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Compute meridian convergence

Compute the meridian convergence for Swedish maps.

Compute the meridian convergence for Swedish maps, by entering coordinates either in SWEREF 99 TM or RT 90 2.5 gon V. The user interface is in Swedish.

Description

Illustration av begreppet meridiankonvergens samt förhållandet mellan sant norr och kartnorr.
Klicka på bilden för att se den större.

The meridian convergence at given a point is the difference between grid north, i.e. the northing map coordinate line, and the true north along the meridian at the point. It is positive when grid north lies to the right of the meridian and negative when grid north lies to the left. This is illustrated in the map below. Meridian convergence is usually denoted by c and depends on the map projection and on the position.

When a compass is used for orientation, the bearing refers to true north. To increase accuracy a correction should be made for declination, which is due to the fact that the magnetic and geographic poles do not coincide. The Geological Survey of Sweden (in Swedish, new window) can provide more information about magnetic declination.

Both SWEREF 99 TM and RT 90 2.5 gon V use the Transverse Mercator map projection. In this projection meridians are depicted as arcs that converge northward towards the central meridian. The central meridian is placed approximately in the centre of Sweden for both systems.

Compute meridian convergence

Enter coordinates in SWEREF 99 TM or one of the twelve local projection zones for SWEREF 99 (SWEREF 99 dd mm).

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