gridcal -- compute the great-circle distance between two grid locators
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`gridcal` computes the short-path great-circle distance between two grid
locators. The Grid Locator System divides Earth into a series of
rectangles identified by a combination of letters and numbers, so that
the approximate position of a point can be expressed with a short
identifier like IO91vl.

Usage: gridcal <loc1> [<loc2> [<pwr>]] 

If `gridcal` is given only one locator, it prints on output the latitude
and longitude of the centre of the corresponding grid square: 

    gridcal IO91vl
    IO91vl 51.4792 -0.208333 0.898481 -0.0036361  

With two locators as input, `gridcal` prints on output the two locators
and their great-circle distance, both in km and miles:

    gridcal IO91vl JN65od
    IO91vl JN65od 1213.71 754.164

If `gridcal` is given as third numerical argument, that number is
considered a "power" value in Watts, and `gridcal` will print on output
a longer line containing the two locators, the distance in km and miles,
the power value, and the corresponding km/W and miles/W:

    gridcal IO91vl JN65od 1.2
    IO91vl JN65od 1213.71 754.164 1.2 1011.42 628.47

The latter can be useful to check if a QSO with another ham radio
station qualifies for one of the thousand miles per Watt awards.


Dependencies
============

`gridcal` is written in ANSI C has no dependencies.