Lamberts and Mercator Plotting

Wing Commander Rajagopal

Plotting on Charts – Lambert vs Mercator

Lambert Projection maintains accurate angles and is suitable for long-distance flight planning. Mercator Projection preserves direction and is mainly used for navigation over equatorial regions.

Lambert’s Plotting – Find Magnetic Bearing

  • Convert relative bearings to magnetic bearings.
  • Magnetic Bearing = Relative Bearing + Magnetic Heading
  • Subtract 360° if the value exceeds 360°.
  • Convert magnetic bearings to the station into magnetic bearings from the station.
  • Convert QDM to QDR.
  • Add or subtract 180°.

Lambert’s Plotting – Find True Bearing

Relative Bearing to True Bearing Conversion

  • True Bearing = Relative Bearing + True Heading
  • Subtract 360° if the value exceeds 360°.

True Bearing from ADF and VOR

  • If the bearing is measured at the ground station (e.g., VOR):
    • Apply the station variation to the magnetic bearing to obtain the true bearing.
  • If the bearing is measured at the aircraft (e.g., ADF):
    • Apply the aircraft variation to the magnetic bearing to obtain the true bearing.
    • Find the reciprocal bearing from the station.

Lambert’s Plotting – Apply Chart Convergence

  • Obtain the bearing to plot by applying chart convergence.
  • Plot from the false meridian at the ground station.
  • Alternatively, calculate the chart convergence and then plot.

Mercator Plotting

  • The lateral direction of radio signals from VDF, VOR, and NDB follows the great-circle path (the shortest path).
  • On Mercator charts:
    • Rhumb lines are straight lines.
    • Great circles are curved and concave toward the equator.
  • Measured great-circle bearings must be converted into rhumb-line directions before plotting on a Mercator chart.

Calculation of Bearing to Plot on Mercator

  • Apply the conversion angle (½ convergence) at the point where the bearing is measured to convert from a Great Circle (GC) to a Rhumb Line (RL).
  • For VOR and VDF (bearings measured at the station):
    • Apply the station variation and the conversion angle at the station.
  • For ADF and AWR (bearings measured at the aircraft):
    • Apply the aircraft variation and the conversion angle at the aircraft.
    • Plot the reciprocal bearing from the ground station.