How Much Azimuth Distortion?

Convergence of the Meridian

The formula for computing the convergence of the meridianranges from very simple (0 for the Mercator-based SRFs)to very complex for Transverse Mercator.

• P is a reference location in the projectedsystem.

• The central meridian appears as a straightline (the y axis).

• Meridians may or may not curve(one exception is the Mercator projection).

• T is the tangent line to the meridian at P.

• ? is the Convergence of the Meridian.

• The convergence of the meridian is theangle between SRF “North” and true Northon the source ellipsoid (positive clockwise).

• The angle ? is the rotation angle needed torotate a vector in the Projection-based SRFto true North when siting a reference vectoronto a canonical LTP.

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