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OPUS: What is it?
OPUS (Online Positioning User Service) is a free service
provided by the NGS (National Geodetic Survey.)
From the NGS Website:
“This Online Positioning User Service (OPUS) provides
simplified access to high-accuracy National Spatial
Reference System (NSRS) coordinates. Upload a GPS data
file collected with a survey-grade receiver and obtain an
NSRS position via email.
OPUS requires minimal user input and uses software which
computes coordinates for NGS' Continuously Operating
Reference Station (CORS) network. The resulting positions
are accurate and consistent with other National Spatial
Reference System users.”
Here are direct links to more detailed information:
http://geodesy.noaa.gov/INFO/OnePagers/OPUSOnePager.pdf
http://geodesy.noaa.gov/OPUS/about.jsp
One of the most important contributors to vertical accuracy
computed by OPUS-Static is the length of occupation.
Longer times are better.
If you are concerned about elevation, please remember that
a 2 hour OPUS static observation has an expected height
accuracy of 2.5 cm. A 6-hour occupation has an expected
accuracy of 1.5 cm.
Again, longer times are better. Your expectations should be
tempered by this NGS graph:
