User Friendly CORS (UFCORS)

User Friendly CORS (UFCORS) FAQ


1) What is User Friendly CORS (UFCORS)?
2) How do I choose the day and time that I want?(See also FAQ #3)
3) Which time zone do I select? Do I have to convert to UTC (Universal Time Coordinated)?
4) What are the available Satellite Systems or How can I get GLONASS data?
5) Why can't I find the site/stations I want from the pull down list of sites?
6) What is a coordinate file?
7) What are the IGS orbits and how can they improve my results by using them?
8) Where can I find out more about a site/station? (e.g. equipment, responsible agency)
9) Why did I not get, or get an incomplete, data set? (See also FAQ #5)
10) How can I download more than 1 site?
11) Why won't my software process a file? or My software says that the downloaded file is unrecognized how can I solve this?
12) Why am I not getting data with my Trimble Pathfinder software?
13) What has changed between UFCORS 3.x and 4.x?
14) Is there a way to bypass the UFCORS web interface and write a script to submit requests directly to UFCORS?

1) What is User Friendly CORS (UFCORS)?

The National Geodetic Survey (NGS) has designed UFCORS as a web-interface to facilitate the retrieval of GNSS data (prior to version 4.0 only GPS data could be retrieved) and associated metadata from the Continuously Operating Reference Station (CORS) Network. In particular, users can for a specific CORS site:

  • Obtain observation data for a particular day starting at a specific time and a duration, even across an end of UTC day in a single file
  • Decimate the sampling rate for the requested data
  • Included automatically with a request is the "broadcast" GPS and GLONASS orbits, and the station log that contains the official current and historical equipment hosted at the site.
  • Choose optional metadata files with official positions and velocities in either coordinate file (contains global and National Spatial Reference System (NSRS) positions and velocities), and NGS datasheet (contains only NSRS positions),
  • Choose optional precise GPS and GLONASS satellite orbits calculated by the International GNSS Service (IGS)

2) How do I choose the day and time that I want?

You should choose a date and start time that matches the start date you collected your observation data and a duration that covers all the data you collected. NGS recommends that in addition you buffer this time period by 30 min to 1 hour before and after to ensure you have complete overlap with the data you collected.

3) Which time zone do I select? Do I have to convert to UTC (Universal Time Coordinated)?

The RINEX files you receive are provided in the time format of the satellite system requested (which is very close to UTC time). Some users find it easier to work in their local time zone to identify their start times in which case switch from UTC to the appropriate GMT time.

e.g. Eastern Standard (GMT - 5)
Eastern Daylight Savings (GMT - 4)
Central Standard (GMT - 6)
Central Daylight Savings (GMT - 5)
Mountain Standard(GMT - 7)
Mountain Daylight Savings (GMT - 6)
Pacific Standard (GMT - 8)
Pacific Daylight Savings (GMT - 7)
Alaska Standard (GMT - 9)
Alaska Daylight Savings (GMT - 8)
Hawaii-Aleutian (GMT -10)
Guam, Saipan, Rota (GMT +10)

4) What are the available Satellite Systems or How can I get GLONASS data?

Some CORS stations are able to collect GPS +GLONASS data, if a station is collecting additional signals to GPS the box for GLONASS will automatically be selectable.

5) Why can't I find the site/stations I want from the pull down list of sites?

If the four-character identifier for a particular site does not appear in the list, then the site is not part of the CORS network. To check that you have the correct 4-character identifier go to the main CORS web page and check the CORS map to identify if the site is part of the CORS network.

6) What is a coordinate file?

A "coordinate" file contains the NGS computed position and velocity for the site's antenna reference point (ARP) as well as for its L1 phase center and possibly for the MON (monument). The ARP usually corresponds to the center point on the bottom of the CORS antenna. The coordinate file contains positions and velocities in both a global frame IGS08 International GNSS Service (IGS) and the North American Datum of 1983 (NAD 83). This file differs from the NGS datasheet for the site, which does not contain velocities or IGS08 coordinates, but which may contain orthometric heights. For additional information, including a discussion on how CORS positions and velocities are derived.

7) What are the IGS orbits and how can they improve my results by using them?

A "broadcast/navigation" orbit file (one for GPS and one for GLONASS) is automatically included with every request. The satellite orbit positions in this file have an accuracy of 2-5 meters. If your post-processing software supports the use of the International GNSS Service (IGS) orbits (sp3c format) you may select those as an optional additional data set. The IGS orbits have an accuracy of between one and several centimeters and should result in more accurate coordinates being computed by your post-processing software. The IGS provides three orbit products for GPS data in increasing order of accuracy and latency: ultra-rapid within ~6 hrs., rapid ~17 hrs. and final ~15 days. For GLONASS it only provides the final orbits ~ 15 days. UFCORS will include the most accurate orbits available at the time of the request. If your data request spans two UTC days then a single orbit file spanning both days is included.

8) Where can I find out more about a site/station? (e.g. equipment, responsible agency)

Current and historical equipment information about a site is available in a site's station log. This is automatically included with a data request. The RINEX header information may be incorrect and the site log should always be viewed as containing the most accurate information with regards to the equipment at the site. The coordinate in the log file and RINEX header is not accurate and the coordinate file or datasheet should be consulted. You can also go to the site specific page on our website to see photographs of the site. Go to our main CORS website, then type in the 4-character id or use the map to find the site.

9) Why did I not get, or get an incomplete, data set? (See also FAQ #4)

There are three possible causes for not getting data or not getting all the data requested:

  • You have requested data for a site but for a day and time when NGS does not have data. If you are looking for data in the past 15 days try again in one or more days. If you are looking for data more than 15 days ago it is likely that NGS will not obtain data for that site.
  • You have requested data for a site and only got partial data. This implies that NGS has not obtained data for the missing portion of the time period you requested. See previous bullet.
  • You want GNSS data and you only GPS data. Not all sites provide GPS and GLONASS data.
  • Some non-NGS software connects to the UFCORS web page directly to request data automatically using an automated query. This bypasses some of our quality control checks. Please double check that the site you are requesting is part of the CORS network. Try downloading the data you want from the interactive UFCORS site. If you are able to get data then contact your software vendor.
  • If none of these explanations are satisfactory let us know by submitting a problem report.

10) How can I download more than 1 site?

You can write a script to do batch downloads of CORS data from our anonymous ftp servers. Please read our README file to obtain information on directory structure, file types, and retention rules ftp://geodesy.noaa.gov/cors/README.txt.

11) Why won't my software process a file? or My software says that the downloaded file is unrecognized how can I solve this?

With UFCORS 4.x we began providing the full GPS constellation signals L1+L2+L2C+L5 along with GLONASS. If you requested just GPS you will receive L1+L2+L2C+L5 older GPS processing software does not recognize these new signals. We added on 2014-Aprxx a new option called "GPS (L1+L2 Only)". This option allows a user to only obtain L1 and L2 data like the old UFCORS 3.x provided. This should resolve most issues for legacy users.

12) Why am I not getting data with my Trimble Pathfinder software?

NGS does not use/support the Trimble Pathfinder software> directly, therefore we recommend that you contact Trimble support for assistance. You might also try and download the data you want directly from NGS to see if UFCORS is working.

13) What has changed between UFCORS 3.x and 4.x?

  • UFCORS 3.x provided RINEX files in RINEX2.10 excluding GPS L2C, L5 and all GLONASS data.
  • UFCORS 4.x provides RINEX files in RINEX2.11 including all available GPS signals, GLONASS data when available and will in the future support additional constellations.
  • See FAQ 14 for changes in the URL retrieval commands.

14) Is there a way to bypass the UFCORS web interface and write a script to submit requests directly to UFCORS?

As mentioned in FAQ 9 users can write their own scripts to submit request data via URL command see examples at the bottom of the page.
The options are as follows:
timezone = UTC
starttime = [hh:mm] start hour in hours and minutes e.g. 04:00
duration = [h/hh] number of hours after start hour maximum value is 24hrs e.g. 6 or 12
year = [yyyy] 4-digit start year e.g. 2006
yearday = [jjj] 3-digit start day-of-year e.g. Jan 15 = 015
epic(epochInterval) = [As Is, 1, 5, 15, 30] seconds data) e.g. As Is or 1
siteselection = [ssss] i.e. 4 characters siteID e.g. ab33
coordinatefile = [no/yes]
datasheets = [no/yes]
orbits= [no/yes]
observables = = [gps/gnss/gpsl1l2] if blank or omitted GPS only data (L1+L2+L2C+L5) will be provided. Currently if gnss is specified only GPS+GLONASS data will be provided (not all sites track both GPS+constellations)

For Version 4.0:
Version 4.0 Parameters: (backward compatible with version 3.x)

GNSS data request (GPS+GLONASS):
https://geodesy.noaa.gov/UFCORS/ufcors?timezone=UTC&starttime=04:00&duration=6&year=2012&dayOfYear=214&epochInterval=As%20Is&coordinatefile=yes&datasheets=yes&orbits=yes&siteselection=1nsu&observables=gnss

GPS data request (GPS L1+L2+L2C+L5) default:
https://geodesy.noaa.gov/UFCORS/ufcors?timezone=UTC&starttime=04:00&duration=6&year=2012&dayOfYear=214&epochInterval=As%20Is&coordinatefile=yes&datasheets=yes&orbits=yes&siteselection=1nsu&observables=gps

GPS restricted data request (L1+L2):
https://geodesy.noaa.gov/UFCORS/ufcors?timezone=UTC&starttime=04:00&duration=6&year=2012&dayOfYear=214&epochInterval=As%20Is&coordinatefile=yes&datasheets=yes&orbits=yes&siteselection=1nsu&observables=gps12

or

https://geodesy.noaa.gov/UFCORS/ufcors?timezone=UTC&starttime=04:00&duration=6&year=2012&dayOfYear=214&epochInterval=As%20Is&coordinatefile=yes&datasheets=yes&orbits=yes&siteselection=1nsu