GPS Data Collection Best Practices

1. GPS Data Collection Best Practices Mapping & GIS

2. What is Trimble DeltaPhase Technology? • Postprocessing engine with significant upgrades to both code and carrier processing • Uses Carrier or Doppler data to smooth GPS measurements • GLONASS measurements used

3. Trimble DeltaPhase Technology Code Improvements • Forward and Backward processing • Automatic measurement selection for improved yield • No longer need a human to adjust the slider • For best results, use left-slider setting to give all measurements to the processor • Better outlier detection • Carrier measurement usage

4. Requirements For Improved Accuracy • Supported GPS receiver • Supported software • Software settings • GPS data collection best practices

5. Relevant Software for Accuracy • Office • GPS Pathfinder Office v4.20 or later • GPS Analyst v2.20 or later • Field • TerraSync v4.10 or later • GPScorrect v3.10 or later • GPS Pathfinder Tools v2.40 or later HOWEVER ENCOURAGE TO BE CURRENT! MOVE TO 5.30!

6. Software Settings If you intend to postprocess: • Always use left-slider ‘Productivity’ field software settings • Correct using the new ‘Smart automatic filtering’ setting For real-time-only work (no postprocessing): Use the GPS settings slider as usual, e.g.: • Mid-slider for more accurate positions in easy conditions • Left-slider to improve yield in difficult conditions • Use best practices for GPS data collection

7. Legacy Field Software With PFO v4.20… What is needed for optimal performance in the latest Engine? • Wide open mask settings • Not in Feature positions set to log at 1s • Carrier Logging on More satellites Data in between features All types of data

8. Data Collection Best Practices

9. Make sure your Almanac is Current! • Check Almanac Date • Open TerraSync • Select Status/Receiver • The almanac shouldn’t be older than 1 month • Reset receiver if almanac is “?” or older than 1 month • Go to Setup Menu • Select Options, Reset GNSS receiver • Let GPS log for 12.5 minutes in open sky

10. Between Feature GPS Collect good quality GPS measurements between features (30–60s minimum) For example: • Collect good measurements in the open • while walking towards the ‘tough’ feature • Or if possible stand still in the open • Then collect the feature • Pause GPS if required • Then collect more good measurements while walking away towards the open.

11. Data Collection Technique 1) Collect Good GPS Measurements in Open for 30-60s 2) Collect Feature Immediately for 5-10s 4) Remain in Pause for 30-60s while collecting measurements in open 3.) Pause or OK to Close Feature 5. Close Feature

12. How many positions for a point / vertex? • 5-10s is OK in you have good measurements before • Use the estimated accuracy as a guide to GPS quality • In difficult conditions • Log for longer (eg.30-60s) if the estimated accuracy improves (and you can’t get good measurements between features) • Or you could try walking into the open and carefully back to the feature.

13. Keep GPS antenna correctly oriented • If you aim at the ground, it will pick up reflected signals (multipath), and degrade accuracy • This includes between features! • Consider turning off the device, rather than walking along with it pointing down

14. High Accuracy Receivers (XT/XH/XRT) • Preserve carrier lock • The longer you can hold the carrier lock the better your positions will be • Tip: Sudden movements can break carrier lock in difficult conditions • Use an external antenna in tough environments • Easier to get above your body • Stronger signal reception • Larger groundplane / less multipath

15. Antenna Type is Important • Select the correct Antenna in the field software • Helps the post processor get high accuracy results from data in difficult environments • Only relevant for H-star and Standard Carrier processing

16. GPS Data Collection Best Practices Overview: • Check Almanac Date • Between Feature Logging • Averaging Positions • Antenna Orientation • Antenna Type • Post Processing