Applications: Quality Assurance and Quality Control

In order to maintain consistent levels of accuracy and quality in our coordinate sets, we test both our data and our data collection procedures against known positions in the world to assess the overall accuracy of a given collection. This allows us to provide supporting documentation that demonstrates our measured coordinate values against the stated coordinates for a higher-order benchmark.

To do this, we collect both the customer-specified points, and a published National Geodetic Survey or International GNSS Service benchmark within or near the project area with a dual-frequency GeoXH rover unit, using the same collection procedures for GCPs and the NGS/IGS benchmark.

Once collected, all points are post-processed in Trimble Pathfinder to determine the final coordinates of the GCPs as well as the observed NGS or IGS point. The delta, or difference, between our measured coordinate value and the published benchmark coordinate value is then evaluated to determine the measurement accuracy of the GCPs.

Recent testing has shown that for our GeoXH Sub-meter products, our measurement accuracy has fallen in the .5 horizontal/.7m vertical range; however, we state the accuracy of these points at .7m horizontal/1.25m vertical for guarantee purposes.

For our Decimeter products, our stated accuracy is guaranteed at 10cm horizontal/20 cm vertical. Recent testing against an NGS Calibrated Baseline resulted in 3cm horizontal/15cm vertical using a GeoXH rover and a Trimble 4800 base station, post-processed in Trimble Geomatics Office.

As GPS technology increases, and the constellation of GPS-capable satellites grows, inherent collection accuracies can only increase, providing a significant benefit to the spatial data user community.