iGage
iG8 User Manual
99
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:
OPUS-RS (Rapid Static)
Standard OPUS-Static sessions require 2-hour
observations. OPUS-RS sessions can be as short as 15-
minutes.
However, OPUS-RS solutions are not available
universally. In general, OPUS-RS requires:
3 (or more) CORS within 250 km of your site
your site must be within 50 km of the polygon formed
by the CORS sites
If you are working in Southwest Nevada, along the
highline of Montana or in North or South Dakota,
OPUS-RS probably will not work and you will have to
collect more than 2 hours of data for submission to
OPUS-STATIC!
Prior to collecting data for OPUS-RS check the latest
status map to insure that OPUS-RS will work. The online
OPUS-RS resource
http://geodesy.noaa.gov/OPUSI/Plots/Gmap/OPUSRS_sigmap.s
html
is updated routinely and reflects the probability that an
occupation at a given location will be successful and the
expected accuracy for a 15-minute and 1-hour
occupation.
In some areas there is a risk that if a single CORS site is
unavailable, your OPUS-RS job will not be processed.
Caution and planning are suggested for OPUS-RS jobs.
OPUS-Projects
OPUS Projects is a relatively new online tool. Its use
requires taking a NGS training class, but the invested
time is well worth it as OPUS-Projects will allow you to
combine the observation files from multiple receivers
and multiple sessions.
There is an excellent article and video describing OPUS
Projects in the October 2013 ‘American Surveyor’
magazine. Search for “OPUS-Projects: The Next
Revolution in GPS” to find a full resolution PDF.
OPUS Error Messages and Failures
There are lots of possible error messages when
processing OPUS solutions. It is our experience that
almost all errors fall into a single category:
“There is not enough nearby CORS data to effectively
process your occupation…yet.”
In general, the solution is nearly always the same:
“Wait until more data becomes available and resubmit
your job.”
If you are processing OPUS-RS jobs in an area with very
few CORS stations, and one CORS station was offline,
waiting will not help. OPUS-Static is the solution for
locations where OPUS-RS is not dependable.
CORS stations can report observations hourly or daily.
In some areas (typically UNAVCO PBO sites) most of the
sites report once at the end of each day (GMT.) So data
that is needed to process your job is not available until
4:00 am GMT on the day after you collect data.
The Download tool allows you to submit jobs to
alternative services like AUSPOS and RTX. Typically
these alternative services closely match OPUS.
If you submit an observation to OPUS and nothing
comes back, check your SPAM folder. OPUS solutions
are regularly misidentified as spam.
OPUS is sometimes unavailable or takes longer than
other times.
Interpreting OPUS Results
When you receive an OPUS solution by email from the
NGS, it will look something like this:
USER: [email protected] DATE: May 06, 2014
RINEX FILE: p4490900.14o TIME: 16:08:35 UTC
SOFTWARE: page5 1209.04 master93.pl 022814 START: 2014/03/31 00:00:00
EPHEMERIS: igs17861.eph [precise] STOP: 2014/03/31 23:59:00
NAV FILE: brdc0900.14n OBS USED: 45735 / 47174 :97%
ANT NAME: TRM29659.00 SCIT # FIXED AMB: 162 / 171 :95%
ARP HEIGHT: 0.0083 OVERALL RMS: 0.011(m)
REF FRAME: NAD_83(2011)(EPOCH:2010.0000) IGS08(EPOCH:2014.2452)
X: -2184137.494(m) 0.003(m) -2184138.362(m) 0.003(m)
Y: -3839941.381(m) 0.001(m) -3839940.177(m) 0.001(m)
Z: 4585410.516(m) 0.005(m) 4585410.529(m) 0.005(m)
LAT: 46 15 35.23578 0.005(m) 46 15 35.25052 0.005(m)
E LON: 240 22 8.47069 0.002(m) 240 22 8.40767 0.002(m)
W LON: 119 37 51.52931 0.002(m) 119 37 51.59233 0.002(m)
EL HGT: 208.861(m) 0.003(m) 208.444(m) 0.003(m)
ORTHO HGT: 230.163(m) 0.018(m) [NAVD88 (Computed using GEOID12A)]
UTM COORDINATES STATE PLANE COORDINATES
UTM (Zone 11) SPC (4602 WA S)
Northing (Y) [meters] 5126276.950 103343.987
Easting (X) [meters] 297235.684 566995.383
Convergence [degrees] -1.90148112 0.63125220
Point Scale 1.00010542 0.99993063
Combined Factor 1.00007268 0.99989789
Here are some general rules to help judge the quality of
a solution:
The orbit
[precise]
should be precise or rapid (not-ultra
rapid.)
> 90% observations used or > 80% # Fixed Ambiguities
> 50% Fixed Ambiguities or > 95% observations used
Overall RMS < 0.030(m)
Lat / Lon RMS < 0.030(m)
If you collect data under canopy or in an area where
there are buildings or trees that obstruct the view
