FAQs
- 1) I see there is a 2 hour minimum for a request, what is the maximum?
- There is a 24 hour maximum request at this time
- 2) OPUS selected 3 CORS site for me, but they are not the closest sites
to my location; what is the process for picking the 3 CORS sites used?
- There are approximately 5 tests done for compatibility between the given
location and the CORS sites; e.g., if the time block requested is compatible
with the CORS site, if there is a high multi-path environment, etc. OPUS starts
with the closest site(s) to your given location, and conducts these tests
on each site for its compatibility to these 5 tests, and if the closest site
is not compatible, OPUS then continues to search out sites until it is able
to find 3 sites that are compatible, and uses them.
- 3) I submitted my data file, but haven't received anything back yet.
- If OPUS fails upon processing your data, you should get an email stating
so. If you do not receive an email, it is either because you entered
the wrong email address, or your company has a spam filter that rejects OPUS
reports. OPUS is run from a UNIX machine that is not Windows compatible,
so we can't hit a hyperlink to send a request to your organization asking
to put on the allowed list.
- 4) I got an email saying NO ORBIT DATA AVAILABLE; what does this mean?
- This means the orbit data hasn't been received from IGS yet, and will be
done so within 24 hours, please re-submit your request at a later time.
- 5) I got a warning message that the IGS Precise Orbit was not available
at the time of processing, but the "rapid" was used. What does that
mean??
- We will not have the "final" IGS Precise orbit until the International GPS
Service (IGS) completes a full week (Sunday through Saturday). This final
precise orbit is the combination of seven analysis centers worldwide.
It can take these analysis centers several days to upload the orbit to the
IGS so the availabilty of a Sunday orbit can be 19 days. The IGS rapid
orbit is used in the absence of the IGS precise orbit. However, this
is not cause for alarm since the IGS rapid is nearly as "good" as the IGS
precise.
How does this relate to positions on the ground?
Since most OPUS baselines are less than several hundred kilometers, the
differences between using the IGR (rapid orbit) and the IGS (precise orbit)
is barely detectable if at all. Because of this, OPUS has discontinued
this warning message (1/1/2004).
For more information on the IGS and its products visit them at http://igscb.jpl.nasa.gov
- 6) Do I have to enter an antenna type?
- We recommend you choose the correct antenna type, as it will allow us to
apply the correct antenna phase patterns. If no antenna type is applied, your
data request will still be processed, but the height component of the solution
will not be as accurate.
See May 2003 Question of the Month
- 7) What is the "normal" turnaround time for a data set?
- The usual turnaround time for a data set is 2-3 minutes, depending upon
the file size; it may take as long as a couple hours, for very large file
sizes (e.g., 4+ hours of 1 second data).
- 8) Some of my attempts to submit data generates a return email saying,
"The observations to slip ratio is too low. There were an unusually high
number of cycle slips in the data set. Aborting ..." (Code 1012). What does
this mean, and how can I correct it?
- This error message primarily indicates that your carrier phase data set
contains too many cycle slips to assure an automated hands-off processing
to obtain accurate results. The data may still be useful, but will require
human intervention to efficiently resolve the cycle slips. Perhaps nearby
radio interference or obstructions have caused an unusual amount of cycle
slips.
- 9) I have a Leica antenna model SR 399, with mounting GRT44 for tripod
set-up, how do I compute the height of the ARP (Antenna Reference Point)
above the mark (monument) as requested by OPUS?
- If you have this type of antenna mounting, the ARP height can be determined
by using the following equation:
Height of ARP (meters) = 0.350 + tape measurement (meters)
"Tape Measurement" is the distance in meters from the bottom of the hook
in the antenna mounting to the monument.
- 10) How do I get my data into RINEX format?
- You can use the same software that the National Geodetic Survey uses to
convert the raw data. UNAVCO has developed the software called TEQC
(pronounced TEK) and is freely available at:
http://www.unavco.org/facility/software/teqc/teqc.html
- 11) How do I know which State Plane Coordinates Zone to select?
- If you are not interested in State Plane Coordinates, choose the default
( 0 none). If you know the approximate position of your GPS receiver and want
to find the proper state plane coordinate zone, use the Geodetic Toolkit facility
on the NGS website by navigating www.ngs.noaa.gov->Geodetic Toolkit->
State Plane Coordinates ->Find Zone.
- 12) Why doesn't my OPUS solution contain NAD83 positions?
- Sometimes OPUS uses reference stations outside the CORS network that only
have ITRF positions and no listed NAD83 positions. Your resulting positions
will be just as good as if all CORS stations were used, except the NAD83 positions
will not be listed. You may wish to go to the NGS home page, click on
"Products and Services", and download the program HTDP.
This program converts positions between different reference frames.
- 13) What is this new item called the US National Grid?
- The USNG item in the NGS Tool kit explains
the US National Grid. This new method of representing position has been endorsed
by the Federal Geographic Data Committee. NGS is promoting the US National
Grid by showing values on the OPUS data sheet.
- 14) Will OPUS be available to those who are using L1 only?
- We would like to have a L1 version of OPUS , but preliminary testing indicates
that our current programs are not suitable for L1 processing. We may resume
in the future the programming and testing of L1 OPUS. We have a pseudorange
version of OPUS called OPUS-GIS which is currently being tested and can use
either L1 or L1/L2 data and gives results accurate to a meter or two. We have
this version available on our "beta" page (email us at ngs.opus@noaa.gov for
more information).
- 15) How do I transform orthometric heights NAVD88 currently given by
OPUS using GEOID03 to the orthometric heights computed using the old GEOID99?
- This problem can be resolved by getting the differences of geoid heights
between GEOID03 and GEOID99. At each point, there will be a bias on the geoid
height of the two geoids that should be taken into consideration. For example,
if you want to transform orthometric heights from NAVD88 (GEOID03) to NAVD88
(GEOID99) you should apply the following equation:
NAVD88 (GEOID99) = NAVD88 (GEOID03) + (GEOID03 - GEOID99)
The value of NAVD88(GEOID03) is given directly by OPUS. The values of
the geoidal heights (GEOID03 and GEOID99) can be interactively computed
from NGS Geoid Web page. For this task you need
to know the geographic location of the point, e.g. its geodetic coordinates.
At this time NGS does not have a program to do this computation and you
must calculate them individually point by point.
- 16) During recent solutions that were sent along, beside the antenna
name it shows the word NONE. Why is this?
- We use antenna names as adopted by the International GNSS Service (IGS).
The field (columns 17-20) where NONE is located represents the radome used.
The 4 character Id used can be: NONE (or blank), SPKE, SNOW, SCIS, SCIT, LEIC,
SPKE, CONE, TCWD, UNAV, TZGD, etc.
Please visit this list
for acceptable antenna codes.
- 17) Why do my Trimble Dat files fail in OPUS?
- NGS provides OPUS users with the option to submit receiver native format
data. This has been possible through the use of TEQC software. Most manufacturer
native format data continues to be accepted by OPUS. However we have recently
become aware of possible errors in the translation of the new Trimble DAT
file format that is common with R5 and R7 receivers. We therefore can no longer
support submission in this format. Users with this equipment must convert
their data into RINEX format using Trimble software and resubmit it.
If you need assistance in converting your data please contact Trimble support
at: http://www.trimble.com/netrs_ts.asp
- 18) I am trying to upload a rinex file and I am getting a message that
there are illegal characters in the file name.... This is a new one on me - what am I doing wrong?
- The problem is probably not with the file name, but with the path name. OPUS
is run on a UNIX machine, and it can only read path names that contain numbers,
letters, the period, dash, and the underscore. If you move your file to another
directory, it should be able to be uploaded.
- 19) What does "D.N.E." mean in the output?
- D.N.E. means "Does Not Exist". It is a flag used to indicate that insufficient information
exists to compute the field in question. For example, when D.N.E. is listed under orthometric
height accuracy, this indicates that there is not enough information about the relationship
between the hybrid geoid, the geometric reference frame and the local vertical datum in this
region to estimate the accuracy of the orthometric height.
- 20) What does "No official datum supported" mean in the output?
- This flag is used when there is not enough information for a GPS based solution to yield
access to the official vertical datum of a region, if it exists. Specifically, this means that
the hybrid geoid for this region does not contain information about the GPS derived ellipsoid
heights on benchmarks which have leveling-derived orthometric heights in the official vertical
datum of the region.
- 21) What does "No NGS Geoid Model Available" mean in the output?
- This flag is used in regions where NGS has not computed a high resolution model of the geoid
(such as Guam or American Samoa) or where such a model may exist, but is not supported such
as the portion of the CONUS geoid which overlaps with non-USA territories.
National Geodetic Survey - OPUS Team
Modified 02 April 2008
http://www.ngs.noaa.gov/OPUS/Faqs.html
