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Gcal 3.01

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#### G.2.2.4 Geographical distance and course angle `%[format]bargument` special text

`%[format]b[*][mode]ISO-6709:1983-co-ordinate-1/ISO-6709:1983-co-ordinate-2` references either the approximate air line distance or the approximate course angle (true track)(84) between any of two geographic point locations. The selection, which value has to be calculated by using this special text is done by specifying the mode part of the preceding argument. Actually, exactly three different modes can be used that are represented by the `0'...`2' characters:

 Mode Description `0` Calculates the air line distance between ISO-6709:1983-co-ordinate-1 and ISO-6709:1983-co-ordinate-2. The calculated air line distance value is displayed in kilometers by default. A `*' character directly before this mode character causes Gcal to display the distance value for another quantity, and that in statute miles; where one statute mile is equal to 1.609344 kilometer. If Gcal is unable to compute the approximate distance between the two geographic point locations by reason of a misspecified argument, a `??` text will be created instead of the distance value. `1` Calculates the course angle (true track) between ISO-6709:1983-co-ordinate-1 and ISO-6709:1983-co-ordinate-2. The calculated course angle value is displayed in degrees and arcminutes by default. The course angle is measured clockwise relative to the geographic, true North (not the magnetic North as shown by a compass), where angle values for the North direction are both denoted as 0 degree and 360 degree. A `*' character directly before this mode character causes Gcal to display the course angle value using another style; and that in decimal degrees. If Gcal is unable to compute the approximate course angle between the two geographic point locations by reason of a misspecified argument, a `???d??'` text will be created instead of the course angle value. `2` Like mode `1`, but the course angle (true track) between ISO-6709:1983-co-ordinate-2 and ISO-6709:1983-co-ordinate-1 is calculated.

If no mode is given, Gcal automatically uses that mode, which is enabled by the mode character `0'. If a mode character is given that is not according to one of the `0'...`2' characters, Gcal also automatically uses that mode, which is enabled by the mode character `0'.

After the optional style and mode characters, the latitude and longitude of the geographic co-ordinates follows, for which the calculations must be made. They must be conform the ISO-6709:1983 standard representation of latitude and longitude for geographic point locations. The two co-ordinates have to be separated by a `/' termination character from each other.

See section Arguments of the Sun oriented special texts, for the detailed description of the components of the ISO-6709:1983 standard representation of latitude and longitude for geographic point locations.

For example:

The text `Distance Paris-Tokyo: %b+4852+00220/+3542+13946 km' will be expanded to
==> `Distance Paris-Tokyo: 9746km'.

The text `Distance Paris-Tokyo: %b*0+4852+00220/+3542+13946 ms' will be expanded to
==> `Distance Paris-Tokyo: 6056ms'.

The text `Course angle Paris-Tokyo: %b1+4852+00220/+3542+13946' will be expanded to
==> `Course angle Paris-Tokyo: 033d22''.

The text `Course angle Tokyo-Paris: %b*2+4852+00220/+3542+13946' will be expanded to
==> `Course angle Tokyo-Paris: 333.548'.

While praying, people of Islamic faith always turn their heads into the direction of Makkah, Saudi-Arabia. Now by means of Gcal, these people can easily find out for their respective location, where they have to turn to, and that by:

 ```%b1ISO-6709:1983-co-ordinate-1/+212516+0394929 ```

where ISO-6709:1983-co-ordinate-1 is simply replaced by the co-ordinate of the respective location.

See section Fixed date option `--precise', how to obtain a more precise representation of the values that are caused by this special text.

This special text must always be trailed by a whitespace character which is removed in output!

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