Geodetic Elevations

Geodetic elevations (also called orthometric heights) are heights measured relative to a reference surface called the geoid, which represents mean sea level (MSL). These elevations are important for surveying, mapping, and engineering projects.

Key Concepts

• Geoid: A model of the Earth's gravity field that approximates mean sea level.
• Ellipsoid Height vs. Geodetic Elevation:
  • Ellipsoidal height (h): Measured from the Earth's reference ellipsoid (e.g., WGS84, NAD83).
  • Geodetic elevation (H): Measured from the geoid (mean sea level).
  • Geoid undulation (N): The difference between the geoid and ellipsoid.

The relationship between these heights is:

H = h - N

• H = Geodetic elevation (orthometric height)
• h = Ellipsoidal height (GPS measured height)
• N = Geoid undulation (geoid height relative to the ellipsoid)

Why Are Geodetic Elevations Important?

• Used in construction and land development for accurate grading and drainage.
• Essential for floodplain mapping and hydrological studies.
• Needed for topographic surveys and GIS applications.
• Critical in infrastructure projects like roads, bridges, and pipelines.

In Canada, geodetic elevations follow vertical datums like CGVD2013 (Canadian Geodetic Vertical Datum 2013). Surveyors use GNSS, leveling, and geoid models to determine accurate geodetic elevations.