The Status of the S.C. VRS

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The Status of the S.C. VRS

• Matt Wellslager
• VRS Project Manager

Datums and Projections
Lewis Lapine Chief, South Carolina Geodetic Survey
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The Figure of the Earth
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METADATA

• METADATA IS DATA ABOUT DATA
• DATUMS
• NAD 27, NAD 83(1986), NAD83 (2001), NGVD29,
  NAVD88
• UNITS
• Meters, U.S. Survey Feet, International Feet,
  Chains, Rods, Pole
• ACCURACY
• A, B, 1st, 2nd, 3rd, 3cm, Scaled

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Coordinate Systems

• Plane
• Sphere
• Ellipsoid
• Earth-Centered, Earth-Fixed
• A Geocentric Ellipsoid

All Compatible with SC VRS!!
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DATUM DEFINITIONS

• Datum, Geodetic Datum, Geocentric Datum
• A set of 8 constants specifying the coordinate
  system used for calculating coordinates of points
  on the Earth
• 3 Constants to Define the Coordinate Origin
• 3 Constants to Define the Coordinate Orientation
• 2 Constants to Define the Ellipsoid Shape and
  Size

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THE ELLIPSOIDMATHEMATICAL MODEL OF THE EARTH
N
b
a
S
a Semi major axis b Semi minor axis f
a-b Flattening a
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ELLIPSOID - GEOID RELATIONSHIP
H Orthometric Height (NAVD 88)
h Ellipsoidal Height (NAD 83)
H h - N
N Geoid Height (GEOID 99)

H
TOPOGRAPHIC SURFACE
h
N
GEOID99
Ellipsoid GRS80
Geoid
PERPENDICULAR TO ELLIPSOID
DEFLEC99
PERPENDICULAR TO GEOID (PLUMBLINE)
DEFLECTION OF THE VERTICAL
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IMPROVING POSITIONAL ACCURACY

• TIME NETWORK LOCAL
• NETWORK SPAN ACCURACY ACCURACY
• NAD 27 1927-1986
  10 Meters First-Order
  (1 part in 0.1 million)
• 
  
• NAD 83 1986-1991
  1 Meter
  First-Order(1 part in 0.1 million)
• HARN 1991-1997
  0.1 Meter B-Order(1
  part in 1 million)
• 
  
  A-Order (1 part in 10 million)
• CORS 2001
  0.01 Meter 0.01
  Meter
• SC VRS 2007 0.01 Meter
  0.01 Meter

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Coordinate Systems

• Geodetic Coordinates
• Latitude, Longitude, Elevation
• Global
• Plane Coordinates
• Point Tangent
• Local

Once Again, All Compatible with SC VRS
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PLANE COORDINATE SYSTEMS

• STATE PLANE AND UNIVERSAL TRANSVERSE MERCATOR
  GRID COORDINATES ARE A DIRECT MATHEMATICAL
  CONVERSION FROM LATITUDE AND LONGITUDE TO A
  CARTESIAN NORTHING AND EASTING (Y X) COORDINATE
  SYSTEM, AND MUST MAINTAIN THE SAME DATUM TAG
  e.g. NAD 83(2001) AS THE LATITUDE AND LONGITUDE

Yes, Compatible with SC VRS!!
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Facts about State Plane Projections

• Transverse Mercator and Lambert Polyconic
  Projections are used for SP Coordinates
• Both Projections are Conformal Preserve shape
• TM is used for states having a longer N-S
  elongation such as Indiana
• LP is used for states having a longer E-W
  elongation such as North Carolina
• South Carolina uses the Lambert Polyconic

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Lambert Polyconic Projection
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Lambert Polyconic For SC

• The project zone is set to minimize distortion
  to
• 1 part in 10,000 caused by fitting a plane to
  the ellipsoid
• To maintain the maximum difference between Grid
  and Geodetic Distances (scale) the zones were
  restricted to widths not exceeding 158 miles
• Developed in 1933 for NC to accommodate surveying
  accuracy at the time

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SC Facts

• A Lambert Polyconic Projection is a cone which
  passes through two parallels of Latitude
• 32030N and 34050N
• Scale is 1 at these two latitudes, less than one
  in between and greater than one outside
• Grid and Geodetic Azimuth are the same on the
  central meridian 810 W

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SC Facts Scale and Azimuth Relations
Scale Varies with Latitude
Convergence Varies with Longitude
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SC Facts ScaleRelationship of Ground, Sea
Level and Grid Distance
Center of Earth Grid Distance A to B is smaller
than Geodetic Distance A to B Grid Distance C to
D is larger than Geodetic Distance C to D
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Lambert Projection for SC
Zone Code 3900
Standard Parallels 32030N and 34050N
Central Parallel 33.66935347160N
sinB0 0.554399350127
Central Meridian 0810 W False Easting
2,000,000 iFT
North Origin 31050N Northing 0
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SC State Plane Coordinate System

• When making measurements on the Earths surface,
  the azimuths and distances must be adjusted to
  the regular grid
• Distances must be reduced from slope to
  horizontal to sea level to the ellipsoid and then
  scaled by a grid factor which is dependent on
  Latitude
• Azimuths must be changed from geodetic to grid by
  applying a convergence factor which is
• dependent on Longitude

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Universal Transverse Mercator Coordinates

• Global Coverage
• Military System
• 6 Degree Zones
• SC Zone 17 - CM 0810
• (1800 0810)/6 1 17
• Significant Distortion
• Scale factor on CM 0.9996 or 12500
• Yes, and once more compatible with SC VRS!!!

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Real-time DGPS / RTK
Real-Time Corrections
Reference Station at a known location
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Summary of Accuracy
Autonomous
DGPS
RTK
0.02m
1m
15 m
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The User Network
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VRS Regions
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Servers
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Equipment Cabinet
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VRS/RTK CORS Network

• 45 stations scattered across the State
• Antenna mast mounted on buildings

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Roving receiver sends an NMEA string back to
server using cellular modem. Virtual Reference
Station position is established.
VRS
RTCM or CMR
NMEA
VRS RTK
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Network Multiple Base Station Solution
Let B1, B2 B3 be base stations, R be the rover
B1
B2
                                 
R
B3
The indexes r 1,2,3 are for bases, r0 stands
for the rover

• Four RTK engines run simultaneously
• (1,2)
• (2,3)
• (3,1)
• (1,0)(2,0)(3,0)

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VRS Test Network
51.1 miles
46.1 miles
30.9 miles
57.7 miles
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Scattergram of Positional Error
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Equipment Required to use the SCVRS

• Dual Frequency GPS Receiver - Capable of tracking
  multiple constellations.
• Cell Phone or Cellular Modem SCGS uses the
  Airlink Raven and LG VX5300
• Cellular Carrier Service Digital Service
  required for data. Verizon, Alltel, Cingular
• Data Collector collection software must be
  capable of broadcasting a GPS coordinate.
• Adjustable or Fixed height Pole good if pole
  has a locking mechanism to prevent slippage.

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Bluetooth

• Personal Area Network
• Device to device communication
• Radio signal
• Short range up to 10 m
• Frequency 2.4 GHz to 2.483 GHz

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Because Cellular Modems Are

• Small
• Fits in pocket
• Inexpensive
• Available in a wide range of colors, including
  Yellow
• Not Easily Stolen

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Cellular Digital

• Same radio technology as analog
• Traffic type
• Digital compression
• Packet-switched data (PSD)
• Bandwidth (real world)
• General Packet Radio Service (GPRS/CDMA)
  20 to 35 kbps
• Enhanced Data Rates for GSM Evolution (EDGE) 60
  to 80 kbps
• UMTS 54 to 300 kbps
• EV-DO 90 kbps to 1.1 Mbps

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Example of Digital Coverage
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Current Configuration

• For straight RTK, the IP address for all
  reference stations
• 198.202.228.252
• Port code for the different corrector
  formats/ref. station combination
• xnnn, where
• 7nnn is RTCM
• 8nnn is CMR
• 9nnn is DGPS
• x001 is COLUMBIA CORS ARP
• x002 is YORK COUNTY CORS ARP
• x003 is Myrtle Beach (not a CORS, position
  determined using OPUS)
• x004 is COL OF CHARLESTON CORS ARP
• x005 is GREENVILLE TECHNI CORS ARP
• x006 is GREER CPW CORS ARP
• x008 is WALTERBORO CORS ARP

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Applications
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• Questions ?