On-line Application

GPS·H allows Global Positioning System (GPS), Differential Global Positioning System (DGPS) and Wide Area Differential Global Positioning System (WADGPS) users in Canada to convert their NAD83 (CSRS98) ellipsoidal heights to CGVD28 orthometric heights (heights above mean sea level). It is a Windows© based software providing easy and fast interpolation of a grid. It includes on-line help utilities. Both English and French versions are available.

Orthometric heights derived from GPS ellipsoidal heights and pure gravimetric geoid heights are not equivalent to CGVD28 heights due to errors in the realization of both CGVD28 and the pure gravimetric geoid model, unless use with ellipsoidal heights at bench marks. Here, a Height Transformation is developed based upon survey stations positioned across Canada using GPS and levelling observations. The GPS-derived NAD83 (CSRS98) ellipsoidal heights and levelling-derived CGVD28 orthometric heights, in addition to a pure gravimetric geoid heights, provided the basis for establishing the Height Transformation.

The Height Transformation (HT) allows users to obtain GPS-derived orthometric heights compatible with the surrounding CGVD28 vertical control, without the need to occupy benchmarks during field operations. Overall accuracy of the height Transformation is estimated as ± 5 centimetres (with 95% confidence) in the southern regions of Canada, but may amount to a few decimetres in remote or northern regions where there are few accurate CGVD28 heights to derive a reliable transformation

GPS·H (CD) includes:

Software:

• GPS Hv2.1

Models:

• CGG2000: Scientific model of the geoid for North America solely from gravity data collected up to 2000.
• HTv2.0 = CGG2000 + HRG01 + Transformation ITRF97-NAD83 (CSRS98): The CGG2000 geoid model adjusted to the Canadian primary vertical control (CGVD28) by means of 1285 NAD83 (CSRS98) ellipsoidal heights throughout Canada. HTv2.0 makes possible direct transformation of NAD83 (CSRS98) ellipsoidal heights to CGVD28 orthometric heights (Véronneau, 2001a).

GPS·H grid formats [PDF, 26.0 kb, viewer]

GPS·H is also available with a licence to the CSRS Online Database.

To order or for additional information.