Episode 32 Epochs, Int. Foot vs US Survey Foot as it Applies to Basemaps and GPS Measurements

The GPS manufacturers provide "survey-grade" or "sub-centimeter" GPS solutions for industries and trades that need to measure distances over 100 feet. A centimeter is equivalent to 3/8” or 0.03’ of a foot. This advertising claims of sub-centimeter accuracy are in the narrowest of one sigma circumstances, the unsuspecting GPS user may not realize their measurements could differ by several feet from the GIS basemap, construction plans, or CAD mapping. Outside of the California land surveying profession, most GPS users lack the training or awareness to constrain to a legally defined datum or published epoch.

In California, the GPS measurement issues are particularly severe, and the downstream consequences are significant. Over 30 years ago, the California Legislature enacted the California Public Resource Code sections 8801 through 8902 to mandate documentation of the epochs, datums, and accuracies of coordinates to avoid costly errors in measurements.

The introduction of the North American Terrestrial Reference Frame of 2022 (NATRF2022) and the State Plane Coordinate System of 2022 (SPCS2022), implemented by California Senate Bill 566 (2023-2024), will result in a measurement delta of several feet on all existing GIS platforms and existing GPS coordinate systems.

Enjoy the video!