What is Geodesy?1 Open GIS Consortium for a changing world. Spatial connectivity What is Geodesy ? Roel Nicolai senior consultant Geomatics and GIS Shell Exploration and Production Technology Application and Research (SEPTAR) Rijswijk - The Netherlands

What is Geodesy?2 Open GIS Consortium for a changing world. Spatial connectivity All right then – what is it ? "geo daisia" = "dividing the earth" Aim: determination of the figure of the earth or, more practically: determination of the relative positions on or close to the surface of the earth. oldest profession on earth but one geodesy, not geodetics

What is Geodesy?3 Open GIS Consortium for a changing world. Spatial connectivity Shape of the Earth  flat  large scale mapping   street plans   engineering surveys   sphere  small scale mapping, low accuracy  geography  survey calculations (medium accuracy)   ellipsoid accurate (geodetic) mapping  geodetic & survey calculations   geoid  accurate heighting  satellite orbits  high accuracy geodetic calculations

What is Geodesy?4 Open GIS Consortium for a changing world. Spatial connectivity Geoid equal gravity potential Locus (surface) of points with equal gravity potential approximately at Mean Sea Level  must be measured (  errors) l difficult to describe mathematically l even more difficult to calculate with o reduction of survey observations o map projections  l everyday heights are relative to geoid (MSL) l physically exists

What is Geodesy?5 Open GIS Consortium for a changing world. Spatial connectivity Geoid covering the USA (NGS96) 7.2 m m Note: This image shows the height of the geoid above the US reference ellipsoid

What is Geodesy?6 Open GIS Consortium for a changing world. Spatial connectivity

What is Geodesy?7 Open GIS Consortium for a changing world. Spatial connectivity Ellipsoid ( = spheroid) geoid Approximate the geoid ( not the earth's surface ) l good approximation possible  variations ~10 -5 (±60 m over earth radius ~ 6,400,000 m)  ellipsoidal calculus is feasible  can be defined exactly: semi-major axis (size) and flattening (shape) l computational aid only; no physical reality  ellipsoidal heights are not practical  many choices possible (~50)  optimum local fit with geoid (sometimes global fit)  rotation axis parallel to mean earth rotation axis  based on surface geodetic observations

What is Geodesy?8 Open GIS Consortium for a changing world. Spatial connectivity The geoid and two ellipsoids N N Europe N. America S. America Africa typically several hundreds of metres

What is Geodesy?9 Open GIS Consortium for a changing world. Spatial connectivity Ellipsoids - examples namesemi-major axisflattening Bessel m1/ WGS m1/ Clarke m1/ Bessel 1841: usage: o Europe (German influence sphere), Namibia, Indonesia, Japan, Korea o National control network and mapping. WGS84: usage: o the entire world o the GPS system in conjunction with a datum of the same name. Clarke 1866: usage: o USA except Michigan, Canada, Central America, Philippines, Mozambique o National control network and mapping.

What is Geodesy?10 Open GIS Consortium for a changing world. Spatial connectivity Many ellipsoids …. many datums Approximate the local geoid with different ellipsoids...  different origins  different orientation of axes  different shapes and sizes different GEODETIC DATUMS  different GEODETIC DATUMS What is a ‘Geodetic Datum’? location (origin) orientation shape size of the ellipsoid in space

What is Geodesy?11 Open GIS Consortium for a changing world. Spatial connectivity Geographic coordinates P  X-axis Y-axis Z-axis semi-major axis H Greenwich meridian semi-minor axis oblate at poles   = Geographic Latitude  = Geographic Longitude H = Ellipsoidal height

What is Geodesy?12 Open GIS Consortium for a changing world. Spatial connectivity Latitude is not unique ! 11 22 nor is Longitude  1  2 Due to different Geodetic Datums:

What is Geodesy?13 Open GIS Consortium for a changing world. Spatial connectivity President Ford’s secret Alaskan visit ?

What is Geodesy?14 Open GIS Consortium for a changing world. Spatial connectivity Washington to Tokyo - Orthographic Projection Tokyo Anchorage Washington

What is Geodesy?15 Open GIS Consortium for a changing world. Spatial connectivity Mercator projection Globular projection Orthographic projection Stereographic projection A familiarly shaped ‘continent’ in different map projections

What is Geodesy?16 Open GIS Consortium for a changing world. Spatial connectivity Easting Northing Longitude East Longitude West equator Latitude North Latitude South A A Geographic and map coordinates (N,E) = F (Lat, Lon)  distortions

What is Geodesy?17 Open GIS Consortium for a changing world. Spatial connectivity What errors can you expect?  Wrong geodetic datum: q several hundreds of metres  Incorrect ellipsoid: q horizontally: several tens of metres q height: not effected, or tens to several hundred metres  Wrong map projection:  entirely the wrong projection: hundreds, even thousands of kilometres (at least easy to spot!)  partly wrong (i.e. one or more parameters are wrong): several metres to many hundreds of kilometres  No geodetic metadata  coordinates cannot be interpreted  datum  ellipsoid  prime meridian  map projection Coordinate Reference System

What is Geodesy?18 Open GIS Consortium for a changing world. Spatial connectivity CRS data in the oil industry Average number of CRUD actions per activity Field survey data Well data Reservoir data Facility data Production data Conceptual data Scheduling data Budget data Finance data Transportation/logistics data Materials data Human Resource data Safety and environm. data Geospatial and geodetic data Legal data IC specific data OpCo Managem't Control Data Data module Coordinate Reference System data

What is Geodesy?19 Open GIS Consortium for a changing world. Spatial connectivity Metadata: Spatial Referencing Prime MeridianEllipsoid DatumCoordinate System Coordinate Operation ISO SRS-by-geographic-ID by geographic identifier Spatial Reference System SRS Coordinate Reference System by coordinates CRS Operation method Operation parameters

What is Geodesy?20 Open GIS Consortium for a changing world. Spatial connectivity Coordinate System l Link between the geodetic metadata and coordinates: l Defines the coordinate axes q Names, abbreviations q Angles between the axes (& properties of coord.space) q Units of measure q Order of the coordinates (and axes) l Determined by local custom: l Many parts of Europe: X (= northing), Y (= easting) l Elsewhere: X (= easting), Y (= northing) l Everywhere:Latitude, Longitude

What is Geodesy?21 Open GIS Consortium for a changing world. Spatial connectivity Types of Coordinate (Ref) System Coordinate Ref System Coordinate System Characteristics GeocentricCartesian or spherical Proper 3D spatial modeling; spatial applications Geographic 3DellipsoidalLocations described relative to ellipsoidal surface Geographic 2DellipsoidalLocations described on ellipsoidal surface; for large national/continental geodetic control networks ProjectedCartesianFor national mapping; smaller area than Geographic 2D. Carefully controlled mapping distortions EngineeringvariousEarth curvature ignored; mostly flat-earth model ImageCartesian or oblique Cartesian Distortions due to earth curvature determined by data acquisition characteristics Verticalgravity-related, depth,barometric Gravity-related means relative to geoid (~MSL) Depth: complex reference surfaces (tidal) Earth curvature modelling

What is Geodesy?22 Open GIS Consortium for a changing world. Spatial connectivity EPSG Geodesy WG l Working Group of EPSG q European Petroleum Survey Group q Members: l Roger Lott – BP/Amoco (chair) l Roel Nicolai – Shell l Jim Cain – geodetic consultant, formerly Western Atlas l Bruno Ravanas – TotalElfFina l Alan Faichney – Society of Exploration Geophysicists l Geir Simensen – Statoil (Norway) l Approached by POSC in 1992 q Geodetic advice on EPICENTRE data modelling q Suppliers of geodetic reference parameters l Website: (hosted by IHS Energy) l US sister established in 1999: APSG

What is Geodesy?23 Open GIS Consortium for a changing world. Spatial connectivity EPSG database l Documenting usage q Official CRS’s and CT’s q Commonly used CRS’s and CT’s l Initially oil industry focussed l Later extended to cover GIS users interests l Excluded: q Dubious and/or incomplete data q User-specific, often Local (engineering) systems l History: q Initially MS Excel files (1996) q MS-Access database l Version 4 – internal non-standard data model l Version 5 – EPICENTRE compliant l Version 6 – ISO (& OpenGIS) compliant l Algorithms for transformations q Guidance Note 7 q Version 1 commissioned by POSC q Later additions: EPSG >1800 Coord Ref Systems >1700 Coord Operations

What is Geodesy?24 Open GIS Consortium for a changing world. Spatial connectivity EPSG data usage Coordinate Transformation Application (as delivered) Geodetic data with application Geodetic data from user database Geodetic data with application replaced Coordinate Transformation Application (as used) Industry standard geodetic data (EPSG) User geodetic database User proprietary geodetic data

What is Geodesy?25 Open GIS Consortium for a changing world. Spatial connectivity EPSG data deprecation policy l New policy w.e.f. July 2001 l No data will be deleted q ISO and SEG requirement l Critical data in error q i.e. numerical integrity of coordinate data affected by error q new record(s) created with correct data q incorrect record marked as deprecated (+date and reason) q replacement path will be recorded q dependent records also deprecated and replaced q Change recorded explaining actions l Non-critical data in error q correction of data in record; revision date changed q Change recorded l Superseded data (in usage) q data stays in; comment added

What is Geodesy?26 Open GIS Consortium for a changing world. Spatial connectivity Some myths about EPSG l “Reference to an EPSG number is all I need to solve all my spatial referencing problems” q EPSG cannot hope to record all CRS and CT data q You need to check whether data is still valid l “EPSG precribe how they believe CRS data should be used” q EPSG record common usage and established practice l “EPSG is liable for any errors in their database” q EPSG makes every effort to minimize the number of errors q EPSG have made a disclaimer on liability resulting from errors l “ISO is going to make the EPSG database obsolete” q ISO only collects ‘official’ parameters q ISO data will be included in the EPSG dataset

What is Geodesy?27 Open GIS Consortium for a changing world. Spatial connectivity Geodetic skills l Are definitely needed in any “spatial” business l You need very little of it (like Vitamin ‘C’) l Deficiency will lead to the dreaded disease: Corporate GEO-SCURVY !!!