The Details
New CORS Site Guidelines
Potential New Sites - Write to Us Here
ngs coordinates | station log | rinex | directory structure |
The major difference between Coop CORS and National CORS is that the Coop CORS participant is responsible for making the data and metadata available to the public. Another difference is that National CORS has all the data available all the time and Coop CORS may have a limit on the amount of data that is available online. Both run daily solutions to calculate a position for the day and plot the difference from the published position.
The following defines the requirements:
Participants in the Cooperative CORS offer their GPS base station data free-of-charge to the public with access to it via the web or some ftp server with anonymous access.
- Equipment
- Dual frequency, geodetic quality receiver and antenna
- Station will run 24 hours per day, 7 days per week ( effective Nov 1, 2005 )
- was ..... minimum of 8 hours per day, 5 days per week (24/7 preferred)
- Web Site and/or ftp Site to include
- NGS will:
- Place your station on the NGS CORS map
- Provide a hyperlink to your Web site
- Check coordinates daily.
- EQUIPMENT
- Dual Frequency Receiver (L1 and L2)
- L1 C/A-code pseudorange or P-code pseudorange.
- L1 full wavelength carrier phase.
- L2 full wavelength carrier phase.
- pseudorange accurate to better than 0.5 meter RMS.
- tracks a minimum of 8 satellites above 10°.
- automatic switching between operating modes to retain full wavelength L2 when anti-spoofing (AS) is on.
- acceptable collection rates: 1,2,3,5,10,15,30 secs
Antenna
- at least dual frequency
- capable of maintaining 1-cm stability
- has NGS phase center variability model available
(http://www.ngs.noaa.gov/ANTCAL/)
COORDINATES
- NGS will compute an a-priori coordinate from 10 days of data.
- Antenna Reference Point (ARP) and L1 phase center, and monument (if one exists)
- In reference frames ITRF2000 and NAD83
- Daily coordinate computed and plotted
- Provider will link to coordinates residing in the NGS Database
- http://www.ngs.noaa.gov/cgi-cors/pv_ret.prl?siteId=ssss
where ssss is your site ID
STATION LOG - Required Receiver and Antenna Codes
- A station log is a text file containing all necessary information about your base station.
- Must be updated whenever a change takes place.
- coordinate
- equipment (receiver, firmware, antenna, radome)
- contact info
FILE FORMAT
- RINEX
- Hourly or Daily Files
Please Note: Daily files should be not be created from hourly rinex files but rather from the manufacturers raw data. Joining hourly rinex files introduces a "clock jump" at the hour due to clock drift and clock resets.
- File Name
File names should reflect the GPS time period of the data and not Local time.
WEB SERVER
Disk Space Requirements
The amount of disk space required to support a CORS site depends on the type of receiver, the sampling rate, the type of data to be stored, the compression option used, and the number of days of data to be
stored. For example, using an Ashtech ZXII, one hour of data at a 5
second sampling rate amounts to:
Raw data: 690KB
RINEX data 660KB
Compress RINEX data: 246KB
This totals 15.8MB per day for RINEX data or about 6MB if compressed. While this is not a lot, you should keep at least 30 days worth of data on line. This could bring the space requirement to 150MB for compressed data.
RECOMMENDED SYSTEM
If you are operating your own Web server, you will need a system that will allow multiple HTTP connections. Examples are any version of Unix running on RISC-based workstations, LINUX running on a PC or workstation, or Windows NT Server running on a PC. The system should be operational and accessible via the internet 24 hours a day.
DIRECTORY STRUCTURE ( lower case only )
/rinex/yyyy/ddd/site id/data (all in lower case)
example: site=prdu, year=2005, doy=365, beginning hour 3 (d) GPS time (~UTC)
/rinex/2005/365/prdu/prdu365d.zip
where yyyy is four digit year
where ddd is the three digit day of year
where site id is the 4 char assigned site id
where data is the rinex data files in compressed format (see file naming requirements)
NAMING CONVENTION ( lower case only )
Preferred file name: ssssdddh.c
Accepted file name: ssssdddh.yyt.c
ssss 4-character station name designator
ddd day of the year of first observation ( 001, 002 ..., 366 )
h Hour long GPS time block identifier
0 file contains all the existing data of the current day (24 hours)
a file contains data from 0:00:00 GPS - 0:59:55 GPS of the current day (assuming 5 second collection rate)
b file contains data from 1:00:00 GPS - 1:59:55 GPS of the current day
c file contains data from 2:00:00 GPS - 2:59:55 GPS of the current day
. .
. .
x file contains data from 23:00:00 GPS - 23:59:55 GPS of the current day
yy 2 digit year ( 98, 99, 00, 01 .. )
t file type
o observation file
n navigation file
s summary file
m meteorological file
g glonass Navigation file
d obs file with Hatanaka conversion
c compression type
Z UNIX Compressed
zip PKZipped
gz gzipped
data data is the rinex data files in compressed format (see file naming requirements)
COMPRESSION
It is recommended that you compress your files. This saves space for you and time for everyone else. The method of compression is your choice. If you choose PKZIP please leave the "zipped" file with the .zip extension. Do not make it executable. That is, do not run a program zip2exe to make it self extracting since most decompression programs recognize the PKZIP compression.
You should contact your vendor if you are having trouble converting to the required naming convention.
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