Overview of Datums Commonly Used in Michigan and the National Spatial Reference System

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Overview of Datums Commonly Used in Michigan and
the National Spatial Reference System

• Michigan Society of Professional Surveyors
• 70th Annual Meeting
• Frankenmuth , MI
• February 24th 2011

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DATUMS
GRS 80
ITRF 00
NSRS
IGLD 85
IGLD 55
WGS 84
NGVD 29
NAVD 88
NAD 83
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GEODETIC DATUMS

• A set of constants specifying the coordinate
  system used for geodetic control, i.e., for
  calculating coordinates of points on the Earth.
  Specific geodetic datums are usually given
  distinctive names. (e.g., North American Datum of
  1983, European Datum 1950, National Geodetic
  Vertical Datum of 1929)

Characterized by A set of physical monuments,
related by survey measurements and resulting
coordinates (horizontal and/or vertical) for
those monuments
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GEODETIC DATUMS

• HORIZONTAL
• 2-D (Latitude and Longitude) (e.g. NAD 27, NAD 83
  (1986))
• VERTICAL/GEOPOTENTIAL
• 1-D (Orthometric Height) (e.g. NGVD 29, NAVD 88,
  Local Tidal)
• GEOMETRIC
• 3-D (Latitude, Longitude and Ellipsoid Height)
• Fixed and Stable(?) - Coordinates seldom change
• (e.g. NAD 83 (1993), NAD 83 (2007))
• also
• 4-D (Latitude, Longitude, Ellipsoid Height,
  Velocities) Coordinates change with time
• (e.g. ITRF00, ITRF08)

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IGLD what is it?

• The IGLD is a dynamic height system. Dynamic
  heights, by definition, define a water level
  surface. Their use is not limited to the Great
  Lakes. They are useful for large hydraulic
  systems everywhere. IGLD 85 is the current
  version of the Great Lakes datum
• NAVD 88 heights are orthometric heights.
  Orthometric heights do not define a water level
  surface.
• IGLD heights are corrected dynamic heights.
  Hydraulic correctors (HC) are applied to dynamic
  heights to remove various observational and other
  inconsistencies in the NSRS. HCs are based on
  water levels observed at the gauges.

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IGLD Why is it important?

• The Great Lakes are a vast hydraulic system with
  water levels and flows influenced by engineered
  channels and control structures.
• The entire region is tilting due to post-glacial
  rebound (aka glacial isostatic adjustment GIA)
• The absolute rate of change at a given location
  must be considered along with the relative rate
  of change across the region. The overall Great
  Lakes basin is tilting at a rate of about 60 cm
  (two) feet per century.

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IGLD Why is it useful?

• Because it is a dynamic height system, it can be
  used to relate various data to a common water
  level surface
• It provides a mechanism for the US and Canada to
  reference heights to a common datum throughout
  the Great Lakes
• Each country has adopted other vertical datums
  for general use. The Canadian vertical datum is
  CGVD 28. The US vertical datum is NAVD 88.

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IGLD Why is there more than one?

• IGLD 85 is the current datum. It was preceded by
  IGLD 55. Efforts are underway now to compute
  IGLD 2015
• The IGLD is revised about every 30 years to
  remove the effect of GIA from published heights.

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IGLD How are IGLD heights made available?

• Dynamic heights are published by NGS on all bench
  mark datasheets
• IGLD 85 heights are not displayed on NGS
  datasheets
• Hydraulic correctors are determined by CO-OPS
• NOS provided software can be used to convert
  NAVD88 heights to IGLD 85 heights. This software
  applies a hydraulic corrector.

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IGLD Transformation Tools

• VDATUM Performs transformations between NAVD 88
  and IGLD 85
• IGLD85 Currently not available to users.
• Issues with both programs

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NAVD 88 to IGLD 85
HC are not applied to sloping surfaces, use the
Dynamic Height
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IGLD 85 heights some important details

• Hydraulic correctors are applied to dynamic
  heights at locations on or very near the lake
  surface, which is assumed to be flat.
• Hydraulic correctors are not applied on rivers
  and connecting channels, which are sloping water
  surfaces.
• On sloping water surfaces the IGLD 85 height and
  dynamic height are one and the same

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ELLIPSOID - GEOID RELATIONSHIP
H Orthometric Height (NAVD 88)
h Ellipsoidal Height NAD 83 (199x), NAD 83
(2007), NAD 83 (CORS96)
N Geoid Height (GEOID 09)
H h N

h
H
N
GEOID09
Geoid
Ellipsoid GRS80
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NGVD29
The National Geodetic Vertical Datum of 1929 is
referenced to 26 tide gauges in the US and Canada
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NAVD88
The North American Vertical Datum of 1988 is
referenced to a single tide gauge in Canada
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NGVD 29 Referenced to 26 Tide Gages
NAVD 88 Referenced to 1 Tide Gage (Fathers Point)
NAVD88 minus LMSL(1960-1978)
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Problems using traditional leveling to define a
NEW National Vertical Datum

• Leveling the country can not be done again
• Too costly in time and money
• Leveling yields cross-country error build-up
  problems in the mountains
• Leveling requires leaving behind passive marks
• Bulldozers and crustal motion do their worst

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Definitions GEOIDS versus GEOID HEIGHTS

• The equipotential surface of the Earths gravity
  field which best fits, in the least squares
  sense, (global) mean sea level.
• Cant see the surface or measure it directly.
• Can be modeled from gravity data as they are
  mathematically related.
• Note that the geoid is a vertical datum surface.
• A geoid height is the separation between an
  ellipsoidal datum to the geoid.
• Definition from the Geodetic Glossary,
  September 1986

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Transition to the Future GRAV-D
Gravity for the Redefinition of the American
Vertical Datum

• Official NGS policy as of Nov 14, 2007
• 38.5M over 10 years
• Airborne Gravity Snapshot
• Absolute Gravity Tracking
• Re-define the Vertical Datum of the USA by 2018

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Gravity Survey Plan

• National Scale Part 1
• Predominantly through airborne gravity
• With Absolute Gravity for ties and checks
• Relative Gravity for expanding local regions
  where airborne shows significant mismatch with
  existing terrestrial

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Finished up work in Alaska for this year and will
be working along California Coast during the
winter.
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CONTINUOUSLY OPERATING REFERENCE STATIONS (CORS)

• 1500 Installed and operated by more than 200
  Federal-State-Local Govt and private partners
• NOAA/National Geodetic Survey
• NOAA/OAR Global Systems Division
• U.S. Coast Guard - DGPS/NDGPS
• Corps of Engineers - DGPS
• FAA - WAAS/LAAS
• State Department Of Transportations
• County and City
• Academia
• Private Companies

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CONTINUOUSLY OPERATING REFERENCE STATIONS (CORS)

• NGS PROVIDES
• Horizontal and Vertical NSRS Connections
• NAD 83 and ITRF00 Coordinates
• Network Data Collection - Hourly Daily
• Daily 3D Network Integrity Adjustment
• Public Data Distribution - Internet
• 16 Year On-Line Data Holding

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As of 12/09/10
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OPUS

• On-Line Positioning User Service
• Processes GPS data
• Global availability (masked)
• 3 goals
• Simplicity
• Consistency
• Reliability

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(No Transcript)
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How does OPUS compute your position?
3 single baselines computed
CORS solution 2
CORS solution 1
CORS solution 3
3 positions averaged simple mean (equal
weights)
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FLAVORS OF OPUS
OPUS Tool Box
OPUS-Projects Receivers 2-4 Hours of
data Multiple Receivers Network Solution Results
shared or not
OPUS-S Receivers 2 Hours of data Results not
shared
OPUS-RS Receivers 15 Minutes of data Results
not shared
OPUS-Mapper Receivers Minutes of data Results
not shared
OPUS-DB Receivers 4 Hours of data Results
shared
LOCUS Digital Bar-Code Leveling Integration with
GPS? Results shared or not
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OPUS-DB OBSERVATION DATA STREAM
Local References
photo(s)
GPS data
Mark Information
NGS website OPUS-DB
NGS magic
DATASHEET
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OPUS DB
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OPUS DB
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OPUS DB
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OPUS DB
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OPUS DB Simple Shared Data NGS Archived
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Problems with NAD 83 and NAVD 88

• NAD 83 is not as geocentric as it could be
  (approx 1-2 m).
• Surveyors dont see this - Yet
• NAD 83 is not well defined with positional
  velocities.
• NAVD 88 is realized by passive control (bench
  marks) most of which have not been re-leveled in
  40 years or longer.
• NAVD 88 does not account for local vertical
  velocities (subsidence and uplift)
• Post glacial isostatic readjustment
• Subsurface fluid withdrawal
• Sediment loading
• Sea level rise

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The National Geodetic Survey 10 year
plan Mission, Vision and Strategy 2008 2018
http//www.ngs.noaa.gov/INFO/NGS10yearplan.pdf

• Official NGS policy as of Jan 9, 2008
• Modernized agency
• Attention to accuracy
• Attention to time-changes
• Improved products and services
• Integration with other fed missions
• Vetted through NSPS/AAGS
• 2018 Targets
• NAD 83 and NAVD 88 re-defined
• Cm-accuracy access to all coordinates
• Customer-focused agency
• Global scientific leadership

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Ten-Year Milestones (2018)
1) NGS will compute a pole-to-equator,
Alaska-to-Newfoundland geoid model, preferably in
conjunction with Mexico and Canada as well as
other interested governments, with an accuracy of
1 cm in as many locations as possible 2) NGS
redefines the vertical datum based on GNSS

and a gravimetric geoid 3) NGS redefines the
national horizontal datum to remove disagreements
with the ITRF
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Approximate height differences from NAVD 88 to
new gravimetric datum ( 2018).
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PREDICTED POSITIONAL and HEIGHT CHANGES with NEW
DATUMS (Geometric and Geopotential) in 2018
computed for 73609 (pid DL4964)
HORIZONTAL 1.14 m (3.7 ft) ELLIPSOID HEIGHT
- 1.09 m (- 3.6 ft) Predicted with
HTDP ORTHOMETRIC HEIGHT - 0.61 m (- 2.0
ft) Predicted with HTDP and USGG2003
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Simplified Concept of NAD 83 vs. ITRF00
h83
h00
Earths
Surface
Identically shaped ellipsoids (GRS-80) a
6,378,137.000 meters (semi-major axis) 1/f
298.25722210088 (flattening)
ITRF 00
Origin
2.2 meters
NAD 83
Origin
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Reasons for replacing NAD 83 with a geocentric
reference system.

• Elllipsoid hts can be converted to orthometric
  hts in the proposed U.S. geopotential datum via
  the equation Hh-N. Where N is based on a true
  gravimetric geoid.
• Geocentric coordinates would closely approximate
  WGS 84 coordinates.
• Geocentric coordinates would closely approximate
  ITRF coordinates which is popular within the
  scientific community.
• Geocentric coordinates would closely approximate
  the official coordinates used in Mexico. Europe
  and South America have each adopted a geocentric
  reference system.
• Wide Area Augmentation System (WAAS) uses ITRF.

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Reasons for staying with NAD 83

• State Plane Coordinates are based on NAD 83.
• Legislation in 48 states require the use of NAD
  83.
• The NGSIDB contains only NAD 83 coordinates for
  more than 300,000 passive reference stations.
• Perhaps more that a million passive stations that
  are not in the NGSIDB have only NAD 83
  coordinates.
• Many GIS, Imagery and other products are tied to
  or based on NAD 83.
• The Nationwide Differential GPS service (NDGPS)
  uses NAD 83.
• Canada uses NAD 83.

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Preparing for the Future

• 1 Keep your data holdings.
• 2 Attend webinars offered by NOAA/NGS Corbin
  Training facility.
• 3 Participate in the County Scorecard effort.

NOAA NGS Corbin Training Center
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NGSs Mission Statement
Dave Rigney 517-335-1916 dave.rigney_at_noaa.gov rign
eyda_at_michigan.gov
Questions?