NATIONAL READJUSTMENT
•WHAT
•WHY
•HOW
•WHEN
NAD83(NSRS)
NAD83(NSRS)
NAD27 to NAD83
COMPARISON OF DATUM ELEMENTS
NAD 27 NAD 83ELLIPSOID CLARKE 1866 GRS80 a=6,378,206.4 m a=6,378,137 m 1/f = 294.9786982 1/f = 298.257222101
DATUM POINT Triangulation Station NONE Meades Ranch, Kansas Earth Mass Center
ADJUSTMENT 25k Stations 250k Stations few hundred Base lines 30k EDMI base lines
few hundred Astro Az 5k Astro Azimuths Doppler and VLBI
NAD83(86) DOPPLER STATIONS
Results of NAD83(86)
• Network Accuracy - 1 Meter
• Local Accuracy – First-Order (1 part in 100,000)
NAD 83(86) NETWORK PROBLEMS
Not “GPSABLE”
POOR STATION ACCESSIBILITY
IRREGULARLY SPACED
POSITIONAL ACCURACY
HARN
HIGH ACCURACY REFERENCE NETWORKS
“GPSABLE”Clear Horizons for Satellite Signal Acquisition
EASY ACCESSIBILITYFew Special Vehicle or Property Entrance Requirements
REGULARLY SPACEDAlways within 20-100 Km
HIGH HORIZONTAL ACCURACYA-Order (5 mm + 1:10,000,000)B-Order (8mm + 1:1,000,000)
HIGH ACCURACY REFERENCE NETWORK
HARN ADJUSTMENT
A-Order Adjusted to VLBI-Existing FBN-CORS
B-Order Adjusted to A-Order
Existing Horizontal (Conventional & GPS) Readjusted to A/B-Order
New Adjustment Date Tag e.g. NAD83(1995)
GPS & CLASSICAL ADJUSTMENTS COMPLETED
GPS ADJUSTMENT COMPLETED
1990
-GPS1
70
1990-GPS120
1991GPS222
1992GPS366
1997GPS11791992
GPS412
1992 GPS3831992
GPS450
1992GPS419
1992GPS394
1992GPS341
1993
1993
GPS585
1993 GPS667
1992GPS376
1995GPS887
1997.
GPS577
1991GPS197
GPS2601991
1995GPS908
GPS610
1993
GPS725
HARN & STATEWIDE NETWORK STATUS
1993
1994GPS404
GPS611
1994GPS633
1991 GP S291 reobs 9/97
1994 GPS721
reos 7/96 GPS1047
reos 1/96 GPS936
1997GPS1133
reos-6/95-GPS904
1995GPS852
1995GPS882
1993GPS606
1996GPS1048 1996
GPS8051996GPS941 1994
GPS7301996GPS1121
1997GPS1178
1997 GPS 12001997
GPS1150
reos-1996
Adjustment Tags
• Different statewide adjustments • Different years (epochs)
• Needed to distinguish between adjustments so…..
• The Adjustment tag was created
• NAD83(1995)----NC’s original HARN adjustment
FEDERAL BASE NETWORK (FBN )
Reobserve the FBN to better connect the HARNs to the CORS-MINIMUM 100 KM STATION SPACING-2cm local horizontal accuracy-2cm ellipsoid heights
Also: observed concurrently -CBN Cooperative Base Network-User Densification Network
FBN GPS ADJUSTMENT COMPLETED
FBN/CBN SURVEYS
GPS READJUSTMENT COMPLETED
1999GPS1347
1998GPS1273
1997GPS1250
1998GPS1267 1998
GPS1264
1998GPS1258
1999GPS1394
1999GPS1397
1997GPS1207
1999GPS1378
1999GPS1370
1999GPS1356
1998GPS1288
1998GPS1333
1998GPS1340
1999GPS1377
1999GPS1381
1999GPS1399
2000GPS1411
2001 GPS1629
2000 GPS1463
2000
GPS1462
2000 GPS1481
2000 GPS1492
2000 GPS1506
2000 GPS1514
2000 GPS1519
2000 GPS1530
2000 GPS1188
2001 GPS1712
2001GPS1554
2001GPS1641
2001 GPS1596
2002 GPS1686
2002 GPS1687
2002 GPS1731
2003 GPS1752
2003
GPS1825
2003 GPS1851
2003 GPS1753
2003 GPS 1850 MEANS
2003 GPS1682WILLIAMS
2003 GPS1726 2002
GPS-1547
Reasons for NEW Readjustment
• Multiple epoch dates• Inconsistencies between states• Need to be Consistent with CORS• Compute Network and Local accuracies
September 24, 2003 NGS Executive Steering Committee approved a plan for the readjustment of the horizontal positions and ellipsoid heights for GPS stations in the contiguous United States.
What about Orthometric Heights?
No National Orthometric height Readjustment at this time
Ortho Control = NAVD 88 not the CORS Since no change in control most orthometric
elevations would not change significantly
What about Orthometric Heights?
Decision was made not to perform a National Readjustment of orthometric heights at this time Control = NAVD 88 not the CORS Since no change in control most orthometric
elevations would not change significantly Network & Local Accuracy numbers for the
orthometric heights would be the primary reason for readjustment
Would require relevant network accuracies for the NAVD 88 network-This would require a complete analysis of the NAVD 88 network
NAD 83 READJUSTMENT
ONLY GPS DATA WILL BE USED
-CONTINUOUSLY OPERATING REFERENCE STATIONS-FEDERAL BASE NETWORK-COOPERATIVE BASE NETWORK-USER DENSIFICATION NETWORK-HARN-NGS AIRPORT SURVEYS
The National Readjustment General Comments
The CORS will provide the control Only GPS projects will participate The FBN/CBN Surveys are a key element since
these are high accuracy (2 cm) surveys that tie the HARN to the CORS throughout the contiguous United States and provide more accurate values for the ellipsoid heights of most HARN stations.
The required free adjustment analysis of each GPS project that contributes to the National Spatial Reference System is complete.
Local Accuracy
Local Accuracy of a control point:A value that represents the uncertainty of
its coordinates relative to other directly connected, adjacent control points at the 95-percent confidence level
An approximate average of the individual local accuracy values between this control point and other observed control points used to establish its coordinates
Network Accuracy
Network accuracy of a control pointA value that represents the uncertainty of its
coordinates with respect to the geodetic datum at the 95-percent confidence level
Datum is considered to be best expressed by the Continuous Operating Reference Stations (CORS)
Local and Network accuracy values at CORS sites are considered to be infinitesimal (approach zero)
These accuracies will be implemented with the National Readjustment
NEW STANDARDS FOR GEODETIC CONTROL
(http://fgdc.er.usgs.gov/standards/status/swgstat.html)
• local accuracy -------------- adjacent points• network accuracy ---------- relative to CORS
• Numeric quantities, units in cm (or mm)• Both are relative accuracy measures• Will not use distance dependent expression
IMPROVING POSITIONAL ACCURACY
TIME NETWORK LOCALNETWORK SPAN ACCURACY ACCURACY _
NAD 27 1927-1986 10 METERS (1 part in 100,000)
NAD83(86) 1986-1990 1 METER (1 part in 100,000)
HARN 1990-1997 0.1 METER B -order (1 part in 1 million)
A -order (1 part in 10 million)
CORS 1996 - 0.01 meter 0.01 meter
Important Facts
• DEADLINE for data submittal June 1, 2005• COMPLETION DATE – February 10, 2007• NEW DATUM TAG - NAD83(NSRS)
For the latest information- visit the national readjustment webpage at: (www.ngs.noaa.gov/NationalReadjustment/)
GEODETIC CONTROL DATA SHEET
Station Name Northing (m) Easting (m) Diff. Northing 83/86 – 83/95
Diff. Easting 83/86 – 83/95
Smithport 83/86
199354.569 665067.183
Smithport 83/95
199354.397 665067.513 0.172 (m) -0.330 m)
Smithport83/2001
0.013 (m) 0.013 (m)
0.010 (m)
Smithport83/NSRS
???< 0.010(m)
???< 0.010(m)
http://www.ngs.noaa.gov/NationalReadjustment/
NC Constrained Horizontal residuals
NC Horz Constrained AdjustmentEllip HT residuals
The NAD83(86) Adjustment Team
NGS Adjustment Team (1986)NGS Adjustment Team (2005)
NAD83(NSRS)