(This letter supersedes Circular Letter No. 464)

April 8, 2014


TO ALL BRITISH COLUMBIA LAND SURVEYORS

Re: Official Vertical Datums for Legal Surveys in British Columbia

The General Survey Instruction Rules (GSIR) 4-4(2) and 12-2(1) require an approved vertical datum to be specified by the Surveyor General, and GSIR 12-2(3) requires that an acceptable geoid model also be specified by the Surveyor General. Additionally, the Land Title Act (Part 9 – Air Space Titles - Section 138) defines the term "geodetic elevation" as "an elevation derived from a source approved by the Surveyor General".

It is the responsibility of the land surveyor to ensure that they are using the approved vertical datum and geoid model for all legal surveys requiring elevations within British Columbia. This circular letter is provided to specify the approved vertical datum and geoid model for those surveys.

In November of 2013, Natural Resources Canada (NRCan) introduced a new vertical datum for all of Canada known as the Canadian Geodetic Vertical Datum of 2013 (CGVD2013). While this is officially the current vertical datum for Canada, the previous datum known as Canadian Geodetic Vertical Datum of 1928 (CGVD28) will continue to be the established datum for use on legal surveys within British Columbia.

GeoBC has announced a phased rollout of the new vertical datum (CGVD2013) in which it will publish, through the MASCOT website, the CGVD2013 elevations of all Provincial and Federal Control Points, as well as maintain the ability to access the CGVD28 elevations.

Until this transition has been completed by GeoBC, and an update to this Circular Letter is issued, the approved vertical datum for legal surveys throughout the province is CGVD28 and the acceptable geoid model for all areas of BC outside the Metro Vancouver to Abbotsford area is HTv2.0. When working within the Metro Vancouver to Abbotsford area the acceptable geoid model is HTMVBC00_Abb.

If elevations are derived from passive control points being either Integrated Survey Area (ISA) monuments, Provincial control points or Federal vertical benchmarks the published CGVD28 elevations from the MASCOT database are to be used. The CGVD28 datum is published on MASCOT datasheets in a number of different formats. The following are acceptable variants of this datum: 'CVD28BC', 'CVD28GVRD', '1928 Canadian Vertical Datum'.

GNSS observations can be used to determine ellipsoidal heights anywhere in BC and the accepted geoid models (HTv2.0 or HTMVBC00_Abb, as is appropriate for the location), can be applied to determine orthometric heights. The geoid model CGG2013 can be used to determine elevations relative to the CGVD2013 datum, but this is not yet the adopted vertical datum for British Columbia and the resulting orthometric heights will not agree with MASCOT. The HTv2.0 and CGG2013 geoid models are available for download on NRCan's Geoid Models webpage and the HTMVBC00_Abb geoid model is available from GeoBC's Geospatial Reference downloads webpage (link updated August 24, 2017).

When using Natural Resource Canada's Precise Point Positioning (PPP) service to process GNSS observations to determine elevations, there are now two choices under the ‘Vertical Datum' menu, namely CGVD28 (HT2_0) and CGVD2013. Please ensure you select the CGVD28(HT2_0) option in order to get elevations of your survey points in the approved vertical datum and geoid model.

It is critical that your plan clearly label the vertical datum (specific CGVD28 version from the MASCOT datasheet), the control points (noting published elevation) and, where applicable, the geoid model (HTv2.0 or HTMVBC00_Abb (MASCOT notes this as GVRD00)) that has been used.

Yours sincerely,

Original signed by Mike Thomson

Mike Thomson, BCLS
Surveyor General of British Columbia