The Geoid model contributes to the vertical component of the reference system so that ellipsoidal GPS heights can be converted to orthometric elevations for practical uses.

The geoid is mean sea level plus the natural continuing of mean sea level under the landmass, our topography. This extension must be determined mathematically or modelled. The geoid model is actually based on gravity data collected worldwide. Once we determine the geoid, we can compute the difference between the two surfaces, the ellipsoid and the geoid anywhere in the country.

The real challenge lies in knowing the relationship between the ellipsoid and the geoid. Once we determine the difference between these two surfaces, called the "geoid-ellipsoid separation" or "geoidal height", at a given point, we can then apply the geoidal height to our GPS height measurement to get the mean sea level elevation.

Product Details

These file are precise geoid models that covers a number of different regions of the province. This geoid model/values is loaded into MASCOT for all geodetic control monument (GCMs) in the GVRD, ensuring that MASCOT and the RTK Service are completely compatible.

The file can directly imported into GPS manufacturers software for use in the field or office, e.g. Trimble's Geomatics Office and Leica's SkiPro or Leica Geo Office. Free software is available from Natural Resources Canada (NRCan) Geodetic Survey Division that lets you view and extract geoid values with this file. For more information please go to Canadian Spatial Reference System Software page.

Specifications

For further information on Geoid Model for BC and Municipalities specifications please refer to our Geospatial Reference Standards and Specifications.

How to Get

Geoid data models are available for free download from our Geospatial Reference downloads page.