Co-ordinate Systems Flashcards
Types of co ordinate system
Geographical, spheroid
Projected, planar
Geographic co ordinate systems
Defines locations on a 3D spherical surface
Uses angular units of measurement: (latitude and longitude)
Line of zero latitude- equator
Line of zero longitude-prime meridian
Reference surface or datum
Height in geographic systems
Geoid: surface to the earths grav. Field. Approximates sea level, is irregular over space and variable over time
Ellipsis/spheroid: geometric inventions that approximate the food, but are defined mathematically and so are regular and constant
Datum: defines position of spheroid relative to the centre of the earth.
3D geographic co-ordinates
Obtained by introducing height into the system, the height is the vertical distance from point above the datum
WGS84
World geodetic system 84 Used by gps Global standard co-system Meridian Greenwich Several reviews and updates Uses EGM geoid captures difference MSL and ellipsis
Projected co-ordinate systems
Cylindrical projections
Azimuthal projections
Stereo graphic projections
Compromises with projected systems
Preserving true directions
Showing equal areas
Showing true distances
Showing true shapes
NO BEST SYSTEM
Cylindrical projections
Retains True angle- good for navigation
Lines of latter use and longitude are straight
Classic example-Mercator
Azimuthal projections
Simple perspective view
Orthographic, Stereogrpahic and gnomic
Stereographic projections
Conformal-preserves angles
Does not preserve distances or areas
Gnomic projections
Great circles as straight lines
Not conformal
Conic projections
Good for middle latitudes
Distances only true along selected lines
Directions, shapes and area reasonably accurate depending on exact projections.
Secant projections
Cone cuts sphere giving 2 standard parallels and less distortion
UTM
Not a single map projection but a series (60 in total of bands 6 degrees each 20 lattitudinal zones Based on wgs84 Conformal Distorts distance and areas
Considerations when choosing projections
Size of area Latitude range Properties needed-distance, area, directions, Ultimate use of data displayed Map orientation
