Calculating the True Bearing Between Two Points
Date: 9/20/95 at 8:43:4 From: Anonymous Subject: Calculation of true bearing How can I calculate the true bearing between two points on the earth's surface? I know their grid coordinates, and their lat- long coordinates, and how to get from the grid coordinates to a grid bearing, but how can I calculate the true bearing between the two points? Thanks in advance, David
Date: 11/19/95 at 16:13:59 From: Doctor Jonathan Subject: Re: Calculation of true bearing To find the true bearing from point A to point B on a sphere, project the chord AB on to the tangent plane of A. Call this projection AB'. The angle between AB' and the line segment pointing north in the tangent plane will be the true heading. The latter segment may be found by projecting the chord between A and the north pole onto the tangent plane of A. In fact, with this method you may find the heading relative to any point, not just the "north" pole. This would be useful for finding the heading according to a real life compass which gives headings relative to magnetic north, not true north. For example, if you know the coordinates for magnetic north (which I don't, offhand) N, you could would find the angle between the projection of AN and AB in the tangent plane of A--this would be the heading as measured by a "real" compass. -Doctor Jonathan, The Geometry Forum
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