Modify Keywords
The Modify Keywords command adds, modifies, or renames keyword data in the image header. This command works with any displayed image and with files in FITS format. New keyword data may be added, existing keywords may be modified, and keyword names may be changed to other names. A FITS image header consists of individual lines containing a Name (keyword name), Value (keyword data), and an optional Comment, in the format
Name Value / Comment
The Modify Keywords table collects the information needed to add and modify 1 or more header lines in this format.
The Modify Keywords command is opened from the Process > Calibration menu.
Modify Keywords Properties
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Action |
Specifies the action to take for the specified keyword. Add If the Keyword does not exist in the image header, it is added. If the Keyword already exists in the image header, its value is changed to the entered Value. Rename If the named Keyword exists in the image header, its name is changed to the specified Value. The Comment is not used. (none) Specifies that there is no action taken for this line of the table. Use this option if you want to keep a keyword in the list but not apply it at the current time. |
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Type |
Specifies the type of keyword as a String, Number, or Integer. These are described a separate table below. |
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Keyword |
Specifies the name of the Keyword. You can use either a standard or conventional name or your own private keyword name. For list of standard and conventional keywords, see FITS Keywords. |
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Value |
Specifies the keyword change to be made in the header. What is changed depends on the Action. Add (Action): The Value is saved as the new value of the keyword. Rename (Action): The Value replaces the keyword name. The previous value and comment in the image header are preserved. |
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Comment |
Optionally, for a new keyword. The comment is saved only when Action=Add. The comment is ignored for Action=Rename. |
The Type of a keyword refers to the kind of value that will be saved in the image header.
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String |
The keyword value is saved as a string between single quotes. The String type is also used for date, time, and angle in HMS/DMS format. Example: 'My great data' '-30:12:14.566' |
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Number |
The keyword is saved as a real (floating point) number including a decimal point or exponential notation. Examples: -1.456E-12 825.421 152. |
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Integer |
The keyword is saved as an integer value with no decimal point. Examples: 68455 -452 |
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Logical |
The keyword is saved as a logical (Boolean) value, either T or F. The SIMPLE keyword is a typical example of this type of value. |
In the screenshot above, notice that the keyword OBSSET is is to be added with Type = Number and the Value = 2412. This results in the value being entered into the image header as the floating point value "2412.", including a decimal point, rather than as the integer "2412".