How do you Create a Custom Horizon?

You can specify an horizon profile in C2A which will then be systematically loaded in all displayed maps. This ability allows you, for example, to show an obstacle, such as a house, when planning observations. Here is an example of a custom horizon:

To specify an horizon, just declare one or more horizon profiles in a text file, then declare this file in the Field tab of the Options dialogue box. You must also declare the name of the horizon to be used if more than one has been defined in the file (see the syntax below). If no horizon name is specified, the first one in the file will be used.

Note that the syntax of user horizon files is exactly the same as that used by the Occult Watcher software, and the same files can be used transparently in both applications.

In defining a custom horizon in text file, the following rules must be respected:

• You can define several horizon profiles in the same file. Each configuration must begin with a line in the form: Name = XXXX where XXXX represents the name of the horizon (for example, the name of an observing location). This name may contain spaces. This is the name you would declare in the Name box of the Field display area of the Field tab of the Options dialogue box.
  
  
• After declaring the name, you must define the points which define the horizon. Each point must be declared in one line and must have the form: xxx, yy where xxx is the azimuth and yy the elevation of the point. Elevations cannot be negative (only values between 0 and 90) and azimuths must be between 0 and 360. Azimuth 0 is North.
  
  
• The first point in the profile must be azimuth 0. The last point in the profile must be azimuth 360.
  
  
• Both azimuths and elevations must be integers. Decimal values are not permitted.
  
  
• Azimuth values may only increase through the profile.
  
  
• Only two consecutive points with the same azimuth value are permitted (to represent a vertical line).
  
  
• Lines which start with a ‘#’ are taken to be comments and are ignored. Similarly, lines containing only spaces are ignored.

If a syntax error is found, the reading of the horizon file and display of the map in C2A are interrupted and an error message is displayed containing the line number where the error occurred. Her is an example of a user horizon profile:

Remember that azimuths may only increase sequentially, and you cannot create shapes which would result in azimuth reversal (decrease).

You can define several horizon profiles in the same file so that you can quickly switch the displayed profile.

An example of a user horizon profile is provided in the C2A installation package. The filename is UserHorizonUS.txt

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