Studies in Applied Global Positioning Systems for Geographic Information Systems
This course covered the principles and fundamentals of GPS and the use of GPS units in the field for graduate students. Lecture topics focused on GPS/GNSS system principles, fundamentals, operations and techniques to improve accuracy.
Additional topics and equipment covered in lecture and field exercises included:
Datums
Projections and coordinate systems
Differential correction and accuracy assessments
Code phase and carrier phase GPS
Seven different types of GPS/field data collection equipment. In addition to traditional GPS handheld units, we worked with Nexus tablets and Juno3 based GPS equipment including transferring field data to and from desktop systems and develop skills integrating GPS data with GIS applications.
The final graduate project follows.
Accuracy Assessment Graduate Project
The Accuracy Assessment project goal was to compare the accuracy of five types of GNSS receivers by collecting data points at a known location under ‘ideal’ conditions and analyzing their location accuracy.
We expected increasing the number of collected data points would also increase accuracy and reduce the measured distance to control point B. However, our findings were inconsistent. The Garmin and Juno 3B units lost accuracy while the Pro6H, ProXH, and Nexus units gained accuracy as the number of points collected increased (when comparing 1 point versus 100 points). General error could have arisen from inaccuracy in the published control point data sheet values or data collection error.
The worst performing unit was the Juno 3B with a 5.3 meter distance measured to control point B. This could have been due to the low number of satellites (4) the unit was able to lock with. Other factors that may have contributed to the problem could have been low battery power, high PDOP, and non-differentially corrected data.
The highest performing GPS unit was the Garmin eTrex with a 0.6 meter distance measured to control point B. GLONASS is likely a contributing factor to the Garmin’s increased accuracy, however other units tested also use GLONASS. Additionally, the Garmin may have had a positional lock longer than other devices which would also contribute to better accuracy.
Overall, the Garmin eTrex and Nexus were surprisingly more accurate than the Pro6H and ProXH external receivers. Improper field data collection, settings and methodology may have led to this. For future studies, we recommend a detailed procedure for each unit’s physical setup in preparation for data collection and specific unit settings. This may provide different results and likely more accurate data.
