Continuously Operating Reference Stations (CORS) FAQs

• HOW CAN I GET AN ACCURATE, UP-TO-DATE ELEVATION?

  The GNSS Continuously Operating Reference Stations (CORS) of GULFNet established by LSU’s Center for GeoInformatics (C4G) provide the latest tools in cutting-edge technology for Professional Land Surveyors throughout the State of Louisiana. Because the land elevations are constantly changing due to geologic subsidence, the positions on the traditional benchmarks used by surveyors for centuries have become obsolete in Louisiana! Homeowners, businesses, and local governments count on reliable elevations to insure safety from flooding due to rainfall-engorged rivers as well as saltwater sheet flow effects from hurricanes. The National Flood Insurance Plan is based on surveyors providing reliable elevations on Flood Surveys for homeowner’s Flood Insurance policies. Subsiding elevations make benchmarks unreliable and useless from the Arkansas State line to the Gulf of Mexico and from The Texas State line to the Mississippi State line!

  The only reliable source of correct and up-to-date elevation data in the entire State of Louisiana is done by data from the LSU GULFNet system of continuously operating reference stations (CORS). Established in accordance with Federal Guidelines and Specifications, the basic backbone of CORS in Louisiana are known as GULFNet. A subset of CORS sites in GULFNet have been adopted by the NOAA CORS Network (NCN). Raw data from these NCN sites are publicly available from C4G or NGS and can be used to perform corrections in geodesy tools or by submitting field observations to free online processing tools like OPUS offered by NGS or the C4Gnet.XYZ Online Processing service offered by C4G. All of these methods use the CORS date from GULFNet to correct the positions to agree with the NGS National Spatial Reference System. These tools are commonly used to check and verify that any data collected agree with other data processing methods before presenting final coordinates and especially final elevations.

  The C4GNet.XYZ Real Time Network is another method to access corrections to survey positions in real time. The C4GNet.XYZ RTN is constrained the NGS published coordinates for all NCN stations which aligns the RTN to the NSRS and makes it possible to speed up the collection of accurate up to date elevations in real time.   

• HOW DO I GET RINEX FILES FOR POST-PROCESSING?

  C4G, in its role as the Louisiana Spatial Reference Center (LSRC), publishes RINEX files to the public and to NGS in 15-second raw data hourly files by HTTP as well as anonymous FTP from most of the CORS sites in Louisiana and our partner sites along the gulf coast. To access CORS data by HTTP, go to http://CORS.LSU.EDU with your browser or by FTP @ ftp://cors.lsu.edu:8021/ or in your FTP client at the following settings.

  Host: cors.lsu.edu
  FTP Port: 8021
  Login Type: Anonymous

  Note: raw CORS data is used in geodesy post-processing tools like Trimble Business Center, Leica Geo Office and Topcon Tools. GIS data collected autonomously can also be differentially corrected against raw CORS data in software tools like Trimble Pathfinder Office.

  Contact your GNSS dealer if you need help setting up a connection to the C4G CORS FTP server or need details on the tools necessary to post-process GNSS data.

  If you require 1 second raw data, C4G offers that as well through a subscription to our Reference Data Shop. Visit the C4G webstore at https://store.c4g.lsu.edu/ if you wish to purchase a subscription. 

• WHAT IS VIRTUAL RINEX STATION?

  Generation of Virtual Rinex Stations (VRS) is a feature available in the C4Gnet.XYZ Reference Data Shop (RDS). This feature requires a subscription to the Reference Data Shop, and it uses network processors and CORS data to create static files modeled from 6-9 stations around a location you specify. To create a VRS users just enter the coordinates of where they want a virtual reference station and the RDS generates RINEX files for the time and duration specified by the user. VRS was developed to reduce the length of static sessions, but recently, UAS (drone) operators have found it is a good option for PPK post-processing.

  The Reference Data Shop is a Web-based application that allows users to easily access RINEX files for post-processing through a simple interface. System users can create custom RINEX files to meet their needs in standard RINEX or compact RINEX data storage formats. Choose from data intervals of 1, 2, 5, 10, 15, 20, 30 or 60 seconds. Data can be emailed or downloaded immediately or at any future time for added convenience. Data is available from all Louisiana NGS CORS and every other site in the C4GNet RTN.