Lecture-2_Bb_1SlidePerPage

Lecture-2_Bb_1SlidePerPage - Georeferencing PROJECTIONS...

Info iconThis preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Georeferencing PROJECTIONS & COORDINATE SYSTEMS Georeferencing • The Act Of Assigning Location To Geographic Information • A Meaningful Georeference Must: – Be ____________ • linking information to exactly one location – Have Shared __________ Between Users – Be __________ Through Time Georeferencing • Types – Nominal: • Simply Description Information – e.g. Place names – Ordering: • e.g. street addresses Georeferencing • Types (Cont.) – Metric: • Define locations using various measurements, often relative to some fixed location – e.g. lat/long, and various coordinate systems • Pros: – Potentially infinitely __________ spatial resolution; – allows distance to be computed Earth as a Grid • Where Do We Start? Earth as a Grid • The Graticule – Combined, Parallels of Latitude & Meridians of Longitude form the Graticule Earth as a Grid • Lat/Long Coordinates – The most comprehensive and powerful method of Georeferencing • Metric, standard/stable, unique – Measured in degrees, minutes and seconds • 1degree = 60 minutes • 1 minute = 60 seconds – Not a measure of time but of an angle • AKA Geographic Coordinate System – Good for location but not for measuring distance East longitude: plus West longitude: minus Earth as a Grid • Definition of Longitude – The Earth is seen from above the North Pole, looking along the Axis, with the Equator forming the outer circle. The location of Greenwich defines the Prime Meridian. The longitude of the point at the center of the red cross is determined by drawing a plane through it and the axis, and measuring the angle between this plane and the Prime Meridian. North Pole Equator Greenwich Earth as a Grid • Definition of Latitude – Latitude (of the red point) is the angle between a perpendicular line to the ellipsoid surface and the plane of the Equator North latitude: plus South latitude : minus Map Projections • Map Projection is the process of drawing the Graticule (latitude / longitude) on a flat surface. • All maps display some sort of distortion. – It is IMPOSSIBLE to project a spherical surface onto a flat (two-dimensional) surface without distorting the image The Earth’s curved surface A Flat Map Map Projections • 3 Common Projection Surfaces: Map Projections • Planar Projections – Sometimes referred to as Azimuthal Projections • An Azimuth is simply the direction of a line measure as an angle from a baseline – Retains the property of __________ • See notes to follow – Great for Polar Regions • Polar Azimuthal Projections Map Projections • Cylindrical Projections – Good for Equatorial Regions – Also used for world maps • Worst distortion is at the poles • Where, in the case of world maps, there is generally little interest – Generally are Conformal • See notes to follow Map Projections • Conic Projections – Good for mid-latitudes – USGS 7.5 minute Topographic maps are Polyconic Projections – Has a straight standard central meridian Polyconic Projection Map Projections • Orientation/Aspect – By manipulating the Orientation or Aspect of a projection surface it is possible to localize: • Those areas of __________ • __________ – Will produce very distinct Graticules on our maps Map Projections • Orientation/Aspect (Cont.) – Projections have 3 classes of orientation: • Normal • Transverse • Oblique Map Projections • Orientation (Cont.) – Normal (Point or Line of tangency). • Cylinder – Equator. • Planar – N or S Pole. • Conic – Any parallel with apex over pole. Map Projections • Orientation (Cont.) – Transverse • Projection surface is turned 90 degrees from normal. Map Projections • Orientation (Cont.) – Oblique • Lies at an angle between normal and transverse. Map Projections • Map Projection Distortion – All map projections involve distortion of some kind or another • The kind of distortion (or lack thereof) can be classified by The 4 Properties Of Globes, which in turn can subdivided into two classes: – Major & Minor Map Projections • Map Projection Distortion (Cont.) – Major • Conformality • Equivalence – These two properties are mutually exclusive! – Minor • Distance • Direction Mercator Projection Albers Equal Area Conic ShpChng.mov Azimuthal Equidistant Gnomonic Projection GrCircl.mov Earth as a Grid • When Projecting the Graticule we require: – Projection Surface, Projection Orientation, Light Source AND – __________ • Accounts for the shape of the earth Earth Models: The Geoid • Earth is NOT a perfect sphere. – More like an Ellipse • Equatorial Bulge – Scientists refer to the Ellipse as a Geoid • Due to distorted shape. • The ‘True’ overall shape of the earth. – Ideally, we would employ this Geoid shape when performing projections • However, the shape is far too complicated to accurately model • Represents the perfect shape that all Earth Models aspire to. Earth Models: Spheroids • Spheroids – Given the complexity of Geoids and the overly __________ nature of Spheres • Spheroids are employed instead! – Spheroids account for ‘Polar Flattening’ • The N-S diameter is roughly 1/300 less than the E-W diameter • Flattening 1/f f = (a - b) / a b Flattening f = (a - b) / a • • Where ‘a’ is the equatorial axis or semi-major axis, and ‘b’ is the polar axis or semi-minor axis a History of Spheroids • Historically, many countries have adopted their own Spheroids – i.e. No International Convention. – Spheroids were tailored for each nation • Thus a spheroid that best fits one region be optimal for another. • Today an international standard has been adopted known as – WGS 84 (World Geodetic System of 1984) f = 298.257 Datum and NAD • While a Spheroid approximates the shape of the earth, – a datum defines the __________ of the ellipsoid relative to the __________ of the earth. – A datum also defines the __________ and __________ of latitude and longitude lines. Datum and NAD • North American Datum of 1927 (NAD 27) – Spheroid: Clarke 1866 • North American Datum of 1983 (NAD 83) – Spheroid: Geodetic Reference System of 1980 (GRS 1980), – Almost identical to the WGS 1984 ellipsoid. Datum and NAD • HARN OR HPGN – (High Accuracy Reference Network, or High Precision GPS Network) • Designed by the military with the use of, and for the intended future use by, GPS – Arguably the most accurate datum in the world with worldwide coverage • Throughout North America, difference with NAD 83 is __________ The “Un-Projected” Projection • (Plate Carrée/Cylindrical Equidistant/Geographic Projection) – Simplest Projection • Assigns Longitude to X axis and Latitude to Y axis – No need for Shadow & Globe concept – Coordinates are entered and read as Long/Lat, rather than typical Lat/Long • A Type Of Cylindrical Projection • Neither Conformal Nor Equivalent – Typical Projection for __________Spatial Datasets and __________ Projection for all GIS Universal Transverse Mercator System (UTM) • A Type Of Secant Cylindrical Projection – Transverse Mercator because the cylinder is wrapped around the Poles, not the Equator – Implemented as an internationally standard coordinate system Universal Transverse Mercator System (UTM) • __, 6 degree zones – Starting at the 180 degree longitude line and running eastward back to 180. – Spans from 80° South to 84° North. • Each zone defines a different projection – Two maps of adjacent zones will not fit along their common border Universal Transverse Mercator System (UTM) • Zone boundary is __________. – Jurisdictions that span two zones must make special arrangements. For example: • Use only one of the two projections, and accept the greater-than-normal distortions in the other zone • Use a third projection spanning the jurisdiction – E.g. Italy spans UTM zones 32 and 33 126° 120° 10 11 114° 12 108° 13 102° 14 96° 90° 15 84° 16 78° 17 72° 66° 18 19 State Plane Coordinate System • Provides less distortion than UTM • Applied To Each Of The 50 States. • Does Not Account For __________ Of The Earth: – Planar System. – Used By Surveyors And Government Agencies. • Large States Are Separated Into Multiple Zones. – Separate System For Each State, 120 Zones For The Entire Us. State Plane Coordinate System (Cont.) • Each Zone Has A Central Meridian • E/W Oriented States: – Lambert Conformal projections with a false origin 2,000,000 feet west of the central meridian • N/S Oriented states: – Transverse Mercator projections with a false origin located 500,000 feet west of the central meridian • The false origin is south of the southern edge of the zone in both cases Santa Rosa Escambia Okaloosa Holmes Walton Bay FL_N 903 Jackson Washington Gadsden Calhoun Liberty Bay Gulf Franklin Nassau Leon Jefferson Madison Wakulla Taylor Hamilton Baker Columbia Suwannee Duval Union Bradford Clay Lafayette Gilchrist Alachua Dixie St. Johns Putnam Flagler Levy Marion Volusia Cit rus Sumter Lake Hernando Seminole Orange Brevard Brevard Pasco Pinellas Hillsborough Polk Osceola FL_E 901 Brevard Indian River FL_W 902 Florida NAD83 State Plan Zones Manatee Hardee Highlands DeSoto Sarasota Charlotte Charlotte Charlotte Lee OkeechobeeSt. Lucie Martin Glades Palm Beach Hendry Collier Broward Monroe Miami-Dade Monroe False Origins Implications • Two datasets can differ in both projection and datum – Often answers the question _________________ _______________ • The datum and projection may not be known – knowledge of projections/coordinate systems can help us make an intelligent guess On-the-fly Projection In Arcmap • ArcMap can display data stored in one projection as if it were in another projection. – Data is projected on the fly anytime a layer has a different coordinate system than that of the _____________. – For display and query purposes only. The actual data is not altered. On-the-fly Projection In Arcmap • A ____________Coordinate System Can Be Defined By – adding data with a defined coordinate system or – manually setting the coordinate system (by accessing the data frame’s properties) • ArcMap Will Not Project Data On The Fly If The Coordinate System For The Dataset Has Not Been __________. • Enter the coordinate system of the vector, raster data; • NO change on the actual projection/datum of data • Change the coordinates for features in a feature class Place Names • The Simplest/Earliest Form – The most commonly used in everyday activities – Each country maintains a system of authorized naming • Works At Many Different Scales – From continents to small villages and neighborhoods • Limited Use – Often have very __________ resolution – Many can only be understood by locals – May pass out of use in time Postal Addresses & Postcodes • Introduced after mail delivery in 19th century – Assumptions: • Each dwelling/office is a potential destination for mail • Dwellings/offices are arrayed along streets, and numbered accordingly • Streets names are unique within local areas • Names of Local areas are unique within larger regions • Regions names are unique within countries • If these assumptions are true, then – a postal address is a useful Georeference – Postal address is almost universal for Georeferencing Postal address is usually hierarchical Postal Addresses & Postcodes • Where Do Postal Addresses Fail as Georeferences? – In Rural Areas • Urban-style addresses have been extended recently to many rural areas – Anything Not A Destination For Mail: Natural Features • Lakes, mountains, and rivers cannot be located using postal addresses – When Numbering On Streets Is Not Sequential • E.g. in Japan Postcodes as Georeferences • Defined in many countries in late 20th century for simplifying mail sorting – e.g. ZIP codes in the US • Hierarchically structured – The first few characters (numbers) define _______ areas – Subsequent characters designate ________ areas – Coarser spatial resolution than postal address In Canada, the first three characters of the 6-character postcode form the forward sortation areas (FSAs) • Useful For Mapping – ZIP code boundaries are a convenient way to summarize data in the US. • The dots on the left have been summarized as a Choropleth on the right Linear Referencing • A system for Georeferencing locations on network – Combines the name of the link (path) with an explicit _______ ________ along the link from a fixed point, most often an intersection Uses of Linear Referencing • Widely used in applications centered on a linear network – Transportation infrastructure management • To keep track of pavement quality, signs, traffic conditions on roads – Dealing with emergencies • To record the locations of accidents Linear Referencing Problems • Locations in rural areas may be a long way from an intersection or other suitable reference point • Pairs of streets may _______ more than once • Measurements of distance along streets may be inaccurate – depending on the measuring device • e.g. car odometer Cadasters • Maps of land ownership in an area – Uniquely identified and persistent – For taxation or public record Cadasters • United States Public Land Survey (USPLS) – Land Partitioning System • Used To Locate And Identify Land • Subdivided by Township, Section & Range. – For each region, a principle meridian was established. • Florida’s runs through Tallahassee. – East west base line is established. Each township is subdivided in 36 1 square mile (640 acres) Sections. Note, the sections are numbered in alternating rows, beginning at the northeast corner of the township. Sections can be subdivided numerous times Each township is subdivided in 36 1 square mile (640 acres) Sections. Note, the sections are numbered in alternating rows, beginning at the northeast corner of the township. Sections can be subdivided numerous times W Each township is subdivided in 36 1 square mile (640 acres) Sections. Note, the sections are numbered in alternating rows, beginning at the northeast corner of the township. Sections can be subdivided numerous times Subdivisions of sections are called Aliquot Parts. These are usually equal acreage divisions of sections. Described as ¼ or ½ of a ¼. Anything that does not fit is considered a lot. W NE ¼, NW ¼, Sec. 14, T 2 S, R 3 W, ___ PM Converting Georeferences • GIS Applications Often Require Conversion Of Projections And Ellipsoids To – Combine Datasets, Or – For Desirable Properties • These are standard functions in popular GIS packages • Street addresses must be converted to coordinates for mapping and analysis – Using Geocoding functions Converting Georeferences • Place names can be converted to coordinates – (using gazetteers such as alexandria.ucsb.edu, geonames.usgs.gov/) • GIS relies upon accurate Georeferencing – However, keep in mind Georeferencing can never be perfect A Gazetteer Example End Show ...
View Full Document

This note was uploaded on 09/21/2011 for the course GIS 4043C taught by Professor Roberts during the Spring '11 term at FAU.

Page1 / 93

Lecture-2_Bb_1SlidePerPage - Georeferencing PROJECTIONS...

This preview shows document pages 1 - 12. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online