Surveying with a GPS How to configure a GPS unit to ensure the highest accuracy

Trimble and Terrasync Trimble uses proprietary software to configure and collect spatial data –Terrasync Pathfinder Office –Differentially correct data –Create data dictionaries –Export data for use in ArcMap

Configuration for Survey For the greatest accuracy the unit must be configured properly.

Logging Setting If using an external antenna make sure height is set. Point/Vertex Auto-pause count –Set to 10

GPS Settings Uncheck box next to Productivity – Precision bar DOP type should be horizontal

Accuracy and your GPS Position Dilution of Precision (PDOP) –Value that indicates when satellite geometry can provide the most accurate results –The greater the spread the better –A low PDOP measurement is desirable –PDOP mask is set at 6

Accuracy and your GPS Elevation Mask –Restricts the receiver to using only SV’s above a certain elevation in the sky –Default set to 15 degrees –How will lowering this mask impact your accuracy? Signal-to-noise ratio (SNR) –Measure of the information content of the signal relative to the signal noise The higher the value the better

Real-time Settings Integrated SBAS is the WAAS system

Correction method Real-Time Differential –A base station continuously broadcasts corrections via a radio signal –Often referred to as RTCM (Radio Technical Commission for Maritime Services) –Post processing a real-time differential data set can still improve accuracy

Carrier Phase The most accurate method for data collection on our GPS units Requires more rigorous data collection techniques –Accurate antenna height –5 SV and a clear view of the sky –Within 50 km of a base station

Coordinate System System –US State Plane 1983 Zone –North Carolina 3200 Datum –NAD 1983 (CONUS) Altitude Reference –Mean Sea Level (MSL) Altitude Units –Survey feet Geoid Model –Other Geoid –DMA 10X10 (Global) Coordinate Units –US Survey Feet Display USNG –Off

Units This window is set to your preferences. It will not affect the accuracy of data –Use the units you prefer

Create an new file Assign a unique file name Can also open an existing file or the file manager