Coastal Zone Management
March, 1992
 
Investigation of Alternatives for Adjusting Charts on
Non Standard Horizontal Datums to Known Standard Datums
One of the mandates of the Canadian Hydrographic Services (CHS) is to provide hydrographic charts of Canada's inland and coastal waters for public use, including both commercial and recreational purposes. With the rapid adoption of global positioning systems (GPS) for shipboard and pleasure craft, CHS has committed to convert existing Charts to NAD83. Although the majority of the Charts are related to NAD27 and may be adjusted to NAD83, nearly one-quarter of the 1,575 charts and charts inserts in the inventory of the CHS need reconstruction or a survey to related them to datum.

Hunter and Associates was contracted by CHS to:

  • investigate the alternative methods and options available for referencing these non-datum charts to a known modern horizontal datum;
  • apply various methods to sample charts and evaluate the results including the accuracy, costs and benefits;
  • summarize the results of the investigations and recommend how the results can be optimally applied to referencing these non-datum charts.

Four hydrographic charts were selected for investigation, two depicting the western and eastern shorelines of Georgian Bay, and two portraying the Trent River system and the Welland Canal. Control points were obtained from a variety of sources, including the National Geodetic Data Bank (NGDB), CHS Geodetic Survey Control, Ontario Ministry of Natural Resources (OMNR) COSINE data base, OMNR Ontario Basic Mapping (OBM) topographic maps, National Topographic Services (NTS) topographic maps, and CHS field sheets. Least squares and piecewise linear transformations were applied to the chart locations coincident with the control points. In addition to the evaluation of the residuals associated with tranformations, adjusted shoreline segments were evaluated against the OBM shorelines utilizing a polygon displacement analyzer.

The transformation methodology utilized by Hunter and Associates was recommended as a suitable means for the CHS to adjust the non datum charts.

 © 2001, Hunter GIS