Thursday, July 16, 2015

Salient features of selected projections

SALIENT FEATURES OF POLYCONIC PROJECTION

  1. All parallels are projected without distortion (Scale is exact along all parallels)
  2. Parallels are arcs of circles but they are not concentric
  3. It is neither conformal nor equal area
  4. Central meridian and equator are straight lines; All other meridians are complex curves
  5. There is NO DISTORTION ONLY AT CENTRAL MERIDIAN
  6. It is used in India for all topographical mapping on 1:25,000; 1:50,000 and 1:250,000 scales
The disadvantages of this projection are listed below:
  1. It can have a rolling fit only
  2. Meridians and parallels do not intersect at right angles
  3. Inability to show seamless data in a rectangular coordinate system
The polyconic projection is not being used for mapping anywhere in the world except India and a few adjacent countries.


SALIENT FEATURES OF LAMBERT CONFORMAL CONIC PROJECTION

  1. It is a conical projection
  2. It is conformal
  3. Parallels are unequally spaced arcs of concentric circles, more closely spaced near the center of the map
  4. Meridians are equally spaced radii of the same circles, thereby cutting parallels at right angles
  5. Scale is true just along two standard parallels or along just one
  6. Intersection of central parallel and central meridian is the origin of rectangular coordinate system
  7. Central meridian is Y-axis and a line perpendicular to it is X-axis
  8. A large value is given to the origin so that ALL coordinates for the projection are POSITIVE
  9. The origin assumes a value (0,0) is also known as 'FALSE ORIGIN'

SALIENT FEATURES OF TRANSVERSE MERCATOR PROJECTION

  1. It is a widely used conformal projection
  2. It is a cylindrical projection
  3. It is conformal
  4. The central meridian, each meridian 90 degrees from the central meridian and equator are straight lines
  5. Other meridians and parallels are complex curves
  6. Scale is true along central meridian or along two straight lines equidistant and parallel to central meridian
  7. Scale becomes infinite 90 degrees from central meridian
  8. It is used extensively for quadrangle maps at scales 1:24,000 to 1:250,000
  9. It was presented by lambert in1772
  10. It is not used in India but extensively used in USA
  11. The State Plane Coordinate System (SPCS) is based on the Transverse Mercator Projection in USA for states with North-South extent
  12. It is used for quadrangle maps in the USA
  13. It is used for army map service in the USA
  14. Ordnance Survey of Great Britain switched to transverse mercator from cassini
  15. It is used in Canada in three zones.

SALIENT FEATURES OF UNIVERSAL TRANSVERSE MERCATOR PROJECTION

  1. It is a particular case of transverse mercator projection
  2. Transverse mercator in this projection is 6 degrees wide
  3. Reference ellipsoid for North America was given by Clark in 1866
  4. Central meridian is the origin for the longitude
  5. Equator is the origin for the latitude
  6. Unit for distance is metre (m)
  7. False northing is 0m for northern hemisphere and 10,000,000m for southern hemisphere
  8. False easting is 500,000m
  9. Scale factor at central meridian is 0.9996
  10. Zone numbering begins at 1 for zone between 180 W and 174 W and increases to 60 for zone bounded by meridians 174 E and 180 E (Each zone 6 degrees wide)
  11. Latitude limits 80 N and 80 S
  12. Nearly 60 countries use this projection as the general use projection within the country
  13. It is NOT the universal projection for all countries.
  14. In India, it is used by NAVAL HYDROGRAPHIC SURVEYS for their maps and charts
Conversion among coordinate systems are carried-out mathematically using map projection equations and their inverses.