OPUS
Online Positioning
User Service
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
http://www.ngs.noaa.gov/OPUS/
National Geodetic Survey
[email protected] Positioning America for the Future
National Ocean Service
WHAT IS OPUS?
• On-line Positioning
User Service
• Provide GPS users
faster & easier access
to the National Spatial
Reference System
(NSRS)
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
HOW DOES OPUS WORK?
• Submit RINEX file through NGS web page
• Processed automatically with NGS
computers & software
• With respect to 3 suitable National CORS
• Solution via email (usually in minutes)
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
OPUS USES 3 CORS SITES
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
HOW DO I USE OPUS?
Go to OPUS web page www.ngs.noaa.gov/OPUS
1 - Enter your email address
2 - Enter/Select RINEX file
3 - Select antenna type from menu
4 - Enter antenna height in meters (defaults to ARP)
5 - Optional:State Plane Coordinates
6 - Select up to 3 base stations (optional)
7 - Upload File
Check your email (usually only takes a few minutes)
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
WHAT ARE SOME OPUS
GUIDELINES?
•
•
•
•
•
Must submit dual-frequency (L1/L2) data
Must submit at least 2 hrs of data
No kinematic/Rapid Static
No Glonass
Correct vertical requires:
•antenna type
•antenna height
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
GETTING TO OPUS
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
OPUS Web Page
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
OPUS - Select Reference Site(s)
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
HOW IS THE ANTENNA
HEIGHT MEASURED?
ARP
The height is measured vertically (NOT the slant
height) from the mark to the ARP of the antenna.
The height is measured in meters.
The ARP is almost always the center of the
bottom-most, permanently attached, surface of
the antenna.
See GPS Antenna Calibration for photo’s and
diagrams that show where the ARP is on most
antennas:
http://www.ngs.noaa.gov/ANTCAL/
If the default height of 0.0000 is entered, OPUS
will return the position of the ARP.
MARK
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
WHY DO I NEED THE
ANTENNA TYPE?
You do not need to know
these offsets. They are
passed to the processing
software through the
antenna type
The antenna phase centers are
located somewhere around
here.
The antenna offsets
are the distance
between the phase
centers and the ARP
The Antenna Reference Point
(ARP) is almost always located
in the center of the bottom
surface of the antenna.
If the user selects NONE
as the antenna type, the
offsets are set to 0.000
and the antenna phase
center becomes the
reference
Incorrect or missing antenna type  big vertical errors
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
Why NGS uses the ARP
• The ARP is a known point on the antenna
• The phase center varies depending on the elevation
angle from the antenna to the satellite
•If there are 8 satellites, there are 8 phase centers that
must be modeled and averaged
•The Phase center for L1 is different from the L2
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
Antenna Phase Center Variation
Antenna
Type A
.
.
.
Different .
Phase Patterns
.
.
.
.
Antenna
.
Type B
.
.
.
Note that SV elevation and
varying phase patterns affect
signal interpretation
differently
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
ELECTRONIC PHASE
CENTER
Phase Center Variation (mm)
Elevation Angle (deg.)
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
GPS Antenna Phase Pattern Calibrations
http://www.grdl.noaa.gov/GRD/GPS/Projects/ANTCAL
 Each antenna type has a unique phase pattern
 GPS antennas must be calibrated
 Mixing uncorrected antenna types can produce errors
of up to 10 cm in the vertical component
 NGS is at the forefront in relative field
calibration of GPS antennas
 NGS maintains a calibration database with
parameters for 88 antenna types (03-26-01)
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
Antenna Calibration Facility in Corbin, Virginia
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
HOW ARE OPUS POSITIONS
COMPUTED?
• NGS PAGES software
• Ionosphere free
• Tropospheric scale height adjusted
• Fixed ambiguities
• Average solution to 3 suitable CORS
• ITRF and NAD83 positions returned
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
WHAT DOES OPUS OUTPUT LOOK
LIKE?
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
READING OPUS
OUTPUT (input)
• The version of the PAGES software used for processing
• The ephemeris used (OPUS will use the best available):
• “igs” final post-fit orbit-better than 5 cm (14 days wait)
• “igr” rapid post-fit orbit-better than 10 cm (2 days wait)
• “igu” ultra-rapid predicted orbit-better than 25 cm
(available immediately)
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
• The antenna
name and antenna reference point height you
National Ocean Service
entered
National Geodetic Survey
Positioning America for the Future
READING OPUS
OUTPUT (process results)
• Start/end dates/times of your file
• Ratio and % of observations used in solution
• Ratio and % of fixed/total ambiguities
• Overall RMS of the solution
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
READING OPUS
OUTPUT (coordinates)
•
•
•
•
•
Reference Frames
Independent NAD83 & ITRF solutions
Peak to peak error is the difference between max and min error for individual
solutions
Peak to peak error may differ between NAD and ITRF solutions
Orthometric ht. is based on current geoid model
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
READING OPUS
OUTPUT (coordinates)
• Universal Transverse Mercator (UTM) coordinates
• US National Grid
• State Plane coordinates are given (if requested)
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
READING OPUS
OUTPUT (control)
• Base Stations used in positioning
• The closest published station listed in the NGS IDB
•
Disclaimer
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
WHAT IS A GOOD SOLUTION?
• No hard rules - only guidelines
• Make sure antenna type and antenna height
are correct
• Review statistics
• should use 90% or more of your observations
• at least 50% of the ambiguities should be fixed
• overall RMS should seldom exceed 3.0 cm
• peak to peak should seldom exceed 5.0 cm
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
HOW CAN I IMPROVE MY RESULTS?
• The best way to get more accurate results is
to observe longer sessions
• Data sets of at least
four hours have been
shown to produce
more reliable results
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
HOW DO I GET HELP?
• First use the Links on the OPUS page
• detailed discussions of guidelines
• description of processing techniques
• description of output
• guidelines for successful use
• Submit specific questions at OPUS web page
• http://www.ngs.noaa.gov/OPUS/
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
WHAT CHANGES ARE PLANNED
IN THE FUTURE?
• Inclusion of Cooperative CORS in the base
station selection process
• Better treatment of RINEX-2 header errors is
being implemented. Some translators are not
compliant with the RINEX-2 standard
• Single frequency data processing is being
considered
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
QUESTIONS?
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
http://www.ngs.noaa.gov/OPUS/
National Geodetic Survey
[email protected] Positioning America for the Future
National Ocean Service
Demonstration
Application II
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
CONTROLLING A BRIDGE SURVEY
The accompanying slides were presented
at the
2002 CORS Forum
by
Gary Thompson
of the
North Carolina Department of Transportation.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
National Ocean Service
National Geodetic Survey
Positioning America for the Future
Using OPUS to control Bridges
• On a typical bridge job, NCDOT
• Sets an azimuth pair (
)
• Uses approximately 6-7 control panels (
• Controls the site with 2 receivers
)
TIP: B-9999
P1
Place the Base Station over your first point and begin
RTK survey ensuring that you are collecting Raw Data
for at least 2 hours (This data will be sent to OPUS).
We will now refer to this as OPUS1.
P4
P2
P5
B9999-1
B9999-2
Be sure to measure to opposite Azimuth Pair point.
P3
Start Rover and begin setting and controlling your panels
P6
TIP: B-9999
P1
Move the Base Station over your second point and begin RTK
survey ensuring that you are collecting Raw Data for 2 hours.
(This data will also be sent to OPUS).
We will now refer to this as OPUS2.
P4
P2
P5
B9999-1
Again, Be sure to measure to opposite Azimuth Pair point.
P3
B9999-2
Start Rover and begin controlling your panels from the second
location. If you use one controller and name the points the same
the controller will provide comparisons in the field.
P6
Field Work is now complete.
The following steps need to be taken to
finish the process:
Office Process
• Download the Raw Data and RTK dc files
• Convert both blocks of raw data to
RINEX format using Trimble’s utility
• Upload the files to:
http://www.ngs.noaa.gov/OPUS/
• Receive the results from OPUS via email
in minutes
Continued...
• Import the dc file into Trimble Geomatics
Office
• Update the initial base position for the first
base to the coordinates provided by OPUS1
• After a recompute, everything in the dc file
should be corrected relative to the first base
location (OPUS1)
Continued ...
• The position for OPUS2 is only used for
comparison to what was derived from OPUS1
• Coordinates can now be utilized as needed
OPUS & RTK
Savings to NCDOT
Staff
Hours
Static
OPUS & RTK
Savings
Vehicles
GPS
Receivers
Cell Phones
24 - 48
3
3
3
6 - 12
1
1
*1
18 - 36
2
2
2
* The cell phone listed in the OPUS & RTK surveying comparison was not
used in the survey work, but was available for contacting the office.