1. CORS-Based Coordinate System WHAT IS CORS
CORS-Based Coordinate System WHAT IS CORS? Presented by Michael Schoder, PLS
Continuously Operating Reference Stations
A national array of dual frequency survey grade GPS receivers collecting carrier phase data on a continuous basis (24/7/365) for which data is distributed via the Internet by NGS free of charge.

2. CORS-Based Coordinate System CORS Overview
CORS system designed to initially provide country wide coverage at 400km level (except Alaska of course due to funding) with ultimate goal of 100km coverage US-wide.
In addition to NGS, a number of participating agencies provide CORS systems such as DOTs, Academia, Scientific organizations & private industry as full CORS or co-operative CORS sites with NGS oversite.

3. CORS-Based Coordinate System CORS Coverage's
Alaska CORS Coverage end 2002

4. CORS-Based Coordinate System CORS Overview Continued
CORS data is monitored daily by NGS automated computation utilities to determine SV orbits and verify system stability. NGS also provide automated geodetic positioning service OPUS dependent on CORS as web-based service.
Future support of geodetic positioning by NGS will be densifying CORS network, not ground networks.

5. CORS-Based Coordinate System CORS Datums
U.S. CORS stations participate in world-wide IGS CORS system as basis of ITRF reference datum, and ITRF positions provided to current ITRF epoch. NGS established NAD83(CORS) datum as country-wide high precision datum not influenced by non-GPS data and to be as compatible as possible to prior geodetic NAD83 data.
NAD83(CORS) found to be consistent with NAD83(92) by GPS survey ties at 10-30cm level in Alaska.
Current NAD83(CORS) epoch , updates for crustal motion events & motion predictions for “dynamic positioning” for scientific high accuracy applications.

6. CORS-Based Coordinate System CORS Services
Some CORS stations provide additional services such as providing broadcast code corrections (enables real-time positioning to several meter accuracy) or RTK carrier phase corrections (enables real-time positioning to centimeter accuracy).
OPUS utility is web based free utility provided by NGS to compute geodetic position for dual-frequency RINEX formatted GPS data sets ed to OPUS site. Results provided in minutes by referenced to NAD83(CORS) and ITRF with typical accuracy of sub-decimeter.
HTDP utility is horizontal time-dependent positioning program that allows users to predict horizontal displacements and/or velocities at locations throughout the United States.

7. CORS-Based Coordinate System ADVANTAGES of CORS-Based Reference
Current NGS datum most compatible with GPS positioning and free of old data influences.
Supported in future by NGS
Easily available and retrievable.
Positioning results easily repeatable regardless of issues related to monument stability & destruction.
Supported by NGS computation utility to eliminate need for specialized processing.
Consistent with variety of GPS positioning, and prior survey datums.
Easily used for GIS population with resource-grade GPS data.
Consistent with and/or relatable to local, state and National GIS datasets.

8. CORS-Based Coordinate System ISSUES concerning CORS-Based Reference
Transformation of existing NAD83, NAD83(92) data must be accounted for for data to be related to highest accuracy. Transformation can be ignored for lower accuracy needs (meter level positioning).

9. CORS-Based Coordinate System ISSUES concerning CORS-Based Reference
Attention to changes in CORS stations (updated receivers, antennas, positions) needs to be monitored as the data is used to account for specific CORS site upgrades.
Proper meta-data needs to accompany positioning data to allow documentation and future uses / differing applications of CORS based data.

10. CORS-Based Coordinate System TO FIND OUT MORE ABOUT CORS
CONTACT NGS at
Contact ADOT&PF Surveys or
This Presentation
ftp://chugach.dnr.state.ak.us/dot-cadastral/
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