Geodetics: Implications for GIS Professionals...Datum code Base CRS Code Projn Conv Code Cmpd Hor...
Transcript of Geodetics: Implications for GIS Professionals...Datum code Base CRS Code Projn Conv Code Cmpd Hor...
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APSG at Esri Petroleum GIS Conference | Houston May 2018
Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Michael BarnesAPSG Education Foundation Chair 2010-2020APSG Chair 2008-2009
Geodetics: Implications for GIS ProfessionalsMay 10, 2018
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APSG at Esri Petroleum GIS Conference | Houston May 2018
Content
30 minutes
• Geodetic Datums and Map Projections
• Ten geodetic awareness topics for you
• A Random Thought: geodetics on the world stage
• Finally …
References:
www.apsg.info
www.iogp.org
www.epsg-registry.org
http://www.apsg.info/http://www.apsg.info/http://www.iogp.org/http://www.epsg-registry.org/
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APSG at Esri Petroleum GIS Conference | Houston May 2018
Hierarchy of Mapping
Datum (ellipsoid & origin)
is the Foundation
X,Y,Z Cartesian and Lat, Long, Ht
Equator
Zp
XpYp
Php
Ellipsoid
λp Φp
stable Unstable w/o Datum
Projected
CRS
is a derivative
of the Datum
(Geog CRS)
Easting, Northing,
Elevation (above MSL)
3Source: APSG
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APSG at Esri Petroleum GIS Conference | Houston May 2018
Beware . . .
Knowing the map projection and all its
parameters is insufficient
(even if the ellipsoid is known)
…Unless associated with a Geographic Coordinate
Reference System / Datum
The Map Projection coupled with a
GeogCRS / Datum makes a Projected Coordinate
Reference System (or ProjCRS)
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Terrain
Geodesy Reference Surfaces
GeoidEquipotential surface which
approximates to MSL
GeoidNormal to Geoid
a
b
EllipsoidSurface where Computations are made
1/f = a/(a-b)
Ellipsoid
Normal to Ellipsoid
hH
N
N=h-H
5Source: APSG
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APSG at Esri Petroleum GIS Conference | Houston May 2018
Reference Ellipsoids
• Fundamental to hundreds of Geodetic Datums
• 77 in the epsg-registry
• Most commonly used in petroleum are:
Half of the story
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EPSG Code Reference Ellipsoid Name Used% of
total
7022 International 1924 125 24%
7019 GRS 1980 92 17%
7012 Clarke 1880 (RGS) 47 9%
7004 Bessel 1841 38 7%
7030 WGS 84 29 5%
7008 Clarke 1866 24 5%
7011 Clarke 1880 (IGN) 19 4%
7024 Krassowsky 1940 14 3%
Others 70 15%
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APSG at Esri Petroleum GIS Conference | Houston May 2018
Examples of Geodetic Datums
Two part story
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Wrong Datum, Wrong Location
-1000 -500 0 500 1000-1000
-500
0
500
1000
( meters )
( m
ete
rs )
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Source: Phil Summerfield
Selected 8 Projects Datums in Red
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APSG at Esri Petroleum GIS Conference | Houston May 2018
Consequences of Poor Datum Handling
-450 -225 0 225 450-450
-225
0
225
450
( meters )
( m
ete
rs )
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WGS 84
Abidjan
Aratu
Cape
Minna
NAD 27
NAD 83
(CSRS)
Pulkova
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PSAD
56
SAD 69
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Map Projections characteristics
Distortion is unavoidable in any projection
AreaAzimuth & Angle
LengthShape
General
Shear
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Typical Map Projection Methods
• Universal Transverse Mercator
• Transverse Mercator
• Lambert Conformal Conic
• Albers
• Mercator
• Others less frequently: Stereographic,
Oblique Stereographic, Oblique Mercator
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Map projections: Area Calculations for CONUS
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Albers Equal Area Conic 8,072,019.56 km2 [+0.06%]Lambert Conformal Conic 7,193,234.60 km2 [-10.83%]Mercator Cylindrical 13,702,681.84 km2 [+69.86%]
Areas:Ellipsoidal 8,067,169.67 km2
Source: Phil Summerfield
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APSG at Esri Petroleum GIS Conference | Houston May 2018
Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
10 Self Assessment Questions:
10 seconds response
Easy !
Don’t know, I need more awareness
What is Barnes talking about?
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Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Q1. How many Horizontal Geodetic Datums are
databased in the EPSG registry?
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Review www.epsg-registry.org
460 Horizontal Geodetic
Datums in the Database
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Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Q2. What is the definition difference between a
Coordinate System and a Coordinate
Reference System?
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CS is a subset of CRS
• Coordinate Systems are:– Cartesian, Ellipsoidal, Spherical, Vertical
• Coordinate Reference System:– Geographic 2D, Geographic 3D, Geocentric,
Projected, Compound, Engineering, Vertical
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Coordinate Reference SystemCode -
CRSCRS Name Area code CRS Type
Coord Sys
code
Datum
code
Base CRS
Code
Projn Conv
Code
Cmpd Hor
CRS Code
Cmpd Vert
CRS CodeCRS Scope
32615 WGS 84 /
UTM zone
15N
2028 projected 4400 4326 16015 Large and
medium
scale
topographic
mapping
and
engineering
survey.
Coordinate SystemCode - CS CS Name CS Type Dimension Remarks
4400 Cartesian 2D CS. Axes:
easting, northing (E,N).
Orientations: east, north.
UoM: m.
Cartesian 2 Used in projected and
engineering coordinate
reference systems.
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APSG at Esri Petroleum GIS Conference | Houston May 2018
Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Q3. What accuracy dilution can I expect from a
horizontal geodetic datum transformation?
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Estimated accuracies of 2,114 Datum Transformations
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Less than 1 m56%
1-5 m17%
5-10 m7%
10-25 m4%
25-100 m6%
100-800 m0.3%
absentia10%
Source: EPSG Registry v9.2
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Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Q4. Name 3 common map projections that
preserve area ratios?
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Equal Area Map Projections
• Albers Equal Area Conic
• Lambert Azimuthal Equal Area
• Lambert Cylindrical Equal Area
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Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Q5. How many Reference Norths are used?
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True North = Direction of the meridian through a
point
Magnetic North = Differs from True North by
declination and varies with time
Grid North = Differs from True North by
convergence
Gyro North = a measurement of True North by
instrument
Plant or Project or Rig North = strictly a “local”
non-georeferenced orientation
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5 kinds of Reference North
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Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Q6. What is the meaning of EPSG code 32615?
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EPSG CRS 32615
WGS 84 UTM zone 15N
Definition codes are really useful,
they assist data handling
(ensuring; consistency, completeness,
correctness and verified)
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Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Q7. How many Units of Measure do we
encounter?
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13 kinds of feet and 2 kinds of meters in use
Reference Units: Biggest Petroleum Industry Problem
US Survey Foot vs. International Foot
1 ftUS = 1.000002 ft (Intl), but this is still important for UTM, generating 30-60 foot errors, depending on latitude
Other Feet: Clarke’s Foot, Sears 1922, 2 for Benoit (both 1895), Gold Coast Ft., 4 Indian Ft. (1865, 1937, 1962 & 1975) and 2 British Feet (1865 & 1935)
2 meters: International Meter and German Legal Meter
Other linear units: Chains, Links, and Yards
There is no standard foot
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Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Q8. Where is a good source of guidance for
understanding of Vertical Data in GIS?
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www.iogp.org
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Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Q9. What types of lines are used for delineation
of Block Licenses?
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Block License Delineation
Basic geodetic considerations
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• Joining Turn Points➢ grid (plane)➢ parallel, meridian, geodesic➢ loxodrome (rhumb line)
But also note:
• Calculation of Area➢ Map Grid (with and without corrected area scale factor)➢ Ellipsoidal➢ Ground or other surface level Ref: OGP GN’s and Prior
APSG presentations for
technical explanations
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APSG at Esri Petroleum GIS Conference | Houston May 2018
Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Q10. Decimal degrees truncated at 0.000001
degrees implies what realistic metric
accuracy?
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0.000001 degrees ≡ 6 to 60 cm
Latitude dependent
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Original source: APSG
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APSG at Esri Petroleum GIS Conference | Houston May 2018
If you remember nothing else….. “not unique”
• Latitudes and Longitudes are not unique unless
qualified with datum name
• Projection Coordinates are not unique unless
qualified with projection name, zone and datum
• Heights are not unique unless qualified with
Surface Reference (Vertical Datum)
• Reference Norths are not unique unless qualified
with Heading Reference
• Units of Measure are not unique unless qualified
with Unit Reference
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Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
A random thought:
Geodetics matters to International Peace
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Exclusive Economic Zones (EEZ) at 200 nM
Core to UNCLOS is maritime states rights to resources
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200 nautical miles = 230 miles = 370 km
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Disputes over boundaries and transboundary resources
Boundaries are politically sensitive, legally and technically complex, and need good geodesy
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Subject to an additional ISA Royalty Payments ?
20 nations with license blocks beyond 200 nM
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Geopolitical tangle in South China Sea
Complex Multiple Overlapping Claims
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Before GIS, we had 200 years of geodetic surveying and mapping .. the science is still the same ..
National Geodetic Survey of Nepal 1981-1983
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APSG at Esri Petroleum GIS Conference | Houston May 2018
Experts in Geomatics, Surveying, Positioning,
Geospatial Data, and Mapping Sciences
Final thoughts on
“Geodetics: Implications for GIS Professionals”
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