utilize it for positioning. As the gps satellite moves lower on the horizon, the potential for signal degradation increases.

The SNR is a calculated value that measures various atmospheric variables that can degrade signal quality.

Collecting GPS data in 3-D manual mode forces the receiver to only record information when four or more satellites are available and meet the other critical setting criteria.

These settings are the default values in Trimble eqiupment so under most circumstances the user will not have to make any adjustments to the data collection device. Although the relationship these settings have on data quality are now a subject of debate it is still prudent to adhere to the accepted standards.

To learn more about the fundamentals of GPS and the factors that affect the quality of GPS data, view Trimble's online tuturial.

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