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I am subscribed to the State of Arizona's RTN network. I've inventoried the 55 mountpoints and found varying results. When the reception is good I get reliable information confirmed by existing record data. I've been told that it is not recommended for topo work, the vertical is subject to a shift or
phase which I am researching.
Could someone please explain this shift or share their experiences with RTNs?
Your help would be appreciated.
This Content Originally Published by a land surveyor to Land Surveyors United Network
Thanks for your input Bill...this discussion is gaining ground, I appreciate your input and will keep you posted to what I and others may contribute or find...Thanks Again...Paul
GPS/GLONASS (GNSS) satellites are rarely positioned directly overhead, but always on your horizon. Your will get good horizontal readings because the geometry of the angles are far apart. You will always get poor vertical readings because the satellites are not at a large angle of incidence to your location.
Taking a vertical reading with a GNSS is like trying to calculate a location 50 meters away by doing a distance-distance calculation from 2 points that are only 2 meters apart. Your error ellipse is huge because the angles intersect only a few degrees apart and you have no redundancy. It is a miracle that you can actually get something within a few centimeters period.
GNSS should never be used to get anything but a topographic elevation.
Above 50 degrees of Latitude you probably encounter the situations you listed above.
Here in Texas I've taken Leica SmartNet measurements on points with at least 2 hours of Static occupation with results with in 0.10' (3 cm) x,y & z. Setting up on these GNSS static points and measuring between them with my Leica Robot normally yields +/-0.02' x & y and +/- 0.05 in z (elev).
NGS has been using GNSS for the last decade for Height Modernization projects down here in the lower 48.
Natural Resources Canada (NRCan) has released the Canadian Geodetic Vertical Datum of 2013 (CGVD2013), which is now the new reference standard for heights across Canada. This new height reference system is replacing the Canadian Geodetic Vertical Datum of 1928 (CGVD28), which was adopted officially by an Order in Council in 1935.
The 3cm you quote above is about what you can expect - not much better, which is what seems to be the issue in this discussion.
Thank you gentlemen for your input...and thank you to all who have contributed to this discussion. Through your efforts I've gained a better understanding which I can apply to my surveys...Thank You!