Passive Control Networks
Networks of passive control points were established by geodetic agencies in federal and provincial governments over the past 100 years. As proximity to a monument was critical for access to the reference frame using terrestrial methods, several hundreds of thousands of monuments were established across Canada (Table 3). The federal primary horizontal and vertical networks accounted for about half of these control points. More recently, 3D control points of the CBN and HPN networks were established to better serve users equipped with GPS. The federal CBN and provincial HPN network points were nominally spaced every 200 and 50 km. Since the early 1990’s, a few tens of thousands of 3D control points have been established by CGRSC agencies and occupied with GPS at least once. Of these, a subset of about 160 CBN monuments have been re-observed periodically, nominally at 5 year intervals.
Table 3. Number of passive control points.
*Heights are published with the horizontal coordinates. No control points published with height information only.