1. NYSDOT CORS Past, Present and Future
Ron Frederiks

2. Lots of Acronyms!!!!!! GPS – Global Positioning System
ABGPS – Airborne Global Positioning System
CORS – Continuously Operating Reference Stations
NGS – National Geodetic Survey
GIS – Geographic Information System
RTK – Real Time Kinematic Positioning versus Post Processed Positioning

3. What is GPS? Global Positioning System
Satellite-based timing and position
24 satellites (very high orbit)
Developed by U.S. Department of Defense
Considered a Public “Utility”
Signals available free of charge

4. Satellite Ranging Measuring the distance from a satellite
Measuring the travel time of radio signals
Signal travels at the speed of light
40 milliseconds
70 milliseconds
60 milliseconds

5. Ideally, the three spheres will intersect at a discrete point.
Trilateration
Ideally, the three spheres will intersect at a discrete point.
3 seconds out
5 seconds out
7 seconds out

6. Accuracy of GPS Depends on several variables
Time spent on measurements
Design of receiver
Relative positions of satellites
Can be more than 20 meters – autonomous
Sub meter to 5 meters with differential GPS
Sub centimeter with survey products and differential GPS

7. Differential Correction
What is it?
Differential Correction is the process of correcting GPS data collected by a user, with data recorded simultaneously at a base station, in order to improve accuracy.
CORS stations serve as the base stations for differential correction
Best results achieved when distance is minimized between users receiver and the base station.
Dense network of reference stations is desirable.

8. Differential GPS
Two receivers track the SAME signals and, therefore, errors at the SAME time
User
Base

9. Base Stations
Before NYSDOT CORS, we had to rely on the NGS CORS network
Many gaps in the NGS CORS network
NGS CORS stations collect data at different rates
NGS CORS stations were not always reliable

10. NGS CORS Network

11. Data Availability (OSPA)

12. Data Availability (SYCN)

13. NYSDOT CORS Conceptualized requirements in 2004
Contract let in Spring 2005
Installation Fall of 2005 thru February 2006
Publishing Static Data to NGS: March 2006
Publishing RTK Corrections Summer/Fall 2006

14. What is the NYSDOT CORS? Initially, a Network of 36
Stations Across NYS
Intended Benefits of CORS
Primary Benefit is Publication of Static GPS Data for Positioning of Project Control
Secondary Benefit is Publication of RTK Corrections (for Terrain Data Positioning and Construction Equipment Guidance)

15. NYSDOT CORS

16. CORS on 3/30/2006

17. Data Availability

18. CORS Station Installations
GPS Receivers Installed on Secure DOT Buildings
Each Antenna Mounted on an 3” Aluminum Mast
Most Masts are Attached to Masonry Load Bearing Walls
Connected to DOT Statewide (WAN) Network
GPS Data Collection is Totally Automated
Collects & Transmits Data 24/7/365
Automated Network Processing at MO DOT in Albany
Automated Data Backup – In Case of Network Outage
NYSDOT CORS System Will Include Leica Hardware & Software

19. CORS Installation

20. CORS Hardware

21. Central Statewide Data Management
Network Monitored & Managed by DOT Network Administrators
Stations Can be Controlled Remotely from Albany (Set collection rates – view satellites)
Alarm System is Included to Warn of Data Flow Interruptions
24 Hour Turnaround on Hardware Repairs
UPS Backup Power Source at all Stations
Continuous Monitoring of CORS Network Integrity to Detect Movement
NGS and Leica also Monitor CORS Network Integrity

22. NYDOT CORS IT Infrastructure
Control Sites/
Log Static Data
Distribute Static Data
Produce Real Time Data Streams with
Corrections
Distribute Real Time Data Streams
Distributes Static Data
18 Stations
Distribute:
1 sec hourly RINEX Static Data
Single Baseline RTCM
Nearest Site RTCM
Single Cell Network RTCM
Automatic Cell Network RTCM
18 Stations
Real Time Network Processing
Two Site servers control 18 sites each, store raw static data and distribute static data products.
Network server controls real time network and distributes real time data products to Proxy Server.
2 cluster servers process the real time network corrections.
Proxy server makes static and real time data streams available to GPS users.
Distribute:
1 sec hourly static RINEX Files to RTK Proxy Server
1 sec hourly static RINEX for internal archive.
.5 second ½ hourly raw data files to NGS
.5 second 12 hour RINEX files to NYSDOT Photogrammetry
Log .5 sec.
Static data
½ hourly files
Stream 1 sec.
Raw Data for RTK
net processing

23. Servers
Site server 24
Network server 25
Site server 45

24. Publication of Static GPS Data
Automated Publishing of Static Data Files to National Geodetic Survey (NGS)
Static Data Files will be Available to Public from NGS – via CORS Website
Static Data will be Published by NGS in RINEX Format
RINEX Format can be Used by Most GPS Processing Software
NGS Adjusts National Network, Publishes Positions for Reference Stations, and Distributes Station Data For the National Spatial Reference Network
Possibly (in the Future) Incorporate 5 New CORS Stations Being Installed by NY City

25. Envisioned Web Delivery
NGS
NGS
Spider Web

26. Publication of Real Time Kinematic (RTK) Corrections
Automated Publishing of RTK Correction via Internet IP Address
RTK Corrections can Either be Solved by a Single Baseline from a CORS Station, or by a Modeled Network Solution From a Group of CORS Stations
RTK Corrections will be Streamed Out Thru an IP Address on the Web (User determined data format)
User Accounts Will be Necessary to Access RTK Corrections
DOT Will Not Charge $ For User Accounts or for Data
Data Can be Accessed by Wireless Phone with Internet Data Service Plan from a Wireless Provider
Unlimited Number of Users Can Access Data

27. RTK Clusters

28. GPS Technology
GPS Rovers Tracking From a GPS Base Station or CORS Station
Use of GPS for Quality Control on ATVs

29. Methods For Machine Navigation Systems
GPS Receivers Tracking From a GPS Base Station or CORS
Robotic Total Station Tracking a Prism (Could Include Laser Guidance)

30. RTK Saratoga test of Cell

31. Verizon Coverage

32. Future of NYSDOT Cors

33. NYSDOT CORS Mission Ensure Accuracy By: Ensure Reliability By:
Network Positions Monitored by NGS & by DOT CORS Software
Station Positions Processed Against National Spatial Reference Network
Station Positions Reliant on Continuous Network Monitoring, not Single Station Coordinate
Ensure Reliability By:
Data Interruptions or Station Movements Linked to DOT Alarm System
24 Hr Contracted Maintenance and Hardware Repair
Data Backups Eliminates Data Loss if System Should Go Down
Single Point of Contact and Control of Data Collection Settings
Provide Ease-Of-Use By:
Standardized Non-Proprietary Data Formats
Universally Usable With Most Major Manufacturers
Easily Accessible RTK Data Via Internet
No User Cost Charges for Data
RTK Usable Anywhere Wireless Access is Available

34. Sample ABGPS CORS Project
Block of photographs near Watertown
ABGPS data used for QA/QC of the aerial photos
ABGPS data used in Aerotriangulation adjustment to reduce the amount of ground control

35. Project Area Flight Line Diagram
Strips of photos laid out to maximize coverage and allow for Photogrammetric Mapping
It is impossible to fly the job exactly as it is laid out
ABGPS allows us to see if the project is flown to within allowable tolerances
Early detection of errors (over the allowed tolerances) allow NYSDOT to request a re-flight

36. ABGPS Antenna

37. What is ABGPS? ABGPS stands for Airborne Global Positioning System
GPS antenna mounted on top of aircraft fuselage
Time stamped “event marker” created when aerial camera collects image

38. Obtaining XYZ Coordinates
ABGPS data post-processed using a base station near the project area
Used NYSDOT CORS station in Watertown (NYWT)
Processed with GrafNav software
Specifically designed for differential correction of ABGPS data

39. GrafNav Software

43. Plotted in GIS

44. Fall 2005 Flights in GIS

45. ABGPS Summary ABGPS used in Photogrammetry to:
Provide early QA/QC of aerial photography
Reduce the amount of ground control required to do large scale mapping
Differential correction of GPS data is required for Photogrammetric accuracies
The NYSDOT CORS network provides the base station data needed for differential correction
NYSDOT CORS will be a vast improvement over the NGS CORS network

46. In Conclusion NYSDOT Currently has 36 CORS stations
NYSDOT is planning to expand
NYSDOT working with NGS to make NY CORS part of the National CORS
Data will be made available at no cost
Data will be delivered through web (non RTK) and registered users (RTK only)
Data delivery to be easy, accurate and reliable

47. Questions?