Geodetics: Implications for GIS Professionals...Datum code Base CRS Code Projn Conv Code Cmpd Hor CRS Code Cmpd Vert CRS Code CRS Scope 32615 WGS 84 / UTM zone 15N 2028 projected 4400

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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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/


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


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)


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


Reference Ellipsoids

• Fundamental to hundreds of Geodetic Datums

• 77 in the epsg-registry

• Most commonly used in petroleum are:

Half of the story

6

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%


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 )

8

Source: Phil Summerfield

Selected 8 Projects Datums in Red


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

42

PSAD

56

SAD 69


Map Projections characteristics

Distortion is unavoidable in any projection

AreaAzimuth & Angle

LengthShape

General

Shear


Typical Map Projection Methods

• Universal Transverse Mercator

• Transverse Mercator

• Lambert Conformal Conic

• Albers

• Mercator

• Others less frequently: Stereographic,

Oblique Stereographic, Oblique Mercator


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




10 Self Assessment Questions:

10 seconds response

Easy !

Don’t know, I need more awareness

What is Barnes talking about?

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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




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.




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




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

21




Q5. How many Reference Norths are used?

22


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




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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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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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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Q9. What types of lines are used for delineation

of Block Licenses?

30


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




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


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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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


Disputes over boundaries and transboundary resources

Boundaries are politically sensitive, legally and technically complex, and need good geodesy

37


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




Final thoughts on

“Geodetics: Implications for GIS Professionals”

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Documents

Geodetics: Implications for GIS Professionals...Datum code Base CRS Code Projn Conv Code Cmpd Hor CRS Code Cmpd Vert CRS Code CRS Scope 32615 WGS 84 / UTM zone 15N 2028 projected 4400