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Avoiding the Common GPS Pitfalls: “GPS Best Practices” Jay Riester Mapping Tech Support

Avoiding the Common GPS Pitfalls: “GPS Best Practices” Jay Riester Mapping Tech Support http://seilermapsupport.wordpress.com/. Equipment Setup. Current OS and GPS Firmware installed. Current Date and Time on the data collector. Data collector is fully charged.

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Avoiding the Common GPS Pitfalls: “GPS Best Practices” Jay Riester Mapping Tech Support

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  1. Avoiding the Common GPS Pitfalls: “GPS Best Practices” Jay Riester Mapping Tech Support http://seilermapsupport.wordpress.com/

  2. Equipment Setup • Current OS and GPS Firmware installed. • Current Date and Time on the data collector. • Data collector is fully charged. • Turn off WiFi and Bluetooth to conserve battery. • Automobile charger and serial clip for charging.

  3. Current 2005 Geo OS and GPS FWStart/Settings/System/System Information

  4. Current 2008 WM6.1Geo OS and GPS FWStart/Settings/System/System Information

  5. Current 2008 WM6.1Geo OS and GPS FWStart/Settings/System/System Information

  6. Best Practices: In the field • Antenna Height – Internal or External

  7. Best Practices: In the field Logging Settings • 1 second interval is default. • Auto Pause Count for point/vertex. • Horizontal/Vertical and In the Field/Post Processed accuracy settings. • Post Processing Distance from Base. • Accuracy based logging. • Estimated Accuracy icon on the status bar (click on it to display).

  8. Open conditions: Sub-foot to Decimeter

  9. Multipath • Occasionally multipath errors • still occur. • Estimated error doesn’t always • include multipath. • Zephyr/Tornado Antenna • has better multipath • rejection (Stealth technology).

  10. Best Practices: In the field Minimizing multipath: • Multipath is like TV ghosting, caused by reflected signals adding errors to the distance measured to the satellite. • Multipath is worst when you collect GPS measurements in only a single location (point features). • Multipath tends to cancel out when you collect GPS measurements while moving.

  11. Best Practices: In the field Collect good GPS measurements between features • Maintain the GPS unit in an upright position and don’t drop the GPS unit to your in side in between feature collecting (or you will pick up multipath). • Collect good quality data before and after you collection your feature (maintain GPS lock). • Keep the data collector unit “high”. • Face antenna to the Southern Sky when using unit without external antenna. • Hold the antenna horizontal or verticle (depending on type) while walking.

  12. Best Practices: In the field (cont’) Collect positions for 30 seconds at each point feature: • In theory, you don’t have to collect too many positions in a point feature, once the accuracy indicator readings are good enough. • But if you collect for about 30 seconds, you increase the chance of acquiring more satellites or cancelling out short-term multipath errors. • If the accuracy indicator readings are poor, you should log more positions. • This will typically be necessary in a hostile GPS environment.

  13. Best Practices: In the field (con’t) Antenna position • Can you really hold the antenna still directly over the target? • Use a pole with a bracket for data collector, and plum line or bubble level.

  14. Log Now or Later • Log Now – start a feature and simultaneously start collecting GPS position. • Log Later – start a feature, enter attributes and start collecting GPS positions later. Use this for lines and areas too. Also best for points if not using an external antenna.

  15. Best Practices: In the field Pause logging before entering attribute information: • Allows you to concentrate on positioning: • Holding the antenna over the location to be measured. • Holding the antenna horizontal with a good view of the sky. • It is not easy to do this while concentrating on entering attribute information.

  16. Best Practices: In the field • Log GPS again if not satisfied with accuracy

  17. Best Practices: In the field • Avoid blocking satellites with your own body by using an external antenna and pole. • Monitor your “In The Field Accuracy”. • The majority of satellites are between you and the equator. • Be aware of surrounding Obstacles. Denver, USA Frankfurt, Germany Christchurch, New Zealand

  18. Planning Sky plot View future satellite constellation, including trajectories and trails. Use time in the field more efficiently Increase productivity In Field Planning

  19. Best Practices: In the field Be Mindful - Buildings or other obstructions • Wait for stable carrier lock. • Avoid blocking satellites. • In difficult locations, move the antenna slowly. • Use the Planning software to see if better DOP will be available later. • Use offset measurements or Laser Rangefinder.

  20. Under trees: Not always subfoot Depends on: • Number of satellites tracking carrier (5 plus). • Carrier lock duration (2 minutes). • Distance to base station (50 miles).

  21. Heavy Canopy Light Canopy Best Practices: In the field Trees and canopy • Use an external antenna on a pole. • Wait for a stable lock before entering canopy environments. • Collect data before and after entering canopy environments (carrier data that is free of cycle slips). • Use the Planning software to see if better DOP will be available later. • Use offset measurements or Laser Rangefinder.

  22. Best Practices: In the field Difficult environments • Losing lock often Sometimes it may not be possible to get a carrier solution • In this case, the code solution will give better results than the carrier solution when you process your data. • Use “Automatic” carrier/code processing (Office). • Use Smart Post Processing with PFO or GPSA Office Software.

  23. Real-time Subfoot operation • Real-time Subfoot requires carrier correction • Beacon & WAAS are Code corrections (not sub-foot). • Real-time Subfoot requires L1/L2 • Hurricane antenna is L1, so not sub-foot in real time. • Hurricane antenna is sub-meter after post-processing. • For GeoXH 2008, Geo 6000: The real-time Subfoot processing is done in the application, not in the receiver • So NMEA & TSIP are not sub-foot. • Need to use Trimble software: TerraSync, GPScorrect, Pathfinder Tools and connection to a VRS via a cell phone w/data plan, MiFi pod, Droid Phone with WiFi Hotspot.

  24. Datum Shift • Know your correction source. • WAAS and Beacon are different! • Confirm your base station if post-processing. • Find one base station that works and stick with it for post processing • Do a test point on a certified known location/control point before starting a project.

  25. Datum's • Choosing the wrong datum can greatly shift your data! • NAD27 to NAD83 could mean 50 feet or more Horizontal. • “NAD83” has different versions • NAD83 (86) • NAD83 (91) • NAD83 (97) • NAD83 (CORS 96) • NAD83 (CORS 96 ?) coming soon. NAD83 (CORS96) I’m in “NAD83”

  26. Questions? Jay Riester Mapping Tech Support jriester@seilerinst.com http://solutions.seilerinst.com http://seilermapsupport.wordpress.com/

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