Basic Coordinate Systems Grid Systems

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Basic Coordinate Systems Grid Systems. RG 620 May 09, 2013 Institute of Space Technology, Karachi. After projection it is necessary to set up a coordinate system on the map that will allow a point to be described in X-Y space (or northing and easting)

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### Basic Coordinate SystemsGrid Systems

RG 620

May 09, 2013

Institute of Space Technology, Karachi

After projection it is necessary to set up a coordinate system on the map that will allow a point to be described in X-Y space (or northing and easting)

To describe a location in a universally understandable manner a grid system is necessary

For a useful grid it is necessary for it to define an origin and a uniform grid spacing

There are several types of Coordinate System to represent the Earth’s surface

Coordinate Systems
Some commonly used Coordinate Systems are:

Geographic

Latitude and Longitudes are used

UTM

Shape is preserved and precise measurements in meter

State Plane

Local surveying (with minimum distortion)

Coordinate Systems
Global coordinate system

Globe is divided into narrow longitude zones

Best used for north-south oriented areas (little distortion in this direction)

Successive swaths of relatively undistorted regions created by changing the orientation of the cylinder slightly

These swaths are called UTM zones

Each zone is six degrees of longitude wide

Total 60 zones

Universal Transverse Mercator Coordinate System
These zones are numbered from west to east

Zone 1 begins at the International Date Line (1800 W), Zone 2 at 174°W and extends to 168°W

Each Zone is further divided into Eastern and Western halves by drawing a center line called Central Meridian

Zones are further split north and south of the equator

Universal Transverse Mercator Coordinate System
At equator a zone is about 40,000/60 = 667 Km wide

Any point can be described by ‘Easting’ and ‘Northing’ values

Northing is the distance to the equator, while easting is the distance to the "false easting", which is uniquely defined in each UTM zone

The equator is used as the northing origin for all north zones (northing value of zero)

South zones have a false northingvalue added to ensure all coordinates within a zone are positive

For UTM south zones, the northing values at the equator are set to equal 10,000,000 meters

Universal Transverse Mercator Coordinate System
Universal Transverse Mercator Coordinate System
• Important thing to remember

Coordinate values are discontinuous across

UTM zone boundaries, therefore, analyses are

difficult across zonal boundaries

Horizontal Zoning
• Latitudes are divided into zones lettered from A at the South Pole to Z at the North Pole
• Spacing is not regular throughout
• A and B zones are within the south circle of 80 degrees
• Zones Y and Z cover the north polar region north of 84
• Rest of the zones extend from 80 degrees south latitude to 84 degrees north latitude degrees
• Zone X is 12 degrees wide (from 72 to 84 degrees North)
• I and O not used
• Rest of the zones are 8 degree wide
• Zone M and N are just South and North of Equator respectively
Finding Grid Zone for any Latitude

In calculation take west longitude as (-) negative and east longitude as (+) positive

Add 180 and divide by 6

Round off the resultant value to the next higher number

Example: Greenwich Prime Meridian is at …….. Longitude?

UTM – Finding Grid Zone
Measuring Distance Distortion
• Comparing map distance with the Great Circle Distance
• Remember the Example from Text Book where the Great Circle Distance between two point A and B was = 412.906 KM
• Identify coordinates of the equivalent points on UTM grid
• Calculate the distance between these points
• Negative scale distortion when features are compresses or reduced in size
• Positive scale distortion when features are expanded

Specifies positions in Cartesian coordinate systems for each state

Used for local surveying and engineering applications

Points are projected from their geodetic latitudes and longitudes to x and y coordinates in the State Plane systems

Conformal mapping system for US with a maximum scale distortion of one part in 10,000

State Plane Coordinate (SPC) Systems
Large states are divided into zones to limit distortion error and maintain said accuracy

One or more zones in each state with slightly different projection in each zone

Boundaries of zones follow state and county lines

The number of zones in each state is determined by the area the state covers

The number of zones ranges from 1 to 10 (in Alaska)

Each zone has a unique central meridian

State Plane Coordinate Systems
Zones have different projections

Lambert Conformal Conic: for states that are longer east–west, such as Tennessee, Kentucky, North Carolina, Virginia, etc.

Transverse Mercator projection: for states that are longer north–south, such as Illinois, Arizona, New Hampshire, etc.

The Oblique Mercator projection: for the panhandle of Alaska (AK zone 1) because it lays at an angle

State Plane Coordinate Systems
Originally based on the North American Datum of 1927 and the measurement unit was feet

Now being converted to North American Datum of 1983 (NAD83) (will use meters as unit of measure)

Due to datum change some zones are redefined

State Plane 1927 vs. 1983
Variation between Datums

Reference: David Corner

References
• http://www.ncgia.ucsb.edu/giscc/units/u013/u013_f.html