Welcome to the Cobb County Cooperative CORS Web site

GPS Data Download

We are happy to offer our GPS reference station data free of charge. Including these data in your GPS processing can tie your survey to national or international datums. Data use warning

ANTENNA TYPES WERE CHANGED TO

ADV NULL ANTENNAS IN RINEX FILES ON ALL THREE STATIONS ON DECEMBER 8, 2006.  PHYSICAL ANTENNAS STILL LEICA 1202 TYPE.

DUE TO AN OVERSIGHT IN A SETUP IN

THE SOFTWARE,  DATA IS

UNAVAILABLE FROM FEBRUARY 6

THROUGH FEBRUARY 11

TIP:  FOR THOSE EXPERIENCEING DIFFICULTY WITH IMPORTING COBB

COUNTY RINEX FILES DATED JANUARY 3, 2007 FORWARD, IN SOFTWARE

OTHER THAN LEICA, CHANGE 2.11 ON THE FIRST LINE IN THE RINEX FILE

TO 2.10 AND IT SHOULD IMPORT.

Station Details:
(site log - equipment & contact info)

East: CCGE | North: CCGN | South: CCGS


Data Use Warning:

We provide these data in good faith and shall in no event be liable for any lost profits, and special, indirect or consequential damages to any party, arising out of or in connection with the use or the inability to use the data hereon or the services provided. We provide these data and services as a convenience to the public. Furthermore, we reserve the right to change, revise, or otherwise discontinue published data and/or these services at any time without further notice.

Any use of or reliance upon these data is at the sole risk of the user as the County makes no warranties or representations as to the data's accuracy or usefulness or fitness for any particular purpose




What is GPS?
The Global Positioning System (GPS) is a satellite-based navigation system made up of a constellation of 24 radio-emitting satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day.

How it works
GPS satellites circle the earth twice a day in very precise orbits and transmit signal information to GPS receivers on earth. GPS receivers take this information and use triangulation to calculate the receiver’s (user's) exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. With distance measurements from a few more satellites, the receiver can calculate its own location through triangulation.

Benefits
Prior to installing the CORS (Continuously Operating Reference Stations), it was necessary to set up temporary base stations each day in order to utilize Real-Time Kinematic GPS procedures, a process that could easily take 1 to 2 hours. This would also mean an extra crew member had to be present to monitor the temporary base station equipment while other crew members collected survey measurements. In addition to setting up temporary base stations, research had to be done to find existing station information and field reconnaissance had to be done to find the stations (if they had not been destroyed) and then their use for GPS had to be assessed. In addition, this method was generally limited to line of sight radio transmission which generally limited reception to 3 to 4 miles at most. With the implementation of a network of base stations that provide coverage over the entire county, the base station set up time is eliminated, and data can be collected with fewer crew members per site.

In addition, as the surveying/business community (especially developers) in Cobb County begins utilizing the system, the county will receive more data in the Georgia State Plane Coordinate System. This will improve the accuracy of the data (compared to performing surveys relative to land lot corners) and help reduce the amount of time required to input/convert the survey data into the county's geographic information system databases. In short, the CORS will improve the level of service and lower costs typically associated with this type of work.


Cobb County installed three CORS Stations in August-September 2004

Cobb County has the FIRST COOPERATIVE CORS NETWORK IN GEORGIA gps.cobbcountyga.gov Cobb County Board of Commissioners 100 Cherokee Street, Suite 300 Marietta, GA 30090 770-528-1000 www.cobbcounty.org

In 2004 Cobb County GIS, DOT and Water System jointly funded a CORS network installation to facilitate the collection of data on the common datum of Georgia State Plane Coordinates, West Zone. This allows data to be collected and assimilated on a common datum that allows for the best analysis of data and project planning as these stations collect data at 5 second intervals and store that data in 24 hour Rinex zip files available for free download at gps.cobbcountyga.gov. The stations are Leica GRX 1200 Pro receivers with Leica AX 1202 Geodetic antennas and run 24/7. The stations are streaming RTK data in Leica proprietary format and in RTCM 18,19 (version 2) format for real time coordinate values in the field. In January of 2005 application was made to NGS to become a part of the Cooperative CORS Program. Cobb County’s three stations were accepted and on March 8, 2005 the values were sent to Cobb County by NGS and the stations were listed as new stations on the NGS Cooperative CORS web page for the state of Georgia. www.ngs.noaa.gov/CORS/Coop/ In addition to static data availability, Cobb County will be offering subscriptions to the RTK component of the network to those interested in this aspect of the network. The timetable on the availability is expected to be within the next 3 to 6 months. As this network covers a large part of the metro-Atlanta area, we believe it can be of service to many surveying and engineering firms. On the inside of this brochure is a map that shows the approximate geographical area we believe Cobb County’s network will cover. Coverage will depend on equipment and the technology the equipment utilizes. Any equipment capable of receiving corrections via cell phones or cellular modems that can connect to the internet will be able to utilize this system. It is the responsibility of the surveying/engineering firm and their equipment’s vendor to be sure the particular equipment being used is capable of using cellular devices to connect to the internet and that the equipment used is capable of using one or the other correction format being streamed from the system. For more information about the network, capabilities or subscriptions, please contact: Henry Bryan Cobb County DOT 1890 County Services Parkway Marietta, GA 30008 Phone 770-528-1662 e-mail: hbryan@cobbcounty.org

DATA USE WARNING:
We provide these data in good faith and shall in no event be liable for any lost profits, and special, indirect or consequential damages to any party, arising out of or in connection with the use or the inability to use the data hereon or the services provided. We provide these data and services as a convenience to the public. Furthermore, we reserve the right to change, revise, or otherwise discontinue published data and/or these services at any time without further notice.

Any use of or reliance upon these data is at the sole risk of the user as the County makes no warranties or representations as to the data's accuracy or usefulness or fitness for any particular purpose

 

                                  MONUMENT UPDATE              

 

 

September 12, 2006

 

Cobb County Monument Project

 

Cobb County has implemented a countywide survey control network.  The program began in 1997 as a joint effort between Cobb County Storm Water and Cobb County DOT as Cobb County Storm Water was developing a basis for an inventory of storm drainage structures and wanted a method to tie all the structure data together on a common datum.  Brass disks connected to a No. 4 rebar were set in concrete that is approximately three feet deep.  Witness posts were set approximately (3) feet behind the monuments.  There are some 120 pairs or so of monuments in the county, however, not all monuments have values established on them yet. 

Specifications were developed for the establishment of values on the monuments using GPS methodology.  The specifications followed recommendations found in NGS specifications for the most part.  The data on the disks were collected using static GPS methods and then reduced.  The data was established by tying into HARN monuments, first order NGS stations and some NGS second order stations outside of Cobb County along with stations in Cobb County.  The horizontal datum is NAD 1983 and 1994 HARN adjustment and the vertical datum is NAVD 1988 and 1994 HARN adjustment and based on the 1996 Geoid.  All data is in the Georgia State Plane Coordinate System, West Zone, NAD83.

In 2004 Cobb County established three (3) Continuously Operating Reference Stations (CORS) and Cobb County was the first National Geodetic Survey (NGS) Cooperative CORS in the State of Georgia.  The values for the CORS stations were provided to Cobb County by NGS.

With the establishment of the CORS stations, many monuments previously without values have had values established on them by utilizing the CORS stations and these are so indicated in the Access Database Forms by statements to this fact.

The values on the original monuments were not recomputed to the CORS stations. 

In conjunction with Cobb County Storm Water hydrology studies, additional disks were set on culverts and bridges over streams and in curbs and sidewalks near streams beginning in 2002.  Values for some of these monuments were established by a consultant utilizing existing monuments via RTK methods.  Monuments in the Benchmark database t established by this method are so noted and those having values established utilizing the CORS stations are so noted in the corresponding Benchmark Database file.

The monuments for the most part are designated with a numbering system.  For example, a monument with the number 010071-1 is located in Land District 1, land lot 71 and the 1 is the number of the monument within that land lot.  Another example is 170642-2.  This monument is located in Land District 17, land lot 642, and is the second monument within that land lot.  The information for these monuments will be found in the Access file named Monuments.

  

Monuments on culverts and bridges and near streams use the same style designation except that the letters BM are in front of the numbers.  Thus one of these disks would be BM171020-1.  The information for these monuments will be found in the Access file named Benchmarks.

The data file is in Microsoft’s Access 2000 data file format.  The file must be unzipped first and you must use Microsoft’s Access 2000 or later software to view and retrieve the data.  The form view has a sketch showing the location and ties to permanent objects near the monument.  The above numbering format was used for ease in locating the monuments and for being able to use the find query in Access as there are two digit land districts and four digit land lots and some land districts there is more than one monument.  In Access form view, the monument number must be highlighted, the find (binocular icon) clicked on and opened and the number typed in as 01007-1 and click on find next and the software should go right to the monument you need.

The other file is an ACAD R12 map of the county with roads and road names, land lots and their numbers, and the monument names on the map.  The file will need to be unzipped and it can be opened with ACAD release 12 or later and also in any Microstation product that can import ACAD R12 drawings or later ACAD versions.

I have also included a PDF version of these files.  However, in the PDF version, you will not have the form view of the monuments that has the sketch with ties.  I have included the ACAD map with these files as well.

Recommended usage:  A field survey should tie between two or three different monuments (should be a monument of other pairs, not their mates) and a check made before surveying for any design or construction or other activities take place.

NOTE: THERE ARE BRASS DISKS IN PLACE ON BRIDGES AND CULVERTS OVER STREAMS AND IN OTHER LOCATIONS NEAR STREAMS THAT WERE PUT IN DURING SOME AVAILABLE TIME.  A FEW OF THESE BENCHMARK MONUMENTS ARE STILL WITHOUT VALUES AT PRESENT AND WHEN TIME ALLOWS, VALUES WILL BE ESTABLISHED FOR THESE REMAINING BENCHMARK MONUMENTS.  THERE IS NOT A TIME LINE SET UP AS TO WHEN DATA VALUES WILL BE ESTABLISHED FOR THESE DISKS.

 

THERE ARE ALSO SOME PAIRS OF MONUMENTS IN THE GROUND THAT DO NOT HAVE DATA AVAILABLE ON THEM AT PRESENT EITHER.  SOME MONUMENTS HAVE HAD VALUES ESTABLISHED ON THEM AND THEY ARE INCLUDED IN THE CURRENT DATABASE.  WHEN TIME ALLOWS, VALUES WILL BE ESTABLISHED FOR THESE REMAINING MONUMENTS.  THERE IS NOT A TIME LINE SET UP AS TO WHEN DATA VALUES WILL BE ESTABLISHED FOR THESE EITHER.

 

 

Cobb County Government Licensing Agreement

 

License Agreement, Limited Warranty & Liability Statement

This License Agreement, Limited Warranty and Liability Statement is a legal and binding agreement between you, the user of Cobb County monument data and the digital monument location map and the Cobb County Government for use only under the terms and conditions as set forth herein.

Installing and /or using the data indicate that you accept and agree to abide by the terms and conditions of this Agreement.  If you do not agree to accept and honor these terms and conditions, immediately delete the data from all computers within your organization.

License Agreement

 

1. GRANT OF LICENSE

  

Cobb County Government grants you the right to use the monument data and digital monument location map on any computer or network server that you desire and for survey use.  You may use any of the data on any computer or network server provided they are owned by your organization.  You are permitted to use the monument data for any type of survey work your organization may engage in.  You may transfer and or/load the monument data and digital map to any computer hard drive within your organization.  You may print unlimited numbers of maps using the data and digital map.  You may use the monument data to develop new or enhance existing survey data maintained by your organization.  You may use the data to create files for use in presentations and/or reports.

       2.  COPYRIGHT

 

You are hereby notified that Cobb County monument data are protected by United States copyright laws and international treaty provisions.

 

            OTHER RESTRICTIONS

 

• You may not loan, rent, lease, sub-license or pledge Cobb County monument data and digital monument map without the express written permission of Cobb County Government.

• You may not sell, trade, or bargain any computer files containing any of the monument data and digital monument location map provided to you by Cobb County Governmetnt.

 

• You may not reverse engineer, decompile, disassemble, or create derivative works without the express written permission of Cobb County Government.

 

• You may not reproduce the monument data and digital monument location map for distribution outside your organization without the express written permission of Cobb County Government.

 

1. GENERAL

 

The laws of the state of Georgia shall govern this License Agreement.

 

 

LIMITED WARRANTY

 

Monument Data and Digital Location Map

Cobb County Government or its agencies makes no warranty as to the accuracy of the monument data and digital monument location map.  The user is expected to determine if the accuracy and quality of the monument data and digital monument location map will meet their specific needs.  No oral or written information or advice given by Cobb County Government, its agencies or employees shall increase in scope the before mentioned warranties or create any new warranties.

LIABILITY STATEMENT

 

LIMITED LIABILITY

 

In no event shall Cobb County Government be liable for any damages whatsoever (including without limitation, damages for loss of business profits, business interruption, loss of data, or other pecuniary loss) arising out of the use of or inability to use the monument data and digital monument location map.

Data Description

 

Access 2000 data file with state plane coordinates, geographic coordinates, orthometric heights, ellipsoid heights, geoid separation, convergence angle, combined scale factor, and a  sketch showing the location of the monument and ties to existing features from the monument.

AutoCAD R12 drawing showing the location of the monuments within the county and the monument number.  The drawing shows land districts, land lots and numbers, roads, and road names.