Frequently Asked Questions

This FAQ was compiled from actual queries to the CB, arranged here by category. If you have a specific question not addressed below, please submit your query via e-mail to the Central Bureau.

Data and Products

Where can I obtain IGS data/products? From [year]?

Tracking data and orbit products are archived at the IGS Data Centers. Access and directory information for each DC is available in the Data & Products area of this site. Products are also available directly from the Central Bureau here.

Are there costs/restrictions?

Data and products are currently available, free of charge, to all users. Although the IGS strives for the highest quality of data and data products, it can not make any warranty, express or implied, or assume any legal liability or responsibility for the accuracy, completeness or usefulness of any information or product. Use of the IGS data and products is the sole responsibility of the user.

How accurate are they?

You can find a table of product accuracies on the Products page. Further information is available from the Analysis Center Coordinator page. More detail regarding the IGS Final orbits is available in the IGS Report archives (see messages entitled "IGS Final Orbits"). Detailed statistics on the rapid and ultrarapid products are available in the files ending in ".sum" available alongside each product, for example igr11553.sum.

What are qualitative/quantitative differences in Analysis Center products?

Each of the Analysis Centers employs different software and a unique set of measurement and orbit models to produce weekly solutions, which are then used to generate the IGS orbit combination. Summaries of various AC processing strategies are provided here, along with contact information and technical references for further study. Weekly reports from the ACs and combination reports from the AC Coordinator are distributed via IGS Report. (See a sample combination report for week 1134.)

Where can I find GPS navigation message files?

Both RINEX observation and navigation files are available from most Data Centers. Go to the Data page for more information.

Meteorological observation files?

These are provided in RINEX format by several of the Data Centers (currently CDDIS, GODC, IGN and NRCan). Go to the Data page for more information.

Specifications for the [...] data format?

Information on RINEX, SINEX, SP3 and other data formats used within the IGS can be found here. If your computer does not decompress files ending in .Z, please visit one of:

• http://www.gzip.org
• http://download.cnet.com/downloads/0-10097-100-1757502.html

Software for [...]?

Look here for data verification and compression tools developed for various platforms. An Analysis Center may be able to offer assistance on more complex needs (data conversion, processing, etc.). Get AC contact information here.

Information on the GPS constellation status?

The Central Bureau maintains current GPS constellation information here.

Stations

Where can I find coordinates/velocities for station [...]?

Approximate coordinates for each site are listed on the Stations page. Precise coordinates, in the ITRF reference frame, are available here. In addition, station solutions in SINEX format are produced by Analysis Centers and Associate ACs participating in the Densification Project. These weekly SINEX files are available at the CDDIS and IGN Data Centers.

In the [...] reference frame? At epoch [...]?

The IGS is committed to improving and extending the IERS Terrestrial Reference Frame (ITRF). Station coordinates from ITRF92 through ITRF96 are available here, and transformation source and documentation are available at NRCan. The WGS 84 reference frame is coincident with the ITRF at a level better than 2 cm.

What is the status of station [...]?

For the most current information -- logs, performance, mail and pictures -- go the Stations page and click on the corresponding site .

Do you have sites in the vicinity of [...]? Is there one being planned?

View the clickable map in the Network area of this site. This map is updated daily and reflects the most current configuration of the network. Ask us regarding stations which are resolving communications and data paths.

How can my site become an IGS station? What are your implementation procedures and requirements?

Read the full procedure here. At some point it will be necessary to fill out and submit a site log to the Central Bureau.

Whom should I contact with my satellite-, receiver- and antenna-specific questions?

Send your questions to the Central Bureau and we'll do our best to answer them. If we can't we will forward your query to the appropriate contacts within the IGS.

Why does the official IGS igs_01.pcv table differ from the NGS calibration tables? Which one should I use?

igs_01.pcv is the official table to be used in IGS analysis. And yes, it does differ from NGS' latest table, and even if you look closely, also from NGS' previous table. The history is that some years back, NGS and other groups doing calibrations collaborated to make a definitive IGS table by averaging the various measurements available. Some time later the NGS table you see now came out. We have not updated the IGS values to NGS' latest in all cases for a few reasons:

• we want to limit changes in IGS analysis to avoid jumps
• need new effort to determine "best" values to use (it is thought now that averaging might mask some information)

We currently have an ad-hoc committee which is working to obtain quality satellite pcv tables, which would enable use of absolute rather than relative calibrations in a future update of the igs_01.pcv file.

At present, when we get an antenna not yet in igs_01.pcv, we inquire with a few regional networks such as EUREF whether they have any calibrations for it, and if not, we add the current NGS value.

In short, if you are doing IGS analysis you should be using igs_01.pcv. If not you should just be certain whatever you choose is consistent with your requirements.

What about satellite antenna offsets?

IGS Analysis Centers use

• Block II/IIA: 0.279 0.000 1.023 X, Y, Z in meters
• Block IIR: 0.000 0.000 0.000 X, Y, Z in meters

An archive of the discussion leading to this decision is available. Please note that this convention is subject to change as the IGS refines its antenna offset treatment.

All IGS sp3 orbits and clocks refer to the satellite center of mass (CM).

Mail and Publications

Do you have regular mailing lists?

The Central Bureau maintains several mailing lists:

IGSMail

updates and major announcements relevant to the entire community

IGSStation

notices of temporary station outages, RINEX data replacement, station configuration changes, etc.

IGSReport

regular Analysis and Data Center reports

IGSLEO

Low-Earth Orbiter working group

IGS-DCWG

Data Center working group

IGS-RTWG

Real Time working group

AFREF Mail

mail for discussion of an initiative for a continental reference frame for Africa

Receive them automatically or browse them in the Mail area of this site.

I am a station operator; when should I send IGSStation messages?

Please see the IGS Site Guidelines for some pointers.

How do I send e-mail to the mailing lists?

To send a message to an IGS mailing list, email it to listname@igscb.jpl.nasa.gov , substituting the listname (igsmail, igsstation, igsleo, igs-rtwg, igs-dcwg, or afref) for listname. Please ensure the first line of the body of your message starts with the string "Author: " followed by the names of the author(s) of the message. Also, the Subject field of the email should not be blank.

• Send plain ASCII text only
• Do not send attachments
• Do not send HTML mail

For example, the following text between the horizontal lines meets the format (if not content) requirements for IGS Mail if sent in a plain text email with a non-null Subject field.

---

Author: Ptolemy

Dear IGS Colleagues:

Please be informed that the Sun and Moon revolve around the Earth immobile.

Sincerely, Claudius Ptolemy

---

How do I contact [...]?

Browse the web-version of the IGS Directory.

Could you include/update me in the IGS Colleague Directory?

Yes. Send your current contact information to directory-changes@igscb.jpl.nasa.gov. Include your mailing address, phone, fax, e-mail and website address (URL).

Do you have a list of other IGS publications?

Yes. See the Publications page. Electronic versions (PDF, PS) are available in some cases.

How do I obtain copies? Is there a cost?

The Central Bureau currently provides these publications without charge as a service to the scientific community. Send your request and mailing address to the CB and we will be happy to send you a hardcopy.

History of this Document

This page last updated: 10 Jun 2004
Please send comments about this website to: IGS Central Bureau.