ntt@dciem.UUCP (Mark Brader) (04/16/84)
David Smith (David.Smith@cmu-cs-ius.arpa) notes: ... Given the coordinates of origin and destination, spherical trigonometry can be used to produce the arc length between them, expressed in angular measure (vertex of angle at center of earth). This arc is historically measured in degrees, minutes, and seconds. The nautical mile is defined to be one arc-minute over the surface of the earth. I will tiptoe quietly away from the question of how the earth's oblateness is handled. Phil Karn (allegra!karn) adds: By the way, the kilometer has a nice geophysical significance to it - [it] was originally defined as 1/10000 the distance between the north pole and the equator.* It has since been redefined** (and the earth measured more accurately) but it is still a good approximation. *Via Paris. **Three times! (artifact, wavelength of light, speed of light) Well, in at least some countries, the nautical mile has also been redefined. According to a publication I have from the Canadian Standards Association, the nautical mile is now defined as <flourish of trumpets>: 1852 meters.* *Actually they spell it metres, but let's not get into that. Mark Brader