DuPage county provides various forms of geodetic Control information for public consumption. This includes physical monuments for both vertical and horizontal control (still separate monumentation networks). These networks provide coordinates and elevation in NAD27 and NGVD29, respectively. There is a county plan for coming years to upgrade the datums to NAD83 and NAVD88. While elevations of vertical control are available online, horizontal control monument coordinates must be requested from the GIS department and tie-in information purchased from the County Recorder.

The county had recently completed the installation of 6 GPS base stations throughout the county and has been operating them since mid 2004. RINEX data for each of these stations is freely available through our FTP site. In addition, it is possible to utilize these reference stations for RTK GPS surveying. Interested parties must submit a request which includes company information and a fixed IP address (of the modem used by the GPS rover), and upon approval of the review process access will be granted for free of charge. The RTK signal is transmitted over the internet using RTCM 18, 19, version 2.2, which should be usable for all GPS receiver types.

About DuPage County and our participation in the Coop CORS Program

DuPage County and our local cooperators believe that providing high order Global Positioning System (GPS) reference data will help establish greater accuracy and flexibility while performing surveying for a variety of applications. Most important is providing a reliable and consistent base for establishing spatial relationship for legal boundaries, infrastructure projects, environmental assessment and private enterprise development. And by integrating with the national network our methods are upheld to nationally recognized standards.

The principle advantage to using GPS is increased positional accuracy anywhere within the network. With an initial cost to purchase the necessary equipment and training, a survey team can be far more productive and reduce potential hazards associated with traversing along a busy thoroughfare.

The DuPage County GPS CORS Network supports both static and RTK surveying. Static surveying involves occupying a point and collecting satellite telemetry for a period (usually 2 hours) and comparing that to the RINEX data provided by the base stations we support. RTK is surveying on the fly, without loss of accuracy, and is supported by base stations with internet TCP/Com transmission.

The entire DuPage County CORS Network is managed via Spider V3.1.2. This Software package links all of the GPS bases to a central location so they can be controlled remotely and the RINEX data collected.

We expect further expansion of the DuPage County CORS Network in the near future. Additional sites will assure that there is RINEX data available near any location surveyed in the county and surrounding areas. This will also assist in error trapping by providing the opportunity to compare positional corrections of one nearby site with that of another. For more information on GPS and the DuPage County CORS Network please refer to other sections within the DuPage County website, the NGS or contact DuPage County GIS Division directly.