Skip to content
Week 15 - Geographic Datums
This lab focused on understanding geographic datums and how errors in coordinate order and vertical reference can significantly impact UAS datasets. Using a real ground control point file with known issues, the goal was to identify problems, correct them in ArcGIS Pro and ArcGIS Earth, and understand how ellipsoid and orthometric heights relate to one another.
The first part of the lab involved importing a ground control file with incorrectly labeled coordinate fields. When added directly as XY data, the points appeared in an incorrect location, which made it immediately clear that something was wrong with the dataset.
After identifying the issue, the dataset was re-imported using the correct Y-X-Z field order. Once corrected, the ground control points appeared in their proper location and could be evaluated more realistically within the project area.
Figure 2. Corrected GCP import showing points plotted in the proper location.
To investigate vertical differences, the corrected points were also viewed in ArcGIS Earth. This allowed the terrain surface to be visualized and compared against the Z-values provided by the survey data. The elevation differences observed highlighted the mismatch between ellipsoid heights and elevations referenced to mean sea level.
Using information from the National Geodetic Survey, a geoid offset was identified and applied to the original ellipsoid heights. This adjustment brought the corrected Z-values much closer to the elevations shown in ArcGIS Earth, confirming that the discrepancy was caused by a vertical datum issue rather than bad terrain data.
The final step was creating a complete map layout showing the corrected ground control points, coordinate values, and vertical datum information. This layout combined proper cartographic elements with clearly labeled coordinate and datum details.
Figure 4. GCP distribution and coordinate map with vertical datum Layout
Overall, this lab demonstrated how critical it is to understand datums and coordinate structure when working with survey and UAS data. Small mistakes in metadata or coordinate order can lead to major errors, while careful validation and correction can restore a dataset to usable condition.
Want to print your doc?
This is not the way.
This is not the way.
Try clicking the ··· in the right corner or using a keyboard shortcut (
CtrlP
) instead.