Geodetic Control Networks

The maintenance of geodetic control networks and their integration into the NAD83(CSRS) national standard is a key activity of CGRSC member agencies.  In addition, the Canadian Geodetic Survey (CGS) ensures that the Canadian Spatial Reference System (CSRS) is compatible with international standards and that Canadians have open access to essential products and services for GNSS precise positioning.

Different applications in surveying, mapping, remote sensing and navigation rely on accurate and stable control points with precise coordinates. At the highest accuracy level, monuments anchored to bedrock monitor the motion of the Earth’s crust.  These monuments are known as geodetic control points.  The networks they form are the physical realizations of terrestrial reference frames that underpin coordinate-based georeferencing and the measure of the dynamics of various Earth systems.

A number of other monumented points with assigned coordinates are also available for land surveys.  The majority were established with line-of-sight instruments to densify the geodetic fabric and facilitate access to the reference frame.  With an average precision of a few parts per million (ppm) over regional areas, these survey control points are usually not suitable to verify the quality of high-precision GNSS surveys, which typically offer 1cm and 1 ppm precisions with respect to the reference frame and neighboring points.

Today, accuracy has become a key factor that distinguishes geodetic and survey control points.  While coordinates for about half a million passive control points are published by CGRSC member agencies, only a thousand or so active and passive high-precision 3D stations now  contribute to the maintenance and improvement of our national reference frames.