Simple Conical Projection

Wg Cdr Rajagopal

Conical Projections

Index

Introduction to Conical Projections

  • Conical projections are made by wrapping the paper in a conical shape
  • When the cone is cut open the projection is a circle with a sector missing
  • Parallel of tangency is the latitude where the cone touches reduced earth
  • Scale is correct only at the parallel of tangency and expands rapidly at higher as well as lower latitudes
  • Scale expansion in all directions around a point is same and hence the projection is orthomorphic or conformal
  • Latitudes are concentric arcs and longitudes are radial straight lines
  • Meridians and parallels intersect at right angles

Parallel of Tangency in Conical Projection

  • Parallel of Tangency or Origin is the latitude where the cone touches reduced earth
  • A conical projection appears as a sector of a circle
  • 360 degrees of longitude is depicted as les than 360 degrees

Apex Angle in Conical Projection

  • Apex angle is angle subtended by arc of sector at the apex of the cone
  • It can be proved geometrically that the apex angle would be equal to twice the parallel of tangency
  • For example, if the parallel of tangency is at 30 degrees apex angle would be 60 degrees

Cone Constant of Conical Projection

  • Sector of projection depends on the Constant of Cone
  • Constant of cone is equal to the sine of parallel of origin
  • Cone Constant = Sin of latitude (parallel) of origin

Chart Convergence in a Conical Projection

  • Chart Convergence of a conical projection depends on its Cone Constant
  • Chart Convergence = Change of Longitude x Cone Constant

Scale of Conical Projection

  • Scale is correct at its Parallel of Tangency and expands rapidly away from that parallel
  • Cone touches the reduced earth at its parallel of tangency

Best of luck