derive a distance matrix for a set of locations given their longitude and latitude
coordinates

**-a***float*- switch to XY modus, using aspect ratio (>= 1.0)
**-l***filename*- file with numbered labels
**-o***filename*- output file

This program calculates the distance matrix of a set of locations, given
their coordinates, which must be defined in longitude and latitude
(unless the option **-a** is used).
Resulting distances are in kilometres. The results are not entirely
accurate due to two assumptions which are neither entirely accurate:

- earth is a perfect sphere;
- earth has a circumference of 40000km.

The file with locations is a coordinate
file with coordinates defined as longitude and latitude.

With the option **-a**, the program switches to XY modus. The
coordinates are not in longitude and latitude, but are ordinary
X and Y coordinates in a rectangular grid. The resulting distances
are not in kilometres, but in whatever unit the grid uses.

The value to option **-a** is the aspect ratio between distances
along the X axis and the Y axis. It is a value equal to or
greater than 1. Distances along the X axis are reduced by
dividing them with this value.

If the option **-l** is used to specify a
label file, the difference matrix for
that set of labels is created.

If no label file is specified, a difference matrix for all locations is created, using the locations in the order they are given in the file with locations.

The output file is a difference matrix
file with distances defined in kilometres.